JP2012098513A - Wavelength selection filter, and filter device and laser device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength selection filter capable of connecting with incident light in a smaller area than a conventional guided mode resonance filter (GMRF), not necessitating materials of high refractive index and separately extracting the desired wavelength light and other wavelength light.SOLUTION: The wavelength selection filter is provided with: a waveguide core 2; a DBR11 arranged on the waveguide core 2; a phase adjustment interval p1; a GC10; a phase adjustment interval p2; and a DBR12. When incident light including the light of the desired wavelength and the light other than the desired wavelength make incidence on the GC10, the light of the desired wavelength making incidence on the GC10 is reflected by having the waveguide light propagated through the waveguide core 2 diffracted by the GC10 and emitted from a first surface of the waveguide core 2. In addition, the light of the desired wavelength transmitted through the waveguide core 2 by making incidence on the GC10 is cancelled by having the waveguide light propagated through the waveguide core 2 diffracted by the GC10 and emitted from the second surface of the waveguide core 2. The light other than the desired wavelength is transmitted through the waveguide core 2.

Description

  The present invention relates to a wavelength selective filter formed in a planar shape on a substrate of an optical device, the wavelength selective filter filtering incident light by separating it into transmitted light and reflected light, and such wavelength selection The present invention relates to a filter device including a filter and a laser device.

  As filters for optical devices, for example, those disclosed in Patent Documents 1 to 4 are known, and also guided wave mode resonance filters (GMRF: disclosed in Patent Documents 5 to 6 and Non-Patent Documents 1 to 5). Guided Mode Resonance Filter) is known.

  The GMRF is an optical filter that exhibits steep reflection characteristics or transmission characteristics at a certain wavelength with respect to a light wave incident perpendicularly to the substrate by providing a waveguide and a sub-wavelength periodic structure on the substrate. This steep wavelength dependence is a phenomenon that cancels the transmission or reflection of incident light when the excited guided light is coupled to the emitted light again at a wavelength where the periodic structure functions as a grating coupler (GC). As understood. In order to obtain a high reflectance or transmittance, it is necessary to sufficiently excite and emit guided light to cancel and extinguish the radiation mode light. Therefore, when a GC having a small coupling coefficient is used, the GC area and It is assumed that the beam diameter of incident light is increased (for example, several mm).

JP-A-2005-331581. Japanese Patent Application Laid-Open No. 6-221921. JP-A-9-236760. JP 2000-258704 A. JP 2009-288718 A. U.S. Patent No. 6,154,480.

S. S. Wang and R. Magnusson, "Theory and applications of guided-mode resonance filters", Applied Optics, vol. 32, pp. 2606-2613, May 10, 1993. Z. S. Liu, S. Tibuleac, D. Shin, P. P. Young, and R. Magnusson, "High-efficiency guided-mode resonance filter", Optics Letters, vol. 23, pp. 1556-1558, October 1, 1998. S. Tibuleac and R. Magnusson, "Diffractive narrow-band transmission filters based on guided-mode resonance effects in thin-film multilayers", IEEE Photonics Technology Letters, Vol. 9, No. 4, pp. 464-466, April 1997 . Alok A. Mehta, Raymond C. Rumpf, Zachary A. Roth, and Eric G. Johnson, "Guided Mode Resonance Filter as a Spectrally Selective Feedback Element in a Double-Cladding Optical Fiber Laser", IEEE Photonics Technology Letters, Vol. 19 , No. 24, pp. 2030-2032, December 15, 2007. Ye Zhou, Michael Moewe, Johannes Kern, Michael CY Huang, and Connie J. Chang-Hasnain, "Surface-normal emission of a high-Q resonator using a subwavelength high-contrast grating", Optics Express, Vol. 16, No. 12, pp. 17282-17287, October 27, 2008. K. Kintaka, J. Nishii, A. Mizutani, H. Kikuta, and H. Nakano, "Antireflection microstructures fabricated upon fluorine-doped SiO2 films", OPTICS LETTERS, Vol. 26, No. 21, pp. 1642-1644, November 1, 2001. Akio Mizutani, Hisao Kikuta, Koichi Iwata, and Hiroshi Toyota, "Guided-mode resonant grating filter with an antireflection structured surface", J. Opt. Soc. Am. A, Vol. 19, No. 7, pp. 1346-1351 , July 2002.

  Since the light output from the end face of the optical fiber has a beam diameter of, for example, about 10 μm, a lens is required to reduce the beam diameter of the incident light to the GC to several millimeters. On the other hand, when using a wavelength selective filter, in many cases, light output from an optical waveguide or an optical fiber can be coupled without a lens, that is, incident light having a beam diameter of about several μm to several tens of μm is left as it is. It must be able to be filtered.

  Moreover, although the conventional filter may require a material with a high refractive index for the grating (for example, Patent Document 1 and Non-Patent Document 5), the material can be flexibly selected without such a requirement. preferable.

  Further, a conventional filter is formed integrally with an active layer of a laser light source, and may be used so as to output only light having a desired wavelength by filtering (for example, Patent Document 6 and Non-Patent Document 5). . However, it is preferable that light of a desired wavelength and light of other wavelengths can be extracted separately by filtering.

  The object of the present invention is to solve the above-described problems, and can be coupled with incident light in a smaller area than conventional GMRF, does not require a material with a high refractive index, and has light of a desired wavelength and light of other wavelengths. And a laser device provided with such a wavelength selection filter.

The wavelength selective filter according to the first aspect of the present invention includes:
A waveguide having first and second waveguide directions opposite to each other, and is provided between first and second surfaces extending along the first waveguide direction and facing each other. Waveguides,
A first reflecting means, a first phase adjusting section, a diffracting means, a second phase adjusting section, and a second reflecting means provided in the waveguide in order along the first waveguide direction. Prepared,
The diffraction means has a grating period along the first waveguide direction,
The diffracting means is guided light that propagates in the first waveguide direction in the waveguide when incident light including light having a first wavelength corresponding to the grating period of the diffracting means is incident on the diffracting means. The diffracting means diffracts the guided light propagating in the first waveguide direction and radiates it from the first and second surfaces of the waveguide,
The second reflecting means reflects the guided light propagated in the first waveguide direction in the second propagation direction,
The first reflecting means reflects the guided light propagated in the second waveguide direction in the first propagation direction,
In the first phase adjustment section, when guided light propagating in the second propagation direction is reflected by the first reflecting means, the reflected guided light is reflected by incident light incident on the diffracting means. Having a length set to have the same phase as the phase of the guided light propagating in the first propagation direction,
When incident light including light having a wavelength other than the first wavelength and light having a wavelength other than the first wavelength is incident on the diffraction unit,
By diffracting the guided light propagating in the first waveguide direction by the diffracting means and emitting it from the first surface of the waveguide, the light having the first wavelength incident on the diffracting means is reflected. ,
By diffracting the guided light propagating in the first waveguide direction by the diffracting means and radiating it from the second surface of the waveguide, the first light that is incident on the diffracting means and transmitted through the waveguide is transmitted. Cancel the light of
Light having a wavelength other than the first wavelength is transmitted through the waveguide.

