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Photonics, Volume 6, Issue 2 (June 2019) – 40 articles

Cover Story (view full-size image): Continuous wave (cw) optically injected semiconductor lasers have important practical applications because optical injection can not only control the emitted wavelength but also increase the modulation bandwidth and relaxation oscillation frequency. Outside the injection locking region a cw optically injected laser displayed a wide range of dynamic regimes when the laser current of the master laser varied or was detuned. This figure shows the relative height of the oscillation intensity of the injected laser. In dark regions the intensity was either constant or pulsed regularly. In colored regions the height of the pulse was irregular, and the color code displays the height (relative to the mean) of the highest pulse. View this paper.
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10 pages, 1584 KiB  
Article
Stability Boundaries in Laterally-Coupled Pairs of Semiconductor Lasers
by Martin Vaughan, Hadi Susanto, Nianqiang Li, Ian Henning and Mike Adams
Photonics 2019, 6(2), 74; https://doi.org/10.3390/photonics6020074 - 25 Jun 2019
Cited by 6 | Viewed by 4154
Abstract
The dynamic behaviour of coupled pairs of semiconductor lasers is studied using normal-mode theory, applied to one-dimensional (slab) and two-dimensional (circular cylindrical) real index confined structures. It is shown that regions of stable behaviour depend not only on pumping rate and laser separation, [...] Read more.
The dynamic behaviour of coupled pairs of semiconductor lasers is studied using normal-mode theory, applied to one-dimensional (slab) and two-dimensional (circular cylindrical) real index confined structures. It is shown that regions of stable behaviour depend not only on pumping rate and laser separation, but also on the degree of guidance in the structures. Comparison of results between normal-mode and coupled-mode theories for these structures leads to the tentative conclusion that the accuracy of the latter is determined by the strength of self-overlap and cross-overlap of the symmetric and antisymmetric normal modes in the two lasers. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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Figure 1
<p>(<b>a</b>) Schematic of two coupled slab waveguides. (<b>b</b>) Schematic of two coupled circular cylindrical waveguides.</p>
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<p>Variation of coupling rate with <span class="html-italic">d</span>/<span class="html-italic">a</span> for pairs of circular cylindrical guides with three values of <span class="html-italic">v</span> and for a slab guide with <span class="html-italic">v</span> = 1.571. Symbols (circles, squares, triangles, diamonds) are calculated from normal-mode theory; dashed and dotted lines are fitted from analytic results given in the text.</p>
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<p>Overlap factors versus <span class="html-italic">d</span>/<span class="html-italic">a</span> for coupled circular cylindrical guides with <span class="html-italic">v</span> = 1.571.</p>
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<p>Overlap factors versus <span class="html-italic">d</span>/<span class="html-italic">a</span> for coupled circular cylindrical guides with <span class="html-italic">v</span> = 2.255.</p>
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<p>Overlap factors versus <span class="html-italic">d</span>/<span class="html-italic">a</span> for coupled circular cylindrical guides with <span class="html-italic">v</span> = 3.740.</p>
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<p>Stability boundaries in the plane of <span class="html-italic">P</span>/<span class="html-italic">P<sub>th</sub></span> versus <span class="html-italic">d</span>/<span class="html-italic">a</span> for coupled circular cylindrical guides with <span class="html-italic">v</span> = 1.571. Curves labelled ‘inf’ are obtained using the values of overlap factors in the limit of large <span class="html-italic">d</span>/<span class="html-italic">a</span>.</p>
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<p>Stability boundaries in the plane of <span class="html-italic">P</span>/<span class="html-italic">P<sub>th</sub></span> versus <span class="html-italic">d</span>/<span class="html-italic">a</span> for coupled circular cylindrical guides with <span class="html-italic">v</span> = 2.255.</p>
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<p>Stability boundaries in the plane of <span class="html-italic">P</span>/<span class="html-italic">P<sub>th</sub></span> versus <span class="html-italic">d</span>/<span class="html-italic">a</span> for coupled circular cylindrical guides with <span class="html-italic">v</span> = 3.740.</p>
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13 pages, 11248 KiB  
Article
Long-Range, High-Resolution Camera Optical Design for Assisted and Autonomous Driving
by Furkan E. Sahin
Photonics 2019, 6(2), 73; https://doi.org/10.3390/photonics6020073 - 25 Jun 2019
Cited by 22 | Viewed by 30246
Abstract
High-quality cameras are fundamental sensors in assisted and autonomous driving. In particular, long-range forward-facing cameras can provide vital information about the road ahead, including detection and recognition of objects and early hazard warning. These automotive cameras should provide high-resolution images consistently under extreme [...] Read more.
High-quality cameras are fundamental sensors in assisted and autonomous driving. In particular, long-range forward-facing cameras can provide vital information about the road ahead, including detection and recognition of objects and early hazard warning. These automotive cameras should provide high-resolution images consistently under extreme operating conditions of the car for robust operation. This paper aims to introduce the design of fixed-focus, passively athermalized lenses for next-generation automotive cameras. After introducing an overview of essential and desirable features of automotive cameras and state-of-the-art, based on these features, two different camera designs that can achieve traffic sign recognition at 200 m distance are presented. These lenses are designed from scratch, with a unique design approach that starts with a graphical lens material selection tool and arrives at an optimized design with optical design software. Optical system analyses are performed to evaluate the lens designs. The lenses are shown to accomplish high contrast from 40 °C to 100 °C and allow for a 4 × increase in resolution of automotive cameras. Full article
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<p>Simplified imaging geometry of a stop sign. (Not drawn to scale.)</p>
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<p>Athermal glass map for Schott preferred glasses [<a href="#B24-photonics-06-00073" class="html-bibr">24</a>]. Lens glasses used in the two designs presented in this paper are highlighted. The straight line has a thermal power axis intercept value of <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>24</mn> </mrow> </semantics></math>, which is the negative of aluminum’s CTE. Zemax has a built-in function called “Athermal Glass Map” that can generate similar plots [<a href="#B28-photonics-06-00073" class="html-bibr">28</a>].</p>
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<p>Schematic drawing of the multi-element lens design. The lens is <span class="html-italic">f</span>/2 and with only spherical surfaces.</p>
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<p>Modulation transfer function (MTF) plot for the designed <span class="html-italic">f</span>/2 lens (as shown in <a href="#photonics-06-00073-f003" class="html-fig">Figure 3</a>) at nominal temperature of 20 °C. Tangential (T) components are shown with solid lines, sagittal (S) components are shown with dashed lines.</p>
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<p>Minimum MTF at 111 lp/mm for the designed <span class="html-italic">f</span>/2 lens (as shown in <a href="#photonics-06-00073-f003" class="html-fig">Figure 3</a>) at different temperatures. For off-axis fields, smaller of the tangential or sagittal MTF value at each temperature is plotted.</p>
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<p>Schematic drawing of the multi-element lens design. The lens is <span class="html-italic">f</span>/1.6 and with two aspherical surfaces (L1S1 and L3S1).</p>
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<p>Modulation transfer function (MTF) plot for the designed <span class="html-italic">f</span>/1.6 lens (as shown in <a href="#photonics-06-00073-f006" class="html-fig">Figure 6</a>) at nominal temperature of 20 °C. Tangential (T) components are shown with solid lines, sagittal (S) components are shown with dashed lines.</p>
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<p>Minimum MTF at 111 lp/mm for the designed <span class="html-italic">f</span>/1.6 lens (as shown in <a href="#photonics-06-00073-f006" class="html-fig">Figure 6</a>) at different temperatures. For off-axis fields, smaller of the tangential or sagittal MTF value at each temperature is plotted.</p>
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10 pages, 2236 KiB  
Article
On-Chip Guiding of Higher-Order Orbital Angular Momentum Modes
by In Joon Lee and Sangin Kim
Photonics 2019, 6(2), 72; https://doi.org/10.3390/photonics6020072 - 23 Jun 2019
Cited by 8 | Viewed by 4506
Abstract
Higher-order orbital angular momentum (OAM) mode guiding in a waveguide which is suitable for on-chip integration has been investigated. Based on the relation between the Laguerre-Gaussian mode and the Hermite-Gaussian mode, it has been shown that two degenerate guided modes of π/2l [...] Read more.
Higher-order orbital angular momentum (OAM) mode guiding in a waveguide which is suitable for on-chip integration has been investigated. Based on the relation between the Laguerre-Gaussian mode and the Hermite-Gaussian mode, it has been shown that two degenerate guided modes of π/2l-rotation symmetry can support the l-th order OAM mode. In order to mimic the rotational symmetry, we have proposed the waveguide structure of a cross-shaped core and designed a waveguide that can support OAM modes of ±1 and ±2 topological charges simultaneously at a wavelength of 1550 nm. Purity of the OAM modes guided in the designed waveguide has been assessed by numerically calculating their topological charges from the field distribution, which were close to the theoretical values. We also investigated the guiding of OAM modes of ±3 and ±4 topological charges in our proposed waveguide structure, which revealed the possibility of the separate guiding of those OAM modes with relatively lower purity. Full article
(This article belongs to the Special Issue Optical Angular Momentum in Nanophotonics II)
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Graphical abstract

Graphical abstract
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<p>Decomposition of LG modes into HG modes: (<b>a</b>) <span class="html-italic">l</span> = 2; (<b>b</b>) <span class="html-italic">l</span> = 3; and (<b>c</b>) <span class="html-italic">l</span> = 4. In each case, HG modes of the same azimuthal symmetry are grouped and dubbed <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>LG</mi> </mrow> <mrow> <mn>0</mn> <mi>i</mi> </mrow> <mi>e</mi> </msubsup> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>LG</mi> </mrow> <mrow> <mn>0</mn> <mi>i</mi> </mrow> <mi>o</mi> </msubsup> </mrow> </semantics></math> according to their symmetry.</p>
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<p>(<b>a</b>) Waveguide structure for simultaneously guiding <span class="html-italic">l</span> = ±1 OAM mode and <span class="html-italic">l</span> = ±2 OAM modes; and (<b>b</b>) mode effective index dependency on waveguide parameters. Optimal design parameters are W<sub>1</sub> = 1.118 μm, L<sub>1</sub> = 0.921 μm, W<sub>2</sub> = 1.626 μm, and L<sub>2</sub> = 1.504 μm.</p>
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<p>HG-similar mode field distributions in the designed waveguide. The mode effective indices (n<sub>eff</sub>) of (<b>a</b>) HG<sub>01</sub>; (<b>b</b>) HG<sub>10</sub>; (<b>c</b>) <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>LG</mi> </mrow> <mrow> <mn>02</mn> </mrow> <mi>o</mi> </msubsup> </mrow> </semantics></math>; and (<b>d</b>) <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>LG</mi> </mrow> <mrow> <mn>02</mn> </mrow> <mi>e</mi> </msubsup> </mrow> </semantics></math> are 3.215525, 3.215482, 3.05968, and 3.059751, respectively.</p>
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<p>Field (Ex, horizontal component) and phase distributions of the OAM modes with the designed component guided modes: (<b>a</b>) electric field and (<b>b</b>) phase distributions for the <span class="html-italic">l</span> = ±1 OAM mode; and (<b>c</b>) the electric field and (<b>d</b>) phase distributions for <span class="html-italic">l</span> = ±2.</p>
Full article ">Figure 5
<p>HG-similar component mode field distributions in the designed waveguide for <span class="html-italic">l</span> = ±3 OAM mode: (<b>a</b>) <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>LG</mi> </mrow> <mrow> <mn>03</mn> </mrow> <mi>e</mi> </msubsup> </mrow> </semantics></math> and; (<b>b</b>) <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>LG</mi> </mrow> <mrow> <mn>03</mn> </mrow> <mi>o</mi> </msubsup> </mrow> </semantics></math> modes. Field (Ex, horizontal component) and phase distributions of the resulting OAM mode: (<b>c</b>) electric field and (<b>d</b>) phase distributions.</p>
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<p>HG-similar component mode field distributions in the designed waveguide for <span class="html-italic">l</span> = ±4 OAM mode: (<b>a</b>)<math display="inline"><semantics> <mrow> <msubsup> <mrow> <mrow> <mtext> </mtext> <mi>LG</mi> </mrow> </mrow> <mrow> <mn>04</mn> </mrow> <mi>e</mi> </msubsup> </mrow> </semantics></math> and;(<b>b</b>) <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>LG</mi> </mrow> <mrow> <mn>04</mn> </mrow> <mi>o</mi> </msubsup> </mrow> </semantics></math> modes. Field (Ex, horizontal component) and phase distributions of the resulting OAM mode: (<b>c</b>) electric field and (<b>d</b>) phase distributions.</p>
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<p>Fabrication process of the proposed waveguide.</p>
Full article ">
9 pages, 2458 KiB  
Article
Modeling and Analysis of SOI Gratings-Based Opto-Fluidic Biosensor for Lab-on-a-Chip Applications
by Venkatesha Muniswamy, Prasant Kumar Pattnaik and Narayan Krishnaswamy
Photonics 2019, 6(2), 71; https://doi.org/10.3390/photonics6020071 - 20 Jun 2019
Cited by 5 | Viewed by 4056
Abstract
The design, modeling, and analysis of a silicon-on-insulator (SOI) grating coupler integrated with a microfluidic channel for lab-on-a-chip applications are presented. The grating coupler was designed to operate at 1310 nm. The simulated SOI structure consisted of a 220 nm top-Si device layer [...] Read more.
The design, modeling, and analysis of a silicon-on-insulator (SOI) grating coupler integrated with a microfluidic channel for lab-on-a-chip applications are presented. The grating coupler was designed to operate at 1310 nm. The simulated SOI structure consisted of a 220 nm top-Si device layer with an integrated waveguide, grating coupler, and a buried oxide layer of 2 µm. A rectangular microfluidic channel was deposited on the SOI optical grating structure for light and fluid interaction. The fluidic flow through the device was driven by centrifugal and Coriolis forces. The grating structure was designed to achieve a maximum coupling efficiency at the optimized injection angle of the light source. The sensitivity of the grating structure could be analyzed and evaluated using the change in coupled power as a function of the effective refractive index and was found to be 0.928 × 10−6 RIU. The SOI optical grating structure along with the micro fluidic channel on top could be effectively used as an absorbance-based lab-on-a-chip biosensor. Full article
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<p>A 3D view of the silicon-on-insulator (SOI) grating structure.</p>
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<p>Grating structure dimensions.</p>
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<p>Front views of the SOI grating coupler: (<b>a</b>) without a PDMS microfluidic channel and (<b>b</b>) with a PDMS microfluidic channel.</p>
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<p>(<b>a</b>) The structure (two-dimensional view) of the PDMS microfluidic channel and (<b>b</b>) the SOI grating coupler with the PDMS microfluidic channel.</p>
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<p>Pressure along the central axis of the channel.</p>
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<p>Injection angle as a function of coupled power.</p>
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<p>Combined coupled power plots using the direct method (shown in yellow) and the indirect method (shown in black) as a function of wavelength.</p>
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<p>Effective index as a function of wavelength.</p>
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<p>Fabrication process flow steps of the SOI grating coupler simulated using the Intellisense simulation package.</p>
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13 pages, 4146 KiB  
Article
Theoretical Study of a Surface Collinear Holographic Memory
by Soki Hirayama, Ryushi Fujimura, Shinsuke Umegaki, Yoshito Y. Tanaka and Tsutomu Shimura
Photonics 2019, 6(2), 70; https://doi.org/10.3390/photonics6020070 - 19 Jun 2019
Cited by 3 | Viewed by 4621
Abstract
Holographic memory is currently attracting attention as a data storage system capable of achieving a data transfer rate of about 105~106 times that of an optical disc such as Blu-ray disc. In conventional holographic memory, data is generally recorded by [...] Read more.
