Optical processing device, optical processing method, and optical coupling system

Abstract

The present invention achieves highly efficient optical coupling even when a grating coupler having polarization dependency is used.　This optical processing device is provided with an optical processing unit. In the optical processing unit, incident light is separated into a first linearly polarized wave and a second linearly polarized wave. The polarization plane of the first linearly polarized wave and the polarization plane of the second linearly polarized wave are orthogonal to each other. The first linearly polarized wave has a first polarization plane. The optical processing unit outputs a first final emission light corresponding to the first linearly polarized wave and a second final emission light corresponding to the second linearly polarized wave. The polarization plane of the first final emission light is different from the first polarization plane.

Description

Optical processing device, optical processing method, and optical coupling system

[0001] The present technology relates to an optical processing device, an optical processing method, and an optical coupling system, and more particularly to an optical processing device that can be applied when performing optical coupling using a polarization-dependent grating coupler.

[0002] For example, Patent Document 1 discloses a technique in which incident light (randomly polarized optical signal) is split into two linearly polarized waves that are orthogonal to each other using a birefringent crystal, and each linearly polarized wave is coupled to a different waveguide. This technique is an invention for the edge coupler method, and cannot be simply applied to optical coupling using a grating coupler that has polarization dependency.

[0003] Furthermore, for example, Patent Document 2 discloses a technology for eliminating polarization dependency in a grating coupler by using a grating coupler with a mesh-like coupling portion. This technology generally has low coupling efficiency, making it difficult to guarantee a loss budget.

[0004] Japanese Patent Publication No. 2023-544384 Japanese Patent Publication No. 2021-157130

[0005] The purpose of this technology is to achieve highly efficient optical coupling even when using polarization-dependent grating couplers.

[0006] The concept of the present technology is an optical processing device including an optical processing unit that separates light incident on an incident surface into a first linearly polarized wave and a second linearly polarized wave, and outputs a first final outgoing light corresponding to the first linearly polarized wave and a second final outgoing light corresponding to the second linearly polarized wave, wherein the first linearly polarized wave has a first polarization plane, the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane, and the polarization plane of the first final outgoing light is different from the first polarization plane.

[0007] Another concept of the present technology is an optical processing method including: a step of separating incident light into a first linearly polarized wave and a second linearly polarized wave; and a step of outputting a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave, wherein the first linearly polarized wave has a first polarization plane, the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane, and the polarization plane of the first final output light is different from the first polarization plane.

[0008] Yet another concept of the present technology resides in an optical coupling system including: an optical fiber; an optical processing section that separates incident light from the optical fiber into a first linearly polarized wave and a second linearly polarized wave, and outputs a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave; a first grating coupler onto which the first final output light is incident; and a second grating coupler onto which the second final output light is incident, wherein the first linearly polarized wave has a first polarization plane, the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane, and the polarization plane of the first final output light is different from the first polarization plane.

[0009] Exemplary embodiments of the present technology will be described with reference to the following drawings. FIG. 1 is a perspective view showing an example configuration of an optical coupling system. FIGS. 2A to 2C are top, front, and side views, respectively, corresponding to FIG. 1. FIG. 3 is a perspective view showing another example configuration of an optical coupling system. FIGS. 4A to 4C are top, front, and side views, respectively, corresponding to FIG. 3. FIG. 5 is a perspective view showing another example configuration of an optical coupling system. FIGS. 6A to 6C are top, front, and side views, respectively, corresponding to FIG. 5. FIG. 7 is a perspective view showing another example configuration of an optical coupling system. FIGS. 8A to 8C are top, front, and side views, respectively, corresponding to FIG. 7. FIGS. 9A and 9B show index ellipsoids of a uniaxial positive crystal and a uniaxial negative crystal, respectively. FIG. 10 is a diagram showing the relationship between the polarization direction of ordinary light and the direction of the optical axis. FIG. 11 is a diagram showing the relationship between the optical paths of ordinary light and extraordinary light and the total reflection surface. Figures 12A and 12B are diagrams showing the optical path and polarization direction of ordinary light and the optical path and polarization direction of extraordinary light near a total reflection surface, respectively. Figure 13 is a contour graph showing the incident angle θbo of reflected ordinary light on a total reflection surface for a set of the incident angle θi of incident light and the exit angle θoo of ordinary light. Figure 14 is a contour graph showing the incident angle θbe of extraordinary light on a total reflection surface for a set of the incident angle θi of incident light and the exit angle θoo of ordinary light. Figure 15 is a diagram showing a selective reflection region. Figure 16 is a contour graph showing the proportion of S-polarized light in the selective reflection region. Figure 17 is a contour graph showing the optical path length difference between ordinary light and extraordinary light for a set of the incident angle θi of incident light and the exit angle θoo of ordinary light. Figure 18 is a diagram for explaining the optical coupling optical system of a receiving system. Figure 19 is a diagram showing an example configuration of an optical unitary converter. Figure 20 is a diagram for explaining the optical coupling optical system in a measurement system.