In the wavelength selective filter,
The incident light is incident on the diffracting means so as to be perpendicular to the first surface of the waveguide;
The diffracting means is guided light that propagates in the first waveguide direction in the waveguide when incident light including light having a first wavelength corresponding to the grating period of the diffracting means is incident on the diffracting means. And the guided light propagating in the second waveguide direction, and the diffracting means diffracts the guided light propagating in the first waveguide direction to diffract the first and second surfaces of the waveguide. Diffracted guided light propagating in the second waveguide direction and radiated from the first and second surfaces of the waveguide,
In the second phase adjustment section, when the guided light propagating in the first propagation direction is reflected by the second reflecting means, the reflected guided light is reflected by incident light incident on the diffracting means. Having a length set to have the same phase as the phase of the guided light propagating in the second propagation direction,
When incident light including light having a wavelength other than the first wavelength and light having a wavelength other than the first wavelength is incident on the diffraction unit,
The guided light propagating in the first waveguide direction is diffracted by the diffracting means and radiated from the first surface of the waveguide, and the guided light propagating in the second waveguide direction is diffracted by the diffracting means. By diffracting and radiating from the first surface of the waveguide, the light of the first wavelength incident on the diffracting means is reflected,
The guided light propagating in the first waveguide direction is diffracted by the diffracting means and radiated from the second surface of the waveguide, and the guided light propagating in the second waveguide direction is diffracted by the diffracting means. By diffracting and radiating from the second surface of the waveguide, the light of the first wavelength incident on the diffracting means and transmitted through the waveguide is canceled,
Light having a wavelength other than the first wavelength is transmitted through the waveguide.

  In the wavelength selective filter, each of the first reflecting means and the second reflecting means is a distributed Bragg reflector having a grating period along the first waveguide direction.

  In the wavelength selective filter, each of the first reflecting means and the second reflecting means is a metal mirror.

  In the wavelength selective filter, the diffraction means has a non-reflective structure.

In the wavelength selective filter, the incident light is incident on the diffractive means with a predetermined incident angle inclined toward the first reflecting means from a direction perpendicular to the first surface of the waveguide. ,
The diffracting means is coupled to the waveguide light propagating in the first waveguide direction and not coupled to the waveguide light propagating in the second waveguide direction. And a predetermined distance from the first surface of the waveguide between the second surface and the second surface,
The first and second reflecting means are coupled to both the guided light propagating in the first waveguide direction and the guided light propagating in the second waveguide direction. And a predetermined distance from the first surface of the waveguide between the first surface and the second surface.

A filter device according to a second aspect of the present invention is a filter device including two wavelength selective filters according to the first aspect of the present invention,
The filter device further includes a substrate having first and second surfaces facing each other and parallel to each other,
A first wavelength selection filter of the two wavelength selection filters is formed on the first surface of the substrate,
A second wavelength selection filter of the two wavelength selection filters is formed on the second surface of the substrate, and the first and second waveguide directions of the waveguide of the second wavelength selection filter are: It is in a plane parallel to the second surface of the substrate and is orthogonal to the first and second waveguide directions of the waveguide of the first wavelength selective filter.

A filter device according to a third aspect of the present invention is a filter device including two wavelength selective filters according to the first aspect of the present invention,
The filter device is
One common waveguide provided between the first and second surfaces facing each other and parallel to each other;
In the first surface of the waveguide, the first reflecting means, the first phase adjusting section, the diffracting means, the second phase adjusting section of the first wavelength selecting filter of the two wavelength selecting filters, and Comprising second reflecting means;
A first reflecting means, a first phase adjusting section, a diffracting means, a second phase adjusting section of the second wavelength selecting filter of the two wavelength selecting filters; Comprising second reflecting means;
The first and second waveguide directions of the waveguide of the second wavelength selective filter are in a plane parallel to the first and second surfaces of the waveguide, and the first wavelength selective filter It is characterized by being orthogonal to the first and second waveguide directions of the waveguide.

The filter device according to the fourth aspect of the present invention is a filter device including two wavelength selective filters according to the first aspect of the present invention,
The filter device is
One common waveguide provided between the first and second surfaces facing each other and parallel to each other;
In the first surface of the waveguide, the first reflecting means, the first phase adjusting section, the diffracting means, the second phase adjusting section of the first wavelength selecting filter of the two wavelength selecting filters, and Comprising second reflecting means;
A first reflecting means, a first phase adjusting section, a diffracting means, a second phase adjusting section of the second wavelength selecting filter of the two wavelength selecting filters; Comprising second reflecting means;
The diffractive means of the second wavelength selective filter has a grating period different from the grating period of the diffractive means of the first wavelength selective filter along the first waveguide direction.

  A laser apparatus according to a fifth aspect of the present invention is characterized in that the wavelength selection filter is provided as an external mirror.

  According to the wavelength selective filter of the present invention, it is possible to couple with incident light in a smaller area than that of the conventional GMRF, and it is not necessary to use a material with a high refractive index, so that light of a desired wavelength and light of other wavelengths are separated. It is possible to provide a wavelength selective filter that can be taken out. Further, it is possible to provide a filter device and a laser device provided with such a wavelength selection filter.

It is sectional drawing which shows the structure of the wavelength selection filter 100 which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the detailed structure of GC10 vicinity of FIG. (A) shows the component of the desired wavelength of the incident light incident on the wavelength selective filter 100 of FIG. 1, and (b) shows the component other than the desired wavelength of the incident light incident on the wavelength selective filter 100 of FIG. FIG. It is a graph which shows the reflection spectrum and transmission spectrum which were simulated about the wavelength selection filter 100 of FIG. It is a graph which shows the reflection spectrum and transmission spectrum which were calculated from the analysis model of the wavelength selection filter 100 of FIG. It is a figure which shows the electric field profile when incident light injects into the wavelength selection filter 100 of FIG. It is sectional drawing which shows the structure of the wavelength selection filter 101 which concerns on the 2nd Embodiment of this invention. It is a figure which shows an electric field profile when incident light injects into the wavelength selection filter 101 of FIG. It is sectional drawing which shows the structure of the wavelength selection filter 102 which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the structure of the filter apparatus which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the structure of the filter apparatus which concerns on the 5th Embodiment of this invention. It is sectional drawing which shows the structure of the filter apparatus which concerns on the 6th Embodiment of this invention. It is sectional drawing which shows the structure of the VCSEL laser apparatus which concerns on the 7th Embodiment of this invention. It is sectional drawing which shows the structure of the wavelength selection filter 110 which concerns on the modification of the 1st Embodiment of this invention. It is sectional drawing which shows the detailed structure of GC10 vicinity of FIG. (A) shows the component of the desired wavelength of the incident light incident on the wavelength selective filter 110 in FIG. 14, and (b) shows the component other than the desired wavelength in the incident light incident on the wavelength selective filter 110 of FIG. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, similar components are denoted by the same reference numerals.