Holographic memory is currently attracting attention as a data storage system capable of achieving a data transfer rate of about 105~106 times that of an optical disc such as Blu-ray disc. In conventional holographic memory, data is generally recorded by optical writing using volume holograms. However, a volume hologram has the problem not only that it is required to have high mechanical accuracy of a system and low coefficient of thermal expansion of a recording medium, because reconstruction tolerance is extremely low, but also that duplicating time efficiency is poor because whole data cannot be recorded at once. In this paper we proposed surface holographic memory that achieved a high data transfer rate, stable readout performance, and collective duplication by expressing holograms with fine surface asperity. Furthermore, the theoretical formulas of recording and reconstruction processes in the proposed system were derived and the reconstruction characteristics of the hologram were evaluated by numerical simulation. As a result, the proposed method generated reconstructed image readout with sufficient signal for a single page recording. However, the reconstructed image had noise, which was particular to a surface holographic memory. Full article
(This article belongs to the Special Issue Holographic Optical Memory and Related Technologies)
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<p>(<b>a</b>) Schematic of the optical system in case of reconstruction; (<b>b</b>) schematic of the optical system assumed for calculation in the case of hologram design.</p>
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<p>Original intensity pattern of signal pixels and reference pixels.</p>
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<p>(<b>a</b>) Original pattern of signal area; (<b>b</b>) intensity distribution of reconstructed signal area. (omitting unnecessary interference).</p>
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<p>(<b>a</b>) Histogram of the reconstructed signal (including unnecessary interference), <math display="inline"><semantics> <mrow> <mrow> <mi>signal</mi> <mtext> </mtext> <mi>to</mi> <mtext> </mtext> <mi>noise</mi> <mtext> </mtext> <mi>ratio</mi> <mtext> </mtext> </mrow> <mrow> <mo>(</mo> <mrow> <mi>SNR</mi> </mrow> <mo>)</mo> </mrow> <mo>=</mo> <mn>3.8</mn> <mrow> <mtext> </mtext> <mi>dB</mi> </mrow> </mrow> </semantics></math>; (<b>b</b>) histogram of the reconstructed signal (omitting unnecessary interference), <math display="inline"><semantics> <mrow> <mi>SNR</mi> <mo>=</mo> <mn>5.1</mn> <mrow> <mtext> </mtext> <mi>dB</mi> </mrow> <mo>.</mo> </mrow> </semantics></math></p>
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<p>Shift selectivity of the surface collinear holographic memory.</p>
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<p>Histogram of the reconstructed signal area in case of three multiplexed hologram, SNR = <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>0.9</mn> <mrow> <mtext> </mtext> <mi>dB</mi> </mrow> <mo>.</mo> </mrow> </semantics></math></p>
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<p>Each intensity distribution on the reconstructed image plane calculated by separating only each order diffracted light, (<b>a</b>) <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </semantics></math>nd-order; (<b>b</b>) <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math>st-order; (<b>c</b>) <math display="inline"><semantics> <mn>0</mn> </semantics></math>th-order; (<b>d</b>) <math display="inline"><semantics> <mrow> <mo>+</mo> <mn>1</mn> </mrow> </semantics></math>st-order; (<b>e</b>) <math display="inline"><semantics> <mrow> <mo>+</mo> <mn>2</mn> </mrow> </semantics></math>nd-order.</p>
Full article ">
9 pages, 930 KiB  
Article
Third-Order Nonlinear Spectrum of GaN under Femtosecond-Pulse Excitation from the Visible to the Near Infrared
by Gustavo F. B. Almeida, Sabrina N. C. Santos, Jonathas P. Siqueira, Jessica Dipold, Tobias Voss and Cleber R. Mendonça
Photonics 2019, 6(2), 69; https://doi.org/10.3390/photonics6020069 - 18 Jun 2019
Cited by 12 | Viewed by 4810
Abstract
Gallium nitride (GaN) has been established as a promising candidate for integrated electro-optic and photonic devices, aiming at applications from optical switching to signal processing. Studies of its optical nonlinearities, however, lack spectral coverage, especially in the telecommunications range. In this study, we [...] Read more.
Gallium nitride (GaN) has been established as a promising candidate for integrated electro-optic and photonic devices, aiming at applications from optical switching to signal processing. Studies of its optical nonlinearities, however, lack spectral coverage, especially in the telecommunications range. In this study, we measured the two-photon absorption coefficient (β) and the nonlinear index of refraction (n2) of GaN from the visible to the near-infrared by using femtosecond laser pulses. We observed an increase of β from (1.0 ± 0.2) to (2.9 ± 0.6) ×10−11 m/W as the photon energy approached the band gap from 1.77 up to 2.25 eV (700–550 nm), while n2 varied from (90 ± 30) ×10−20 up to (265 ± 80) ×10−20 m2/W within a broad spectral range, from 0.80 up to 2.25 eV (1550–550 nm). The results were modeled by applying a theory based on the second-order perturbation theory and the Kramers-Kronig relationship for direct-gap semiconductors, which are important for the development of GaN-based nonlinear photonic devices. Full article
(This article belongs to the Special Issue Advanced Optical Materials and Devices)
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<p>Open- and closed-aperture Z-scan signatures and their corresponding fitting curves at 1.77 eV (700 nm) (<b>a</b>,<b>b</b>, respectively) and at 0.88 eV (1400 nm) (<b>c</b>,<b>d</b>, respectively).</p>
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<p>Experimental (solid circles) and theoretical (line) dispersion of the two-photon absorption coefficient (β) of GaN with respect to its band gap energy of 3.39 eV. Literature data are plotted as a hollow circle [<a href="#B37-photonics-06-00069" class="html-bibr">37</a>], star [<a href="#B38-photonics-06-00069" class="html-bibr">38</a>], pentagons [<a href="#B39-photonics-06-00069" class="html-bibr">39</a>], asterisks [<a href="#B40-photonics-06-00069" class="html-bibr">40</a>], up-triangle [<a href="#B41-photonics-06-00069" class="html-bibr">41</a>], and down-triangle [<a href="#B42-photonics-06-00069" class="html-bibr">42</a>].</p>
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<p>Experimental (solid circles) and theoretical (line) dispersion of the nonlinear refractive index (n<sub>2</sub>) of GaN with respect to its band gap energy of 3.39 eV. Literature data are plotted as pentagons [<a href="#B39-photonics-06-00069" class="html-bibr">39</a>], up-triangles [<a href="#B41-photonics-06-00069" class="html-bibr">41</a>], and hollow squares [<a href="#B43-photonics-06-00069" class="html-bibr">43</a>].</p>
Full article ">
9 pages, 1026 KiB  
Article
High Concentration Photovoltaics (HCPV) with Diffractive Secondary Optical Elements
by Furkan E. Sahin and Musa Yılmaz
Photonics 2019, 6(2), 68; https://doi.org/10.3390/photonics6020068 - 12 Jun 2019
Cited by 17 | Viewed by 16172
Abstract
Multi-junction solar cells can be economically viable for terrestrial applications when operated under concentrated illuminations. The optimal design of concentrator optics in high concentration photovoltaics (HCPV) systems is crucial for achieving high energy conversion. At a high geometric concentration, chromatic aberration of the [...] Read more.
Multi-junction solar cells can be economically viable for terrestrial applications when operated under concentrated illuminations. The optimal design of concentrator optics in high concentration photovoltaics (HCPV) systems is crucial for achieving high energy conversion. At a high geometric concentration, chromatic aberration of the primary lens can restrict the optical efficiency and acceptance angle. In order to correct chromatic aberration, multi-material, multi-element refractive elements, hybrid refractive/diffractive elements, or multi-element refractive and diffractive systems can be designed. In this paper, the effect of introducing a diffractive surface in the optical path is analyzed. An example two-stage refractive and diffractive optical system is shown to have an optical efficiency of up to 0.87, and an acceptance angle of up to ±0.55° with a 1600× geometric concentration ratio, which is a significant improvement compared to a single-stage concentrator system with a single material. This optical design can be mass-produced with conventional fabrication methods, thus providing a low-cost alternative to other approaches, and the design approach can be generalized to many other solar concentrator systems with different cell sizes and geometric concentration ratios. Full article
(This article belongs to the Special Issue Nonimaging Optics in Solar Energy)
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<p>Solar spectrum in the visible and near-infrared regions. Relative weights for wavelengths used in the optimization and analyses are shown with the red triangles [<a href="#B15-photonics-06-00068" class="html-bibr">15</a>].</p>
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<p>Schematic drawing of the designed high-concentration photovoltaics (HCPV) system with a diffractive secondary optical element. (Not drawn to scale).</p>
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<p>Angular efficiency curves for the different optical configurations studied. DOE: diffractive optical element.</p>
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<p>Angular efficiency curves for the different optical configurations studied, with 2 mm misalignment between the Fresnel lens and the diffractive SOE.</p>
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15 pages, 4951 KiB  
Article
Optoacoustic Calcium Imaging of Deep Brain Activity in an Intracardially Perfused Mouse Brain Model
by Oleksiy Degtyaruk, Benedict Mc Larney, Xosé Luís Deán-Ben, Shy Shoham and Daniel Razansky
Photonics 2019, 6(2), 67; https://doi.org/10.3390/photonics6020067 - 12 Jun 2019
Cited by 10 | Viewed by 5627
Abstract
One main limitation of established neuroimaging methods is the inability to directly visualize large-scale neural dynamics in whole mammalian brains at subsecond speeds. Optoacoustic imaging has advanced in recent years to provide unique advantages for real-time deep-tissue observations, which have been exploited for [...] Read more.
One main limitation of established neuroimaging methods is the inability to directly visualize large-scale neural dynamics in whole mammalian brains at subsecond speeds. Optoacoustic imaging has advanced in recent years to provide unique advantages for real-time deep-tissue observations, which have been exploited for three-dimensional imaging of both cerebral hemodynamic parameters and direct calcium activity in rodents. Due to a lack of suitable calcium indicators excitable in the near-infrared window, optoacoustic imaging of neuronal activity at deep-seated areas of the mammalian brain has been impeded by the strong absorption of blood in the visible range of the light spectrum. To overcome this, we have developed and validated an intracardially perfused mouse brain preparation labelled with genetically encoded calcium indicator GCaMP6f that closely resembles in vivo conditions. By overcoming the limitations of hemoglobin-based light absorption, this new technique was used to observe stimulus-evoked calcium dynamics in the brain at penetration depths and spatio-temporal resolution scales not attainable with existing neuroimaging techniques. Full article
(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)
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<p>Imaging system design and baseline brain images (<b>a</b>) Layout of the experimental functional optoacoustic neuro-tomography (FONT) setup used to record the blood clearing procedure. ACSF: artificial cerebrospinal fluid; HC: heating coil; PT: pressure transducer; STA: spherical transducer array; OPO: optical parametric oscillator; DAQ: data acquisition unit; PC: personal computer (<b>b</b>) Maximum intensity projections (MIPs) of volumetric FONT images of a GCaMP6f-labeled brain before clearing.</p>
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<p>Recorded signal changes during cardiac perfusion (<b>a</b>) Volumetric FONT images of a GCaMP6f-labeled brain during the blood clearing process. Sixty seconds after start of the cardiac perfusion, signals from vessels diminished while signals deeper in the brain could be detected with 488 nm excitation. Red dot—Vessel; Blue dot—Cortex; Green dot—Hippocampus. OA: optoacoustic (<b>b</b>) Time-traces of the normalized FONT data recorded during the clearing procedure along with the moving averages over 10 images are shown from volumes of interest indicated in panel A with the corresponding colors. Following 40 s of perfusion, blood vessels (red) lose nearly all of their signal strength at both wavelengths as blood is removed. In a cortical area at 0.3 mm depth (blue) &gt;98% of the 650 nm and ~80% of the 488 nm signal diminishes following perfusion, indicating the separation of the GCaMP signal component from the blood background. In a deeper brain area at 1.5 mm (green), a strong increase in GCaMP-related 488 nm signal was detected following perfusion, indicating that blood removal increases the maximum observable depth.</p>
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<p>(<b>a</b>) Planar wide-field fluorescence images of the blood clearing procedure in a GCaMP6f-labeled mouse. F: fluorescence; SSS: superior sagittal sinus; Acer: anterior cerebral artery (<b>b</b>) Time-traces of the normalized fluorescence data are shown from regions of interest indicated in panel A. While overall signal intensity increases as blood is removed, planar fluorescence cannot distinguish signal changes at different depths. (<b>c</b>) Transverse orthoslice from the volumetric FONT recordings at 1.5 mm depth is shown along with the corresponding coronal slice during perfusion. After 60 s, the median FONT signal increases, enabling the identification of several brain structures. L/RC: left/right cortex; h: hippocampus; Cb: Cerebellum. Red lines indicate slice positions for both views. Reference images are taken from the Allen Mouse Common coordinate Framework [<a href="#B35-photonics-06-00067" class="html-bibr">35</a>].</p>
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<p>Validation of perfused brain viability with electroencephalography (EEG) and planar wide-field fluorescence recordings. (<b>a</b>) EEG signals recorded in a GCaMP6f mouse before and after cardiac perfusion. The signal power spectra represent the frequency distribution of the brain activity. Following the addition of Pentylenetetrazol (PTZ) to the perfusion solution, an increase in both signal amplitude and its 10–20 Hz frequency components could be detected. (<b>b</b>) Temporal sequence of fluorescence-recorded brain activation maps in response to PTZ injection at t = 0. (<b>c</b>) Background-subtracted and normalized fluorescence signal traces whose position is indicated in panel B.</p>
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<p>Volumetric FONT imaging of neuronal activation in the perfused GCaMP mouse model at 488 nm. (<b>a</b>) Time-traces of the normalized FONT data along with moving averages over 10 image frames are shown from individual voxels at 0.3 and 1.5 mm brain depth—positions are indicated in panel C. (<b>b</b>) Normalized, averaged FONT traces at 0.3 mm depth following a PBS injection (control experiment) exhibit no signal changes. (<b>c</b>) Temporal progression of the relative FONT signal changes in three representative slices located at depths of 0.3, 1.5, 3 and 4.5 mm in a GCaMP6f-expressing mouse brain. PTZ injection was performed at t = 0.</p>
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27 pages, 2481 KiB  
Review
A Review of Intrinsic Optical Imaging Serial Blockface Histology (ICI-SBH) for Whole Rodent Brain Imaging
by Joël Lefebvre, Patrick Delafontaine-Martel and Frédéric Lesage
Photonics 2019, 6(2), 66; https://doi.org/10.3390/photonics6020066 - 11 Jun 2019
Cited by 6 | Viewed by 5740
Abstract
In recent years, multiple serial histology techniques were developed to enable whole rodent brain imaging in 3-D. The main driving forces behind the emergence of these imaging techniques were the genome-wide atlas of gene expression in the mouse brain, the pursuit of the [...] Read more.
