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Advanced Optics and Photonics Technologies for Sensing Applications
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Advanced Optics and Photonics Technologies for Sensing Applications

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: 30 May 2025 | Viewed by 5672

Special Issue Editors

Dr. Manuel Filipe P. C. M. Costa

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Guest Editor
Center of Physics of the Universities of Minho and Porto, School of Sciences, University of Minho, 4710-057 Braga, Portugal
Interests: optical metrology; image processing; thin films, micro- and nanostructures and systems; optics and science education
Special Issues, Collections and Topics in MDPI journals
Dr. Susana Silva

E-Mail Website
Guest Editor
INESC TEC—Institute for Systems and Computer Engineering, Technology and Science, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
Interests: fiber optic sensors; fiber optic interferometry; interrogation systems; fiber optic lasers; Raman spectroscopy
Special Issues, Collections and Topics in MDPI journals
Dr. Susana Novais

E-Mail Website
Guest Editor
INESC TEC—Institute for Systems and Computer Engineering, Technology and Science, Rua do Campo Alegre 687, 4150-179 Porto, Portugal
Interests: fiber optic sensors; microcavities; Fabry-Perot interferometer; biomedical applications; Raman spectroscopy

Special Issue Information

Dear Colleagues,

The 6th International Conference on the Applications of Optics and Photonics (AOP2024) will be held in Aveiro, Portugal, 16–29 July 2024. Since its first edition in 2011, the AOP conference has provided an excellent opportunity to foster, in an open and friendly environment, the establishment of the widest range of cooperation projects and relationships with colleagues and institutions involved in optics and photonics research worldwide. With this conference open to contributions in all domains of optics and photonics and application fields, we expect to review the state of the art in these subjects and discuss the future directions of research in optics and photonics. Many plenary and keynote lectures by world-renowned researchers in all fields of optics and photonics will set the quality standards of a varied and exciting scientific program.

We are honored to serve as Guest Editors of this Special Issue of Sensors, which will contain a selection of relevant papers submitted and accepted at the AOP2022 conference. Its main scope is to provide a timely and broad collection of the most innovative topics discussed in the latest edition of the conference related to the applications of optics and photonics. We warmly invite researchers to submit their contributions, both original research articles and review papers, to this Special Issue. Topics include but are not limited to the following:

  • Nanophotonics, plasmonics, theoretical optics, and quantum and nonlinear optics;
  • Optical communications and sensors;
  • Optical fibers and applications;
  • Biophotonics and biomedical and medical applications of optics and photonics;
  • Ultrafast lasers, ultrafast optics, and power lasers;
  • Optical metrology, image processing, and industrial applications;
  • Optometry, ophthalmic optics, and color and visual sciences;
  • Optoelectronics;
  • Microwave photonics;
  • Photonics and optical instrumentation for space and astronomy;
  • Optics and photonics for smart mobility and smart cities.

Dr. Manuel Filipe P. C. M. Costa
Dr. Susana Silva
Dr. Susana Novais
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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  • Greater discoverability: Special Issues support the reach and impact of scientific research. Articles in Special Issues are more discoverable and cited more frequently.
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  • External promotion: Articles in Special Issues are often promoted through the journal's social media, increasing their visibility.
  • e-Book format: Special Issues with more than 10 articles can be published as dedicated e-books, ensuring wide and rapid dissemination.

Further information on MDPI's Special Issue polices can be found here.

Published Papers (4 papers)

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Research

12 pages, 1814 KiB  
Article
Comparative Analysis of Physiological Vergence Angle Calculations from Objective Measurements of Gaze Position
by Linda Krauze, Karola Panke, Gunta Krumina and Tatjana Pladere
Sensors 2024, 24(24), 8198; https://doi.org/10.3390/s24248198 - 22 Dec 2024
Viewed by 519
Abstract
Eccentric photorefractometry is widely used to measure eye refraction, accommodation, gaze position, and pupil size. While the individual calibration of refraction and accommodation data has been extensively studied, gaze measurements have received less attention. PowerRef 3 does not incorporate individual calibration for gaze [...] Read more.
Eccentric photorefractometry is widely used to measure eye refraction, accommodation, gaze position, and pupil size. While the individual calibration of refraction and accommodation data has been extensively studied, gaze measurements have received less attention. PowerRef 3 does not incorporate individual calibration for gaze measurements, resulting in a divergent offset between the measured and expected gaze positions. To address this, we proposed two methods to calculate the physiological vergence angle based on the visual vergence data obtained from PowerRef 3. Twenty-three participants aged 25 ± 4 years viewed Maltese cross stimuli at distances of 25, 30, 50, 70, and 600 cm. The expected vergence angles were calculated considering the individual interpupillary distance at far. Our results demonstrate that the PowerRef 3 gaze data deviated from the expected vergence angles by 9.64 ± 2.73° at 25 cm and 9.25 ± 3.52° at 6 m. The kappa angle calibration method reduced the discrepancy to 3.93 ± 1.19° at 25 cm and 3.70 ± 0.36° at 600 cm, whereas the linear regression method further improved the accuracy to 3.30 ± 0.86° at 25 cm and 0.26 ± 0.01° at 600 cm. Both methods improved the gaze results, with the linear regression calibration method showing greater overall accuracy. Full article
(This article belongs to the Special Issue Advanced Optics and Photonics Technologies for Sensing Applications)
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Figure 1