First embodiment.
FIG. 1 is a cross-sectional view showing a configuration of the wavelength selective filter 100 according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a detailed configuration in the vicinity of the GC 10 in FIG. In FIG. 1 and others, reference is made to XYZ coordinates shown in the drawing. The wavelength selective filter 100 according to the present embodiment includes a substrate 1 made of a transparent dielectric material, a waveguide core 2 formed on the substrate 1, and a grating coupler (GC) formed on the waveguide core 2. ) 10 and Distributed Bragg Reflectors (DBR) 11 and 12. Each of the GC 10 and the DBRs 11 and 12 is composed of a grating having a predetermined grating period (that is, irregularities are periodically arranged) along the Z-axis direction. The DBR 11 is formed by sandwiching a predetermined phase adjustment section p1 between the DB 10 and the GC 10 so as to be positioned in the −Z direction of the GC 10. Similarly, the DBR 12 is connected to the GC 10 so as to be positioned in the + Z direction of the GC 10. A predetermined phase adjustment section p2 is interposed therebetween. The wavelength selection filter 100 of the present embodiment reflects light of a desired wavelength in the −X direction and transmits light of other wavelengths in the + X direction when incident light enters the GC 10 from the −X direction. Features.

  The GC 10 does not require a large length of several millimeters as the length L in the Z-axis direction as in the prior art, and is equivalent to the beam diameter of light output from the end face of an optical fiber or other optical waveguide, for example. It has a length (for example, a length L = 10 μm). The grating of GC10 has a grating period Λ (for example, Λ = 950 nm) in the Z-axis direction corresponding to a desired wavelength component of incident light, and the concave and convex portions forming the grating of GC10 are each in the Z-axis direction. Has a length of about Λ / 2. When incident light including a desired wavelength corresponding to the grating period Λ enters the GC 10 perpendicularly from the −X direction, the waveguide core 2 has a predetermined wavelength in the waveguide corresponding to the grating period Λ, and the + Z direction and The guided light propagating in the −Z direction (that is, guided light propagating in the direction of the arrow d1 in FIG. 2 and guided light propagating in the direction of the arrow d2) is excited. Each of the DBRs 11 and 12 has a length in the Z-axis direction that is sufficiently long (for example, 170 μm) to completely reflect the guided light propagating through the waveguide core 2 from the position of the GC 10 toward the original GC 10 position. ). The gratings of the DBRs 11 and 12 have a grating period Λ / 2 in the Z-axis direction, and the concave and convex portions forming the gratings of the DBRs 11 and 12 each have a length of about Λ / 4 in the Z-axis direction. Further, on the condition that the phase adjustment sections p1 and p2 between the GC 10 and the DBRs 11 and 12 are in the Z-axis direction, the guided light is reciprocated and superimposed in the waveguide core 2 to obtain a desired wavelength of the incident light. The guided light corresponding to the component resonates in the waveguide core 2. The length of the phase adjustment section p1 formed between the GC 10 and the DBR 11 in the Z-axis direction is such that the guided light reflected by the DBR 11 and propagating in the + Z direction is excited by the incident light incident on the GC 10 in the + Z direction. It is determined to have the same phase as the propagating guided light. The length of the phase adjustment section p2 formed between the GC 10 and the DBR 12 in the Z-axis direction is such that the waveguide light reflected by the DBR 12 and propagating in the −Z direction is excited by the incident light incident on the GC 10. It is determined to have the same phase as the guided light propagating in the direction. These phase adjustment sections p1 and p2 have, for example, a length L1 = Λ / 8 in the Z-axis direction. The waveguide core 2 has a thickness Tc (for example, Tc = 275 nm) sufficient to generate one waveguide mode as the thickness Tc in the X-axis direction. The convex portions of the gratings of the GC 10 and the DBRs 11 and 12 have, for example, a thickness Tg = 150 nm as the thickness Tg in the X-axis direction.

  The refractive index of the waveguide core 2 is set higher than the refractive indexes of the substrate 1, GC 10 and DBRs 11 and 12. For example, the waveguide core 2 is made of silicon nitride, and the substrate 1, the GC 10 and the DBRs 11 and 12 are made of quartz. In the following description, it is assumed that the refractive index of the waveguide core 2 is 2.0, and the refractive indexes of the substrate 1, the GC 10, and the DBRs 11 and 12 are 1.5.

The wavelength selection filter 100 of this embodiment has a configuration in which a GC 10 having a short coupling length is inserted between the DBRs 11 and 12. The effective coupling length of the GC 10 is usually given by the reciprocal of the radiation loss coefficient α representing the strength of coupling. When the wavelength in vacuum of the component of the desired wavelength of the incident light is λ ₀ , the effective refractive index of the waveguide core 2 is N, and the grating period of the GC 10 is Λ, the wavelength λ ₀ that satisfies the following formula is included. When incident light enters the GC 10 perpendicularly, the guided light propagating through the waveguide core 2 in the + Z direction and the −Z direction is excited.

Here, β is the propagation constant of guided light, and K _GC is the magnitude of the grating vector.

  3A shows a desired wavelength component of the incident light incident on the wavelength selective filter 100 of FIG. 1, and FIG. 3B shows a desired component of the incident light incident on the wavelength selective filter 100 of FIG. It is the schematic which shows components other than a wavelength. 3A and 3B are cross-sectional views similar to FIGS. 1 and 2, but hatching is omitted for the sake of explanation. As described above, when incident light enters the GC 10 from the −X direction, the desired wavelength component of the incident light excites the guided light propagating in the + Z direction and the −Z direction in the waveguide core 2. The guided light propagating in the + Z direction is diffracted by the GC 10, so that the emitted light in the −X direction and the emitted light in the + X direction (that is, perpendicular to the −X direction surface and the + X direction surface of the waveguide core 2). The guided light that generates (radiated light) and propagates in the −Z direction is also diffracted by the GC 10, so that the −X direction emitted light and the + X direction emitted light (that is, the −X direction of the waveguide core 2). (Radiant light perpendicular to the plane and the plane in the + X direction). The emitted light in the −X direction becomes reflected light with respect to incident light. The emitted light in the + X direction has an opposite phase to the transmitted light that is incident on the GC 10 from the −X direction and is transmitted to the substrate 1 side, and cancels out the transmitted light. On the other hand, when the incident light is incident on the GC 10 from the −X direction, components other than the desired wavelength in the incident light are directly transmitted to the substrate 1 side without exciting the guided light. As described above, when the incident light is incident on the GC 10 from the −X direction, the wavelength selection filter 100 of the present embodiment reflects the component of the desired wavelength in the incident light as the reflected light in the −X direction, The components other than the desired wavelength are transmitted in the + X direction as transmitted light. Therefore, the wavelength selection filter 100 of this embodiment can filter incident light by separating it into transmitted light and reflected light.

  The filtering function of the wavelength selective filter 100 of this embodiment was verified by the FDTD (Time Domain Difference) method. FIG. 4 is a graph showing a reflection spectrum and a transmission spectrum simulated for the wavelength selective filter 100 of FIG. 1, and FIG. 6 is a diagram showing an electric field profile when incident light is incident on the wavelength selective filter 100 of FIG. It is. In FIG. 4, the circle plot indicates the reflectance, and the square plot indicates the transmittance. In the simulation of FIG. 4, it is assumed that incident light of a rectangular wave beam having a beam diameter (10 μm) of the same size as the opening of the GC 10 and having a uniform intensity is incident. According to FIG. 4, a reflectance of 95% and a full width at half maximum of 1.5 nm are obtained in the vicinity of the resonance wavelength of 1.5518 μm. By making the reflectivities of the DBRs 11 and 12 almost 100%, a peak of a reflection spectrum was obtained. FIG. 6 is an electric field profile (normalized electric field strength) in the vicinity of the wavelength selective filter 100 when incident light having a wavelength of 1.5518 μm is incident. FIG. 6 shows a part of the same cross section as in FIGS. 1 to 3 at different scales in the X-axis direction and the Z-axis direction. Incident light is incident on the GC 10 (not shown) provided at the position “185 μm” in the Z-axis direction from the −X direction. DBRs 11 and 12 (not shown) are respectively provided in the −Z direction and the + Z direction of the GC 10. In the waveguide core 2, the guided light is confined within a predetermined distance from the GC 10 by reflection by the DBRs 11 and 12. Referring to FIG. 6, outside the wavelength selective filter 100, the electric field in the region in the −X direction (incident light at the position of GC10 and the GC10) rather than the position of GC10 (that is, the position of “185 μm” in the Z-axis direction). (Including the reflected light from the position of). On the other hand, in the + X direction relative to the waveguide core 2, the transmitted light and the emitted light cancel each other, and the electric field is gradually weakened.