In recent years, multiple serial histology techniques were developed to enable whole rodent brain imaging in 3-D. The main driving forces behind the emergence of these imaging techniques were the genome-wide atlas of gene expression in the mouse brain, the pursuit of the mouse brain connectome, and the BigBrain project. These projects rely on the use of optical imaging to target neuronal structures with histological stains or fluorescent dyes that are either expressed by transgenic mice or injected at specific locations in the brain. Efforts to adapt the serial histology acquisition scheme to use intrinsic contrast imaging (ICI) were also put forward, thus leveraging the natural contrast of neuronal tissue. This review focuses on these efforts. First, the origin of optical contrast in brain tissue is discussed with emphasis on the various imaging modalities exploiting these contrast mechanisms. Serial blockface histology (SBH) systems using ICI modalities are then reported, followed by a review of some of their applications. These include validation studies and the creation of multimodal brain atlases at a micrometer resolution. The paper concludes with a perspective of future developments, calling for a consolidation of the SBH research and development efforts around the world. The goal would be to offer the neuroscience community a single standardized open-source SBH solution, including optical design, acquisition automation, reconstruction algorithms, and analysis pipelines. Full article
(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)
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<p>Examples of various intrinsic optical contrast mechanisms that can be used to image the brain: (<b>A</b>) Reflectivity, (<b>B</b>) absorption from photo-acoustics microscopy (PAM), (<b>C</b>) attenuation, (<b>D</b>) retardance from Optical Coherence Tomography (OCT) imaging, (<b>E</b>) nonlinear optics such as third-harmonic generation (THG), and (<b>F</b>) Raman scattering. The images for <a href="#photonics-06-00066-f001" class="html-fig">Figure 1</a>A,C come from our previous work [<a href="#B16-photonics-06-00066" class="html-bibr">16</a>]. For more information about the images presented, consult the appropriate references. The absorption image is an excerpt from a still frame from the supplementary video 3 of Wong2017 [<a href="#B17-photonics-06-00066" class="html-bibr">17</a>], the THG image is a reproduction of Figure 3 from Farrar2011 [<a href="#B18-photonics-06-00066" class="html-bibr">18</a>], the retardance image comes from Wang2014 [<a href="#B19-photonics-06-00066" class="html-bibr">19</a>], and the Coherent Anti-stokes Raman Spectroscopy (CARS) image is taken from Fu2008 [<a href="#B20-photonics-06-00066" class="html-bibr">20</a>].</p>
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<p>A representation of a fully automated dual-resolution serial OCT imaging system (Right) and a diagram of the workflow pipeline used to control the acquisition (Left): The 2R-SOCT consists in a vibratome coupled to two OCT arms, a 3X arm to acquire low-resolution data (25 µm/voxel) used for the whole mouse brain reconstruction, and a 40X arm used to acquire high-resolution images (1.5 µm/voxel) in automatically chosen regions of interests (ROIs). The solid lines represent the order of operation of acquisition. The dashed lines represent data transfer to other parts of the workflow (e.g., sending in situ assembled slices to generate 40X ROIs). The green shaded boxes are tasks necessitating mechanical movements, and the blue shaded boxes represent data generation or transfer operations. FM: Flip mirror, M: Mirror. Adapted from our previous work [<a href="#B80-photonics-06-00066" class="html-bibr">80</a>].</p>
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<p>A representation of the principal data reconstruction steps used for SBH, which consists in preprocessing (here, vignetting correction is illustrated), lateral (XY) reconstruction of each tissue slices, and the stitching of each slices along the z-axis to obtain a complete 3-D representation of the whole mouse brain.</p>
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<p>Examples of tissue sectioning artefacts for a serial OCT mouse brain: (<b>A</b>) Agarose tearing, (<b>B</b>) coronal slice exhibiting shadowing effects due to floating fibers, (<b>C</b>) horizontal slice with missing tissue due to tissue/agarose separation (arrow), (<b>D</b>) B-Scan corresponding to the horizontal red line of image B showing water-tissue interface denivelation, and (<b>E</b>) B-Scan corresponding to the vertical green line in <a href="#photonics-06-00066-f004" class="html-fig">Figure 4</a>B, showing floating tissue fibers and their shadow. The scale bar is 1.5 mm.</p>
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17 pages, 4723 KiB  
Review
Photonic and Iontronic Sensing in GaInAsP Semiconductor Photonic Crystal Nanolasers
by Toshihiko Baba
Photonics 2019, 6(2), 65; https://doi.org/10.3390/photonics6020065 - 10 Jun 2019
Cited by 11 | Viewed by 4900
Abstract
The GaInAsP semiconductor photonic crystal nanolaser operates at room temperature by photopumping and emits near-infrared light at a wavelength longer than 1.3 μm. Immersion of the nanolaser in a solution causes its laser characteristics to change. Observation of this phenomenon makes it possible [...] Read more.
The GaInAsP semiconductor photonic crystal nanolaser operates at room temperature by photopumping and emits near-infrared light at a wavelength longer than 1.3 μm. Immersion of the nanolaser in a solution causes its laser characteristics to change. Observation of this phenomenon makes it possible to perform biosensing without a fluorescent label or a chromogenic substrate. The most common phenomenon between many photonic sensors is that the resonance wavelength reflects the refractive index of attached media; an index change of 2.5 × 10−4 in the surrounding liquid can be measured through an emission wavelength shift without stabilization. This effect is applicable to detecting environmental toxins and cell behaviors. The laser emission intensity also reflects the electric charge of surface ions. The intensity varies when an electrolyte or a negatively charged deoxyribonucleic acid (DNA), which is positively or negatively charged in water, is accumulated on the surface. This effect allows us to detect the antigen-antibody reaction of a biomarker protein from only the emission intensity without any kind of spectroscopy. In detecting a small amount of DNA or protein, a wavelength shift also appears from its concentration that is 2–3 orders of magnitude lower than those of the conventional chemical methods, such as the enzyme-linked immuno-solvent assay. It is unlikely that this wavelength behavior at such low concentrations is due to the refractive index of the biomolecules. It is observed that the electric charge of surface ions is induced by various means, including plasma exposure and an electrochemical circuit shifting the wavelength. This suggests that the superhigh sensitivity is also due to the effect of charged ions. Thus, we call this device an iontronic photonic sensor. This paper focuses on such a novel sensing scheme of nanolaser sensor, as an example of resonator-based photonic sensors, in addition to the conventional refractive index sensing. Full article
(This article belongs to the Special Issue Photonic Crystal Laser and Related Optical Devices)
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<p>Passive microcavities and nanolasers used for sensing applications.</p>
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<p>Schematic of GaInAsP PC nanolaser and its bio-sensing application. The magnified view of H0 type nanocavity with a nanoslot shows calculated distribution of modal electric field. Right lower figure schematically shows the laser wavelength before and after the sensing.</p>
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<p>Top view of fabricated GaInAsP PC nanolasers. (<b>a</b>) Single device with asymmetric H0 type nanocavity structure and a nanoslot. The dotted line in the magnified view shows areas in which hole sizes were reduced. (<b>b</b>) Arrayed device.</p>
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<p>Liquid sensing with a nanolaser. (<b>a</b>) Overview of the measurement. (<b>b</b>) Refractive indexes of PBS at various concentrations measured using an Atago PAL-PI refractometer and wavelength shift of the nanolaser when immersed in them.</p>
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<p>Measurement of the gelation reaction between endotoxin and limulus agent through the wavelength shift of nanolaser. (<b>a</b>) Temporal variations of the wavelength during the gelation. (<b>b</b>) Time needed for a wavelength shift of 0.3 nm.</p>
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<p>Live cell imaging using nanolaser array. (<b>a</b>) Concept of imaging. (<b>b</b>) Optical microscopy of cells for two samples and image by 21 × 21 nanolaser array.</p>
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<p>Photoluminescence (PL) characteristics when 300 nm-GaInAsP bulk layer on InP substrate with ZrO<sub>2</sub> coating is immersed in solution with various pHs. (<b>a</b>) PL spectrum. (<b>b</b>) Transient response of PL. (<b>c</b>) pH dependence of PL intensity and lifetime. The arrows correspond to (<b>a</b>) and (<b>b</b>), respectively.</p>
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<p>Change in oscillation wavelength and emission intensity by the adsorption of charged medium. (<b>a</b>) Alternate adsorption of polyelectrolytes. (<b>b</b>) Probe/target DNA adsorption.</p>
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<p>Change in emission intensity in nanolaser by the antigen-antibody reaction of CRMP2 protein which is negatively charged by SDS in advance.</p>
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<p>Wavelength shift in nanolaser against the three types of protein at different concentrations. The gray area shows the detection fluctuation.</p>
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<p>Relation between the wavelength shift and detection limit concentration of the target biomolecules for various label-free photonic biosensors that are operated based on optical resonance.</p>
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<p>Response of GaInAsP nanolaser after plasma exposure. (<b>a</b>) Wavelength shift. The inset shows the appearance of the plasma exposure. (<b>b</b>) Flat band potential.</p>
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<p>Electrical control of emission intensity and wavelength of GaInAsP nanolaser in photo-electrochemical circuit. (<b>a</b>) Configuration of the circuit. CE and RE denote counter and reference electrodes, respectively. (<b>b</b>) Screen print cell used as the circuit. WE denotes a working electrode. (<b>c</b>) Emission spectrum for different bias voltages <span class="html-italic">V</span>. The <span class="html-italic">V</span> value was calibrated by Ag/AgCl standard electrode. (<b>d</b>) Dependency of emission intensity and wavelength on bias voltage. For (<b>c</b>) and (<b>d</b>), pH was set at 8.</p>
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18 pages, 2552 KiB  
Review
Statistical Assessment of Open Optical Networks
by Emanuele Virgillito, Alessio Ferrari, Andrea D’Amico and Vittorio Curri
Photonics 2019, 6(2), 64; https://doi.org/10.3390/photonics6020064 - 5 Jun 2019
Cited by 11 | Viewed by 3423
Abstract
In order to cope with the increase of the final user traffic, operators and vendors are pushing towards physical layer aware networking as a way to maximize the network capacity. To this aim, optical networks are becoming more and more open by exposing [...] Read more.