Figure 1
<p>PowerRef 3 setup with custom-built stimulus construction on rails (<b>a</b>), and Maltese cross stimulus (<b>b</b>).</p> Full article ">Figure 2
<p>Expected vergence angle (<span class="html-italic">EVA</span>, black dashed line) and total physiological vergence angle obtained using the two proposed calibration methods: (<b>a</b>) kappa angle calibration and (<b>b</b>) linear regression calibration. Gaze data are represented over a duration of 4 s at each of the 5 distances for four participants: P1 (FD = −10, largest exo fixation disparity, blue line), P2 (FD = 0, closest to <span class="html-italic">EVA</span>, light gray line), P3 (FD = 0, largest deviation from <span class="html-italic">EVA</span>, dark gray line), and P4 (FD = 4, largest eso fixation disparity, green line). FD—fixation disparity.</p> Full article ">Figure 2 Cont.
<p>Expected vergence angle (<span class="html-italic">EVA</span>, black dashed line) and total physiological vergence angle obtained using the two proposed calibration methods: (<b>a</b>) kappa angle calibration and (<b>b</b>) linear regression calibration. Gaze data are represented over a duration of 4 s at each of the 5 distances for four participants: P1 (FD = −10, largest exo fixation disparity, blue line), P2 (FD = 0, closest to <span class="html-italic">EVA</span>, light gray line), P3 (FD = 0, largest deviation from <span class="html-italic">EVA</span>, dark gray line), and P4 (FD = 4, largest eso fixation disparity, green line). FD—fixation disparity.</p> Full article ">
10 pages, 3759 KiB  
Communication
From Fiber Layout to the Sensor: Preparation Methods as Key Factors for High-Quality Coupled-Core-Fiber Sensors
by F. Lindner, J. Bierlich, M. Alonso-Murias, D. Maldonado-Hurtado, J. A. Flores-Bravo, S. Sales, J. Villatoro and K. Wondraczek
Sensors 2024, 24(21), 6999; https://doi.org/10.3390/s24216999 - 30 Oct 2024
Viewed by 685
Abstract
During recent years, the optical-fiber-based simultaneous sensing of strain and temperature has attracted increased interest for different applications, e.g., in medicine, architecture, and aerospace. Specialized fiber layouts further enlarge the field of applications at much lower costs and with easier handling. Today, the [...] Read more.
During recent years, the optical-fiber-based simultaneous sensing of strain and temperature has attracted increased interest for different applications, e.g., in medicine, architecture, and aerospace. Specialized fiber layouts further enlarge the field of applications at much lower costs and with easier handling. Today, the performance of many sensors fabricated from conventional fibers suffers from cross-sensitivity (temperature and strain) and relatively high interrogation costs. In contrast, customized fiber architectures would make it possible to circumvent such sensor drawbacks. Here, we report on the development of a high-quality coupled-core fiber and its performance for sensors—from the initial fiber layout via elaboration of the preform and fiber up to the sensor evaluation. A compact, high-speed, and cost-effective interrogation unit using such a specialized coupled-core fiber has been designed to monitor reflectivity changes while even being able to distinguish the direction of the force or impact. Several fiber core material techniques and approaches were investigated, which made it possible to obtain a sufficient volume of material for the required fiber core number and a specialized fiber core geometry in terms of core distances and radial refractive index profile, whilst handling the non-symmetrical fiber architectures of such modeled, complex structures and balancing resources and efforts. Full article
(This article belongs to the Special Issue Advanced Optics and Photonics Technologies for Sensing Applications)
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Figure 1