  Hereinafter, the characteristics of the wavelength selective filter 100 of this embodiment will be described with reference to an analysis model based on the mode coupling theory.

(Incident light emission mode notation)
The wave numbers in the air and the substrate are k _a and k _s respectively, and the wave number in the Z-axis direction is β _v . Consider that incident light that is incident substantially vertically (β _v ≈0) is expressed in the air-side and substrate-side radiation modes. The field distribution E _IN (x) of the incident plane wave is expressed by the following equation by approximating the wave number β _ν = 0 in the Z-axis direction.

Here, a _IN is a predetermined amplitude coefficient, and r _IN and t _IN are a reflection coefficient and a transmission coefficient. The field distribution E _a (x) of the air side radiation mode is given by the phase conjugate (time reversal wave) of the above equation. That is, using a predetermined amplitude coefficient a _a, it is expressed by the following equation.

  Here, the superscript “*” indicates a complex conjugate.

Similarly, the field distribution E _s (x) of the substrate-side radiation mode is given by the phase conjugate of the virtual incident light from the substrate 1. That is, using a predetermined amplitude coefficient a _s, is expressed by the following equation.

When an incident plane wave field distribution _E IN (x) to attempt is made to represent a superposition of the field distribution _E a (x) and the field distribution _E s of the substrate-side radiation mode (x) of the air-side radiation _{mode, a} a _{t IN} ^* + _a ^s _r s * = 0 and ^{_{a a r IN * + a s}} t s * = a IN must hold. From this, the following equation is obtained.

GC10 area when the light wave incident at (0 <z <L) to a uniform amplitude distribution, using a predetermined amplitude coefficient a _0, the spectral components a _IN is expressed by the following equation.

(Mode coupling equation)
The + Z direction propagation waveguide mode is A (z), the −Z direction propagation waveguide mode is B (z), and the air side and substrate side radiation modes are a _νa (z) and a _νs (z), respectively. . The propagation constants of propagation waveguide modes A (z) and B (z) in the Z-axis direction are β _A and β _B (= −β _A ), respectively, and the magnitude of the grating vector is K _GC = 2π / Λ. The mode coupling equation is expressed as follows.

Here, the parameter i indicates a (in the air) or s (in the substrate). E _ν i (x) and E _g (x) are the normalized electric fields of the radiation mode and the waveguide mode, respectively. Further, ε ₀ , ω, and Δε are a dielectric constant in vacuum, an angular frequency, and a relative dielectric constant representing the structure of GC10. The composite on the left side of Equation 10 corresponds to the positive or negative of the wave number β _{ν in} the Z-axis direction. _{2Δ A = β ν - (β} A -K GC), 2Δ B = β ν - If (β _g + _{K GC)} introducing, number 8 and number 9 can be summarized as follows.

(General solution)
The following formulas A ′ (z) and B ′ (z) are introduced.

  When the target is limited to 0 <z <L, S (s, L) = 1 from Equation 17, and Equations 12 and 13 are transformed into the following equations.

として、κ_ＧＣ＝κ_ＧＣ ^＊＝αであることを用いると、次式のように書ける。 Expressions 20 to 22 are non-homogeneous linear simultaneous differential equations related to A ′ (z) and B ′ (z). The general solution is

As follows, using κ _GC = κ _GC ^* = α, it can be written as:

The radiation mode amplitude is obtained by integrating Equation 10 with respect to _βν .

The transmitted light power P _sub and the reflected light power P _air are given by the following equations, respectively.

Assuming that the total power dissipated from the structure is P _total , the power transmittance and power reflectance of the incident light can be obtained by P _sub / P _total and P _air / P _total , respectively.

(Applying boundary conditions)
When A (0) = 1, A (0) / B (0) = r _DRB and B (L) / A (L) = r _DRB are introduced as boundary conditions, the following equation is obtained.

Therefore, c ₁ , c ₂ , and α _EX are expressed by the following equations.

(Calculation example)
FIG. 5 is a graph showing the reflection spectrum and the transmission spectrum calculated from the analysis model of the wavelength selective filter 100 of FIG. It can be seen that the graph of FIG. 5 closely matches the simulation result of the FDTD method of FIG.

  As described above, according to the wavelength selective filter 100 of the present embodiment, it is possible to couple with incident light in a smaller area than that of the conventional GMRF, and a light having a desired wavelength can be combined with light having a high refractive index without requiring a high refractive index material. It is possible to provide a wavelength selective filter that can separately extract light of wavelengths other than those. The wavelength selective filter 100 according to the present embodiment can be expected to have a function equivalent to that of the conventional GMRF having a large area even if the coupling length of the GC 10 is short.

  In the above description, the waveguide core 2 and the GC 10 and the DBRs 11 and 12 are formed of materials having different refractive indexes, but they may be formed of the same material. In this case, the wavelength selection filter 100 is formed by depositing the waveguide core 2 on the substrate 1 by, for example, chemical vapor deposition, applying a resist thereon, and performing mask exposure, electron beam direct drawing exposure, or the like. It is possible to obtain an uneven pattern of the grating on the substrate and transfer the pattern onto the waveguide material by dry etching or the like. Further, the present invention is not limited to the formation of the waveguide core 2 and the GCs 10 and the DBRs 11 and 12 on the substrate 1. The GCs 10 and the DBRs 11 and 12 are formed on the waveguide core 2 and the wavelength selective filter 100 of the present embodiment. If formed in the same manner, the same function as the wavelength selective filter 100 of this embodiment can be realized.

Modification of the first embodiment.
FIG. 14 is a cross-sectional view showing a configuration of the wavelength selective filter 110 according to a modification of the first embodiment of the present invention, and FIG. 15 is a cross-sectional view showing a detailed configuration in the vicinity of the GC 10 in FIG. The embodiment of the present invention is not limited to the case where incident light is incident on the GC 10 perpendicularly, and the incident light may be incident with a predetermined incident angle from a direction perpendicular to the GC 10.