[0010] Modes for carrying out the invention (hereinafter referred to as "embodiments") will be described below. The description will be given in the following order: 1. Embodiments 1-1. Configuration example of optical coupling system (twisted arrangement) 1-2. Configuration example of optical coupling system (parallel arrangement) 1-3. Configuration example of optical coupling system (cross arrangement 1) 1-4. Configuration example of optical coupling system (cross arrangement 2) 1-5. Application examples of optical coupling system 1-5-1. Receiving system 1-5-2. Measurement system 2. Modified examples

[0011] 1. Embodiments 1-1. Configuration Example of Optical Coupling System (Skew Arrangement) FIG. 1 is a perspective view showing a configuration example of an optical coupling system 100A. This optical coupling system 100A has a birefringent crystal 101, a grating coupler 102, and a grating coupler 103. FIGS. 2A to 2C are a top view, a front view, and a side view corresponding to FIG. 1, respectively. Note that the grating couplers 102 and 103 are omitted from FIGS. 2A to 2C.

[0012] The birefringent crystal 101 has, for example, a rectangular parallelepiped shape. The x-axis, y-axis, and z-axis represent coordinate axes in three-dimensional space and form a global Cartesian coordinate system. Hereinafter, any plane whose normal direction is parallel to the x-axis will be referred to as the yz-plane, any plane whose normal direction is parallel to the y-axis as the xz-plane, and any plane whose normal direction is parallel to the z-axis as the xy-plane. In the illustrated example, the birefringent crystal 101 is arranged in the coordinate system so that each side is perpendicular or parallel to each axis.

[0013] The birefringent crystal 101 is, for example, a negative uniaxial crystal, and in the illustrated example, has an optic axis 111 parallel to the y-axis. The birefringent crystal 101 includes, for example, calcite (CaCO3) or alpha barium borate (α-BBO) (α-BaB2O4). Incident light 121, which is light output from an optical fiber, is obliquely incident on the top surface of the birefringent crystal 101 from a direction perpendicular to the optic axis 111 (y-axis).

[0014] In a certain xz plane, incident light 121 incident on a birefringent crystal 101 at an incident angle θi is refracted by the birefringent crystal 101. At this time, the incident light 121 is separated into ordinary light 131 and extraordinary light 132 in the xz plane. Therefore, the birefringent crystal 101 is an example of a polarization splitter. The incident light 121 is light having an arbitrary polarization state, for example, output from an optical fiber. In the figure, the optical path and polarization direction corresponding to the ordinary light 131 are represented by dashed lines, and the optical path and polarization direction corresponding to the extraordinary light 132 are represented by dashed lines.

[0015] The ordinary light 131 is a first linearly polarized light, and the extraordinary light 132 is a second linearly polarized light. The polarization directions of the ordinary light 131 and the extraordinary light 132 are orthogonal to each other. The polarization direction of the ordinary light 131 is parallel to the xz plane, and the polarization direction of the extraordinary light 132 is parallel to the y axis.

[0016] In the xz plane, extraordinary light 132 (second linearly polarized light) is emitted from the lower surface of the birefringent crystal 101 at an emission angle (refractive angle) θoe to become (final) emergent light 142. The polarization direction of this emergent light 142 is parallel to the y-axis. Generally, a grating coupler exhibits polarization dependence, which means that high coupling efficiency cannot be achieved unless the direction of its slits (grating) is parallel to the polarization direction of the light incident on the slits. The grating coupler 103 is positioned in a position (orientation) corresponding to the emergent light 142 such that the polarization direction (y direction) of the incident emergent light 142 is parallel to its plane (the emergent light 142 becomes S-polarized light). The grating coupler 103 may be positioned in an xy plane, for example, so that the direction of multiple slits aligned in the x-axis direction is parallel to the y-axis. Therefore, the emitted light 142 is coupled to this grating coupler 103 .

[0017] Furthermore, within the xz plane, ordinary light 131 (first linearly polarized light) is emitted from the lower surface of birefringent crystal 101 at an emission angle (refractive angle) θoo to become (final) emitted light 141. The polarization direction of this emitted light 141 is parallel to the xz plane. Grating coupler 102 is disposed in a position (orientation) corresponding to emitted light 141 such that the polarization direction of incident emitted light 141 (direction parallel to the xz plane) is horizontal to its own surface (the emitted light 141 becomes S-polarized light). Therefore, the emitted light 141 is coupled to this grating coupler 102.