Figure 1
<p>Sketch of the coupled core fiber.</p> Full article ">Figure 2
<p>Concept of the coupled-core fiber sensor fabrication steps.</p> Full article ">Figure 3
<p>Radial refractive index profiles of (<b>a</b>) the GeO<sub>2</sub>-doped MCVD core preform and (<b>b</b>) an exemplary REPUSIL preform.</p> Full article ">Figure 4
<p>Front views of two-coupled-core fiber preforms using the MCVD method to fabricate GeO<sub>2</sub> doped core rods (marked in red in the photographs). (<b>a</b>) Hexagonal stacking of SiO<sub>2</sub> cladding rods and GeO<sub>2</sub>-doped core rods; and (<b>b</b>) drilled preform with two core rods.</p> Full article ">Figure 5
<p>Refractive index profile of the fabricated Ge-doped two-coupled-core fiber (TCF). The inset photograph shows the cross-section of the fabricated fiber.</p> Full article ">Figure 6
<p>Schematics of the sensor architecture. SMF is single-mode fiber, TCF is two-coupled-core fiber, and <span class="html-italic">L</span> is the length of the TCF segment.</p> Full article ">Figure 7
<p>FBG sensor fabrication. (<b>a</b>) Micrograph of the splicing point between the standard single-mode fiber and the two-core fiber. (<b>b</b>) Micrograph of the femtosecond point-by-point FBG inscription in the off-center core. (<b>c</b>) FBG spectrum (blue: reflected optical power, red: transmitted optical power). The black ellipses indicate the areas of interest (<b>a</b>,<b>b</b>).</p> Full article ">Figure 8
<p>Illustration of the bending effect on the two-coupled-core fiber with FBGs in both cores. The blue color indicates that the light in this core is weaker than in the other core of the TCF. The arrows indicate the direction of bending.</p> Full article ">Figure 9
<p>Experimental results of nearly isothermal bending on a TCF with Bragg grating. The direction of bending with respect to the core orientation of the TCF is indicated with the arrow. (<b>a</b>) Downward bending, (<b>b</b>) upward bending.</p> Full article ">
20 pages, 4229 KiB  
Article
Comparison of Refractive Index Matching Techniques and PLIF40 Measurements in Annular Flow
by Yago Rivera, Dorian Bascou, David Blanco, Lucas Álvarez-Piñeiro, César Berna, José-Luis Muñoz-Cobo and Alberto Escrivá
Sensors 2024, 24(7), 2317; https://doi.org/10.3390/s24072317 - 5 Apr 2024
Viewed by 1082
Abstract
This paper investigates non-invasive techniques for annular two-phase flow analysis, focusing on liquid film characterization to understand the interfacial phenomena that are crucial for heat and mass transfer. Limited methods allow the study of the temporal and spatial evolution of liquid film, such [...] Read more.
This paper investigates non-invasive techniques for annular two-phase flow analysis, focusing on liquid film characterization to understand the interfacial phenomena that are crucial for heat and mass transfer. Limited methods allow the study of the temporal and spatial evolution of liquid film, such as Planar Laser-Induced Fluorescence (PLIF). However, this method possesses optical challenges, leading to the need for improved techniques to mitigate refraction and reflection, such as Refractive Index Matching (RIM). This study utilizes an experimental annular flow facility to analyze both RIM and non-RIM PLIF over a range of liquid Reynolds numbers from 4200 to 10,400. Three configurations—PLIF RIM90, PLIF RIM40, and PLIF nRIM40—are compared from both qualitative and quantitative perspectives. In the quantitative analysis, key variables of the liquid film are measured, namely mean film thickness, disturbance wave height, and frequency. Variations in the analyzed variables indicate minor deviations, which are not likely to be caused by the technique used. However, all three methodologies exhibited errors that are estimated to be within a maximum of 10%, with a mean value of approximately 8%. Full article
(This article belongs to the Special Issue Advanced Optics and Photonics Technologies for Sensing Applications)
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Figure 1