  The wavelength selective filter 110 of this modification includes a substrate 1 made of a transparent dielectric material, a waveguide core 2 formed on the substrate 1, and a −X of the waveguide core 2 in the waveguide core 2. GC10 and DBR11, 12 each having a predetermined distance in the X-axis direction from the direction surface. In the wavelength selective filter 110 of this modification, the GC 10 is formed in the waveguide core 2 with a distance 0 in the X-axis direction from the −X direction surface of the waveguide core 2 (that is, −X of the waveguide core 2). DBRs 11 and 12 are formed in the waveguide core 2 so as to have the same distance Tc as the thickness of the waveguide core 2 in the X-axis direction from the −X direction surface of the waveguide core 2. (That is, formed on the surface of the waveguide core 2 in the + X direction). The DBR 11 is formed by sandwiching a predetermined phase adjustment section p1 between the DB 10 and the GC 10 so as to be positioned in the −Z direction of the GC 10. Similarly, the DBR 12 is connected to the GC 10 so as to be positioned in the + Z direction of the GC 10. A predetermined phase adjustment section p2 is interposed therebetween.

  In the wavelength selective filter 110 of this modification, as shown in FIG. 16, the wavelength selective filter 110 has a predetermined incident angle θ in the ZX plane from the direction (−X direction) perpendicular to the surface of the waveguide core 2 (that is, Incident light is incident on the GC 10 (with an incident angle θ inclined to the DBR 11 side). The grating of the GC 10 has a grating period Λ 3 corresponding to the incident angle θ and a desired wavelength component of the incident light, and when incident light including the desired wavelength component is incident on the GC 10 at the incident angle θ. Only the guided light is excited. However, the wavelength selection filter 110 according to the present modification uses only one of the guided light propagating in the −Z direction and the + Z direction (the guided light propagating in the + Z direction in this modification) by the incident light incident on the GC 10. It is configured to be excited. The guided light propagating in the + Z direction is reflected by the DBR 12 and propagates in the −Z direction, and the guided light propagating in the −Z direction is reflected by the DBR 11 and propagates again in the + Z direction. In this modification, the guided light modes propagating in the + Z direction and the guided light propagating in the −Z direction have different waveguide modes and different electric field profiles (distributions). Therefore, the refractive index distribution of the waveguide core 2 is appropriately designed, and the distance of the GC 10 from the surface of the waveguide core 2 in the −X direction is adjusted to a position where the electric field of the guided light propagating in the −Z direction becomes zero. In other words, the guided light propagating in the −Z direction is not excited by the incident light incident on the GC 10, and the guided light propagating in the −Z direction is diffracted by the GC 10 to generate radiated light. There is nothing. That is, when the waveguide core 2, GC10, and DBR11, 12 are configured as described above, only the guided light propagating in the + Z direction is excited by the incident light incident on the GC 10, and only the guided light propagating in the + Z direction is further excited. Is diffracted by the GC 10 and becomes radiated light. The DBRs 11 and 12 reflect the guided light propagating in the + Z direction and the guided light propagating in the −Z direction between the −X direction surface and the + X direction surface of the waveguide core 2 in order to reflect the guided light. Both electric fields are formed at positions where they exist with sufficient strength. Therefore, the distance between the DBRs 11 and 12 from the surface of the waveguide core 2 in the −X direction is different from the distance of the GC 10 from the surface of the waveguide core 2 in the −X direction. Since the wavelength selective filter 110 according to the present modification operates with incident light having an incident angle θ and incident on the GC 10, the grating period Λ3 of the GC 10 in the wavelength selective filter 110 according to the present modification is the same as that of the first embodiment. This is different from the grating period Λ of the GC 10 in the wavelength selective filter 100. The grating periods Λ4 of the DBRs 11 and 12 in the wavelength selection filter 110 of the present modification have different waveguide modes for the guided light propagating in the + Z direction and the guided light propagating in the −Z direction. This is different from the grating period Λ / 2 of the DBRs 11 and 12 in the filter 100. The recesses and projections forming the grating of the GC 10 each have a length of about Λ3 / 2 in the Z-axis direction, and the recesses and projections forming the gratings of the DBRs 11 and 12 are each about Λ4 / Has a length of two. The length of the phase adjustment section p1 formed between the GC 10 and the DBR 11 in the Z-axis direction is such that the guided light reflected by the DBR 11 and propagating in the + Z direction is excited by the incident light incident on the GC 10 in the + Z direction. It is determined to have the same phase as the propagating guided light.

  FIG. 16A shows a desired wavelength component of the incident light incident on the wavelength selective filter 110 in FIG. 14, and FIG. 16B shows a desired component of the incident light incident on the wavelength selective filter 110 in FIG. It is the schematic which shows components other than a wavelength. FIGS. 16A and 16B are cross-sectional views similar to FIGS. 14 and 15, but hatching is omitted for the sake of explanation. As described above, when the incident light enters the GC 10, the component of the desired wavelength in the incident light excites only the guided light propagating in the + Z direction. The guided light propagating in the + Z direction is diffracted by the GC 10 to emit radiated light from the surface in the −X direction and the surface in the + X direction. The emitted light emitted from the plane in the −X direction has a predetermined reflection angle θ in the ZX plane from the direction perpendicular to the surface of the waveguide core 2 (the −X direction), and becomes reflected light with respect to the incident light. . The radiated light radiated from the surface in the + X direction has an opposite phase to the transmitted light that enters the GC 10 and transmits to the substrate 1 side, and cancels out the transmitted light. On the other hand, when incident light is incident on the GC 10, components other than the desired wavelength in the incident light are directly transmitted to the substrate 1 side without exciting the guided light. As described above, when the incident light enters the GC 10, the wavelength selection filter 110 according to the present modification reflects a component having a desired wavelength in the incident light as reflected light, and removes a component other than the desired wavelength in the incident light. Transmit as transmitted light. Therefore, the wavelength selection filter 110 of this modification can be filtered by separating incident light into transmitted light and reflected light.

  The positions of the GC 10 and the DBRs 11 and 12 are not limited to the −X direction plane and the + X direction plane of the waveguide core 2 as shown in FIGS. 14 to 16. As long as it is coupled to only one of the guided light propagating in the + Z direction and the DBRs 11 and 12 are coupled to both guided light propagating in the −Z direction and the + Z direction, they can be formed at any position. . For example, the GC 10 may be formed on the surface of the waveguide core 2 in the + X direction, the DBRs 11 and 12 may be formed on the surface of the waveguide core 2 in the −X direction, and the GC 10 and the DBRs 11 and 12 may be formed in the waveguide core. 2 may be formed at a predetermined position between the surface in the −X direction and the surface in the + X direction. The thickness and refractive index profile of the waveguide core 2 are determined so as to allow such coupling between the GC 10 and the DBRs 11 and 12 and the guided light.

  As described above, according to the wavelength selective filter 110 of the present modification, the incident light is not limited to the case where the incident light is incident on the GC 10 perpendicularly, and the incident light has a predetermined incident angle from the direction perpendicular to the GC 10. Even if it is incident, it can be combined with incident light in a smaller area than the conventional GMRF, and does not require a material having a high refractive index, and separately extracts light of a desired wavelength and light of other wavelengths. A wavelength selective filter that can be provided can be provided. Furthermore, according to the wavelength selective filter 110 of this modification, the GC 10 is coupled only to the guided light propagating in the + Z direction, so that the guided light propagating in the −Z direction is diffracted by the GC 10 to an extra angle. Generation of emitted radiant light can be suppressed.

Second embodiment.
FIG. 7 is a cross-sectional view showing the configuration of the wavelength selective filter 101 according to the second embodiment of the present invention. The wavelength selection filter 101 of the present embodiment is characterized in that metal mirrors 21 and 22 are provided instead of the DBRs 11 and 12 in the first embodiment.