In order to cope with the increase of the final user traffic, operators and vendors are pushing towards physical layer aware networking as a way to maximize the network capacity. To this aim, optical networks are becoming more and more open by exposing physical parameters enabling fast and reliable estimation of the lightpath quality of transmission. This comes in handy not only from the point of view of the planning and managing of the optical paths but also on a more general picture of the whole optical network performance. In this work, the Statistical Network Assessment Process (SNAP) is presented. SNAP is an algorithm allowing for estimating different network metrics such as blocking probability or link saturation, by generating traffic requests on a graph abstraction of the physical layer. Being aware of the physical layer parameters and transceiver technologies enables assessing their impact on high level network figures of merit. Together with a detailed description of the algorithm, we present a comprehensive review of several results on the networking impact of multirate transceivers, flex-grid spectral allocation as a means to finely exploit lightpath capacity and of different Space Division Multiplexing (SDM) solutions. Full article
(This article belongs to the Special Issue Lightwave Communications and Optical Networks)
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<p>(<b>a</b>) Pan-EU COST topology—28 nodes, 41 links, 637 km average link length, 2.98 average node degree; (<b>b</b>) average bit-rate per LP using different fiber types and multi-rate transceivers (adapted from [<a href="#B26-photonics-06-00064" class="html-bibr">26</a>]).</p>
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<p>(<b>a</b>) Pan-EU IDEALIST topology—49 nodes, 68 bidirectional fiber links. Edge labels are then lengths of each fiber pair in km; (<b>b</b>) PDF of <math display="inline"><semantics> <mrow> <mo>&lt;</mo> <msub> <mi>R</mi> <mrow> <mi>b</mi> <mo>,</mo> <mi>λ</mi> </mrow> </msub> <mo>&gt;</mo> </mrow> </semantics></math> showing the convergence of the Monte Carlo algorithm obtained with <math display="inline"><semantics> <mrow> <msub> <mi>k</mi> <mrow> <mi>M</mi> <mi>A</mi> <mi>X</mi> </mrow> </msub> <mo>=</mo> <mn>4</mn> </mrow> </semantics></math> and TDHMF; (<b>c</b>) <math display="inline"><semantics> <mrow> <mo>&lt;</mo> <msub> <mi>R</mi> <mrow> <mi>b</mi> <mo>,</mo> <mi>λ</mi> </mrow> </msub> <mo>&gt;</mo> </mrow> </semantics></math> vs <math display="inline"><semantics> <msub> <mi>N</mi> <mi>m</mi> </msub> </semantics></math>using TDHMF. MCA converges for <math display="inline"><semantics> <mrow> <msub> <mi>N</mi> <mi>m</mi> </msub> <mo>&gt;</mo> <mn>2000</mn> </mrow> </semantics></math> (adapted from (<b>a</b>) [<a href="#B7-photonics-06-00064" class="html-bibr">7</a>]; (<b>b</b>,<b>c</b>) [<a href="#B24-photonics-06-00064" class="html-bibr">24</a>]).</p>
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<p><math display="inline"><semantics> <mrow> <mo>&lt;</mo> <msub> <mi>R</mi> <mrow> <mi>b</mi> <mo>,</mo> <mi>λ</mi> </mrow> </msub> <mo>&gt;</mo> </mrow> </semantics></math> versus <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> </mrow> </semantics></math> for the two considered modulation strategies. Solid lines include ASE and NLI, dashed lines include ASE only (adapted from [<a href="#B24-photonics-06-00064" class="html-bibr">24</a>]).</p>
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<p>NLI models comparison in terms of (<b>a</b>) <math display="inline"><semantics> <mrow> <mo>&lt;</mo> <msub> <mi>R</mi> <mrow> <mi>b</mi> <mo>,</mo> <mi>λ</mi> </mrow> </msub> <mo>&gt;</mo> </mrow> </semantics></math>; (<b>b</b>) required computational time (adapted from [<a href="#B24-photonics-06-00064" class="html-bibr">24</a>]).</p>
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<p>(<b>a</b>) average blocking probability vs. average total allocated network traffic; (<b>b</b>) average link spectral load at <math display="inline"><semantics> <mrow> <mrow> <mi>B</mi> <mi>P</mi> </mrow> <mo>=</mo> <mn>1</mn> <mo>%</mo> </mrow> </semantics></math>. The thicker the lines, the more saturated the links (adapted from [<a href="#B26-photonics-06-00064" class="html-bibr">26</a>]).</p>
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<p>(<b>a</b>) description of the spectral-allocation techniques and flexible transceiver rates; (<b>b</b>) Italian network topology; 44 nodes, 3.36 average node degree (adapted from [<a href="#B29-photonics-06-00064" class="html-bibr">29</a>]).</p>
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<p>Upper row: blocking probability against the total traffic per residual spectral unit for (<b>a</b>) fix-grid and (<b>b</b>) flex-grid spectral uses. Blue, red and yellow lines refer to <math display="inline"><semantics> <msub> <mi>R</mi> <mi>G</mi> </msub> </semantics></math> of 20, 40, 100 Gbps, respectively. Dotted, dash-dotted and dashed lines refer to 25%, 50% and 75% of residual bandwidth percentage <math display="inline"><semantics> <mrow> <mi>R</mi> <mi>B</mi> <mi>P</mi> </mrow> </semantics></math>, respectively. Lower row: total traffic per residual spectral unit <span class="html-italic">T</span> at <math display="inline"><semantics> <mrow> <mrow> <mi>B</mi> <msub> <mi>P</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </mrow> <mo>=</mo> <mn>1</mn> <mo>%</mo> </mrow> </semantics></math> for fix- and flex-grid and different <math display="inline"><semantics> <mrow> <mi>R</mi> <mi>B</mi> <mi>P</mi> </mrow> </semantics></math> for <math display="inline"><semantics> <msub> <mi>R</mi> <mi>G</mi> </msub> </semantics></math> of (<b>c</b>) 20 Gbpsl; (<b>d</b>) 40 Gbps; (<b>e</b>) 100 Gbps (adapted from [<a href="#B29-photonics-06-00064" class="html-bibr">29</a>]).</p>
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<p>(<b>a</b>) German topology—17 nodes, 26 links, 207 km average link length, 3.06 average node degree; (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>B</mi> <mi>P</mi> </mrow> </semantics></math> vs. Total Allocated Traffic per Core varying the SDM cardinality (3 orange, 5 blue, 7 green) and SDM solutions: SCMCF w/o NLM (dotted), SCMCF (solid), UFR-CCC (dash-dotted) and UFR-InS (dashed); (<b>c</b>) relative gain respect to SCMCF w/o NLM on the Total Allocated Traffic per Core varying the SDM cardinality and scenarios at <math display="inline"><semantics> <mrow> <mrow> <mi>B</mi> <mi>P</mi> </mrow> <mo>=</mo> <msup> <mn>10</mn> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </mrow> </semantics></math> (adapted from [<a href="#B32-photonics-06-00064" class="html-bibr">32</a>]).</p>
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12 pages, 4187 KiB  
Article
An Optical Power Divider Based on Mode Coupling Using GaN/Al2O3 for Underwater Communication
by Retno Wigajatri Purnamaningsih, Nji Raden Poespawati, Tomy Abuzairi and Elhadj Dogheche
Photonics 2019, 6(2), 63; https://doi.org/10.3390/photonics6020063 - 3 Jun 2019
Cited by 13 | Viewed by 3914
Abstract
This paper details the design of a 1 × 8 optical power divider, using a gallium nitride (GaN) semiconductor on sapphire, which can be applied to underwater optical wireless communication. The design consists of nine parallel rectangular waveguides which are based on mode [...] Read more.
This paper details the design of a 1 × 8 optical power divider, using a gallium nitride (GaN) semiconductor on sapphire, which can be applied to underwater optical wireless communication. The design consists of nine parallel rectangular waveguides which are based on mode coupling phenomena. Analysis of the design was performed using the beam propagation method (BPM). The optimization was conducted using the 3D finite difference (FD)-BPM method with an optical signal input at the wavelength required for maritime application of λ = 0.45 µm. The signal was injected into the central waveguide. The results showed that at a propagation length of 1480 µm the optical power is divided into eight output beams with an excess loss of 0.46 dB and imbalance of 0.51 dB. The proposed design can be further developed and applied in future underwater communication technology. Full article
(This article belongs to the Special Issue Advanced Optical Materials and Devices)
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<p>Schematic structure of the proposed eight branch optical power divider in the x-z plane.</p>
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<p>Illustration of the GaN/sapphire semiconductor’s structural layers.</p>
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<p>Relative output power for various waveguide widths.</p>
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<p>Relative optical power as a function of waveguide thickness for the 4 µm waveguide width.</p>
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<p>Power loss for various gaps between adjacent waveguides.</p>
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<p>Relative power along the propagation distance for each waveguide.</p>
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<p>Field distribution of the proposed optical power splitter.</p>
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<p>Propagation for λ = 0.45 µm at (<b>a</b>) input z = 0 and (<b>b</b>) output ports z = 1480 µm.</p>
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<p>The optical field profiles at the output ports for various wavelengths close to the operating wavelength.</p>
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<p>The excess loss of the transverse electric (TE) mode in the proposed optical power divider.</p>
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<p>The power imbalance of the transverse electric (TE) mode in the proposed optical power divider.</p>
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11 pages, 4689 KiB  
Article
Fabrication of Modified Random Phase Masks with Phase Modulation Elements Exhibiting Gaussian Profiles Using Molecular Migration under Photopolymerization
by Akira Emoto, Junya Honda, Kou Suzuki, Takumi Kimoto and Takashi Fukuda
Photonics 2019, 6(2), 62; https://doi.org/10.3390/photonics6020062 - 3 Jun 2019
Cited by 1 | Viewed by 4265
Abstract
Random phase masks are important technical elements for realizing holographic memory systems that enable high density recording. However, the broadly distributed Fourier spectrum often presents a problem because wide recording spots result in reduced total storage capacity for a recording medium. In the [...] Read more.
Random phase masks are important technical elements for realizing holographic memory systems that enable high density recording. However, the broadly distributed Fourier spectrum often presents a problem because wide recording spots result in reduced total storage capacity for a recording medium. In the present study, we propose modified random phase masks with phase modulation elements exhibiting Gaussian profiles to suppress the spread of the recording spot and keep it in a narrow area, based on the reduction of the high-frequency components in a random phase pattern. We confirm the effectiveness of the proposed random phase mask using simulations of a computer-generated binary hologram. However, issues still remain in terms of the fabrication of random phase masks with Gaussian profiles. Therefore, we evaluate the feasibility of fabricating the proposed random phase mask using molecular diffusion under photopolymerization. The results confirm the feasibility of this approach over a relatively wide area for actual fabrication. Full article
(This article belongs to the Special Issue Holographic Optical Memory and Related Technologies)
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<p>Three types of two-dimensional random modulation patterns.</p>
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<p>Various random phase patterns, computer-generated binary hologram (CGBH) distributions, and reconstruction results.</p>
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<p>Comparison of the (<b>a</b>) root-mean-square error (RMSE), (<b>b</b>) signal-to-noise ratio (SNR), and (<b>c</b>) hologram area of the CGBHs. The data labels of (A)–(E) correspond to the labels in <a href="#photonics-06-00062-f002" class="html-fig">Figure 2</a>.</p>
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<p>Surface volume changes in the photopolymer material film.</p>
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<p>(<b>a</b>) Optical setup for pattern irradiation and irradiation patterns for (<b>b</b>) Gaussian-like and (<b>c</b>) continuous Gaussian-like random phase masks.</p>
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<p>(<b>a</b>) Binary irradiation pattern, (<b>b</b>) top view and (<b>c</b>) three-dimensional image of the patterned PVA film, and (<b>d</b>) cross-sectional distribution of the volume changes.</p>
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<p>Two-dimensional surface volume changes and the cross-sectional distributions for Gaussian-like random phase masks under photopolymerization depending on both the photopolymer layer thickness and UV irradiation time.</p>
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<p>Two-dimensional surface volume changes and the cross-sectional distributions for continuous Gaussian-like random phase masks under photopolymerization depending on both the photopolymer layer thickness and UV irradiation time.</p>
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<p>Wide-area measurement of surface modulations for (<b>a</b>,<b>b</b>) Gaussian-like and (<b>c</b>,<b>d</b>) continuous Gaussian-like random phase masks.</p>
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17 pages, 4373 KiB  
Article
Validation of an Inverse Fitting Method of Diffuse Reflectance Spectroscopy to Quantify Multi-Layered Skin Optical Properties
by Chiao-Yi Wang, Tzu-Chia Kao, Yin-Fu Chen, Wen-Wei Su, Hsin-Jou Shen and Kung-Bin Sung
Photonics 2019, 6(2), 61; https://doi.org/10.3390/photonics6020061 - 30 May 2019
Cited by 15 | Viewed by 5305
Abstract
Skin consists of epidermis and dermis layers that have distinct optical properties. The quantification of skin optical properties is commonly achieved by modeling photon propagation in tissue using Monte Carlo (MC) simulations and iteratively fitting experimentally measured diffuse reflectance spectra. In order to [...] Read more.
Skin consists of epidermis and dermis layers that have distinct optical properties. The quantification of skin optical properties is commonly achieved by modeling photon propagation in tissue using Monte Carlo (MC) simulations and iteratively fitting experimentally measured diffuse reflectance spectra. In order to speed up the inverse fitting process, time-consuming MC simulations have been replaced by artificial neural networks to quickly calculate reflectance spectra given tissue geometric and optical parameters. In this study the skin was modeled to consist of three layers and different scattering properties of the layers were considered. A new inverse fitting procedure was proposed to improve the extraction of chromophore-related information in the skin, including the hemoglobin concentration, oxygen saturation and melanin absorption. The performance of the new inverse fitting procedure was evaluated on 40 sets of simulated spectra. The results showed that the fitting procedure without knowing the epidermis thickness extracted chromophore information with accuracy similar to or better than fitting with known epidermis thickness, which is advantageous for practical applications due to simpler and more cost-effective instruments. In addition, the melanin volume fraction multiplied by the thickness of the melanin-containing epidermis layer was estimated more accurately than the melanin volume fraction itself. This product has the potential to provide a quantitative indicator of melanin absorption in the skin. In-vivo cuff occlusion experiments were conducted and skin optical properties extracted from the experiments were comparable to the results of previously reported in vivo studies. The results of the current study demonstrated the applicability of the proposed method to quantify the optical properties related to major chromophores in the skin, as well as scattering coefficients of the dermis. Therefore, it has the potential to be a useful tool for quantifying skin optical properties in vivo. Full article
(This article belongs to the Special Issue Biomedical Photonics Advances)
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<p>Schematic diagram of the experimental system.</p>
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<p>The absorption coefficient spectrum of pure collagen [<a href="#B26-photonics-06-00061" class="html-bibr">26</a>].</p>
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<p>Learning curves of training the ANN model for (<b>a</b>) SDS = 0.22 mm, (<b>b</b>) SDS = 0.45 mm and (<b>c</b>) SDS = 0.73 mm, respectively. The green circles indicate the epochs number of best validation performance where the validation loss is the lowest.</p>
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<p>Learning curves of training the ANN model for (<b>a</b>) SDS = 0.22 mm, (<b>b</b>) SDS = 0.45 mm and (<b>c</b>) SDS = 0.73 mm, respectively. The green circles indicate the epochs number of best validation performance where the validation loss is the lowest.</p>
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<p>Comparisons between extracted values and true values of (<b>a</b>) f<sub>blood</sub>, (<b>b</b>) StO<sub>2</sub>, and (<b>c</b>) f<sub>mel</sub> × th<sub>2</sub> from 40 sets of simulated target spectra using fitting condition YA. The red lines indicate when the extracted and true values are identical.</p>
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<p>Comparisons between extracted values and true values of (<b>a</b>) f<sub>blood</sub>, (<b>b</b>) StO<sub>2</sub>, and (<b>c</b>) f<sub>mel</sub> × th<sub>2</sub> from 40 sets of simulated target spectra using fitting condition YA. The red lines indicate when the extracted and true values are identical.</p>
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<p>Example of fitted spectra and target in-vivo spectra measured from detection fibers located at SDS equal to (<b>a</b>) 0.22 mm, (<b>b</b>) 0.45 mm, and (<b>c</b>) 0.73 mm.</p>
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<p>Extracted f<sub>blood</sub> and StO<sub>2</sub> during the arterial occlusion experiment.</p>
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<p>Extracted f<sub>blood</sub> and StO<sub>2</sub> during the venous occlusion experiment.</p>
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<p>Extracted (<b>a</b>) <b>μ<sub>s2</sub>′</b> (<b>b</b>) <b>μ<sub>s3</sub>′</b> of in-vivo inner forearm skin of healthy volunteers.</p>
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<p>Extracted (<b>a</b>) <b>μ<sub>s2</sub>′</b> (<b>b</b>) <b>μ<sub>s3</sub>′</b> of in-vivo inner forearm skin of healthy volunteers.</p>
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<p>Log of reflectance of SDS 0.22 mm on 500 nm vs. f<sub>mel</sub> × th<sub>2</sub>.</p>
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12 pages, 3256 KiB  
Article
Multiple-Code Technique for Multi-Rate Transmissions in Optical Packet Switching Networks Based on OCDMA Labels
by Kai-Sheng Chen
Photonics 2019, 6(2), 60; https://doi.org/10.3390/photonics6020060 - 30 May 2019
Cited by 3 | Viewed by 3320
Abstract
Supporting multi-rate transmission is an essential factor in current optical packet switching (OPS) networks. In this paper, the author studied a multi-rate scheme capable of forwarding packets with different signal rates based on label switching. The multiple-code (MC) technique was employed to label [...] Read more.