[0018] In the optical coupling system 100A, incident light 121 having an arbitrary polarization state output from an optical fiber is separated by a birefringent crystal 101 into a first linearly polarized wave (ordinary light 131) and a second linearly polarized wave (extraordinary light 132) that are orthogonal to each other, and (final) output light 141 corresponding to the first linearly polarized wave and (final) output light 142 corresponding to the second linearly polarized wave are obtained, and the (final) output light 141 can be coupled to a grating coupler 102, and the (final) output light 142 can be coupled to a grating coupler 103. Even when a polarization-dependent grating coupler is used, the optical coupling system 100A can achieve highly efficient optical coupling.

[0019] Note that, as long as the emitted light beams 141 and 142 become S-polarized with respect to the grating couplers 102 and 103, respectively (and are coupled to the grating couplers 102 and 103), an arrangement different from that illustrated is also possible. For example, the grating coupler 103 may be arranged on a plane tilted about the y-axis from the xy plane. In this case, the slits of the grating coupler 103 are not aligned in the x-axis direction. However, because the direction of the slits is parallel to the y-axis, the emitted light beam 142 remains S-polarized with respect to the grating coupler 103.

[0020] 1-2. Example of the Configuration of an Optical Coupling System (Parallel Arrangement) FIG. 3 is a perspective view showing an example of the configuration of an optical coupling system 100B. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed descriptions thereof will be omitted where appropriate. This optical coupling system 100B has a birefringent crystal 101, a grating coupler 102, a grating coupler 103, and a polarization rotator 104. The optical coupling systems 100A and 100B have a common structure with respect to the birefringent crystal 101 and the grating coupler 103. FIGS. 4A to 4C are top, front, and side views, respectively, corresponding to FIG. 3. Note that the grating couplers 102 and 103 are not shown in FIGS. 4A to 4C.

[0021] In a certain xy plane, the grating couplers 102 and 103 are respectively arranged at a first position and a second position. That is, the grating couplers 102 and 103 are arranged on the same plane. The grating couplers 102 and 103 are aligned in a direction parallel to the x-axis and have slits parallel to the y-axis.

[0022] Unlike the optical coupling system 100A, the polarization direction of the output light 141 is rotated by 90 degrees by the polarization rotation element 104 to become the final output light 143. The output light 143 has the same polarization direction (y direction) as the output light 142 and is incident on the corresponding grating coupler 102 to be coupled. In this case, the polarization rotation element 104 adjusts the polarization directions of the first linearly polarized wave (ordinary light 131) and the second linearly polarized wave (extraordinary light 132) so that they are parallel to a predetermined plane (the xy plane) on which the grating couplers 102 and 103 are arranged. Therefore, the polarization rotation element 104 is an example of a polarization direction adjustment unit.

[0023] The optical coupling system 100B can achieve highly efficient optical coupling, similar to the optical coupling system 100A. Furthermore, in the illustrated optical coupling system 100B, the grating couplers 102 and 103 are arranged on the same plane (the xy plane), so that the grating couplers 102 and 103 can be easily formed using silicon photonics.

[0024] The two grating couplers 102 and 103 may be replaced by a single grating coupler. This can be achieved, for example, by using a grating coupler that is long in the x-axis direction, or by refracting or reflecting at least one of the emitted beams 141 to 143 in the xz plane using a lens or mirror. However, to prevent the emitted beams 143 and 142 from canceling each other out, it may be necessary to adjust the phase and / or optical path length of the emitted beams 143 and 142 in some cases.

[0025] Note that, as long as the output beams 143 and 142 are S-polarized with respect to the grating couplers 102 and 103, respectively, different arrangements from those illustrated are possible. For example, the grating couplers 102 and 103 may be arranged on two different planes. That is, the positions of the grating couplers 102 and / or 103 may be moved along the optical paths of the output beams 143 and / or 142 while maintaining their orientation (orientation). Furthermore, for example, one or two planes on which the grating couplers 102 and 103 are arranged may be tilted about the y-axis from the x-y plane. Furthermore, for example, the polarization rotation element 104 may rotate the output beam 141 at an angle other than 90 degrees. In this case, the grating coupler 102 is arranged on a plane tilted about the x-axis from the x-y plane. Furthermore, the polarization rotation element 104 may rotate the output beam 142 instead of or in addition to the output beam 141.