  In the wavelength selection filter 101 of the present embodiment, the GC 10 is configured in the same manner as the GC 10 of the first embodiment. The metal mirror 21 is formed so as to be positioned in the −Z direction of the GC 10 with a predetermined phase adjustment section p1 sandwiched between the GC 10 and similarly, the metal mirror 22 is positioned in the + Z direction of the GC 10. , GC10 and a predetermined phase adjustment section p2. The metal mirrors 21 and 22 are made of, for example, aluminum having a complex refractive index n = 1.44−j16.0. In FIG. 7, the metal mirrors 21 and 22 are shown in close contact with the end portion in the −Z direction and the end portion in the + Z direction of the waveguide core 2, but for example, the waveguide core 2 (or the waveguide core 2). The metal mirrors 21 and 22 may be formed by forming a groove in the X-axis direction in the substrate 1) and pouring a metal material (for example, aluminum) into the groove. According to the wavelength selection filter 101 of the present embodiment, the size of the wavelength selection filter 101 in the Z-axis direction can be greatly reduced as compared with the wavelength selection filter 100 of the first embodiment.

  FIG. 8 is a diagram showing an electric field profile when incident light is incident on the wavelength selective filter 101 of FIG. FIG. 8 is an electric field profile (normalized electric field strength) when incident light having a wavelength of 1.5518 μm is incident. FIG. 8 shows a part of the same cross section as FIG. 7 at different scales in the X-axis direction and the Z-axis direction. In the waveguide core 2, a standing wave is generated by reflection between the metal mirrors 21 and 22 (not shown). This standing wave is generated according to the positions of the concave and convex portions that form the grating of the GC 10. The reflectance of the wavelength selection filter 101 of this embodiment was calculated to be 58%.

  According to the second embodiment, the size of the wavelength selection filter 101 can be made smaller than that of the first embodiment, but the reflectance of the wavelength selection filter 101 is the same as that of the wavelength selection filter 100 of the first embodiment. Is good. Therefore, the DBR in the first embodiment may be combined with the metal mirror in the second embodiment. In this case, the DBR and the metal mirror shortened in the Z-axis direction are formed in each of the −Z direction and the + Z direction of the GC 10. According to such a configuration, it is possible to realize a wavelength selective filter that achieves sufficient reflectance according to the available substrate area.

Third embodiment.
FIG. 9 is a cross-sectional view showing the configuration of the wavelength selective filter 102 according to the third embodiment of the present invention. In order to increase the extinction ratio of the reflection spectrum, it is effective to reduce the reflectance other than the desired wavelength. For this purpose, a non-reflective structure (also referred to as “moth-eye” structure) as described in Non-Patent Documents 6 to 7 may be introduced on the surface of the GC on which incident light is incident. For example, Non-Patent Document 7 discloses a GMRF having a structure in which a grating having a triangular cross-sectional shape is coated with a thin film having a high refractive index. The wavelength selection filter 102 of the present embodiment is characterized by including a non-reflection GC 30 having a triangular cross-sectional shape instead of the GC 10 having a rectangular cross-sectional shape in the wavelength selection filter 100 of the first embodiment. By having a triangular cross-sectional shape, Fresnel reflection caused by the refractive index boundary can be reduced. While the specular reflection from a medium having a refractive index of 1.5 is about 4%, the specular reflection can be reduced to 0 in principle by adopting the structure of this embodiment. According to the wavelength selection filter 102 of the present embodiment, the component of the desired wavelength of the incident light is radiated as emitted light in the −X direction by diffracting the guided light in the waveguide core 2 by the non-reflecting GC 30. (That is, reflected light with respect to incident light). Components of the incident light other than the desired wavelength pass through the non-reflecting GC 30 without reflection and are transmitted to the substrate 1 side.

Fourth embodiment.
FIG. 10 is a cross-sectional view showing a configuration of a filter device according to the fourth embodiment of the present invention. Since GMRF uses a guided mode, it generally depends on the polarization direction. This also applies to the wavelength selective filters 100 to 102 according to the embodiments described above. However, in some cases, it is desirable to provide a wavelength selective filter that does not depend on the polarization direction. For this reason, the filter device of this embodiment includes two wavelength selective filters 103 and 104 similar to the wavelength selective filter 100 of the first embodiment on both the −X direction surface and the + X direction surface of the substrate 1. It is formed. Specifically, the filter device of the present embodiment includes the waveguide core 2 and the GC 10 in which irregularities are periodically arranged in the Z-axis direction on the surface in the −X direction of the substrate 1, and the surface in the + X direction of the substrate 1. 1 includes a waveguide core 3 and a GC 13 in which irregularities are periodically arranged in the Y-axis direction. The concave and convex periods (grating periods) of the GCs 10 and 13 are the same. Since the GCs 10 and 13 have the above-mentioned directions, when incident light including a desired wavelength according to the grating period is incident on the GC 10 from the −X direction, the waveguide core 2 has a predetermined guide according to the grating period of the GC 10. Waveguide light having a wavelength in the waveguide and propagating in the + Z direction and the −Z direction (that is, waveguide light propagating in the direction of arrow d1 and waveguide light propagating in the direction of arrow d2 in FIG. 10) is excited and guided. In the core 3, guided light having a predetermined wavelength in the waveguide corresponding to the grating period of the GC 13 and propagating in the + Y direction and the −Y direction (that is, guided light and arrow propagating in the direction of the arrow d 1 ′ in FIG. 10) guided light propagating in the direction of d2 ′) is excited. Although omitted for simplification of illustration, a phase adjustment section and a DBR similar to those of the wavelength selection filter 100 of the first embodiment are formed in the −Z direction and + Z direction of the GC 10, respectively, and the −Y direction of the GC 13 is formed. Also in the + Y direction, it is necessary to form the same phase adjustment section and DBR as in the wavelength selective filter 100 of the first embodiment. The substrate 1 and the waveguide cores 2 and 3 are assumed to have a sufficient size to support these phase adjustment sections and the DBR. Similar to the second embodiment, a metal mirror may be provided instead of the DBR. Similarly to the third embodiment, a non-reflective GC having a triangular cross-sectional shape may be provided instead of the GC having a rectangular cross-sectional shape. According to the filter device of the present embodiment, it is possible to provide a filter device that does not depend on the polarization direction by including the GCs 10 and 13 in which the grating directions are orthogonal to each other.

