JP2015175902A - Optical waveguide, spot size converter, polarization filter, optical coupler, optical detector, optical splitter, and laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide that can be manufactured by a simplified process, is high in accuracy and has a function equal to a vertical taper waveguide, and to provide a spot size converter, polarization filter, optical coupler, optical detector, optical splitter, and laser element that use the optical waveguide.SOLUTION: An optical waveguide comprises: a core area 1 in which incident light is confined to waveguide the incident light and whose thickness is substantially even; and a clad area 2 that sandwiches the core area 1 from both surfaces in a thickness direction. The core area 1 is an optical waveguide 10 of which an effective refractive index consecutively varies along a waveguide direction of the core area 1 and in which the effective refractive index of the core area 1 is at least higher than a refractive index of the clad area 2. The core area 1 comprises: a first area 1a; and a second area 1b that is lower in the refractive index than the first area 1a, and the first area 1a and second area 1b are arranged so as to have a cycle almost equivalent to a wavelength of the incident light or a small cycle.

Description

  The present invention relates to an optical waveguide, a spot size converter, a polarizing filter, an optical coupler, a photodetector, an optical multiplexer / demultiplexer, and a laser element.

  Conventionally, in the field of optical communication, optical waveguides having various functions using quartz glass as a material have been proposed. Such an optical waveguide confines light in the core region by sandwiching the core region on a flat plate with a high refractive index and a uniform thickness from both sides of the core region with a cladding region having a lower refractive index than the core region. Realizes low propagation loss.

  Here, a vertical taper waveguide having a taper structure with respect to the vertical direction is disclosed. The vertical taper waveguide has a taper structure in which the thickness of the core portion is gradually reduced or gradually increased along the direction in which incident light is guided. Such a vertical taper waveguide is suitable for use in, for example, a spot size converter for coupling light of an optical fiber to a Si (silicon) thin wire waveguide with low loss (for example, Non-Patent Document 1). ).

R. S. Balmer et al. “Vertically Tapered Epilayers for Low-Loss Waveguide-Fiber Coupling Achieved in a Single Epitaxy Growth RUN”, JOURNAL OFGHITEL 21, NO. 1, January 2003

  However, since such a vertical taper waveguide is formed by etching or vapor deposition in a vertical taper structure, the process is complicated and it is difficult to produce a taper structure with high accuracy. .

  The present invention has been made in view of the above, and an optical waveguide that can be manufactured by a simple process, has high accuracy, and has the same function as a vertical tapered waveguide, and the optical waveguide are used. It is an object of the present invention to provide a spot size converter, a polarizing filter, an optical coupler, a photodetector, an optical multiplexer / demultiplexer, and a laser element.

  In order to solve the above-described problems and achieve the object, an optical waveguide according to the present invention includes a core region having a substantially uniform thickness for confining and guiding incident light, and the core region having the thickness. A cladding region sandwiched from both sides of the direction, the core region, the effective refractive index is continuously changing along the waveguide direction of the core region, the effective refractive index of the core region, It is at least higher than the refractive index of the cladding region.

  In the optical waveguide according to the present invention, in the above invention, the core region includes at least a first region and a second region having a refractive index lower than that of the first region, and the first region and the first region The two regions are arranged so as to have a period substantially equal to the wavelength of the incident light or a period smaller than the wavelength of the incident light.

In the optical waveguide according to the present invention, the core region includes a first region and a second region having a refractive index lower than that of the first region, and the refractive index of the first region is n. _a, the refractive index n _b of the second _region, wherein among the wave number of the light k _a propagating the first _region, the wave number of the light k _b propagating in the second _region, the wave number of the incident light The component in the waveguide direction of the core region and the direction perpendicular to the thickness direction is k _x , the width of the first region is w _a , the width of the second region is w _b , the period is Λ, and the incident light and the wavelength lambda, the propagation constant is beta, wherein the core region, wherein the (a) (C), or formula (B) and the k _a and k _b satisfies at least one for two formulas (C) combine as one or with _{two, n a, n b, w} a, _{that w b} is set JP To.

  The optical waveguide according to the present invention is characterized in that, in the above-mentioned invention, the effective refractive index of the core region increases linearly or decreases linearly along the waveguide direction.

  In the optical waveguide according to the present invention, in the above invention, the first region has a tapered shape in which a width in a width direction perpendicular to the thickness direction is increased along the waveguide direction. The two regions have a tapered shape in which the width in the width direction decreases along the waveguide direction.

  A spot size converter according to the present invention includes the optical waveguide according to the invention, a light input unit that receives light, and a light output unit that outputs light, and the light waveguide includes the light input unit. The spot size of the light input from is converted and output from the light output unit.

  The polarizing filter according to the present invention is a light that absorbs at least a part of TM mode light that is polarized in parallel with the thickness direction, among the light incident on the optical waveguide according to the present invention and the light waveguide. The optical waveguide has a TE-mode light perpendicular to the TM mode of the incident light that has a smaller electric field distribution in the thickness direction than the TM-mode light. The cladding region has a thickness such that at least a part of the TM mode light of the incident light and the light absorbing portion overlap with each other. And the light absorber absorbs more TM mode light than TE mode light.

  The optical coupler according to the present invention is the optical waveguide according to the invention described above, and is formed on one side of the optical waveguide, confins and guides incident light, has a substantially uniform thickness, and the cladding layer A second core region having a higher refractive index, and a second cladding region formed on a surface of the second core region opposite to the surface facing the optical waveguide, and having a lower refractive index than the second core region; It is characterized by providing.

  In addition, a photodetector according to the present invention includes the optical waveguide according to the invention described above and a light detection unit that detects light intensity of the optical waveguide, and the core region has the effective refractive index in the waveguide direction. It has a minimum detection unit, and the light detection means is arranged close to the detection unit.

  The optical multiplexer / demultiplexer according to the present invention forms a core region having a substantially uniform thickness for confining and guiding incident light and sandwiching the core region from both sides in the thickness direction to form an optical resonator. The core region is characterized in that the effective refractive index of the core region continuously changes along the waveguide direction of the core region.

  The laser element according to the present invention includes a first reflecting mirror and a second reflecting mirror constituting an optical resonator, an active layer disposed between the first reflecting mirror and the second reflecting mirror, An electrode for injecting current into the active layer, and a surface emitting laser that outputs light from the first reflecting mirror side, and an optical waveguide layer formed on the first reflecting mirror side of the surface emitting laser. The optical waveguide layer is formed between a third reflecting mirror, the first reflecting mirror, and the third reflecting mirror, and has a thickness for confining and guiding light output from the surface emitting laser. A substantially uniform core region, wherein the core region has an effective refractive index continuously changing along a waveguide direction parallel to a plane orthogonal to the output direction of the surface emitting laser. And

In the laser device according to the present invention, in the above invention, the effective thickness of the core region in the region immediately below the surface emitting laser is such that the laser oscillation wavelength of the laser device is λ and the effective refractive index of the core region is _Where n _eff is λ / 2n _eff .

  The laser element according to the present invention is characterized in that, in the above invention, the effective refractive index of the core region increases linearly or decreases linearly along the waveguide direction.

  In the laser device according to the present invention, in the above invention, the core region includes a first region and a second region having a refractive index lower than that of the first region, and the first region and the second region. Has a period approximately equal to the wavelength of light output from the surface emitting laser and incident on the core region, or a period smaller than the wavelength of light output from the surface emitting laser and incident on the core region. It is arranged so that it may be arranged.

  In the laser device according to the present invention, in the above invention, the first region has a tapered shape in which a width in a width direction perpendicular to the thickness direction is increased along the waveguide direction. The two regions have a tapered shape in which the width in the width direction decreases along the waveguide direction.

  According to the present invention, an optical waveguide that can be manufactured by a simple process, has high accuracy, and has the same function as a vertical tapered waveguide, a spot size converter using the optical waveguide, a polarizing filter, There is an effect that an optical coupler, a photodetector, an optical multiplexer / demultiplexer, and a laser element can be provided.