Supporting multi-rate transmission is an essential factor in current optical packet switching (OPS) networks. In this paper, the author studied a multi-rate scheme capable of forwarding packets with different signal rates based on label switching. The multiple-code (MC) technique was employed to label a packet by conveying its payload bits to multiple optical code-division multiple-access (OCDMA) labels. Spectral-amplitude-coding (SAC), which represents the chips in an OCDMA code as a set of wavelengths, was introduced to remove the multiple-access interference (MAI) from the overlapping among labels. The author tested the system effectiveness by conducting numerical analysis to formulate bit-error probability (BEP) and spectral efficiency (SE). The simulation results showed that the proposed network had a stable BEP performance when switching the packet flows of multiple data-rates. Full article
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<p>Proposed optical packet switching (OPS) topology and multi-rate operation. CR: core router; ER: edge router; GMPLS: generalized multi-protocol label switching; LSP: label switching path.</p>
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<p>Label distribution of two-class transmission.</p>
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<p>Optical packet structure with stacked labels for high-rate and low-rate users.</p>
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<p>Spectrum of label stack for (<b>a</b>) low-rate; (<b>b</b>) high-rate packet.</p>
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<p>Plots of three correlation functions of BIBD codes of <span class="html-italic">w</span> = 3 and <span class="html-italic">L</span> = 7.</p>
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<p>Optical packet generation for multi-rate network.</p>
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<p>Encoding of optical label of BIBD code C<sub>1</sub> = (1 1 0 0 1 0 0).</p>
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<p>Optical packet processing for multi-rate network.</p>
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<p>Decoding of optical label code.</p>
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<p>Bit-error probability (BEP) versus the user class of bit-rates <span class="html-italic">m</span> for different LSP numbers.</p>
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<p>BEP versus the LSP number <span class="html-italic">p</span> for different user distributions.</p>
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<p>User class <span class="html-italic">m</span> versus the LSP number <span class="html-italic">p</span> for different BEPs.</p>
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<p>SE versus the LSP number <span class="html-italic">p</span> for different BEPs.</p>
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8 pages, 1391 KiB  
Article
Bias Current of Semiconductor Laser: An Unsafe Key for Secure Chaos Communication
by Daming Wang, Longsheng Wang, Pu Li, Tong Zhao, Zhiwei Jia, Zhensen Gao, Yuanyuan Guo, Yuncai Wang and Anbang Wang
Photonics 2019, 6(2), 59; https://doi.org/10.3390/photonics6020059 - 29 May 2019
Cited by 13 | Viewed by 3604
Abstract
In this study, we have proposed and numerically demonstrated that the bias current of a semiconductor laser cannot be used as a key for optical chaos communication, using external-cavity lasers. This is because the chaotic carrier has a signature of relaxation oscillation, whose [...] Read more.
In this study, we have proposed and numerically demonstrated that the bias current of a semiconductor laser cannot be used as a key for optical chaos communication, using external-cavity lasers. This is because the chaotic carrier has a signature of relaxation oscillation, whose period can be extracted by the first side peak of the carrier’s autocorrelation function. Then, the bias current can be approximately cracked, according to the well-known relationship between the bias current and relaxation period of a solitary laser. Our simulated results have shown that the cracked current eavesdropper could successfully crack an encrypted message, by means of a unidirectional locking injection or a bidirectional coupling. In addition, the cracked bias current was closer to the real value as the bias current increased, meaning that a large bias current brought a big risk to the security. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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<p>Schematic diagram of two kinds of eavesdroppers: Eve<sub>A</sub> acted a disguiser that was bidirectionally coupled to the transmitter, and Eve<sub>B</sub> tapped and unidirectionally injected the transmitted light to its laser. SL—semiconductor laser; OC—optical coupler; OI—optical isolator; EDFA—erbium-doped optical fiber amplifier; <span class="html-italic">I</span>—bias current. SL<sub>1</sub> and SL<sub>2</sub> are lasers of legal users.</p>
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<p>(<b>a</b>) Power spectrum and (<b>b</b>) the autocorrelation function (ACF) trace of the external-cavity semiconductor laser (ECL) output with a bias current <span class="html-italic">I</span><sub>1</sub> = 1.6<span class="html-italic">I</span><sub>th</sub> and an amplitude feedback strength of 0.08. Arrows denote the <span class="html-italic">f</span><sub>RO</sub> and <span class="html-italic">τ</span><sub>RO</sub>, respectively. The inset plots the temporary waveform of the ECL output.</p>
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<p>Relaxation oscillation signature (ROS) as a function of the bias current of ECL: (<b>a</b>) location <span class="html-italic">τ</span><sub>RO</sub> and (<b>b</b>) height of the ACF side peak. The black curve in (<b>a</b>) the plots <span class="html-italic">τ</span><sub>RO</sub> of the solitary laser calculated from the formula of the relaxation period.</p>
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<p>Examples of eavesdropping with an initial cracked bias current of 1.8<span class="html-italic">I</span><sub>th</sub>. (<b>a1</b>) Temporal waveform of synchronized chaos (red and light blue) and (<b>a2</b>) the decoded signal (blue) of Eve<sub>A</sub> with <span class="html-italic">I</span><sub>EA</sub> = 1.616<span class="html-italic">I</span><sub>th</sub>; (<b>b1</b>) temporal waveform of synchronized chaos (red and light blue) and (<b>b2</b>) the decoded message (blue) of Eve<sub>B</sub> with <span class="html-italic">I</span><sub>EB</sub> = 1.8<span class="html-italic">I</span><sub>th</sub>. The red line is the transmitted chaos carrier with the encoded message.</p>
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<p>BER as a function of Δ<span class="html-italic">I</span> between the transmitter and the eavesdropper: (<b>a</b>) Eve<sub>A</sub> and (<b>b</b>) Eve<sub>B</sub>. The blue and yellow shaded areas denote the cracked areas.</p>
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11 pages, 2625 KiB  
Article
Nonlinear Dynamics of Exclusive Excited-State Emission Quantum Dot Lasers Under Optical Injection
by Zai-Fu Jiang, Zheng-Mao Wu, Elumalai Jayaprasath, Wen-Yan Yang, Chun-Xia Hu and Guang-Qiong Xia
Photonics 2019, 6(2), 58; https://doi.org/10.3390/photonics6020058 - 27 May 2019
Cited by 18 | Viewed by 3686
Abstract
We numerically investigate the nonlinear dynamic properties of an exclusive excited-state (ES) emission quantum dot (QD) laser under optical injection. The results show that, under suitable injection parameters, the ES-QD laser can exhibit rich nonlinear dynamical behaviors, such as injection locking (IL), period [...] Read more.
We numerically investigate the nonlinear dynamic properties of an exclusive excited-state (ES) emission quantum dot (QD) laser under optical injection. The results show that, under suitable injection parameters, the ES-QD laser can exhibit rich nonlinear dynamical behaviors, such as injection locking (IL), period one (P1), period two (P2), multi-period (MP), and chaotic pulsation (CP). Through mapping these dynamic states in the parameter space of the frequency detuning and the injection coefficient, it can be found that the IL occupies a wide region and the dynamic evolution routes appear in multiple forms. Via permutation entropy (PE) calculation to quantify the complexity of the CP state, the parameter range for acquiring the chaos with high complexity can be determined. Moreover, the influence of the linewidth enhancement factor (LEF) on the dynamical state of the ES-QD laser is analyzed. With the increase of the LEF value, the chaotic area shrinks (expands) in the negative (positive) frequency detuning region, and the IL region gradually shifts towards the negative frequency detuning. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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<p>Schematic diagram of the carrier dynamics for the ES-QD lasers. GS: ground-state; ES: excited-state; RS: reservoir.</p>
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<p>Output power (<b>a</b>), carrier number (<b>b</b>), and relaxation oscillation (RO) frequency (<b>c</b>) of the ES-QD laser as a function of the bias current.</p>
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<p>Time series (first column), power spectra (second column), and phase portraits (third column) of the ES-QD laser for ∆<span class="html-italic">ν</span> = −14.00 GHz and different <span class="html-italic">K</span>, where <span class="html-italic">K</span> = 0.30 (a1–a3), <span class="html-italic">K</span> = 0.33 (b1–b3), <span class="html-italic">K</span> = 0.49 (c1–c3), <span class="html-italic">K</span> = 0.64 (d1–d3), and <span class="html-italic">K</span> = 0.90 (e1–e3).</p>
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<p>Bifurcation diagrams of the ES-QD laser for ∆<span class="html-italic">ν</span> = −14.00 GHz.</p>
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<p>(<b>a</b>) Nonlinear dynamics distribution and (<b>b</b>) corresponding chaotic region complexity distribution of the ES-QD laser in the parameter space of injection coefficient and frequency detuning. IL: injection locking, P1: period one, P2: period two, MP: multi-period, CP: chaotic pulsation.</p>
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<p>Mappings of the nonlinear dynamics distribution of the ES-QD Laser in the parameter space of injection strength and frequency detuning for different LEF, where (<b>a</b>) <span class="html-italic">α</span> = 0.5, (<b>b</b>) <span class="html-italic">α</span> = 1.0, (<b>c</b>) <span class="html-italic">α</span> = 1.5, (<b>d</b>) <span class="html-italic">α</span> = 2.0, (<b>e</b>) <span class="html-italic">α</span> = 2.5, and (<b>f</b>) <span class="html-italic">α</span> = 3.0. IL: injection locking, P1: period one, P2: period two, MP: multi-period, CP: chaotic pulsation.</p>
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11 pages, 1534 KiB  
Article
Promote Localized Surface Plasmonic Sensor Performance via Spin-Coating Graphene Flakes over Au Nano-Disk Array
by Raed Alharbi and Mustafa Yavuz
Photonics 2019, 6(2), 57; https://doi.org/10.3390/photonics6020057 - 25 May 2019
Cited by 1 | Viewed by 3757
Abstract
Although localized surface plasmonic resonance (LSPR) sensors have advantages over regular surface plasmonic resonance (SPR) sensors, such as in sensor setup, excitation method, and cost, they suffer from low performance when compared to SPR sensors, which thus limits their commercialization. Among different methods [...] Read more.
Although localized surface plasmonic resonance (LSPR) sensors have advantages over regular surface plasmonic resonance (SPR) sensors, such as in sensor setup, excitation method, and cost, they suffer from low performance when compared to SPR sensors, which thus limits their commercialization. Among different methods applied to promote LSPR sensor performance, metal-two-dimensional (2D) hybrid nanostructure has been shown to be an efficient improvement. However, metal-2D hybrid nanostructures may come in a complex or a simple scheme and the latter is preferred to avoid challenges in fabrication work and to be applicable in mass production. In this work, a new and simple gold-graphene hybrid scheme is proposed and its plasmonic sensing performance is numerically evaluated using the finite different time domain (FDTD) method. The proposed sensor can be fabricated by growing a Au nano-disk (ND) array on a quartz substrate and then spin-coating graphene flakes of different sizes and shapes randomly on top of and between the Au NDs. Very high sensitivity value is achieved with 2262 nm/RIU at a 0.01 refractive index change. The obtained sensitivity value is very competitive in the field of LSPR sensors using metal-2D hybrid nanostructure. This proposed sensor can be utilized in different biosensing applications such as immunosensors, sensing DNA hybridization, and early disease detection, as discussed at the end of this article. Full article
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<p>Schematic representation of the simulation model (<b>a</b>), 3D view (3 G flakes) (<b>b</b>), 3D view (10 G flakes) (<b>c</b>), and cross section view (<b>d</b>) of the gold nano-disk (ND)-graphene (G) flakes hybrid nanostructure.</p>
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<p>Imaginary and real part of Au permittivity (<b>a</b>,<b>b</b>) and of graphene (<b>c</b>,<b>d</b>) as a function of wavelength in Vis-NIR region (0.4–2 µm).</p>
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<p>Absorption spectra of Au ND array and Au-G flakes hybrid nanostructure (<b>a</b>), and the cross section (x-z axis) electric field profile of Au ND array (<b>b</b>) and Au-G hybrid nanostructure (<b>c</b>) at λ = 1203.81 nm.</p>
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<p>Absorption spectra of Au ND-G flakes hybrid nanostructure at different refractive index of sensing medium.</p>
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<p>Resonances A and B shifts vs. refractive index change.</p>
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<p>Sensitivity of resonance modes A and B as the refractive index changes.</p>
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12 pages, 8488 KiB  
Article
Propagation of Cylindrical Vector Laser Beams in Turbid Tissue-Like Scattering Media
by Alexander Doronin, Nicolás Vera, Juan P. Staforelli, Pablo Coelho and Igor Meglinski
Photonics 2019, 6(2), 56; https://doi.org/10.3390/photonics6020056 - 24 May 2019
Cited by 26 | Viewed by 5942
Abstract
We explore the propagation of the cylindrical vector beams (CVB) in turbid tissue-like scattering medium in comparison with the conventional Gaussian laser beam. The study of propagation of CVB and Gaussian laser beams in the medium is performed utilizing the unified electric field [...] Read more.