[0026] 1-3. Configuration Example of Optical Coupling System (Cross Arrangement 1) FIG. 5 is a perspective view showing a configuration example of an optical coupling system 100C. In FIG. 5, parts corresponding to those in FIG. 1 or 3 are given the same reference numerals, and detailed description thereof will be omitted as appropriate. This optical coupling system 100C has a birefringent crystal 101, grating couplers 102 and 103, and a mirror 105. The optical coupling systems 100A to 100C have a common structure with respect to the birefringent crystal 101 and the grating coupler 103. FIGS. 6A to 6C are a top view, a front view, and a side view, respectively, corresponding to FIG. 5. Note that the grating couplers 102 and 103 are not shown in FIGS. 6A to 6C.

[0027] In a certain xy plane, the grating couplers 102 and 103 are located at a first position and a second position, respectively. That is, similar to the optical coupling system 100B, the grating couplers 102 and 103 are located on the same plane. The grating coupler 103 has a slit parallel to the y-axis, and the grating coupler 102 has a slit parallel to the x-axis.

[0028] Unlike the optical coupling systems 100A and 100B, the emitted light 141 is reflected by the mirror 105 to become the final emitted light 144. For example, the mirror 105 may be disposed in such a posture (orientation) that the final emitted light 144 travels in a certain yz plane at an angle of θmo with respect to the z-axis direction.

[0029] Reflection by the mirror 105 causes the polarization direction of the final output light 144 to become parallel to the x-axis. This final output light 144 is incident on the corresponding grating coupler 102. In this case, the mirror 105 adjusts the polarization directions of the first linearly polarized wave (ordinary light 131) and the second linearly polarized wave (extraordinary light 132) so that they become parallel to the predetermined plane (the xy plane) on which the grating couplers 102 and 103 are arranged. Therefore, the mirror 105 is an example of a polarization direction adjustment unit.

[0030] The optical coupling system 100C can achieve highly efficient optical coupling, similar to the optical coupling systems 100A and 100B. Furthermore, in the illustrated optical coupling system 100C, similar to the optical coupling system 100B, the grating couplers 102 and 103 are arranged on the same plane (the xy plane), and therefore the grating couplers 102 and 103 can be easily formed using silicon photonics.

[0031] Note that, as long as the emitted beams 144 and 142 are S-polarized with respect to the grating couplers 102 and 103, respectively, a different arrangement from that illustrated is also possible. For example, the grating couplers 102 and 103 may be arranged on two different planes. That is, the positions of the grating couplers 102 and / or 103 may be moved along the optical paths of the emitted beams 143 and / or 142 while maintaining their posture (orientation). Furthermore, for example, the plane on which the grating coupler 102 is arranged and / or the plane on which the grating coupler 103 is arranged may be tilted about the y-axis and / or the x-axis from the xy plane, respectively. Furthermore, the mirror 105 may reflect the emitted beam 142 instead of or in addition to the emitted beam 141.

[0032] Furthermore, if the final output light 144 becomes S-polarized with respect to the grating coupler 102, the attitude (orientation) of the mirror 105 may be changed. In this case, the optical path (originally in the yz plane) and polarization direction (originally parallel to the x-axis) of the final output light 144 change, so the position and attitude of the grating coupler 102 can be changed accordingly. Conversely, the attitude of the mirror 105 may be changed depending on the position of the grating coupler 102, or the polarization direction of at least one of the output lights 141, 144 may be adjusted using a polarization rotation element or the like depending on the attitude of the grating coupler 102.

[0033] 1-4. Configuration Example of Optical Coupling System (Cross Arrangement 2) FIG. 7 is a perspective view showing a configuration example of an optical coupling system 100D. In FIG. 7, parts corresponding to any of FIG. 1, FIG. 3, and FIG. 5 are assigned the same reference numerals, and detailed description thereof will be omitted as appropriate. This optical coupling system 100D has a birefringent crystal 101D, a grating coupler 102, and a grating coupler 103. The optical coupling systems 100A to 100D have a common structure with respect to the grating coupler 103. FIGS. 8A to 8C are a top view, a front view, and a side view, respectively, corresponding to FIG. 7. Note that the grating couplers 102 and 103 are omitted from the illustration in FIGS. 8A to 8C.

[0034] In a certain xy plane, the grating couplers 102 and 103 are located at a first position and a second position, respectively. That is, similar to the optical coupling systems 100B and 100C, the grating couplers 102 and 103 are located on the same plane. The grating coupler 103 has a slit parallel to the y-axis, and the grating coupler 102 has a slit parallel to the x-axis.