FIG. 1 is a schematic perspective view of an optical waveguide according to the first embodiment. FIG. 2 is a schematic side view of the yz plane of the optical waveguide shown in FIG. FIG. 3 is a schematic cross-sectional view of the core region of the optical waveguide shown in FIG. FIG. 4 is a diagram for explaining the parameters of the equation. FIG. 5 is a schematic perspective view of a spot size converter using the optical waveguide according to the first embodiment. FIG. 6 is a diagram for explaining how light is guided through the spot size converter shown in FIG. FIG. 7 is a schematic cross-sectional view of the core region of the optical waveguide according to the first modification of the first embodiment. FIG. 8 is a schematic cross-sectional view of the core region of the optical waveguide according to the second modification of the first embodiment. FIG. 9 is a schematic side view of the yz plane of the polarizing filter according to the second embodiment. FIG. 10 is a diagram for explaining a state where TE mode and TM mode light is guided through the polarizing filter shown in FIG. 9. FIG. 11 is a schematic side view of the yz plane of the optical coupler according to the third embodiment. FIG. 12 is a schematic cross-sectional view of the first core region of the optical coupler shown in FIG. FIG. 13 is a schematic side view of the yz plane of the photodetector according to the fourth embodiment. FIG. 14 is a schematic cross-sectional view of the core region of the photodetector shown in FIG. FIG. 15 is a schematic perspective view of an optical multiplexer / demultiplexer according to the fifth embodiment. FIG. 16 is a schematic side view of the yz plane of the optical multiplexer / demultiplexer shown in FIG. 17 is a schematic cross-sectional view of the core region of the optical multiplexer / demultiplexer shown in FIG. FIG. 18 is a schematic perspective view of a laser device according to the sixth embodiment. FIG. 19 is a schematic yz cross-sectional view of the laser device shown in FIG. FIG. 20 is a diagram for explaining how light is guided through the optical waveguide layer of the laser element shown in FIG. FIG. 21 is a diagram for explaining a method of manufacturing the laser element shown in FIG. FIG. 22 is a schematic perspective view of a laser device according to the seventh embodiment.

  Hereinafter, embodiments of an optical waveguide, a spot size converter, a polarizing filter, an optical coupler, a photodetector, an optical multiplexer / demultiplexer, and a laser element according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments. In the description of the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. It should be noted that the drawings are schematic, and the relationship between the dimensions of each element, the ratio of each element, and the like may differ from the actual situation. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included.

(Embodiment 1)
First, the optical waveguide according to the first embodiment of the present invention will be described. FIG. 1 is a schematic perspective view of an optical waveguide according to the first embodiment. As shown in FIG. 1, the optical waveguide 10 includes a core region 1 and a cladding region 2. Here, for the sake of explanation, in each of the following drawings, the direction in which the incident light is guided is the z axis, the thickness direction of the core region 1 is the y axis, and the width direction of the core region 1 perpendicular to the y axis is x. Axis.

  Next, the structure of the optical waveguide 10 according to Embodiment 1 of the present invention will be described. FIG. 2 is a schematic side view of the yz plane of the optical waveguide shown in FIG. FIG. 3 is a schematic cross-sectional view of the core region of the optical waveguide shown in FIG.

First, as shown in FIG. 2, the core region 1 of the optical waveguide 10 is formed to have a substantially uniform thickness, and the incident light is confined and guided. However, the substantially uniform thickness is a thickness that satisfies tan θ <1.0 × 10 ⁻³ , for example, where θ is an angle between the lower surface and the upper surface of the core region 1 in the waveguide direction. Furthermore, as shown in FIG. 3, the core region 1 includes a first region 1a and a second region 1b having a refractive index lower than that of the first region 1a. Of the core region 1, the first region 1 a has a tapered shape in which the width in the x-axis direction that is the width direction increases along the z-axis that is the waveguide direction. On the other hand, the second region 1b has a tapered shape in which the width in the x-axis direction that is the width direction decreases along the z-axis that is the waveguide direction. The first regions 1a and the second regions 1b are arranged alternately along the x-axis direction perpendicular to the waveguide direction. The period of the pattern formed by the first region 1a and the second region 1b is, for example, the center-to-center distance in the x-axis direction of the first region 1a, and is the length L1 in FIG. At this time, the length L1 is arranged so as to have a period of the same order as the wavelength of the incident light or a period smaller than the wavelength of the incident light.

  Of the core region 1, the first region 1a is made of various semiconductors such as gallium arsenide (GaAs) and silicon (Si), quartz-based materials, and the like. On the other hand, the second region 1b is, for example, a material having a lower refractive index than the first region 1a, and may be, for example, an air layer, but may be a quartz-based material, various semiconductors, or the like. It may be filled.

  Next, as shown in FIG. 2, the cladding region 2 is arranged so as to sandwich the core region 1 from both sides in the y-axis direction that is the thickness direction. The cladding region 2 is made of, for example, a quartz-based material or various semiconductors, and has a refractive index lower than the effective refractive index of the core region 1 described later.

Here, according to the effective medium theory, the effective refractive index in the xz plane of the core region 1 of the optical waveguide 10 is approximately calculated by the following formula (1) with respect to the TM mode in which the magnetic field is parallel to the x axis. be able to.

In addition, the effective refractive index in the xz plane of the core region 1 of the optical waveguide 10 can be approximately calculated by the following formula (2) with respect to the TE mode in which the electric field is parallel to the x-axis. it can.

In formulas (1) and _{(2), n eff} is the effective refractive index, _{n a} is the refractive index of the material of the first region 1a in the core region 1, _{n b} is the refractive material of the second region 1b of the core region 1 Rate. Η is a duty ratio that is a ratio of the first region 1a to the second region 1b in the unit region of the core region 1. Here, the unit region is a region having a sub wavelength comparable to the wavelength of incident light.

  The optical waveguide 10 is arranged such that the first region 1a and the second region 1b have a period that is approximately the same as the wavelength of the incident light or a period that is smaller than the wavelength of the incident light. That is, for example, when the wavelength of incident light is 1.0 μm to 1.1 μm (1.0 μm band), the length L1 that is the period formed by the first region 1a and the second region 1b is 1.1 μm or less. In the core region 1 of the optical waveguide 10, the duty ratio of the sub-wavelength unit region continuously increases along the z-axis that is the waveguide direction. That is, from the formulas (1) and (2), the effective refractive index of the core region 1 continuously increases along the z-axis that is the waveguide direction.

  Next, the operation of the optical waveguide 10 according to the first embodiment will be described. For example, when the effective refractive index of the core region 1 continuously increases along the z-axis that is the waveguide direction, incident light is guided in the z-axis direction and is more strongly confined in the core region 1. Become.

  Here, as described above, the vertical taper waveguide is suitable for use in the spot size converter, but this is incident when the vertical taper waveguide is thick along the z-axis direction, for example. This is because light is more strongly confined in the core region while being guided in the z-axis direction. The propagation of light in such a vertical taper waveguide and the propagation of light in the optical waveguide 10 can be regarded as substantially equal. Therefore, the optical waveguide 10 according to the first embodiment is an optical waveguide having a function equivalent to that of the vertical taper waveguide.

By the way, for example, when the refractive index difference between the first region 1a and the second region 1b is large, the actual effective refractive index may deviate from the effective refractive index calculated by the effective medium theory. In such a case, the effective refractive index n _eff can be calculated from the boundary condition between the electric field and the magnetic field. Here, FIG. 4 is a diagram for explaining the parameters of the equation. As shown in FIG. 4, it is assumed that the first regions 1a and the second regions 1b are alternately arranged. At this time, in the formula (3) and (4) below, _{n a} is the refractive index of the material of the first region 1a, _{n b} is the refractive index of the material of the second region 1b, _{k a} is the first region 1a wave number of propagating light, k _b is the wave number of light propagating in the second region 1b, k _x the x-axis direction component of the wavenumber of the incident light, w _a is the width of the first region 1a, w _b is The width of the second region 1b, Λ is a period (that is, w _a + w _b ), λ is the wavelength of incident light, and β is a propagation constant.