Figure 1
<p>Summary of major techniques used to measure liquid film thickness experimentally.</p> Full article ">Figure 2
<p>Schematic view of the PLIF technique for liquid film imaging, showing the basic position of the laser film created by the lens system and high-speed camera relative to the test section of the pipe.</p> Full article ">Figure 3
<p>Schematic diagram of the CAPELON facility showing the PLIF measuring system.</p> Full article ">Figure 4
<p>Setup of the three different configurations considered: (<b>a</b>) PLIF RIM90, (<b>b</b>) PLIF RIM40, and (<b>c</b>) PLIF nRIM40.</p> Full article ">Figure 5
<p>Schematic view of the photon’s path from the liquid film to the high-speed camera (based on Refs [<a href="#B13-sensors-24-02317" class="html-bibr">13</a>,<a href="#B20-sensors-24-02317" class="html-bibr">20</a>]).</p> Full article ">Figure 6
<p>Relation between apparent and true liquid film thickness for the three different configurations: (<b>a</b>) PLIFRIM90, (<b>b</b>) PLIF RIM40, and (<b>c</b>) PLIF nRIM40.</p> Full article ">Figure 7
<p>Processing steps of the snapshots: (<b>a</b>) Raw image; (<b>b</b>) wall detection and binarization; (<b>c</b>) image crop, sub-pixel detection showing the detail of the interface; and (<b>d</b>) final film thickness detected.</p> Full article ">Figure 8
<p>Different figures for PLIF RIM90 with a liquid Reynolds number of 7000: (<b>a</b>) Raw image with a disturbance wave passing through; (<b>b</b>) raw image of the film without the disturbance wave; and (<b>c</b>) temporal evolution of the liquid film thickness after treating the whole set run.</p> Full article ">Figure 9
<p>Different figures for PLIF RIM40 with a liquid Reynolds number of 7000: (<b>a</b>) Raw image with a disturbance wave passing through; (<b>b</b>) raw image of the film without the disturbance wave; and (<b>c</b>) temporal evolution of the liquid film thickness after treating the whole set run.</p> Full article ">Figure 10
<p>Different figures for PLIF nRIM40 with a liquid Reynolds number of 7000: (<b>a</b>) Raw image with a disturbance wave passing through; (<b>b</b>) raw image of the film without the disturbance wave; and (<b>c</b>) temporal evolution of the liquid film thickness after treating the whole set run.</p> Full article ">Figure 11
<p>Mean film thickness <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>h</mi> </mrow> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </msub> </mrow> </semantics></math> obtained for all measurements using the three techniques considered in this study.</p> Full article ">Figure 12
<p>Disturbance wave height <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>h</mi> </mrow> <mrow> <mi>D</mi> <mi>W</mi> </mrow> </msub> </mrow> </semantics></math> obtained for all measurements using the three techniques considered in this study.</p> Full article ">Figure 13
<p>Disturbance wave frequency <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>ν</mi> </mrow> <mrow> <mi>D</mi> <mi>W</mi> </mrow> </msub> </mrow> </semantics></math> obtained for all measurements using the three techniques considered in this study.</p> Full article ">
14 pages, 5506 KiB  
Article
Enhanced Sensitivity in Optical Sensors through Self-Image Theory and Graphene Oxide Coating
by Cristina Cunha, Catarina Monteiro, António Vaz, Susana Silva, Orlando Frazão and Susana Novais
Sensors 2024, 24(3), 891; https://doi.org/10.3390/s24030891 - 30 Jan 2024
Cited by 4 | Viewed by 2364
Abstract
This paper presents an approach to enhancing sensitivity in optical sensors by integrating self-image theory and graphene oxide coating. The sensor is specifically engineered to quantitatively assess glucose concentrations in aqueous solutions that simulate the spectrum of glucose levels typically encountered in human [...] Read more.
This paper presents an approach to enhancing sensitivity in optical sensors by integrating self-image theory and graphene oxide coating. The sensor is specifically engineered to quantitatively assess glucose concentrations in aqueous solutions that simulate the spectrum of glucose levels typically encountered in human saliva. Prior to sensor fabrication, the theoretical self-image points were rigorously validated using Multiphysics COMSOL 6.0 software. Subsequently, the sensor was fabricated to a length corresponding to the second self-image point (29.12 mm) and coated with an 80 µm/mL graphene oxide film using the Layer-by-Layer technique. The sensor characterization in refractive index demonstrated a wavelength sensitivity of 200 ± 6 nm/RIU. Comparative evaluations of uncoated and graphene oxide-coated sensors applied to measure glucose in solutions ranging from 25 to 200 mg/dL showed an eightfold sensitivity improvement with one bilayer of Polyethyleneimine/graphene. The final graphene oxide-based sensor exhibited a sensitivity of 10.403 ± 0.004 pm/(mg/dL) and demonstrated stability with a low standard deviation of 0.46 pm/min and a maximum theoretical resolution of 1.90 mg/dL. Full article
(This article belongs to the Special Issue Advanced Optics and Photonics Technologies for Sensing Applications)
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Figure 1

Figure 1
<p>Sensor structure design, where <span class="html-italic">L<sub>CSF</sub></span> corresponds to the CSF length—image not to scale.</p> Full article ">Figure 2
<p>(<b>a</b>) Light propagation; (<b>b</b>) electric field distribution (longitudinal) for a CSF tip with a length of 29.12 mm.</p> Full article ">Figure 3
<p>Scheme of the experimental setup for cleavage.</p> Full article ">Figure 4
<p>Description of the LbL process.</p> Full article ">Figure 5
<p>Spectra results for sensor with 2 bilayers of PEI/GO.</p> Full article ">Figure 6
<p>SEM images of (<b>a</b>,<b>b</b>) uncoated sensors; (<b>c</b>,<b>d</b>) coated sensors with one bilayer of PEI/GO.</p> Full article ">Figure 7
<p>Schematic configuration of the experimental setup.</p> Full article ">Figure 8
<p>Sensor response to the RI experiment.</p> Full article ">Figure 9
<p>Output spectra of the GO-based CSF tip.</p> Full article ">Figure 10
<p>Sensor response to glucose concentration variations.</p> Full article ">Figure 11
<p>Stability test for different sensors coated with one bilayer of PEI/GO.</p> Full article ">
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