Fifth embodiment.
FIG. 11 is a cross-sectional view showing a configuration of a filter device according to the fifth embodiment of the present invention. The filter device of the present embodiment also provides a filter device that does not depend on the polarization direction, like the filter device of the fourth embodiment. For this reason, the filter device of the present embodiment is characterized in that GCs having different directions are formed on both the −X direction surface and the + X direction surface of the waveguide core 2. Specifically, the filter device of the present embodiment includes the GC 10 in which irregularities are periodically arranged in the Z-axis direction on the −X direction surface of the waveguide core 2, and the + X direction surface of the waveguide core 2 (that is, In the layer between the substrate 1 and the waveguide core 2, a GC 14 in which irregularities are periodically arranged in the Y-axis direction is provided. The waveguide core 2 and the GC 10 function as the first wavelength selection filter 105, and the waveguide core 2 and the GC 14 function as the second wavelength selection filter 106. The concave and convex periods (grating periods) of the GCs 10 and 14 are the same. Since the GCs 10 and 14 have the above-described directions, when incident light including a desired wavelength according to the grating period is incident on the GC 10 from the −X direction, the waveguide core 2 has a predetermined guide according to the grating period of the GC 10. While guided light having a wavelength in the waveguide and propagating in the + Z direction and the −Z direction (that is, guided light propagating in the direction of arrow d1 and guided light propagating in the direction of arrow d2 in FIG. 11) is excited, In the waveguide core 2, waveguide light having a predetermined wavelength in the waveguide corresponding to the grating period of the GC 14 and propagating in the + Y direction and the -Y direction (that is, waveguide light propagating in the direction of the arrow d1 'in FIG. 11). And guided light propagating in the direction of the arrow d2 ′). Although omitted for simplification of illustration, DBRs similar to those of the wavelength selection filter 100 of the first embodiment are formed in the −Z direction and + Z direction of the GC 10, respectively, and in the −Y direction and + Y direction of the GC 14. However, it is necessary to form DBRs similar to those of the wavelength selective filter 100 of the first embodiment. The substrate 1 and the waveguide core 2 are assumed to have a size sufficient to support these DBRs. Similar to the second embodiment, a metal mirror may be provided instead of the DBR. Similarly to the third embodiment, a non-reflective GC having a triangular cross-sectional shape may be provided instead of the GC having a rectangular cross-sectional shape. According to the filter device of the present embodiment, it is possible to provide a filter device that does not depend on the polarization direction by providing the GCs 10 and 14 in which the grating directions are orthogonal to each other.

Sixth embodiment.
FIG. 12 is a cross-sectional view showing a configuration of a filter device according to the sixth embodiment of the present invention. For a light wave of a certain frequency, even if it is the same medium, the refractive index of the medium is different between the TE wave and the TM wave, and the wavelength in the medium is also different. For this reason, for the GC having a certain grating period, the reflection spectrum and the transmission spectrum are different between the TE wave and the TM wave. In the filter device of this embodiment, two GCs 10 and 15 having different grating periods are arranged on the plane in the −X direction and the plane in the + X direction of the waveguide core 2 so as to resonate at the same wavelength with respect to each of the orthogonal polarizations. It is characterized by forming. Specifically, the filter device of the present embodiment includes a GC 10 having a grating period Λ1 on the −X direction surface of the waveguide core 2, and the + X direction surface of the waveguide core 2 (that is, the substrate 1 and the waveguide core). 2) is provided with a GC 15 having a grating period Λ2 different from the grating period Λ1. The waveguide core 2 and the GC 10 function as the first wavelength selection filter 107, and the waveguide core 2 and the GC 15 function as the second wavelength selection filter 108. The GCs 10 and 15 are both formed such that irregularities are periodically arranged in the Z-axis direction. Although omitted for simplification of illustration, DBRs similar to those of the wavelength selective filter 100 of the first embodiment are formed in the −Z direction and + Z direction of the GC 10, respectively, and in the −Z direction and + Z direction of the GC 15. However, it is necessary to form DBRs similar to those of the wavelength selective filter 100 of the first embodiment. The substrate 1 and the waveguide core 2 are assumed to have a size sufficient to support these DBRs. Similar to the second embodiment, a metal mirror may be provided instead of the DBR. Similarly to the third embodiment, a non-reflective GC having a triangular cross-sectional shape may be provided instead of the GC having a rectangular cross-sectional shape. According to the filter device of the present embodiment, it is possible to provide a filter device that does not depend on the polarization direction by including the GCs 10 and 15 having different periods of the grating in parallel.

Seventh embodiment.
FIG. 13: is sectional drawing which shows the structure of the VCSEL laser apparatus based on the 7th Embodiment of this invention. A VCSEL (vertical cavity surface emitting laser) is also disclosed in Non-Patent Document 5, for example. The VCSEL laser device of this embodiment is characterized in that a wavelength selection filter 109 similar to the wavelength selection filter 100 of the first embodiment is used as an external mirror for the laser light source 40. At this time, it is possible to obtain laser oscillation whose polarization is controlled by utilizing the dependency of the polarization direction in the wavelength selection filter 109. The laser light source 40 includes an active layer 41 and a multilayer mirror 42, and a component having a predetermined wavelength in the light generated in the active layer 41 is repeatedly reflected between the multilayer mirror 42 and the wavelength selection filter 109. Resonates. This predetermined wavelength component excites guided light in the waveguide core 2 as in the wavelength selective filter 100 of the first embodiment. One of the DBRs 11 and 12 (DBR 11 in this embodiment) has a reflectivity lower than 100% by shortening the length in the Z-axis direction. The VCSEL laser device of this embodiment outputs a part of the guided light from one end of the DBR 11 as its laser output. As a wavelength selection filter used in the laser apparatus of this embodiment, the wavelength selection filter 102 of the third embodiment may be used instead of the wavelength selection filter 100 of the first embodiment. According to the VCSEL laser device of the present embodiment, it is possible to resonate only a component having a predetermined wavelength in the generated light and effectively output only the component having the predetermined wavelength.

  The wavelength selective filter and filter device according to the embodiment of the present invention have the following specific effects as compared with the prior art. For example, although the gratings of Patent Document 1 and Non-Patent Document 5 require a material with a high refractive index, the wavelength selective filter and filter device of the embodiment of the present invention enable highly efficient coupling without such a requirement. To do. Further, for example, the GMRF of Non-Patent Document 4 requires a lens for coupling the GMRF and the optical fiber, but the wavelength selective filter and filter device of the embodiment of the present invention are highly efficient without such a requirement. Allows coupling. Further, for example, the grating of Non-Patent Document 5 has a DBR reflective layer formed on the substrate, but the wavelength selective filter and filter device of the embodiment of the present invention do not require such a structure, and are on the substrate side. Transmitted light can be transmitted.

  The GC of Patent Document 5 is most similar to the wavelength selective filter according to the embodiment of the present invention in that it includes a GC and two DBRs formed on both sides of the GC. The wavelength selective filter according to the embodiment has the following specific effects. The GC of Patent Document 5 aims at high-efficiency coupling between guided light and spatial light with a short coupling length. For this reason, a highly reflective material is used for the substrate. Therefore, the GC of Patent Document 5 cannot extract transmitted light from the substrate side, and the desired wavelength component and the other wavelength components of the incident light as in the wavelength selection filter of the embodiment of the present invention. Cannot be taken out separately. Furthermore, since the GC of Patent Document 5 is simply intended to couple the guided light and the spatial light, the principle of operation is that the components of the desired wavelength and the components of the other wavelengths of the incident light are separated. This is completely different from the operation principle of the wavelength selective filter of the embodiment of the present invention intended to be extracted.

  As described above, according to the wavelength selective filter of the present embodiment, it is possible to couple with incident light in a smaller area than the conventional GMRF, and a light having a desired wavelength and other wavelengths can be combined without requiring a high refractive index material. It is possible to provide a wavelength selective filter that can extract the light separately.

  The wavelength selective filter according to the embodiment of the present invention has a novel configuration in which GC and DBR are integrated, and therefore, a resonator-integrated guided-mode resonance filter (CRIGF). Can be called.