From the boundary condition between the electric field and the magnetic field at x = 0 and x = w _b , the following equation (3) is obtained for the TE mode in which the electric field is parallel to the x axis, and the TM mode in which the magnetic field is parallel to the x axis: On the other hand, the following formula (4) is derived.

Furthermore, Expression (5) is derived from the boundary condition of the propagation constant in the z-axis direction.

The core region 1, when the incident light is TE mode, equation (3), (5), when the incident light is TM mode, equation (4), meet (5) _{k a} N _a , n _b , w _a , and w _b are set so as to have two, more preferably one combination of k _b . That is, the core region 1, the formula (3) and (5), or two combinations of _{k a} and _{k b} satisfies the formula (4) at least one for two equations (5), more preferably 1 N _a , n _b , w _a , and w _b are set so as to have one. At this time, the effective refractive index n _eff is expressed by the following formula (6).

  In this way, by setting the propagation mode in the core region 1 to be one from the boundary condition between the electric field and the magnetic field, the core region 1 can be regarded as a uniform medium, and the incident light is the core region. 1 is propagated as in a uniform medium. In addition, in the case of the two modes of the fundamental even mode and the fundamental odd mode, the coupling coefficient of the two modes is sufficiently small, so that only the propagation constant of the fundamental even mode needs to be considered, and the core region 1 is a uniform medium and The incident light propagates through the core region 1 as in a uniform medium. If the incident angle of the incident light with respect to the surface direction of the core region 1 deviates from parallel, the coupling between the two modes of the fundamental even mode and the fundamental odd mode increases, so that the core region 1 has a uniform medium. Note that it can no longer be considered. Therefore, the incident light is preferably incident in parallel to the surface direction of the core region 1. As described above, the optical waveguide 10 having a desired refractive index distribution can be realized by setting each parameter of the core region 1.

  Next, a method for manufacturing the optical waveguide 10 according to the first embodiment will be described. First, a material to be one side of the cladding region 2 is laminated on a substrate (not shown) by, for example, MOCVD (Metal Organic Chemical Vapor Deposition) method. Furthermore, a material to be the core region 1a is laminated thereon.

  Next, the first region 1a of the core region 1 is formed by photolithography and reactive ion etching. This is a very simple process realized by forming a photoresist in photolithography in the same shape as the first region 1 a of the core region 1. Furthermore, the processing accuracy of photolithography is an accuracy of several tens of nm to several hundreds of nm, which is one digit or more smaller than the length of about 1 μm of the wavelength of light used in optical communication. Accordingly, the period between the first region 1a and the second region 1b can be accurately formed by photolithography.

  Here, it is assumed that the second region 1b of the core region 1 is, for example, an air layer. At this time, the structure of the optical waveguide 10 shown in FIG. 1 is obtained by bonding a material on one side of the cladding region 2 laminated on a substrate (not shown) to the surface of the core region 1 that is not in contact with the cladding region 2. It is formed. As a result, the optical waveguide 10 according to the first embodiment is manufactured, and an optical waveguide that can be manufactured by a simple process, has high accuracy, and has the same function as the vertical taper waveguide is realized. .

  As described above, the optical waveguide 10 according to the first embodiment is an optical waveguide that can be manufactured by a simple process, has high accuracy, and has a function equivalent to that of a vertical tapered waveguide.

  Next, a spot size converter using the optical waveguide 10 according to the first embodiment will be described. FIG. 5 is a schematic perspective view of a spot size converter using the optical waveguide according to the first embodiment. As shown in FIG. 5, the spot size converter 100 includes an optical waveguide 10, an optical fiber 20 connected to the optical input unit 10 a of the optical waveguide 10, and an optical waveguide connected to the optical output unit 10 b of the optical waveguide 10. 30 and an optical waveguide 40 connected to the optical waveguide 30.

  The optical waveguide 10 includes an optical input unit 10 a that is connected to the optical fiber 20 and receives light from the optical fiber 20, and an optical output unit 10 b that is connected to the optical waveguide 30 and outputs light to the optical waveguide 30. However, the other configuration may be the same as that of the optical waveguide 10 of FIG.

  The optical fiber 20 may be a single mode fiber, but may be a multimode fiber.

  The optical waveguide 30 includes a core region 31 in which the width in the x-axis direction that is the width direction decreases along the z-axis that is the waveguide direction, and a cladding region 32 that is formed around the core region 31. The core region 31 and the cladding region 32 may be made of the same material as the first region 1a and the cladding region 2 of the optical waveguide 10, respectively.

  The optical waveguide 40 includes a core region 41 and a cladding region 42. The optical waveguide 40 may be, for example, a Si fine wire waveguide, but may be an optical waveguide made of a quartz-based material or various semiconductors. In FIG. 5, the optical waveguide 40 is illustrated as a buried waveguide, but a waveguide other than the buried type such as a ridge waveguide may be used.

  Next, the operation of the spot size converter using the optical waveguide 10 according to the first embodiment will be described. FIG. 6 is a diagram for explaining how light is guided through the spot size converter shown in FIG. The curve in FIG. 6 represents the electric field distribution in the y-axis direction of the guided light. Here, as an example, it is assumed that the optical fiber 20 is a single mode fiber having a mode field diameter of 9 μm, and the optical waveguide 40 is a Si fine wire waveguide having one side of 1 μm.

  First, light l20 enters the optical waveguide 10 from the optical fiber 20. Here, the light 120 has a spread of the electric field distribution of about 9 μm from the mode field diameter of the optical fiber 20. Therefore, the light l10a incident from the light input portion 10a of the optical waveguide 10 also has a similar electric field distribution spread. Here, the effective refractive index of the core region 1 of the optical waveguide 10 continuously increases along the waveguide direction. Therefore, the incident light is more strongly confined in the core region 1 while being guided. That is, the spread of the electric field distribution in the y-axis direction of the guided light is reduced. The light l10b output from the light output unit 10b of the optical waveguide 10 is input to the optical waveguide 30 as light l30 having a small electric field distribution spread in the y-axis direction, as shown in FIG. Furthermore, by passing through the optical waveguide 30 that is a tapered waveguide that reduces the electric field distribution of light in the x-axis direction as shown in FIG. 5, the optical waveguide 40 that is a Si fine wire waveguide having a side of 1 μm has low loss. Can be combined. Thus, the optical waveguide 10 according to the first embodiment is suitable for application to the spot size converter 100.

  In the optical waveguide 10 according to the first embodiment, the air layer functions as a cladding layer on both side surfaces in the x-axis direction, thereby realizing light confinement in the x-axis direction. However, the clad layer made of the same material as that of the clad region 2, for example, may be further formed on both side surfaces in the x-axis direction.

  As described above, the optical waveguide 10 and the spot size converter 100 according to the first embodiment can be manufactured by a simple process, have high accuracy, and have the same function as the vertical taper waveguide. And a spot size converter using the optical waveguide.

(Modification 1)
Next, an optical waveguide according to Modification 1 of Embodiment 1 will be described. The configuration other than the core region of the optical waveguide according to the first modification of the first embodiment may be the same as the configuration of the optical waveguide 10 according to the first embodiment. FIG. 7 is a schematic cross-sectional view of the core region of the optical waveguide according to the first modification of the first embodiment. As shown in FIG. 7, in the core region 1A of the optical waveguide according to the first modification, the first region 1Aa has a rectangular _{shape in} which the length L _{1Aa of} one side increases along the z-axis that is the waveguide direction. Consists of regions. And the square area | region is arrange | positioned at intervals by length _L1A . On the other hand, the region other than the first region 1Aa is the second region 1Ab, and the second region 1Ab has a refractive index smaller than that of the first region 1Aa. The length L _1A, which is the interval between the square regions in the first region 1Aa, is approximately equal to the wavelength of the incident light or smaller than the wavelength of the incident light. Thereby, the effective refractive index of the core region 1A can be obtained from the equations (1) and (2) or the equations (3) to (6). At this time, the effective refractive index of the core region 1A continuously increases along the z-axis that is the waveguide direction. Thus, in the optical waveguide according to the first embodiment, the period formed by the first region 1Aa and the second region 1Ab is approximately the same as the wavelength of the incident light or smaller than the wavelength of the incident light. If the effective refractive index changes along the waveguide direction, the pattern of the first region 1Aa and the second region 1Ab can be arbitrarily set.