We explore the propagation of the cylindrical vector beams (CVB) in turbid tissue-like scattering medium in comparison with the conventional Gaussian laser beam. The study of propagation of CVB and Gaussian laser beams in the medium is performed utilizing the unified electric field Monte Carlo model. The implemented Monte Carlo model is a part of a generalized on-line computational tool and utilizes parallel computing, executed on the NVIDIA Graphics Processing Units (GPUs) supporting Compute Unified Device Architecture (CUDA). Using extensive computational studies, we demonstrate that after propagation through the turbid tissue-like scattering medium, the degree of fringe contrast for CVB becomes at least twice higher in comparison to the conventional linearly polarized Gaussian beam. The results of simulations agree with the results of experimental studies. Both experimental and theoretical results suggest that there is a high potential of the application of CVB in the diagnosis of biological tissues. Full article
(This article belongs to the Special Issue Biomedical Photonics Advances)
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<p>Schematic presentation of the cross-section of the cylindrical vector laser beams (CVB) with different polarization distribution, defined by <span class="html-italic">l</span> and <math display="inline"><semantics> <mi>σ</mi> </semantics></math>. Here, <b>left</b>: <math display="inline"><semantics> <mrow> <mi>l</mi> <mo>=</mo> <mo>+</mo> <mn>1</mn> <mo>,</mo> <mspace width="3.33333pt"/> <mi>σ</mi> <mo>=</mo> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math>, <b>middle</b>: <math display="inline"><semantics> <mrow> <mi>l</mi> <mo>=</mo> <mo>+</mo> <mn>2</mn> <mo>,</mo> <mspace width="3.33333pt"/> <mi>σ</mi> <mo>=</mo> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math> and <b>right</b>: <math display="inline"><semantics> <mrow> <mi>l</mi> <mo>=</mo> <mo>+</mo> <mn>3</mn> <mo>,</mo> <mspace width="3.33333pt"/> <mi>σ</mi> <mo>=</mo> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math>, respectively.</p>
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<p>The block-diagram showing the principles of GPU-based computations of the resulting intensity of scattered light and its spatial distribution at the detector area (<b>left</b>). Front screen of the online MC tool where each icon is associated with a particular application (<b>right</b>), available online at <a href="http://www.lighttransport.net/" target="_blank">http://www.lighttransport.net/</a>.</p>
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<p>The results of simulation of <math display="inline"><semantics> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>o</mi> <mi>t</mi> </mrow> </msub> </semantics></math>, co- <math display="inline"><semantics> <msub> <mi>I</mi> <mo>‖</mo> </msub> </semantics></math> and cross- <math display="inline"><semantics> <msub> <mi>I</mi> <mo>⊥</mo> </msub> </semantics></math> polarized components of a CVB with <math display="inline"><semantics> <mrow> <mi>l</mi> <mo>=</mo> <mo>+</mo> <mn>1</mn> <mo>,</mo> <mspace width="3.33333pt"/> <mi>σ</mi> <mo>=</mo> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math>, transmitted through the scattering medium of various optical densities (<math display="inline"><semantics> <mrow> <mi>O</mi> <mi>D</mi> </mrow> </semantics></math>): 1.08, 1.56, 2.00, 2.40, 2.73.</p>
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<p>The results of MC simulation of co- <math display="inline"><semantics> <msub> <mi>I</mi> <mo>‖</mo> </msub> </semantics></math> and cross- <math display="inline"><semantics> <msub> <mi>I</mi> <mo>⊥</mo> </msub> </semantics></math> polarized components, and <math display="inline"><semantics> <mrow> <mi>D</mi> <mi>R</mi> </mrow> </semantics></math> for a Gaussian (<b>left</b>, <a href="#app1-photonics-06-00056" class="html-app">supplementary video S1</a>) and CVB (<b>right</b>, <a href="#app1-photonics-06-00056" class="html-app">supplementary video S2</a>) with <math display="inline"><semantics> <mrow> <mi>l</mi> <mo>=</mo> <mo>+</mo> <mn>1</mn> <mo>,</mo> <mspace width="3.33333pt"/> <mi>σ</mi> <mo>=</mo> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math>, transmitted through a turbid medium, with two sets of optical properties: <math display="inline"><semantics> <mrow> <mi>g</mi> <mo>=</mo> <mn>0.0</mn> <mo>,</mo> <msub> <mi>μ</mi> <mi>s</mi> </msub> </mrow> </semantics></math> = 1–30 mm<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>g</mi> <mo>=</mo> <mn>0.9</mn> <mo>,</mo> <msub> <mi>μ</mi> <mi>s</mi> </msub> </mrow> </semantics></math> = 10–300 mm<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, in both cases thickness is 100 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m.</p>
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<p>Schematic representation of the experiment setup to generate the desired CVB with the opposite charge.</p>
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<p>The results of experimental measurements of <math display="inline"><semantics> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>o</mi> <mi>t</mi> </mrow> </msub> </semantics></math>, co- <math display="inline"><semantics> <msub> <mi>I</mi> <mo>‖</mo> </msub> </semantics></math> and cross- <math display="inline"><semantics> <msub> <mi>I</mi> <mo>⊥</mo> </msub> </semantics></math> polarized components of a CVB beam with <math display="inline"><semantics> <mrow> <mi>l</mi> <mo>=</mo> <mo>+</mo> <mn>1</mn> <mo>,</mo> <mspace width="3.33333pt"/> <mi>σ</mi> <mo>=</mo> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math> transmitted through a cuvette containing different concentrations of polystyrene microspheres solutions of various <math display="inline"><semantics> <mrow> <mi>O</mi> <mi>D</mi> </mrow> </semantics></math>: 1.08, 1.56, 2.00, 2.40, 2.73.</p>
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<p>The results of experimental measurements of fringe contrast for CVB propagated through the turbid scattering media in comparison to the results of MC modeling performed for the turbid media with the same optical properties.</p>
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8 pages, 8766 KiB  
Article
Numerical Simulation of Mid-Infrared Optical Frequency Comb Generation in Chalcogenide As2S3 Microbubble Resonators
by Elena A. Anashkina, Maria P. Marisova, Arseny A. Sorokin and Alexey V. Andrianov
Photonics 2019, 6(2), 55; https://doi.org/10.3390/photonics6020055 - 23 May 2019
Cited by 11 | Viewed by 4891
Abstract
Mid-infrared optical frequency comb generation in whispering gallery mode microresonators attracts significant interest. Chalcogenide glass microresonators are good candidates for operating in the mid-infrared range. We present the first theoretical analysis of optical frequency comb generation in As2S3 microbubble resonators [...] Read more.
Mid-infrared optical frequency comb generation in whispering gallery mode microresonators attracts significant interest. Chalcogenide glass microresonators are good candidates for operating in the mid-infrared range. We present the first theoretical analysis of optical frequency comb generation in As2S3 microbubble resonators in the 3–4 μm range. The regime of dissipative soliton plus dispersive wave generation is simulated numerically in the frame of the Lugiato–Lefever equation. Using microbubble geometry allows controlling of the zero-dispersion wavelength and the obtaining of anomalous dispersion needed for soliton generation at the pump wavelength of 3.5 μm, whereas the zero-dispersion wavelength of the analyzed As2S3 glass is ~4.8 μm. It is shown that, for the optimized characteristics of microbubble resonators, optical frequency combs with a spectral width of more than 700 nm (at the level of −30 dB) can be obtained with the low pump power of 10 mW. Full article
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<p>Scheme of the considered system.</p>
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<p>Zero-dispersion wavelength as a function of thickness and radius of a microbubble (<b>a</b>). Dispersion as a function of thickness and radius of a microbubble calculated at <span class="html-italic">λp</span> = 3.5 μm (<b>b</b>).</p>
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<p>Dispersion as a function of wavelength.</p>
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<p>Effective volume of fundamental WGM (<b>a</b>) and nonlinear coefficient (<b>b</b>) as functions of thickness and radius of a microbubble calculated at <span class="html-italic">λp</span> = 3.5 μm.</p>
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<p>Spectra of optical frequency combs (<b>left</b>) and temporal intensity distributions (<b>right</b>). DW is dispersive waves.</p>
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14 pages, 2850 KiB  
Article
Photonic Crystal Circular Defect (CirD) Laser
by Yifan Xiong, Hanqiao Ye, Takuma Umeda, Shun Mizoguchi, Masato Morifuji, Hirotake Kajii, Akihiro Maruta and Masahiko Kondow
Photonics 2019, 6(2), 54; https://doi.org/10.3390/photonics6020054 - 20 May 2019
Cited by 22 | Viewed by 4378
Abstract
We describe the design of photonic crystal circular defect (CirD) lasers to construct a compact optical module with a wavelength division multiplexing function for the application of inter-chip or intra-chip optical interconnects. Subsequently, we investigated the characteristics of CirD lasers including the quality [...] Read more.
We describe the design of photonic crystal circular defect (CirD) lasers to construct a compact optical module with a wavelength division multiplexing function for the application of inter-chip or intra-chip optical interconnects. Subsequently, we investigated the characteristics of CirD lasers including the quality factor of the cavity, the lasing threshold, and the modulation speed with a three-dimensional finite-difference time-domain method and two-dimensional rate equations. Finally, we demonstrated the single mode lasing and wavelength tuning behaviors of the CirD lasers using optical pumping technology under room-temperature continuous-wave conditions. Full article
(This article belongs to the Special Issue Photonic Crystal Laser and Related Optical Devices)
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<p>Schematic of electrically-driven CirD laser.</p>
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<p>Magnetic field intensity (<math display="inline"><semantics> <mrow> <mrow> <mo>|</mo> </mrow> <msub> <mi>H</mi> <mi>z</mi> </msub> <mrow> <mo>|</mo> </mrow> </mrow> </semantics></math>) distribution of Circular Defect (CirD) lasers. Circles represent air holes.</p>
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<p>(<b>a</b>) Schematic of CirD laser array architecture enabled wavelength division multiplexing (WDM). (<b>b</b>) Schematic of CirD laser array in which each cavity is isolated by current blocking trench. 5 μm × 5 μm area outside of cavity is used as the bonding pad.</p>
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<p>(<b>a</b>) Schematic of monolithic integrated optical module combined with wavelength division multiplexing and demultiplexing functions. (<b>b</b>) Schematic of flip-chip boding of integrated optical module to silicon substrate.</p>
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<p>Resonant wavelength (<math display="inline"><semantics> <mi>λ</mi> </semantics></math>) and quality factor (<math display="inline"><semantics> <msub> <mi>Q</mi> <mi>s</mi> </msub> </semantics></math>) of CirD cavity dependent on radius of cavity (<span class="html-italic">R</span>).</p>
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<p>Lasing threshold (<math display="inline"><semantics> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </semantics></math>) versus <span class="html-italic">Q</span> for CirD lasers.</p>
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<p>Relaxation oscillation frequency (<math display="inline"><semantics> <msub> <mi>f</mi> <mi>r</mi> </msub> </semantics></math>) as a function of injection current.</p>
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<p>(<b>a</b>) Top-view and (<b>b</b>) cross-sectional view of SEM pictures for fabricated optically-driven CirD laser.</p>
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<p>Output intensity as a function of excitation power for optically-driven CirD laser.</p>
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<p>Lasing spectrum at pumping power of approximately 800 μW. (reprinted with permission from reference [<a href="#B26-photonics-06-00054" class="html-bibr">26</a>], IEEE).</p>
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<p>Measured and theoretically estimated lasing wavelengths of WGM as a function of <span class="html-italic">R</span>. Fabricated <span class="html-italic">a</span> and <span class="html-italic">r</span> were kept approximately constant at 385 nm and 0.29 <span class="html-italic">a</span>. (reprinted with permission from reference [<a href="#B26-photonics-06-00054" class="html-bibr">26</a>], IEEE).</p>
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11 pages, 3504 KiB  
Article
Efficient Dual-Wavelengths Continuous Mode Lasers by End-Pumping of Series Nd:YVO4 and Nd:GdVO4 Crystals and Speckle Reduction Study
by Mahmoud Mohamed, Bin Zhang, Qianli Ma, Josh Kneller and Chang-Qing Xu
Photonics 2019, 6(2), 53; https://doi.org/10.3390/photonics6020053 - 17 May 2019
Cited by 3 | Viewed by 3509
Abstract
In this paper, diode pumped solid state (DPSS) lasers based on end-pumping series N d : Y V O 4 and N d : G d V O 4 crystals were studied. Dual-, tri-, and quad-wavelength emissions were achieved. In the dual-wavelength emission [...] Read more.
In this paper, diode pumped solid state (DPSS) lasers based on end-pumping series N d : Y V O 4 and N d : G d V O 4 crystals were studied. Dual-, tri-, and quad-wavelength emissions were achieved. In the dual-wavelength emission operation, an optical-to-optical efficiency (O-O) of 48.9% and the power instability was 0.4% were obtained. These are the most efficient and compact lasers operating in continuous wave mode reported to date with series crystals. Besides this, the effect of changing power ratio between the output laser powers on speckle reduction was investigated for the first time. In addition, tri and quad wavelength emissions were achieved with a reasonable efficiency simply by optimizing the cavity parameters. Full article
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<p>Experimental setup used in the measurements: (<b>a</b>) diagram for end pumping series crystals laser and (<b>b</b>) schematic diagram for σ-π configurations.</p>
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<p>Configuration of <math display="inline"><semantics> <mrow> <mi>L</mi> <msub> <mi>C</mi> <mn>1</mn> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>L</mi> <msub> <mi>C</mi> <mn>2</mn> </msub> </mrow> </semantics></math> in multi wavelength emission. (<b>a</b>) A 3D configuration with a tilted angle of θ for <math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mn>2</mn> </msub> </mrow> </semantics></math>, and (<b>b</b>) xy-view of the setup for tri output wavelengths emission with θ = 0.7 mrad and ∅ = 0 rad (left) and quad wavelengths emission (right) with θ = 0.7 mrad and ∅ = 0.78 rad.</p>
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<p>Experimental setup for speckle test.</p>
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<p>(<b>a</b>) and (<b>b</b>) are the single (1063.7 nm) and dual-wavelength normalized emission spectrum respectively.</p>
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<p>The measured output powers of 1062.4 nm (triangle up) and 1063.7 nm (dots) for σ-π configuration.</p>
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<p>The measured output power versus pump power for σ-π configuration, where the total output power, output power for 1062.4 nm, and 1063.7 nm are represented by black dots, red triangle up, and blue square, respectively.</p>
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<p>The measured total output power versus input pump power for σ-π configuration.</p>
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<p>The measured (<b>a</b>) total power for σ-π configuration, (<b>b</b>) power of 1063.7 nm in σ- polarization, (<b>c</b>) power of 1062.4 nm in π- polarization.</p>
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<p>(<b>a</b>) Single-wavelength speckle image, (<b>b</b>) dual-wavelength speckle image.</p>
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<p>The speckle contrast ratio (SCR) as a function of normalized power (P<sub>λ2</sub>/(P<sub>λ1</sub>+P<sub>λ2</sub>)).</p>
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<p>The measured output spectrum of (<b>a</b>) tri-wavelength emission at 1062.4 nm, 1063.6 nm, and 1064.6 nm, and (<b>b</b>) quad-wavelength emission at 1062.3 nm, 1063.6 nm, 1064.5 nm, and 1066.1 nm.</p>
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7 pages, 2606 KiB  
Letter
The Role of Electron Transfer in the Nonlinear Response of Ge2Sb2Te5-Mediated Plasmonic Dimers
by Burak Gerislioglu and Arash Ahmadivand
Photonics 2019, 6(2), 52; https://doi.org/10.3390/photonics6020052 - 16 May 2019
Cited by 13 | Viewed by 3200
Abstract
Here, we study the possibility of exquisitely selective harmonic generation based on the concept of charge transfer plasmons (CTPs) in bridged nanoparticle assemblies. By choosing plasmonic dimer nanoantenna, as a fundamental member of the nanocluster family, and bridging the capacitive gap space between [...] Read more.