  According to the wavelength selective filter of the present invention, it is possible to couple with incident light in a smaller area than that of the conventional GMRF, and it is not necessary to use a material with a high refractive index, so that light of a desired wavelength and light of other wavelengths are separated. It is possible to provide a wavelength selective filter that can be taken out. Further, it is possible to provide a filter device and a laser device provided with such a wavelength selection filter.

1 ... substrate,
2, 3 ... Waveguide core,
10, 13, 14, 15 ... grating coupler (GC),
11, 12 ... DBR,
p1, p2 ... phase adjustment interval,
21,22 ... Metal mirror,
30: Non-reflective GC,
40 ... Laser light source,
41 ... active layer,
42 ... multilayer mirror,
100 to 110: Wavelength selection filter.

Claims (10)

A wavelength selective filter, wherein the wavelength selective filter is:
A waveguide having first and second waveguide directions opposite to each other, and is provided between first and second surfaces extending along the first waveguide direction and facing each other. Waveguides,
A first reflecting means, a first phase adjusting section, a diffracting means, a second phase adjusting section, and a second reflecting means provided in the waveguide in order along the first waveguide direction. Prepared,
The diffraction means has a grating period along the first waveguide direction,
The diffracting means is guided light that propagates in the first waveguide direction in the waveguide when incident light including light having a first wavelength corresponding to the grating period of the diffracting means is incident on the diffracting means. The diffracting means diffracts the guided light propagating in the first waveguide direction and radiates it from the first and second surfaces of the waveguide,
The second reflecting means reflects the guided light propagated in the first waveguide direction in the second propagation direction,
The first reflecting means reflects the guided light propagated in the second waveguide direction in the first propagation direction,
In the first phase adjustment section, when guided light propagating in the second propagation direction is reflected by the first reflecting means, the reflected guided light is reflected by incident light incident on the diffracting means. Having a length set to have the same phase as the phase of the guided light propagating in the first propagation direction,
When incident light including light having a wavelength other than the first wavelength and light having a wavelength other than the first wavelength is incident on the diffraction unit,
By diffracting the guided light propagating in the first waveguide direction by the diffracting means and emitting it from the first surface of the waveguide, the light having the first wavelength incident on the diffracting means is reflected. ,
By diffracting the guided light propagating in the first waveguide direction by the diffracting means and radiating it from the second surface of the waveguide, the first light that is incident on the diffracting means and transmitted through the waveguide is transmitted. Cancel the light of
A wavelength selective filter, wherein light having a wavelength other than the first wavelength is transmitted through the waveguide. The incident light is incident on the diffracting means so as to be perpendicular to the first surface of the waveguide;
The diffracting means is guided light that propagates in the first waveguide direction in the waveguide when incident light including light having a first wavelength corresponding to the grating period of the diffracting means is incident on the diffracting means. And the guided light propagating in the second waveguide direction, and the diffracting means diffracts the guided light propagating in the first waveguide direction to diffract the first and second surfaces of the waveguide. Diffracted guided light propagating in the second waveguide direction and radiated from the first and second surfaces of the waveguide,
In the second phase adjustment section, when the guided light propagating in the first propagation direction is reflected by the second reflecting means, the reflected guided light is reflected by incident light incident on the diffracting means. Having a length set to have the same phase as the phase of the guided light propagating in the second propagation direction,
When incident light including light having a wavelength other than the first wavelength and light having a wavelength other than the first wavelength is incident on the diffraction unit,
The guided light propagating in the first waveguide direction is diffracted by the diffracting means and radiated from the first surface of the waveguide, and the guided light propagating in the second waveguide direction is diffracted by the diffracting means. By diffracting and radiating from the first surface of the waveguide, the light of the first wavelength incident on the diffracting means is reflected,
The guided light propagating in the first waveguide direction is diffracted by the diffracting means and radiated from the second surface of the waveguide, and the guided light propagating in the second waveguide direction is diffracted by the diffracting means. By diffracting and radiating from the second surface of the waveguide, the light of the first wavelength incident on the diffracting means and transmitted through the waveguide is canceled,
2. The wavelength selective filter according to claim 1, wherein light having a wavelength other than the first wavelength is transmitted through the waveguide.   3. The wavelength according to claim 1, wherein each of the first reflecting means and the second reflecting means is a distributed Bragg reflector having a grating period along the first waveguide direction. Selection filter.   3. The wavelength selective filter according to claim 1, wherein each of the first reflecting means and the second reflecting means is a metal mirror.   The wavelength selection filter according to claim 1, wherein the diffraction unit has a non-reflective structure. The incident light is incident on the diffracting means with a predetermined incident angle inclined toward the first reflecting means from a direction perpendicular to the first surface of the waveguide;
The diffracting means is coupled to the waveguide light propagating in the first waveguide direction and not coupled to the waveguide light propagating in the second waveguide direction. And a predetermined distance from the first surface of the waveguide between the second surface and the second surface,
The first and second reflecting means are coupled to both the guided light propagating in the first waveguide direction and the guided light propagating in the second waveguide direction. 2. The wavelength selective filter according to claim 1, wherein the wavelength selective filter is provided between the first surface and the second surface with a predetermined distance from the first surface of the waveguide. A filter device comprising two wavelength selective filters according to any one of claims 1 to 5,
The filter device further includes a substrate having first and second surfaces facing each other and parallel to each other,
A first wavelength selection filter of the two wavelength selection filters is formed on the first surface of the substrate,
A second wavelength selection filter of the two wavelength selection filters is formed on the second surface of the substrate, and the first and second waveguide directions of the waveguide of the second wavelength selection filter are: A filter device, wherein the filter device is in a plane parallel to the second surface of the substrate and is orthogonal to the first and second waveguide directions of the waveguide of the first wavelength selective filter. A filter device comprising two wavelength selective filters according to any one of claims 1 to 5,
The filter device is
One common waveguide provided between the first and second surfaces facing each other and parallel to each other;
In the first surface of the waveguide, the first reflecting means, the first phase adjusting section, the diffracting means, the second phase adjusting section of the first wavelength selecting filter of the two wavelength selecting filters, and Comprising second reflecting means;
A first reflecting means, a first phase adjusting section, a diffracting means, a second phase adjusting section of the second wavelength selecting filter of the two wavelength selecting filters; Comprising second reflecting means;
The first and second waveguide directions of the waveguide of the second wavelength selective filter are in a plane parallel to the first and second surfaces of the waveguide, and the first wavelength selective filter A filter device characterized by being orthogonal to the first and second waveguide directions of the waveguide. A filter device comprising two wavelength selective filters according to any one of claims 1 to 5,
The filter device is
One common waveguide provided between the first and second surfaces facing each other and parallel to each other;
In the first surface of the waveguide, the first reflecting means, the first phase adjusting section, the diffracting means, the second phase adjusting section of the first wavelength selecting filter of the two wavelength selecting filters, and Comprising second reflecting means;
A first reflecting means, a first phase adjusting section, a diffracting means, a second phase adjusting section of the second wavelength selecting filter of the two wavelength selecting filters; Comprising second reflecting means;
The diffractive means of the second wavelength selective filter has a grating period different from the grating period of the diffractive means of the first wavelength selective filter along the first waveguide direction. .   A laser device comprising the wavelength selective filter according to claim 1 as an external mirror.

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