  Such an optical waveguide having the pattern of the first region 1Aa and the second region 1Ab is easily manufactured by changing only the pattern of the photoresist using the same method as the manufacturing method of the first embodiment. be able to.

  Thus, in the optical waveguide according to the first modification of the first embodiment, the first region 1Aa and the second region 1Ab have the same period as the wavelength of the incident light, or the wavelength of the incident light. Arranged to have a smaller period. As a result, the effective refractive index changes along the z-axis that is the waveguide direction of the core region 1A. Therefore, similarly to the first embodiment, the optical waveguide according to the first modification of the first embodiment can be manufactured by a simple process, has high accuracy, and has the same function as the vertical taper waveguide. It is an optical waveguide.

(Modification 2)
Next, an optical waveguide according to Modification 2 of Embodiment 1 will be described. The configuration other than the core region of the optical waveguide according to the second modification of the first embodiment may be the same as the configuration of the optical waveguide 10 according to the first embodiment. FIG. 8 is a schematic cross-sectional view of the core region of the optical waveguide according to the second modification of the first embodiment. As shown in FIG. 8, in the core region 1B of the optical waveguide according to the second modification, the first region includes the first region 1Baa and the first region 1Bab, respectively, along the z axis that is the waveguide direction. And a taper shape in which the width in the x-axis direction, which is the width direction, increases. On the other hand, the second region 1Bb has a tapered shape in which the width in the x-axis direction that is the width direction decreases along the z-axis that is the waveguide direction. The length L _1B, which is the period formed by the first region 1Baa, the first region 1Bab, and the second region 1Bb, is approximately the same as the wavelength of the incident light or smaller than the wavelength of the incident light. .

  Here, the first region 1Baa and the first region 1Bab have different refractive indexes, and the refractive index of the second region 1Bb is smaller than the refractive indexes of the first region 1Baa and the first region 1Bab. As a result, the effective refractive index of the core region 1B continuously increases along the z-axis that is the waveguide direction. As described above, the optical waveguide according to Embodiment 1 has a configuration in which the first region is composed of two or more regions having different refractive indexes as long as the effective refractive index changes along the waveguide direction. Also good. The optical waveguide according to Embodiment 1 may be configured such that the second region 1Bb is composed of two or more regions having different refractive indexes.

  Such an optical waveguide having a pattern of the first region 1Baa and the first region 1Bab and the second region 1Bb, which are the first regions, is obtained by using the same method as the manufacturing method of the first embodiment. It can be easily manufactured by changing only the pattern.

  As described above, in the optical waveguide according to the second modification of the first embodiment, the first region and the second region 1b have the same period as the wavelength of the incident light or the wavelength of the incident light. It arrange | positions so that it may have a small period. As a result, the effective refractive index changes along the z-axis that is the waveguide direction of the core region 1B. Therefore, similarly to the first embodiment, the optical waveguide according to the first modification of the first embodiment can be manufactured by a simple process, has high accuracy, and has the same function as the vertical taper waveguide. It is an optical waveguide.

(Embodiment 2)
Next, a polarizing filter according to Embodiment 2 of the present invention will be described. FIG. 9 is a schematic side view of the yz plane of the polarizing filter according to the second embodiment. As shown in FIG. 9, the polarizing filter 200 according to the second embodiment includes a core region 201, a cladding region 202, and a light absorbing unit 203. The core region 201 and the cladding region 202 may have the same configuration as that of the first embodiment, and the core region 201 includes a tapered first region and a second region as in FIG. The effective refractive index of 201 is continuously increased along the z-axis direction. Here, polarized light parallel to the x axis that is the width direction of the light incident on the polarizing filter 200 is TE mode, and polarized light parallel to the y axis that is the thickness direction of the light incident on the polarizing filter 200 is TM mode. To do. At this time, the optical waveguide composed of the core region 201 and the cladding region 202 guides the TE mode light so that the spread of the electric field distribution of the light in the y-axis direction is smaller than the TM mode light. Further, in the cladding region 202, the thickness of the cladding region 202 on the light absorbing portion 203 side is set such that at least a part of the TM mode light of the incident light and the light absorbing portion 203 overlap.

  The light absorption unit 203 absorbs at least a part of the TM mode light among the light incident on the optical waveguide composed of the core region 201 and the cladding region 202. The light absorbing portion 203 is made of, for example, various semiconductors or carbon. In addition, any material that absorbs light can be used.

  Next, the operation of the polarizing filter according to Embodiment 2 of the present invention will be described. FIG. 10 is a diagram for explaining a state where TE mode and TM mode light is guided through the polarizing filter shown in FIG. 9. As shown in FIG. 10, the spread of the electric field distribution in the y-axis direction of the TE mode light l201aa of the incident light is smaller than the spread of the electric field distribution in the y-axis direction of the TM mode light l201ba of the incident light. Therefore, the light l201aa does not overlap with the light absorption unit 203 or has a small overlap, but the light l201ba sufficiently overlaps with the light absorption unit 203.

  First, as shown in FIG. 10A, for the TE mode light, the light l201aa is guided in the optical waveguide composed of the core region 201 and the cladding region 202, and proceeds in the z-axis direction as it goes along the z-axis direction. Since the effective refractive index of the light becomes higher, the light is strongly confined in the core region 201, and thus the light l201ab has a smaller spread of the electric field distribution in the y-axis direction than the light l201aa. Therefore, among the incident light, the TE mode light hardly overlaps with the light absorbing portion 203 while being guided through the optical waveguide, and is hardly absorbed.

  On the other hand, as shown in FIG. 10 (b), for TM mode light, the light l201ba is guided in the optical waveguide composed of the core region 201 and the cladding region 202, and advances in the z-axis direction as the core region. Since the effective refractive index of 201 becomes higher, the light is strongly confined in the core region 201, so that the light l201bb has a smaller electric field distribution in the y-axis direction than the light l201ba. However, since the light l201ba overlaps with the light absorption unit 203, at least the light is guided through the optical waveguide and is continuously absorbed by the light absorption unit 203 until the spread of the electric field distribution in the y-axis direction becomes sufficiently small. At this time, if the absorption is sufficiently large, all the TM mode light is absorbed, and the light emitted from the polarizing filter 200 is only the TE mode. Thus, the light absorption unit 203 absorbs more TM mode light than TE mode light. Therefore, it can be seen that the polarizing filter 200 functions as a polarizing filter.

  By adjusting the thickness of the cladding region 202 on the light absorbing portion 203 side, the absorptance of the light absorbing portion 203, the length of the polarizing filter 200, etc., how much light of the TM mode is included in the light emitted from the optical waveguide. It is possible to adjust whether to remain.

  In the second embodiment, the light absorption unit 203 is arranged in parallel to the core region 201. However, the light absorption unit 203 may be arranged in parallel to the y-axis direction orthogonal to the core region 201. In this case, TM light in the incident light is hardly absorbed by the light absorber 203, and TE mode light is absorbed by the light absorber 203. However, the cladding region 202 is preferably disposed on the side surface of the core region 201 between the core region 201 and the light absorbing unit 203 so that the TE mode light is not excessively absorbed by the light absorbing unit 203. .

  Such a polarizing filter 200 is manufactured by manufacturing an optical waveguide composed of the core region 201 and the cladding region 202 using the same method as the manufacturing method of the first embodiment, and bonding the light absorbing portion 203 together. It can be manufactured easily. Therefore, the polarizing filter 200 according to the second embodiment is a polarizing filter that uses an optical waveguide that can be manufactured by a simple process, has high accuracy, and has the same function as a vertical tapered waveguide. .