Here, we study the possibility of exquisitely selective harmonic generation based on the concept of charge transfer plasmons (CTPs) in bridged nanoparticle assemblies. By choosing plasmonic dimer nanoantenna, as a fundamental member of the nanocluster family, and bridging the capacitive gap space between the proximal nanoparticles with an optothermally controllable substance, we judiciously showed that variations in the generation of third harmonic light in the visible regime can be possible by considering distinct states of the functional bridge. To this end, the conductive connection between the nanoparticles is mediated with Ge2Sb2Te5 (GST) with inherently opposite optical and electrical properties below (dielectric, amorphous state) and above 477 °C (conductive, crystalline state). This helped to actively control the transition of charges across the bridge and thereby control the excitation of CTP resonances and provide a switching feature between dipolar and CTP modes. This versatile approach also allowed for production of the intended harmonic signal at different wavelengths depending on the conductivity of the interparticle nanojunction. Full article
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<p>(<b>a</b>) General and (<b>b</b>) top-view schematics of a single unit cell. (<b>c</b>) ε<sub>1</sub> and ε<sub>2</sub> values for both GST phases (taken from Ref. 33).</p>
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<p>(<b>a</b>) Simulated extinction spectra of the plasmonic dimer platform for the junction with full Au, a- and c-GST sections. (<b>b</b>) The corresponding 2D |E|-field maps of the proposed system (FDTD): (<b>i</b>) dipolar mode (<span class="html-italic">p</span><sub>2</sub>) at <span class="html-italic">λ</span>~1880 nm for a-GST, (<b>ii</b>) CTP mode (<span class="html-italic">p</span><sub>3</sub>) at <span class="html-italic">λ</span>~2150 nm for c-GST, and CTP mode (<span class="html-italic">p</span><sub>4</sub>) at <span class="html-italic">λ</span>~2400 nm for full Au. (<b>c</b>) The associated 2D surface charge density maps of the design (FEM): (<b>i</b>) dipolar mode (a-GST), (<b>ii</b>) CTP mode (c-GST), and CTP mode (full Au).</p>
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<p>The third harmonic emission spectrum of (<b>a</b>) a-GST and (<b>b</b>) c-GST based metadevice.</p>
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<p>The third harmonic emission spectrum of (<b>a</b>) a-GST and (<b>b</b>) c-GST cases for the variations in L: (<b>i</b>) 50 nm, (<b>ii</b>) 80 nm, and (<b>iii</b>) 100 nm.</p>
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<p>The third harmonic emission spectrum of (<b>a</b>) a-GST and (<b>b</b>) c-GST conditions for the variations in W: (<b>i</b>) 40 nm, (<b>ii</b>) 60 nm, and (<b>iii</b>) 80 nm.</p>
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8 pages, 1472 KiB  
Article
Gasoline Quality Sensor Based on Tilted Fiber Bragg Gratings
by Stenio Aristilde, Cristiano M. B. Cordeiro and Jonas H. Osório
Photonics 2019, 6(2), 51; https://doi.org/10.3390/photonics6020051 - 14 May 2019
Cited by 14 | Viewed by 3724
Abstract
We report on the study of an intensity-based optical fiber sensor for gasoline quality monitoring. The sensor setup employs two Bragg gratings with different spectral responses to interrogate the optical response of a tilted Bragg grating. The sensor operation is based on the [...] Read more.
We report on the study of an intensity-based optical fiber sensor for gasoline quality monitoring. The sensor setup employs two Bragg gratings with different spectral responses to interrogate the optical response of a tilted Bragg grating. The sensor operation is based on the tilted Bragg grating sensitivity to external refractive index changes, which are translated as power variations by the interrogation scheme. Gasoline–ethanol solutions with concentrations ranging from 0% to 60% ethanol were used to demonstrate the sensor performance. The results allowed to estimate that the sensor is able, within its resolution limit, to detect ethanol concentration variations of 1.5% in gasoline–ethanol solutions and discriminate temperature variations of 0.5 °C. The all-optical sensor setup is compact and robust, making it a competitive alternative for the realization of fuel quality analyses in practical applications. Full article
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Graphical abstract

Graphical abstract
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<p>(<b>a</b>) Spectral response of the fiber Bragg gratings (FBG 1 and FBG 2) and of the tilted Bragg grating when it is immersed in the gasoline–ethanol solutions of different concentrations. Zoomed-in view of the spectral ranges (<b>b</b>) between 1534 nm and 1537 nm and (<b>c</b>) between 1557.5 nm and 1551 nm.</p>
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<p>(<b>a</b>) Sensor setup. SLED: superluminescent light-emitting diode; OSA: optical spectrum analyzer; DET: photodetector; F: tunable spectral filter. (<b>b</b>) Spectra measured in OSA 1 (without and with the optical filter: red and blue lines, respectively) and in OSA 2 (green line). Inset shows the transmittance of the filter, which can be tuned conveniently.</p>
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<p>(<b>a</b>) Normalized voltage measured in the photodetectors (DET 1 and DET 2) as a function of the ethanol concentration in gasoline. Inset shows the signal measured by OSA 1 as a function of the ethanol concentration. (<b>b</b>) Normalized voltage variation measured in the photodetectors (DET 1 and DET 2) as a function of the temperature.</p>
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8 pages, 2492 KiB  
Article
Effects of Photonic Band Structure and Unit Super-Cell Size in Graded Photonic Super-Crystal on Broadband Light Absorption in Silicon
by Safaa Hassan, Khadijah Alnasser, David Lowell and Yuankun Lin
Photonics 2019, 6(2), 50; https://doi.org/10.3390/photonics6020050 - 9 May 2019
Cited by 8 | Viewed by 3653
Abstract
The newly discovered graded photonic super-crystal (GPSC) with a large size of unit cell can have novel optical properties that have not been explored. The unit super-cell in the GPSC can be designed to be large or small and thus the GPSC can [...] Read more.
The newly discovered graded photonic super-crystal (GPSC) with a large size of unit cell can have novel optical properties that have not been explored. The unit super-cell in the GPSC can be designed to be large or small and thus the GPSC can have no photonic band gap or several gaps. The photonic band structures in Si GPSC can help predict the light absorption in Si. Photonic resonance modes help enhance the absorption of light in silicon; however, photonic band gaps decrease the absorption for light with a large incident angle. The Si device patterned in GPSC with a unit super-cell of 6a × 6a (a is a lattice constant in traditional photonic crystal) has a broadband high absorption with strong incident-angular dependence. The device with the unit super-cell of 12a × 12a has relatively low light absorption with weak incident-angle dependence. The Si GPSC with a unit super-cell of 8a × 8a combines both advantages of broadband high absorption and weak dependence of absorption on the incident angle. Full article
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<p>(<b>a</b>) Simulated 8-bean interference pattern with a threshold I<sub>th</sub> = 0.35%Imax. The purple, gold and red squares indicate the size of 12a × 12a, 8a × 8a, and 6a × 6a (the lattice constant a = Λ1), respectively, that was used as a unit cell in Si graded photonic super-crystals (GPSCs). (<b>b</b>–<b>d</b>) Simulated photonic band structures in transverse magnetic (TM) modes for Si GPSCs with a unit cell of 6a × 6a, 8a × 8a, and 12a × 12a, respectively. (<b>e</b>–<b>g</b>) Simulated photonic band structures in transverse electric (TE) modes for Si GPSCs with a unit cell of 6a × 6a, 8a × 8a, and 12a × 12a, respectively.</p>
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<p>(<b>a</b>) Schematic of a silicon device patterned with a GPSC with a unit cell of 6a × 6a (a = 350 nm). The dashed yellow indicates the top PEDOT:PSS film for a device application. (<b>b</b>) Absorption spectra for light (x-polarization) incident at 0° onto the silicon device patterned with GPSC, and with a traditional photonic crystal in regular square lattice. (<b>c</b>) Absorption spectrum for light incident at 0 degree into the device in (<b>a</b>) for light with x, y and x-y polarizations. (<b>d</b>) Absorption spectrum for x-polarized light incident at 0° into the GPSC silicon same as the one in (<b>a</b>) but a = 340 and 330 nm.</p>
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<p>(<b>a</b>–<b>c</b>) Simulated light absorption in Si device patterned with GPSC with a unit super-cell size of 6a × 6a (<b>a</b>), 8a × 8a (<b>b</b>) and 12a × 12a (<b>d</b>) (a = 350 nm), respectively. (<b>d</b>) Shows the absorption from s-polarization and p-polarization light incident at 10 degrees for Si device patterned with GPSC with a unit super-cell size of 6a × 6a. (<b>e</b>) Average light absorption between 500–650 nm as a function of incident angles.</p>
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<p>(<b>a</b>) Schematic of x-z cross-section of Si device patterned in GPSC with a unit cell of 6a × 6a at y = 0. C and d indicate the locations in z-direction for obtaining the x-y cross-section in (<b>c</b>) and (<b>d</b>). (<b>b</b>) E-field intensity of x-polarized light incident at 0° onto a GPSC-patterned Si device in x-z cross-section corresponding to (<b>a</b>). Dashed red lines indicate the boundary between Si and air inside the Si GPSC. Dashed yellow line indicates one of light propagation path. (<b>c</b>–<b>d</b>) E-field intensity in x-y cross-section in Si at z-direction locations corresponding to c and d in (<b>a</b>), respectively. White circles indicate the location under the GPSC Si.</p>
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14 pages, 1744 KiB  
Article
Investigation of the Effect of Intra-Cavity Propagation Delay in Secure Optical Communication Using Chaotic Semiconductor Lasers
by Elumalai Jayaprasath, Zheng-Mao Wu, Sivaraman Sivaprakasam, Yu-Shuang Hou, Xi Tang, Xiao-Dong Lin, Tao Deng and Guang-Qiong Xia
Photonics 2019, 6(2), 49; https://doi.org/10.3390/photonics6020049 - 9 May 2019
Cited by 5 | Viewed by 3560
Abstract
The influence of intra-cavity propagation delay in message encoding and decoding using chaotic semiconductor lasers is numerically investigated. A message is encoded at the transmitter laser by a chaos shift keying scheme and is decoded at the receiver by comparing its output with [...] Read more.
The influence of intra-cavity propagation delay in message encoding and decoding using chaotic semiconductor lasers is numerically investigated. A message is encoded at the transmitter laser by a chaos shift keying scheme and is decoded at the receiver by comparing its output with the transmitter laser. The requisite intra-cavity propagation delay in achieving synchronization of optical chaos is estimated by cross-correlation analysis between the transmitter and receiver lasers’ output. The effect of intra-cavity propagation delay on the message recovery has been analyzed from the bit error rate performance. It is found that despite the intra-cavity propagation delay magnitude being less, it has an impact on the quality of message recovery. We also examine the dependency of injection rate, frequency detuning, modulation depth and bit rate on intra-cavity propagation delay and associated message recovery quality. We found that the communication performance has been adequately improved after incorporating intra-cavity propagation delay correction in the synchronization system. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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<p>Time traces of the transmitter and receiver lasers: The black (red) traces correspond to TL (RL) output (chaotic intensity including message signal) respectively for <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>m</mi> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>10</mn> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>R</mi> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>08</mn> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>κ</mi> <mo>=</mo> <mn>9</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>η</mi> <mo>=</mo> <mn>15</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, and <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>. The grey trace corresponds to the difference between the intensities of the transmitter and receiver lasers.</p>
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<p>Chaotic attractors in the phase space of the laser’s intensity output and the carrier density. (<b>a</b>) Transmitter laser and (<b>b</b>) Receiver laser.</p>
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<p>Cross-correlation coefficient between transmitter and receiver laser for <math display="inline"><semantics> <mrow> <mi>κ</mi> <mo>=</mo> <mn>9</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>η</mi> <mo>=</mo> <mn>15</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, and <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>. The inset figure shows the expanded version of CC plot near zero in time scale. The intra-cavity propagation delay <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> is found to be 32.8 ps.</p>
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<p>Maximum cross-correlation coefficient <math display="inline"><semantics> <msub> <mi>C</mi> <mi>m</mi> </msub> </semantics></math> map in the injection parameters (frequency detuning <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> </mrow> </semantics></math>, injection rate <math display="inline"><semantics> <mi>η</mi> </semantics></math>) plane for keeping <math display="inline"><semantics> <mrow> <mi>κ</mi> <mo>=</mo> <mn>9</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, and <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>.</p>
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<p>Intra-cavity propagation delay <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> map in the injection parameters (frequency detuning <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> </mrow> </semantics></math>, injection rate <math display="inline"><semantics> <mi>η</mi> </semantics></math>) plane for keeping <math display="inline"><semantics> <mrow> <mi>κ</mi> <mo>=</mo> <mn>9</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, and <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>.</p>
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<p>Transmitter-receiver maximum correlation coefficient <math display="inline"><semantics> <msub> <mi>C</mi> <mi>m</mi> </msub> </semantics></math> (red trace) and the associated intra-cavity propagation delay <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> (blue trace) as a function of injection rate for keeping <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>κ</mi> <mo>=</mo> <mn>9</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, and <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>.</p>
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<p>Transmitter-receiver maximum correlation coefficient <math display="inline"><semantics> <msub> <mi>C</mi> <mi>m</mi> </msub> </semantics></math> (red trace) and the associated intra-cavity propagation delay <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> (blue trace) as a function of frequency detuning for keeping <math display="inline"><semantics> <mrow> <mi>η</mi> <mo>=</mo> <mn>15</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>κ</mi> <mo>=</mo> <mn>9</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, and <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>.</p>
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<p>Mapping of <math display="inline"><semantics> <msub> <mi>C</mi> <mi>m</mi> </msub> </semantics></math> (<b>a</b>) and the corresponding <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> (<b>b</b>), in the plane of <math display="inline"><semantics> <mi>κ</mi> </semantics></math> and <math display="inline"><semantics> <mi>η</mi> </semantics></math> for keeping other parameters as <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>m</mi> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>10</mn> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>R</mi> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>08</mn> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>.</p>
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<p>Results of unidirectional message encoding and decoding using CSK scheme for <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>m</mi> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>10</mn> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>R</mi> </msub> <mo>=</mo> <mn>1</mn> <mo>.</mo> <mn>08</mn> <msub> <mi>I</mi> <mrow> <mi>t</mi> <mi>h</mi> </mrow> </msub> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>κ</mi> <mo>=</mo> <mn>9</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>η</mi> <mo>=</mo> <mn>15</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> ns, and <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>f</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> under transmitter-receiver configuration. (<b>a</b>) The original message <math display="inline"><semantics> <mrow> <mi>m</mi> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </semantics></math> (red) and the recovered one <math display="inline"><semantics> <mrow> <msup> <mi>m</mi> <mo>′</mo> </msup> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> (blue), and (<b>b</b>) the eye diagram of the recovered message. The digital message transmitted at 1.2 Gbit/s bit rate with <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>=</mo> <mn>0</mn> <mo>.</mo> <mn>2</mn> </mrow> </semantics></math> modulation depth.</p>
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<p>Estimation of BER values of the recovered messages as a function of injection rate for BR = 1.2 Gbit/s, <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>=</mo> <mn>0</mn> <mo>.</mo> <mn>2</mn> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>f</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>. Red and blue traces correspond to BER value prior to and after the intra-cavity propagation delay <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> correction, respectively, in the receiver laser.</p>
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<p>Estimation of BER values of the recovered messages as a function of frequency detuning for BR = 1.2 Gbit/s, <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>=</mo> <mn>0</mn> <mo>.</mo> <mn>2</mn> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <mi>η</mi> <mo>=</mo> <mn>15</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>. Red (blue) trace correspond to BER value prior to (after) the <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> correction in the receiver laser.</p>
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<p>Estimation of BER values of the recovered messages as a function of a modulation depth for BR = 1.2Gbit/s message signal. Red (blue) trace correspond to BER value prior to (after) the <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> correction in the receiver laser.</p>
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<p>Estimation of BER values of the recovered messages for different bit rates at modulation depth <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>=</mo> <mn>0</mn> <mo>.</mo> <mn>2</mn> </mrow> </semantics></math>. Red and blue traces correspond to BER value prior to and after the <math display="inline"><semantics> <msub> <mi>τ</mi> <mrow> <mi>P</mi> <mi>D</mi> </mrow> </msub> </semantics></math> correction, respectively, in the receiver laser.</p>
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24 pages, 2713 KiB  
Review
Multifunctional Smart Optical Fibers: Materials, Fabrication, and Sensing Applications
by Zhengyong Liu, Zhi Feng Zhang, Hwa-Yaw Tam and Xiaoming Tao
Photonics 2019, 6(2), 48; https://doi.org/10.3390/photonics6020048 - 6 May 2019
Cited by 53 | Viewed by 9841
Abstract
This paper presents a review of the development of optical fibers made of multiple materials, particularly including silica glass, soft glass, polymers, hydrogels, biomaterials, Polydimethylsiloxane (PDMS), and Polyperfluoro-Butenylvinyleth (CYTOP). The properties of the materials are discussed according to their various applications. Typical fabrication [...] Read more.