(Embodiment 3)
Next, an optical coupler according to Embodiment 3 of the present invention will be described. FIG. 11 is a schematic side view of the yz plane of the optical coupler according to the third embodiment. As shown in FIG. 11, the optical coupler 300 according to the third embodiment includes a first core region 301, a first cladding region 302 that is a cladding layer sandwiching the first core region from both sides in the thickness direction, A second core region 303 formed on one surface of the first cladding region 302; and a second cladding region 304 formed on a surface of the second core region 303 opposite to the surface facing the first core region 301. .

  The optical waveguide formed by the first core region 301 and the first cladding region 302 may have the same configuration as the optical waveguide 10 of the first embodiment, but the distribution of effective refractive index of the first core region 301 described later is Different. The second core region 303 is a layer having a substantially uniform thickness for confining and guiding incident light. The second core region 303 has a higher refractive index than the first cladding region 302 and a uniform refractive index. The second cladding region 304 has a lower refractive index than the second core region 303.

  FIG. 12 is a schematic cross-sectional view of the first core region of the optical coupler shown in FIG. As shown in FIG. 12, the first core region 301 includes a first region 301a and a second region 301b having a refractive index lower than that of the first region 301a. The first region 301a has a tapered shape in which the width in the x-axis direction, which is the width direction, decreases from the left side of FIG. 12 along the z-axis positive direction toward the center S, and further in the z-axis positive direction. As the distance from the central portion S increases, the width in the x-axis direction increases. The second region 301b is disposed between the tapered shapes of the first region 301a. That is, the first core region 301 is formed in the central portion S so that the effective refractive index is the lowest.

  Next, the operation of the optical coupler 300 according to the third embodiment will be described. First, it is assumed that light is incident on the first core region 301 from the left side in FIG. The incident light propagates through the first core region 301 along the z-axis direction. At this time, the spread of the electric field distribution of the propagating light increases as it approaches the central portion S. When the spread of the electric field distribution increases, the spread of the electric field distribution overlaps with the second core region 303, and incident light is coupled to the second core region 303. Thereafter, the light propagating through the first core region 301 has the electric field distribution spread again and is output from the first core region 301. On the other hand, the light coupled to the second core region 303 is output from the second core region 303. On the other hand, the light incident on the second core region 303 is also branched into the first core region 301 and the second core region 303 and output. Thus, the optical coupler 300 functions as a 1 × 2 optical coupler. The light branching ratio between the first core region 301 and the second core region 303 depends on the thickness of the cladding region 302 between the first core region 301 and the second core region 303, the refractive index of each layer, the first core A desired value can be obtained by adjusting the refractive index distribution or the like of the region 301.

  Such an optical coupler 300 having the pattern of the first region 301a and the second region 301b is easily manufactured by changing the pattern of the photoresist using the same method as the manufacturing method of the first embodiment. can do. Therefore, as in the first embodiment, the optical coupler 300 according to the third embodiment can be manufactured by a simple process, has high accuracy, and has a function equivalent to that of a vertical tapered waveguide. This is an optical coupler using a waveguide.

(Embodiment 4)
Next, a photodetector according to Embodiment 4 of the present invention will be described. FIG. 13 is a schematic side view of the yz plane of the photodetector according to the fourth embodiment. As shown in FIG. 13, the photodetector 400 according to the fourth embodiment includes an optical waveguide formed by the core region 401 and the cladding region 402, a detector D as a light detection unit that detects the light intensity of the optical waveguide, And a monitor M. The optical waveguide formed by the core region 401 and the cladding region 402 may have the same configuration as the optical waveguide 10 of the first embodiment, and the cladding region 402 has a lower refractive index than the core region 401. In addition, the core region 401 includes a detection unit in which the effective refractive index is minimal in the waveguide direction. The detection part of the core region 401 is the central part S. And the detector D is arrange | positioned adjacent to the center part S which is a detection part. The monitor M is connected to the detector D.

  FIG. 14 is a schematic cross-sectional view of the core region of the photodetector shown in FIG. As shown in FIG. 14, the core region 401 includes a first region 401a and a second region 401b having a lower refractive index than the first region 401a. And the 1st core area | region 401 has a taper shape in which the effective refractive index becomes the lowest in the center part S similarly to the 1st core area | region 301 of Embodiment 3. FIG.

  The detector D is not particularly limited as long as it has a function of outputting an electric signal corresponding to the intensity of the input light, but may include a photodiode, for example. The monitor M is configured to receive an electrical signal from the detector D, process the electrical signal, and display the light intensity corresponding to the electrical signal.

  Next, the operation of the photodetector 400 according to the fourth embodiment will be described. First, it is assumed that light is incident on the core region 401 from the left side in FIG. The incident light propagates through the core region 401 along the z-axis direction. At this time, the spread of the electric field distribution of the propagating light is maximized in the central portion S. And the detector D arrange | positioned adjacent to the center part S receives a part of propagating light, and outputs the electrical signal according to the intensity | strength of the received light. Subsequently, an electric signal is input to the monitor M, and based on this, the intensity of the light input to the photodetector 400 is calculated and displayed. Thereafter, the photodetector 400 reduces the spread of the electric field distribution of the propagating light, and outputs light from the right side of the core region 401 in FIG. Note that how much of the propagating light is input to the detector D is determined by adjusting the thickness of the cladding region 402, the refractive index of each layer, the refractive index distribution of the core region 401, and the like. It can be.

  Thus, the photodetector 400 performs light detection in the central portion S where the spread of the electric field distribution is maximized. As a result, the photodetector 400 can cause a part of the propagating light to enter the detector D with high accuracy. Further, light other than the light incident on the detector D is strongly confined in the core region 401 and guided again. Therefore, the photodetector 400 can realize low-loss optical detection.

  The photodetector 400 having the pattern of the first region 401a and the second region 401b can be easily obtained by changing only the pattern of the photoresist using the same method as the manufacturing method of the first embodiment. Can be manufactured. Therefore, as in the first embodiment, the photodetector 400 according to the fourth embodiment can be manufactured by a simple process, has high accuracy, and has a function equivalent to that of a vertical tapered waveguide. This is a photodetector using a waveguide.

(Embodiment 5)
Next, an optical multiplexer / demultiplexer according to Embodiment 5 of the present invention will be described. FIG. 15 is a schematic perspective view of an optical multiplexer / demultiplexer according to the fifth embodiment. As shown in FIG. 15, an optical multiplexer / demultiplexer 500 according to the fifth embodiment includes a core region 501 having a first region 501a and a second region 1b, and an optical resonator that sandwiches the core region 501 from both sides in the thickness direction. A DBR (Distributed Bragg Reflector) mirror 502 as a first reflecting mirror and a DBR mirror 503 as a second reflecting mirror are provided. An optical fiber 520 for light input is connected to one end of the core region 501. FIG. 16 is a schematic side view of the yz plane of the optical multiplexer / demultiplexer shown in FIG. 17 is a schematic cross-sectional view of the core region of the optical multiplexer / demultiplexer shown in FIG. As shown in FIGS. 15 to 17, the core region 501 may have the same configuration as that of the first embodiment, but the effective refractive index of the core region 501 is increased toward the left side of the drawing.

The DBR mirror 502 includes an Al _0.9 Ga _0.1 As layer that functions as a low refractive index layer and a GaAs layer that functions as a high refractive index layer, which are stacked on a substrate (not shown) made of n-type GaAs. For example, several tens of pairs of composite semiconductor layers are stacked as a semiconductor multilayer mirror having a periodic structure. The layer thickness of each layer constituting the composite semiconductor layer of the DBR mirror 502 is an odd multiple of λ / 4n (λ: wavelength of incident light, n: refractive index). For example, when λ is 1060 nm, the Al _0.9 Ga _0.1 As layer has a thickness of about 88 nm, and the GaAs layer has a thickness of about 76 nm.

The DBR mirror 503 is a dielectric having a periodic structure in which, for example, several pairs of composite dielectric layers each having a pair of a SiO ₂ layer functioning as a low refractive index layer and a SiN _x layer functioning as a high refractive index layer are stacked. In the same manner as the DBR mirror 502, the thickness of each layer is an odd multiple of λ / 4n.

  The reflectivities of the DBR mirror 502 and the DBR mirror 503 are determined according to the rate of change of the effective refractive index of the core region 501 along the waveguide direction. For example, when the taper angles of the first region 501a and the second region 501b of the core region 501 are gentle, it is preferable to design the reflectivity higher than when the taper angle is tight in order to reduce the loss during propagation. .

Here, it is known that the vertical taper waveguide can be used as an optical multiplexer / demultiplexer. When light enters the core of the vertical taper waveguide sandwiched between the DBR mirrors from the thicker side to the thinner side, the vertical direction of the light is incident from the position where the core thickness becomes λ / 2n _eff according to the wavelength. Output in the direction. Where λ is the wavelength of incident light and n _eff is the effective refractive index of the core.

On the other hand, the optical multiplexer / demultiplexer 500 according to the fifth embodiment has the same function as the vertical taper waveguide. That is, when the effective refractive index is n _eff , the optical multiplexer / demultiplexer 500 receives light input from the optical fiber 520 from a position where the effective thickness of the core region 501 becomes λ / 2n _eff according to the wavelength. Output in the direction perpendicular to the incident direction of light. Note that the output direction is above the page in FIG. 15 because the refractive index of the DBR mirror 503 is lower than that of the DBR mirror 502.

  Such an optical multiplexer / demultiplexer 500 having the pattern of the first region 501a and the second region 501b is simplified by changing only the pattern of the photoresist using the same method as the manufacturing method of the first embodiment. Can be manufactured. Therefore, as in the first embodiment, the optical multiplexer / demultiplexer 500 according to the fifth embodiment can be manufactured by a simple process, has high accuracy, and has the same function as the vertical taper waveguide. This is an optical multiplexer / demultiplexer using an optical waveguide, and can be used particularly as a wavelength multi-polymerization demultiplexer.

Although the operation of the optical multiplexer / demultiplexer 500 as a demultiplexer has been described, the optical multiplexer / demultiplexer 500 can also be operated as a multiplexer. That is, when light having a corresponding wavelength is input from the upper side of FIG. 15 to a position where the effective thickness of the core region 501 of the optical multiplexer / demultiplexer 500 is λ / 2n _eff , the combined light is illustrated in FIG. 15 is output from the left side of the drawing.

(Embodiment 6)
Next, a laser element according to Embodiment 6 of the present invention will be described. FIG. 18 is a schematic perspective view of a laser device according to the sixth embodiment. FIG. 19 is a schematic yz sectional view of the laser element shown in FIG. As shown in FIGS. 18 and 19, a laser element 600 according to the sixth embodiment includes a surface emitting laser 600a and an optical waveguide layer 600b formed on the surface of the surface emitting laser 600a on the substrate side. The surface emitting laser 600a includes a first reflecting mirror 602 and a second reflecting mirror 612 constituting an optical resonator, an active layer 606 disposed between the first reflecting mirror 602 and the second reflecting mirror 612, and an active layer. An n-side electrode 604 and a p-side electrode 611, which are electrodes for injecting current into 606, are provided, and light is output from the first reflecting mirror 602 side. The optical waveguide layer 600b is formed on the first reflecting mirror 602 side of the surface emitting laser 600a, is formed between the third reflecting mirror 613, and the first reflecting mirror 602 and the third reflecting mirror 613, and is surface emitting. And a core region 614 whose effective refractive index changes along the z-axis, which is a waveguide direction parallel to a plane orthogonal to the output direction of the laser 600a.

  Next, as shown in FIG. 19, a surface emitting laser 600a is an undoped lower DBR mirror that functions as a lower multilayer reflector, which is laminated on a substrate 601 made of n-type GaAs having a plane orientation (001). A first reflecting mirror 602, an n-type contact layer 603, an n-side electrode 604, an n-type cladding layer 605, an active layer 606, a p-type cladding layer 607, a current confinement layer 608, a p-type spacer layer 609, a p-type contact layer 610, A p-side electrode 611 and a second reflecting mirror 612 that is an upper dielectric DBR mirror functioning as an upper reflecting mirror are provided.

  The p-type contact layer 610 and the n-type contact layer 603 are disposed between the first reflecting mirror 602 and the second reflecting mirror 612. The active layer 606 is disposed between the first reflecting mirror 602 and the second reflecting mirror 612. The current confinement layer 608 is disposed between the p-type contact layer 610 and the active layer 606. The p-type spacer layer 609 is interposed between the current confinement layer 608 and the p-type contact layer 610. The p-side electrode 611 is formed on the p-type contact layer 610, and the n-side electrode 604 is formed on the n-type contact layer 603.

  The laminated structure from the n-type cladding layer 605 to the p-type contact layer 610 is formed as a mesa post formed into a columnar shape by an etching process or the like. The mesa post diameter is, for example, 30 μm. The n-type contact layer 603 extends to the outer peripheral side of the mesa post. Further, the first reflecting mirror 602 and the second reflecting mirror 612 constitute an optical resonator.

The first reflecting mirror 602 is formed on an undoped GaAs buffer layer (not shown) stacked on a substrate 601 made of n-type GaAs. The first reflecting mirror 602 includes, for example, 40.5 pairs of composite semiconductor layers in which an Al _0.9 Ga _0.1 As layer functioning as a low refractive index layer and a GaAs layer functioning as a high refractive index layer are paired. It is formed as a stacked semiconductor multilayer mirror having a periodic structure. The layer thickness of each layer constituting the composite semiconductor layer of the first reflecting mirror 602 is λ / 4n (λ: laser oscillation wavelength, n: refractive index). For example, when λ is 1.06 μm, the Al _0.9 Ga _0.1 As layer has a thickness of about 88 nm, and the GaAs layer has a thickness of about 76 nm.

  The n-type contact layer 603 and the n-type cladding layer 605 are formed using n-type GaAs as a material.

The p-type cladding layer 607 is formed using p-type AlGaAs (for example, Al _0.3 Ga _0.7 As is desirable). The p-type spacer layer 609 is formed using p-type AlGaAs as a material. The p-type contact layer 610 is formed using p-type GaAs as a material.

A p-type or n-type dopant is added to the n-type cladding layer 605, the p-type cladding layer 607, and the p-type spacer layer 609 so that the carrier concentration is, for example, about 1 × 10 ¹⁸ cm ^−3. The conductivity type is p-type or n-type. The carrier concentrations of the n-type contact layer 603 and the p-type contact layer 610 are, for example, about 2 × 10 ¹⁸ cm ⁻³ and 3 × 10 ¹⁹ cm ⁻³ , respectively.

The current confinement layer 608 includes an opening 608a as a current injection portion and a selective oxidation layer 608b as a current confinement portion. The opening 608a is made of Al _1-x Ga _x As (0 ≦ x <0.2), and the selective oxide layer 608b is made of (Al _1-x Ga _x ) ₂ O ₃ . X is 0.02, for example.

The current confinement layer 608 is formed by subjecting an Al-containing semiconductor layer made of Al _1-x Ga _x As to selective oxidation heat treatment. That is, the selective oxidation layer 608b is formed in a ring shape on the outer periphery of the opening 608a by oxidizing the Al-containing semiconductor layer by a predetermined range from the outer periphery of the mesa post along the laminated surface. The selective oxidation layer 608b has an insulating property, and the current injected from the p-side electrode 611 is narrowed and concentrated in the opening 608a, whereby the current density injected into the active layer 606 directly below the opening 608a. It has a function to enhance. The opening diameter of the opening 608a is, for example, 6 μm to 7 μm. The thickness of the current confinement layer 608 is 20 nm to 30 nm, for example. Thereby, the surface emitting laser 600a oscillates the laser beam.