This paper presents a review of the development of optical fibers made of multiple materials, particularly including silica glass, soft glass, polymers, hydrogels, biomaterials, Polydimethylsiloxane (PDMS), and Polyperfluoro-Butenylvinyleth (CYTOP). The properties of the materials are discussed according to their various applications. Typical fabrication techniques for specialty optical fibers based on these materials are introduced, which are mainly focused on extrusion, drilling, and stacking methods depending on the materials’ thermal properties. Microstructures render multiple functions of optical fibers and bring more flexibility in fiber design and device fabrication. In particular, micro-structured optical fibers made from different types of materials are reviewed. The sensing capability of optical fibers enables smart monitoring. Widely used techniques to develop fiber sensors, i.e., fiber Bragg grating and interferometry, are discussed in terms of sensing principles and fabrication methods. Lastly, sensing applications in oil/gas, optofluidics, and particularly healthcare monitoring using specialty optical fibers are demonstrated. In comparison with conventional silica-glass single-mode fiber, state-of-the-art specialty optical fibers provide promising prospects in sensing applications due to flexible choices in materials and microstructures. Full article
(This article belongs to the Special Issue Polymer Optical Fibre)
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<p>Summary of typical materials and functions for conventional SMF, polymer optical fibers, and multi-material fibers.</p>
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<p>Schematic of MOF fabrication using drilling, extrusion, and stacking methods.</p>
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<p>Schematic of the FBG inscription setup based on (<b>a</b>) the phase-mask technique and (<b>b</b>) the Talbot interferometer technique.</p>
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<p>Typical configurations of FPI, MZI, and SI interferometers.</p>
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<p>Schematic of a fiber optic sensing system for submarine oil exploitation (permission obtained from [<a href="#B111-photonics-06-00048" class="html-bibr">111</a>]).</p>
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<p>Schematic demonstrating health-care monitoring based on optical fiber sensors, where (<b>a</b>) shows sensor devices in a brace and a bracelet to monitor heart condition, blood pressure, and respiration, (<b>b</b>) illustrates a smart mattress integrated with optical fiber sensors to monitor health condition during sleeping, e.g., heart and respiration rates and the status of lying in bed or leaving the bed.</p>
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21 pages, 3774 KiB  
Article
Design Investigation of 4 × 4 Nonblocking Hybrid Plasmonic Electrooptic Switch
by Maithem S. Jaber, Shelan K. Tawfeeq and Raad S. Fyath
Photonics 2019, 6(2), 47; https://doi.org/10.3390/photonics6020047 - 3 May 2019
Cited by 3 | Viewed by 3862
Abstract
This paper proposes a compact, plasmonic-based 4 × 4 nonblocking switch for optical networks. This device uses six 2 × 2 plasmonic Mach-Zehnder switch (MZS), whose arm waveguide is supported by a JRD1 polymer layer as a high electro-optic coefficient material. The 4 [...] Read more.
This paper proposes a compact, plasmonic-based 4 × 4 nonblocking switch for optical networks. This device uses six 2 × 2 plasmonic Mach-Zehnder switch (MZS), whose arm waveguide is supported by a JRD1 polymer layer as a high electro-optic coefficient material. The 4 × 4 switch is designed in COMSOL environment for 1550 nm wavelength operation. The performance of the proposed switch outperforms those of conventional (nonplasmonic) counterparts. The designed switch yields a compact structure ( 500 × 70   µ m 2 ) having V π L = 12   V · µ m , 1.5 THz optical bandwidth, 7.7 dB insertion loss, and −26.5 dB crosstalk. The capability of the switch to route 8 × 40 Gbps WDM signal is demonstrated successfully. Full article
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<p>Basic configuration of 2 × 2 hybrid plasmonic MZS.</p>
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<p>(<b>a</b>) Cross section of the hybrid plasmonic waveguide phase shifter (HPWPS); (<b>b</b>) cross section of photonic waveguide; (<b>c</b>) 3D view of the designed hybrid plasmonic 2 × 2 MZS.</p>
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<p>4 × 4 nonblocking plasmonic MZS with six control signals <math display="inline"><semantics> <mrow> <msub> <mi>C</mi> <mi>a</mi> </msub> <mo> </mo> <mi>to</mi> <mo> </mo> <msub> <mi>C</mi> <mi>f</mi> </msub> </mrow> </semantics></math>.</p>
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<p>2D (<b>a</b>) and 3D (<b>b</b>) schematics of the 4 × 4 plasmonic switch in the COMSOL environment.</p>
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<p>Scattering parameters of the 4 × 4 switch corresponding to the required transition state, <math display="inline"><semantics> <mrow> <msub> <mi>T</mi> <mrow> <mn>1</mn> <mo>−</mo> <mi>k</mi> </mrow> </msub> <mo>:</mo> </mrow> </semantics></math> from input 1 to the output port <span class="html-italic">k</span> (<span class="html-italic">k</span> = 5–8).</p>
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<p>Field intensity distributions at the four output ports when the signal is applied at input port 1, <math display="inline"><semantics> <mrow> <msub> <mi>P</mi> <mn>1</mn> </msub> </mrow> </semantics></math>, and the required output port is <math display="inline"><semantics> <mrow> <msub> <mi>P</mi> <mn>6</mn> </msub> </mrow> </semantics></math>.</p>
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<p>Crosstalk as a function of the transition number.</p>
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<p>Concept of using the optical switch as a router in optical networks. Six control signals are used to switch one of the four transmitters to one of the four receivers.</p>
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<p>Optical spectra at different points of the WDM optical network. (<b>a</b>) <math display="inline"><semantics> <mrow> <msub> <mi>T</mi> <mrow> <mi>x</mi> <mn>1</mn> </mrow> </msub> </mrow> </semantics></math> output. (<b>b</b>) Switch fourth output port. (<b>c</b>) After 650 km transmission. (<b>d</b>) As in part c but the effect of fiber nonlinear optics is turned off in the used software.</p>
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<p>Eye diagrams of channel 1 (<b>a</b>), channel 4 (<b>b</b>), and channel 8 (<b>c</b>) of the fourth WDM receiver <math display="inline"><semantics> <mrow> <msub> <mi>R</mi> <mrow> <mi>x</mi> <mn>4</mn> </mrow> </msub> </mrow> </semantics></math> after 13-span transmission.</p>
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<p>Optical spectra at the input and output ports of the designed 4 × 4 optical switch.</p>
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12 pages, 1528 KiB  
Article
Modeling the Output Performance of Al0.3Ga0.7As/InP/Ge Triple-Junction Solar Cells for a Venus Orbiter Space Station
by Tony Sumaryada, Panji Fitriansyah, Afgan Sofyan and Heriyanto Syafutra
Photonics 2019, 6(2), 46; https://doi.org/10.3390/photonics6020046 - 27 Apr 2019
Cited by 4 | Viewed by 4690
Abstract
The performance of Al0.3Ga0.7As/InP/Ge triple-junction solar cells (TJSC) at the geosynchronous orbit of Venus had been simulated in this paper by assuming that the solar cells were put on a hypothetical Venus orbiter space station. The incoming solar radiation [...] Read more.
The performance of Al0.3Ga0.7As/InP/Ge triple-junction solar cells (TJSC) at the geosynchronous orbit of Venus had been simulated in this paper by assuming that the solar cells were put on a hypothetical Venus orbiter space station. The incoming solar radiation on TJSC was calculated by a blackbody radiation formula, while PC1D program simulated the electrical output performance. The results show that the incoming solar intensity at the geosynchronous orbit of Venus is 3000 W/m2, while the maximum solar cell efficiency achieved is 38.94%. Considering a similar area of the solar panel as the International Space Station (about 2500 m2), the amount of electricity produced by Venus orbiter space station at the geosynchronous orbit of Venus is 2.92 MW, which is plenty of energy to power the space station for long-term exploration and intensive research on Venus. Full article
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<p>The schematic of distances of the geosynchronous orbit of Venus.</p>
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<p>The schematic picture of power density (intensity) averaging technique. (All units in arbitrary).</p>
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<p>The incoming spectral irradiance at the geosynchronous orbit of Venus and Earth calculated using a blackbody radiation formula. The total power density (intensity) at the geosynchronous orbit of Venus is 3000 W/m<sup>2</sup>, while for Earth it is 1557 W/m<sup>2</sup>.</p>
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<p>The electrical performance (<span class="html-italic">I-V</span> diagram) of Al<sub>0.3</sub>Ga<sub>0.7</sub>As/InP/Ge TJSC at the geosynchronous orbit of Venus. All subcells were connected in a series connection and possess the same current.</p>
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<p>The electrical performance of Al<sub>0.3</sub>Ga<sub>0.7</sub>As/InP/Ge TJSC at geosynchronous of Earth. All subcells were connected in a series and possess the same current.</p>
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7 pages, 2622 KiB  
Article
Exploiting the Nonlinear Dynamics of Optically Injected Semiconductor Lasers for Optical Sensing
by Maria S. Torre and Cristina Masoller
Photonics 2019, 6(2), 45; https://doi.org/10.3390/photonics6020045 - 24 Apr 2019
Cited by 4 | Viewed by 3830
Abstract
Optically injected semiconductor lasers are known to display a rich variety of dynamic behaviours, including the emission of excitable pulses, and of rare giant pulses (often referred to as optical rogue waves). Here, we use a well-known rate equation model to explore the [...] Read more.
Optically injected semiconductor lasers are known to display a rich variety of dynamic behaviours, including the emission of excitable pulses, and of rare giant pulses (often referred to as optical rogue waves). Here, we use a well-known rate equation model to explore the combined effect of excitability and extreme pulse emission, for the detection of variations in the strength of the injected field. We find parameter regions where the laser always responds to a perturbation by emitting an optical pulse whose amplitude is above a pre-defined detection threshold. We characterize the sensing capability of the laser in terms of the amplitude and the duration of the perturbation. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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Figure 1
<p>Relative height of the intensity oscillations when no perturbation is applied (<math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>), as a function of the frequency detuning, <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>ν</mi> </mrow> </semantics></math>, and the injection strength, <math display="inline"><semantics> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>j</mi> </mrow> </msub> </semantics></math>. The color code displays <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>I</mi> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>I</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> <mo>−</mo> <mfenced separators="" open="&#x2329;" close="&#x232A;"> <msub> <mi>I</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </mfenced> <mo>)</mo> </mrow> <mo>/</mo> <mfenced separators="" open="&#x2329;" close="&#x232A;"> <msub> <mi>I</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </mfenced> </mrow> </semantics></math>, with <math display="inline"><semantics> <msub> <mi>I</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </semantics></math> and <math display="inline"><semantics> <mfenced separators="" open="&#x2329;" close="&#x232A;"> <msub> <mi>I</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </mfenced> </semantics></math> being the maximum and the average height of the intensity oscillations, respectively; the symbol indicates the parameters used in <a href="#photonics-06-00045-f002" class="html-fig">Figure 2</a>: <math display="inline"><semantics> <mrow> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>j</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>P</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>50</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </semantics></math> and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>ν</mi> <mo>=</mo> <mo>−</mo> <mn>2.29</mn> </mrow> </semantics></math> GHz.</p>
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<p>Time series of the laser intensity when the variation of the injected power is <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> <mo>=</mo> <mn>6.6</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </semantics></math> (<b>a</b>) and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> <mo>=</mo> <mn>11.4</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </semantics></math> (<b>b</b>). In panel (<b>a</b>) we see that the variation is small and the intensity is always below the threshold, therefore, the variation of <math display="inline"><semantics> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>j</mi> </mrow> </msub> </semantics></math> is not detected. In contrast, in panel (<b>b</b>), <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> </mrow> </semantics></math> is large enough to trigger the emission of intensity pulses that are high enough to cross the threshold (indicated with a dashed line).</p>
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<p>Success rate as a function of the perturbation amplitude, <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> </mrow> </semantics></math>, and duration, <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>T</mi> </mrow> </semantics></math>. The detection time interval is <math display="inline"><semantics> <mrow> <mo>Δ</mo> <msub> <mi>T</mi> <mrow> <mi>d</mi> <mi>e</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>20</mn> </mrow> </semantics></math> ns (<b>a</b>), 100 ns (<b>b</b>). Other model parameters are <math display="inline"><semantics> <mrow> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>j</mi> </mrow> </msub> <mo>=</mo> <mn>50</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>μ</mi> <mo>=</mo> <mn>1.75</mn> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>ν</mi> <mo>=</mo> <mo>−</mo> <mn>1.31</mn> </mrow> </semantics></math> GHz.</p>
Full article ">Figure 4
<p>Success rate when the detection time interval is <math display="inline"><semantics> <mrow> <mo>Δ</mo> <msub> <mi>T</mi> <mrow> <mi>d</mi> <mi>e</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mn>20</mn> </mrow> </semantics></math> ns (<b>a</b>) and 100 ns (<b>b</b>). The parameters are <math display="inline"><semantics> <mrow> <msub> <mi>P</mi> <mrow> <mi>i</mi> <mi>n</mi> <mi>j</mi> </mrow> </msub> <mo>=</mo> <mn>50</mn> </mrow> </semantics></math> ns<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>μ</mi> <mo>=</mo> <mn>2.064</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>ν</mi> <mo>=</mo> <mo>−</mo> <mn>2.589</mn> </mrow> </semantics></math> GHz.</p>
Full article ">Figure 5
<p>Success rate as a function of <math display="inline"><semantics> <msub> <mi>P</mi> <mn>0</mn> </msub> </semantics></math> and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> </mrow> </semantics></math>. The duration of the perturbation is <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>T</mi> <mo>=</mo> <mn>5</mn> </mrow> </semantics></math> ns (<b>a</b>), 10 ns (<b>b</b>), 20 ns (<b>c</b>), 30 ns (<b>d</b>). The detection time interval is 5 ns.</p>
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