  The active layer 606 has an MQW-SCH structure in which both sides of a multiple quantum well (MQW) layer in which well layers and barrier layers are alternately stacked are sandwiched between separate confinement heterostructure (SHC) layers. The well layer is made of a material selected so as to emit light having a desired wavelength, for example, a GaInAs-based semiconductor material. The barrier layer is made of, for example, GaAs. The active layer 606 has a composition and a layer of the semiconductor material that emits spontaneous emission light including light having a wavelength of, for example, 1.0 μm band by the current injected from the p-side electrode 611 and confined by the current confinement layer 608. The thickness is set.

The second reflecting mirror 612 has a periodic structure in which, for example, 9 pairs of composite dielectric layers each having a SiO ₂ layer functioning as a low refractive index layer and a SiN _x layer functioning as a high refractive index layer are stacked. As in the first reflecting mirror 602, the thickness of each layer is λ / 4n.

  The p-side electrode 611 is formed in a ring shape along the outer extension of the p-type contact layer 610. On the other hand, the n-side electrode 604 is formed on the surface of the extended portion of the n-type contact layer 603 extending on the outer peripheral side of the mesa post, and is formed in a C shape so as to surround the periphery of the mesa post.

  The optical waveguide layer 600b is formed between the third reflecting mirror 613, the first reflecting mirror 602, and the third reflecting mirror 613, and is guided in parallel to the plane orthogonal to the y axis that is the output direction of the surface emitting laser 600a. And a core region 614 whose effective refractive index changes along the z-axis that is the wave direction.

The third reflecting mirror 613 may have substantially the same configuration as the first reflecting mirror 602, and is formed on an undoped GaAs buffer layer (not shown) stacked on an n-type GaAs substrate (not shown). . Then, like the first reflecting mirror 602, the third reflecting mirror 613 is a pair of an Al _0.9 Ga _0.1 As layer that functions as a low refractive index layer and a GaAs layer that functions as a high refractive index layer. Is formed as a semiconductor multilayer mirror having a periodic structure in which, for example, 40.5 pairs are laminated. The layer thickness of each layer constituting the composite semiconductor layer of the third reflecting mirror 613 is λ / 4n.

The core region 614 may have the same configuration as that of the first embodiment, and includes a tapered first region and a second region as in FIG. 3, and the effective refractive index of the core region 614 is in the z-axis direction. Along with, it is continuously higher. However, the core region 614 is set to have an effective thickness of λ / 2n _eff in the region immediately below the surface emitting laser 600a for the reason described later. Here, λ is the oscillation wavelength of the laser beam output from the surface emitting laser 600a, and n _eff is the effective refractive index of the core region 614.

  Next, the operation of the surface emitting laser 600a will be described. First, a controller outside the surface emitting laser 600a applies a bias voltage and a modulation voltage signal between the p-side electrode 611 and the n-side electrode 604 to inject current. In the p-type contact layer 610, p-side carriers (holes) flow in the horizontal direction in the drawing, and then pass through the p-type spacer layer 609 and concentrate in the opening 608a of the current confinement layer 608 to increase the density. In this state, it is injected into the active layer 606. On the other hand, n-side carriers (electrons) are injected from the n-side electrode 604 through the n-type contact layer 603 and the n-type cladding layer 605 into the active layer 606.

  Thus, the surface emitting laser 600a has a so-called double intracavity structure in which both the p-side carrier and the n-side carrier are injected into the active layer without passing through the DBR mirror.

  The active layer 606 into which carriers are injected generates spontaneous emission light. The generated spontaneous emission light is laser-oscillated at any wavelength in the 1.0 μm wavelength band by the optical amplification action of the active layer 606 and the action of the optical resonator. As a result, the surface emitting laser 600a outputs laser signal light including a modulation signal from the first reflecting mirror 602.

Here, as described above, it is known that the vertical taper waveguide can be used as an optical multiplexer / demultiplexer. However, in the laser device 600 according to the sixth embodiment, the vertical taper waveguide is used as an optical multiplexer (however, Input light is used as one). That is, assuming that the wavelength of the laser beam output from the surface emitting laser 600a is λ and the effective refractive index of the core is n _eff , the core has an effective thickness of λ / 2n _eff at the output position of the surface emitting laser 600a. Region 614 is formed. At this time, the output light of the surface emitting laser 600a can be output in the z-axis direction with a very small loss and a small configuration. This output light can be coupled to the optical fiber with a very small loss and a small configuration by joining the optical fiber to the laser element 600.

  Furthermore, when a vertical taper waveguide is used, the process is complicated and it is difficult to produce a taper structure with high accuracy. Therefore, the core region 614 of the laser device 600 according to the sixth embodiment is implemented in the implementation. The optical waveguide layer 600b using the same method as the manufacturing method of the first embodiment is used. As a result, the laser element 600 according to the sixth embodiment is a laser element that uses an optical waveguide that can be manufactured by a simple process, has high accuracy, and has the same function as a vertical taper waveguide. is there.

The optical waveguide layer 600b can control the distribution of the effective refractive index n _eff in the core region 614 relatively arbitrarily. That is, the effective refractive index n _eff is appropriately adjusted according to the laser light output position of the surface emitting laser 600a, or the laser light output from the surface emitting laser 600a at the position of the surface emitting laser 600a and the optical waveguide layer 600b. Since the taper angles of the first region and the second region can be adjusted so as to increase the coupling coefficient, the controllability is higher than when a vertical taper waveguide is used.

  FIG. 20 is a diagram for explaining how light is guided through the optical waveguide layer of the laser element shown in FIG. The light l output from the surface emitting laser 600 a passes through the first reflecting mirror 602 and is input to the core region 614. The effective refractive index of the core region 614 increases continuously from the left to the right in FIG. At this time, as shown in FIG. 20, the light l is gradually refracted by the difference in effective refractive index and output from the right end of the core region 614. At this time, by joining an optical fiber to the output end, the output light of the surface emitting laser 600a can be coupled to the optical fiber with a very small loss and a small configuration.

  Next, a method for manufacturing the laser element 600 according to Embodiment 6 of the present invention will be described. FIG. 21 is a diagram for explaining a method of manufacturing the laser element shown in FIG. As the surface emitting laser 600a, a known surface emitting laser manufacturing method may be used. However, the surface emitting laser 600a is assumed to output from the first reflecting mirror 602. The optical waveguide layer 600b can be manufactured by laminating the third reflecting mirror 613 on a substrate and a buffer layer (not shown) and further forming the core region 614 by the same process as in the first embodiment. The laser element 600 is manufactured by bonding the optical waveguide layer 600b to the substrate 601 side of the surface emitting laser 600a.

  Therefore, the laser element 600 according to the sixth embodiment is a laser element using an optical waveguide that can be manufactured by a simple process, has high accuracy, and has a function equivalent to that of a vertical tapered waveguide. Thus, the output light of the surface emitting laser can be coupled to the optical fiber with a very small loss and a small configuration.

(Embodiment 7)
Next, a laser element according to Embodiment 7 of the present invention will be described. FIG. 22 is a schematic perspective view of a laser device according to the seventh embodiment. As shown in FIG. 22, the laser element 700 according to the seventh embodiment includes a surface emitting laser 700a and an optical waveguide layer 700b formed on the surface of the surface emitting laser 700a on the substrate side. Further, the surface emitting laser 700a includes a surface emitting laser 700a1 and a surface emitting laser 700a2.

Here, it is assumed that the surface-emitting laser 700a1 and the surface-emitting laser 700a2 oscillate at λ ₁ and λ ₂ that are different wavelengths, respectively. In this case, _{n eff1} the effective refractive index of the core region directly under the surface emitting laser 700A1, the effective refractive index of the core region directly under the surface emitting laser 700a2 When _{n eff2,} the effective core area immediately below the surface emitting laser 700A1 The actual thickness is λ ₁ / 2n _eff1 , and the effective thickness of the core region immediately below the surface emitting laser 700a2 is λ ₂ / 2n _eff2 . At this time, as in the third embodiment, by joining an optical fiber to the output end, the output light of the surface emitting laser 700a can be coupled to the optical fiber with a very small loss and a small configuration. .

  As described above, by using the optical waveguide of the seventh embodiment, a plurality of surface emitting lasers having different wavelengths can be integrated, and the laser light oscillated by each surface emitting laser can be wavelength-multiplexed. When the difference in wavelength to be multiplexed is small, it may be difficult to arrange the surface emitting lasers side by side in the z-axis direction that is the waveguide direction. In such a case, the surface emitting lasers are integrated in the x-axis direction, which is the width direction, and the output light of each surface emitting laser is coupled to an optical fiber and then combined by a coupler or the like, or each surface emitting Wavelength multiplexing can be performed by coupling the output light of the laser to the optical waveguide and combining it with a Y-shaped optical waveguide or a directional coupler.

  Therefore, the laser device 700 according to the seventh embodiment is a laser device using an optical waveguide that can be manufactured by a simple process, has high accuracy, and has the same function as a vertical taper waveguide. Thus, the output light of the plurality of surface emitting lasers can be coupled to the optical fiber with a very small loss and a small configuration.

  As described above, according to the present embodiment, the spot using the optical waveguide can be manufactured by a simple process, has high accuracy, and has the same function as the vertical taper waveguide. A size converter, a polarizing filter, an optical coupler, a photodetector, an optical multiplexer / demultiplexer, and a laser element can be provided.

  In the above embodiment, an example having a sub-wavelength period is shown as a pattern formed by the first region and the second region in the core region, but the present invention is not limited to this. For example, the arrangement and shape of the first region and the second region in the core region may be random. At this time, it is only necessary that the duty ratio of the unit region of the core region is continuously increased along the z-axis that is the waveguide direction by the pattern formed by the first region and the second region. Then, the effective refractive index of the core region 1 continuously increases along the z-axis that is the waveguide direction according to Expression (1) and Expression (2) or Expression (3) to Expression (6). The effects of the invention can be obtained.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. For example, you may apply the core area | region of the modification 1 or the modification 2 to other embodiment. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

1, 1A, 1B, 31, 41, 201, 401, 501, 614 Core region 1a, 1Aa, 1Baa, 1Bab, 1Ba, 301a, 401a, 501a First region 1b, 1Ab, 1Bb, 301b, 401b, 501b Second Regions 2, 32, 42, 202, 303, 402 Clad regions 10, 30, 40 Optical waveguide 10a Optical input unit 10b Optical output unit 20, 520 Optical fiber 100 Spot size converter 200 Polarizing filter 203 Optical absorption unit 300 Optical coupler 301 First core region 302 First cladding region 303 Second core region 304 Second cladding region 400 Photo detector 500 Optical multiplexer / demultiplexer 502, 503 DBR mirror 600, 700 Laser elements 600a, 700a, 700a1, 700a2 Surface emitting laser 600b 700b Optical waveguide layer 601 Substrate 602 First reflector 603 n-type contact layer 604 n-side electrode 605 n-type cladding layer 606 active layer 607 p-type cladding layer 608 current confinement layer 608a opening 608b selective oxidation layer 609 p-type spacer layer 610 p-type contact layer 611 p-side electrode 612 second reflecting mirror 613 third reflecting mirror D detector L1, L _1A , L _1Aa , L _1B length l, l10a, l10b, l20, l30, l201aa, l201ab, l201ba, l201bb light M monitor S center Part

Claims (15)

A core region having a substantially uniform thickness for confining and guiding incident light;
A clad region sandwiching the core region from both sides in the thickness direction,
The core region has an effective refractive index continuously changing along the waveguide direction of the core region,
The optical waveguide characterized in that the effective refractive index of the core region is at least higher than the refractive index of the cladding region. The core region includes at least a first region and a second region having a refractive index lower than that of the first region,
The first region and the second region are disposed so as to have a period of the same order as the wavelength of the incident light or a period smaller than the wavelength of the incident light. The optical waveguide according to claim 1. The core region includes a first region and a second region having a lower refractive index than the first region,
Wherein the refractive index of the first region n _a, wherein a refractive index n _b of the second _region, wherein the wave number of the light k _a propagating a first _region, wave number k _b of the light propagating through the second region, Of the wave number of incident light, the component in the direction orthogonal to the waveguide direction and the thickness direction of the core region is k _x , the width of the first region is w _a , and the width of the second region is w _b , When the period is Λ, the wavelength of incident light is λ, and the propagation constant is β, the core region is divided into two in at least one of formulas (A) and (C) or formulas (B) and (C). the combination of _{k a} and _{k b} satisfies equation as one or with _two, n _a, n _b, an optical waveguide according to claim 1, characterized in that _w a, w _b is set.

  The optical waveguide according to claim 1, wherein the effective refractive index of the core region increases linearly or decreases linearly along the waveguide direction. The first region has a tapered shape in which a width in a width direction perpendicular to the thickness direction is increased along the waveguide direction;
5. The optical waveguide according to claim 2, wherein the second region has a tapered shape in which the width in the width direction decreases along the waveguide direction. 6. An optical waveguide according to any one of claims 1 to 5,
A light input section for receiving light; and
A light output unit for outputting light,
The spot size converter, wherein the optical waveguide converts a spot size of light input from the light input unit and outputs the spot size from the light output unit. An optical waveguide according to any one of claims 1 to 5,
A light absorbing portion that absorbs at least a part of TM mode light that is polarized light parallel to the thickness direction of the light incident on the optical waveguide;
The optical waveguide guides the TE mode light orthogonal to the TM mode of the incident light so that the spread of the electric field distribution of the light in the thickness direction is smaller than that of the TM mode light,
In the cladding region, the thickness of the cladding region on the light absorption part side is such that at least a part of the TM mode light of the incident light overlaps the light absorption part,
The polarization filter, wherein the light absorption unit absorbs more TM mode light than TE mode light. The optical waveguide according to any one of claims 1 to 3,
A second core region formed on one side of the optical waveguide, confining and guiding incident light, having a substantially uniform thickness and a higher refractive index than the cladding layer;
A second cladding region formed on a surface opposite to the surface facing the optical waveguide of the second core region, and having a refractive index lower than that of the second core region;
An optical coupler comprising: The optical waveguide according to any one of claims 1 to 3,
A light detecting means for detecting the light intensity of the optical waveguide,
The core region has a detection unit in which the effective refractive index is minimal in the waveguide direction,
The photodetector according to claim 1, wherein the photodetector is disposed in proximity to the detector. A core region having a substantially uniform thickness for confining and guiding incident light;
A first reflecting mirror and a second reflecting mirror that sandwich the core region from both sides in the thickness direction to form an optical resonator;
The optical multiplexer / demultiplexer, wherein the effective refractive index of the core region continuously changes along the waveguide direction of the core region. A first reflecting mirror and a second reflecting mirror constituting an optical resonator, an active layer disposed between the first reflecting mirror and the second reflecting mirror, an electrode for injecting a current into the active layer, A surface emitting laser that outputs light from the first reflector side;
An optical waveguide layer formed on the first reflecting mirror side of the surface emitting laser,
The optical waveguide layer is formed between the third reflecting mirror, the first reflecting mirror, and the third reflecting mirror, and has a thickness of confining and guiding the light output from the surface emitting laser. With various core areas,
The laser element, wherein the effective refractive index of the core region continuously changes along a waveguide direction parallel to a plane orthogonal to the output direction of the surface emitting laser. The effective thickness of the core region in the region immediately below the surface emitting laser is λ / 2n _eff, where λ is the laser oscillation wavelength of the laser element and n _eff is the effective refractive index of the core region. The laser device according to claim 11.   The laser device according to claim 11, wherein the effective refractive index of the core region is linearly increased or linearly decreased along the waveguide direction. The core region includes a first region and a second region having a lower refractive index than the first region,
The first region and the second region have the same period as the wavelength of light output from the surface emitting laser and incident on the core region, or output from the surface emitting laser and incident on the core region. The laser device according to claim 11, wherein the laser device is arranged so as to have a period smaller than the wavelength of the light. The first region has a tapered shape in which a width in a width direction perpendicular to the thickness direction is increased along the waveguide direction;
The laser device according to claim 14, wherein the second region has a tapered shape in which the width in the width direction decreases along the waveguide direction.

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