[0035] The birefringent crystal 101D is a birefringent crystal 101 having a total reflection surface 106. In the birefringent crystal 101D, for example, two birefringent crystal members 101a and 101b are bonded together. In this case, the total reflection surface 106 is an adhesive layer (bonding agent layer), and the refractive index of the adhesive is between the ordinary refractive index and extraordinary refractive index of the birefringent crystal 101D so that the total reflection surface 106 reflects ordinary light while transmitting extraordinary light, as will be described later. Furthermore, like the birefringent crystal 101, the birefringent crystal members 101a and 101b are uniaxial negative crystals having an optical axis 111 parallel to the y-axis.

[0036] 9A and 9B show the index ellipsoids of a positive uniaxial crystal and a negative uniaxial crystal, respectively. The refractive indices in the η and ζ axes are n, and the refractive index in the ξ axis is n. In a positive uniaxial crystal, n < n, and ordinary light propagates faster than extraordinary light. In a negative uniaxial crystal, n > n, and ordinary light propagates slower than extraordinary light. The optic axis is in the ξ axis direction. When the electric field of incident light is outside the ηζ plane, ordinary and extraordinary light are generated depending on the polarization state. The refractive index corresponding to ordinary light is n, regardless of the angle φ between the optic axis and the optical axis, while the refractive index neff corresponding to extraordinary light is between n and n, depending on the angle φ. In particular, when φ = 90 degrees, neff = n.

[0037] Like the birefringent crystal 101, the birefringent crystal member 101b is an example of a polarization splitter. In a certain xz plane, incident light 121 incident on the top surface of the birefringent crystal member 101b (birefringent crystal 101D) at an incident angle θi is refracted by the birefringent crystal member 101b. At this time, the incident light 121 is separated into ordinary light 131 and extraordinary light 132 in the xz plane. The incident light 121 is incident from a direction perpendicular to the optical axis 111. Therefore, similar to the case where φ=90 degrees in FIG. 9B , the refractive index corresponding to the ordinary light 131 is n and the refractive index corresponding to the extraordinary light 132 is n, where n > n.

[0038] 7, the extraordinary ray 132 (second linearly polarized wave) passes through the total reflection surface 106 and emerges from the lower surface of the birefringent crystal member 101a (birefringent crystal 101D) in a certain xz plane at an emergence angle (refractive angle) θoe to become (final) emergent light 142. This emergent light 142 has a polarization direction parallel to the y-axis, and is incident on the corresponding grating coupler 103 to be coupled.

[0039] Furthermore, the ordinary ray 131 (first linearly polarized wave) is reflected by the total reflection surface 106 to become reflected ordinary ray 133. In a certain yz-plane, the reflected ordinary ray 133 is emitted from the lower surface of the birefringent crystal member 101b (birefringent crystal 101D) at an emission angle (refractive angle) θoo to become (final) emitted ray 141.

[0040] Due to reflection by the total reflection surface 106, the polarization direction of the output light 141 becomes parallel to the x-axis. This output light 141 is incident on the corresponding grating coupler 102. In this case, the total reflection surface 106 adjusts the polarization directions of the first linearly polarized wave (ordinary light 131) and the second linearly polarized wave (extraordinary light 132) so that they become parallel to a predetermined plane (the xy plane) on which the grating couplers 102 and 103 are arranged. Therefore, the total reflection surface 106 is an example of a polarization direction adjustment unit.

[0041] 10 shows the relationship between the polarization directions of ordinary light 131 and 133 and the direction of optical axis 111. It can be seen that the intersection line between the principal section of ordinary light 131 and the principal section of reflected ordinary light 133 is parallel to optical axis 111 (y-axis). As described above, total reflection surface 106 reflects ordinary light 131 and transmits extraordinary light 132. Therefore, total reflection surface 106 is positioned in a position (orientation) that achieves this selective reflection.

[0042] 11 shows the relationship between the optical paths of ordinary rays 131, 133 and extraordinary ray 132 and the total reflection surface 106. The extraordinary ray 132 is transmitted through the total reflection surface 106. On the other hand, the ordinary ray 131 is reflected at the origin in the figure. Here, a normal vector b of the total reflection surface 106 is defined.

[0043] Figure 12A shows the optical paths and polarization directions of ordinary light 131 and 133 near the total reflection surface 106. Figure 12B shows the optical path and polarization direction of extraordinary light 132 near the total reflection surface 106. In the figure, no represents the ordinary refractive index of the birefringent crystal 101D, ne represents the extraordinary refractive index of the birefringent crystal 101D, and ncem represents the refractive index of the adhesive that realizes the total reflection surface 106. Also, s and p represent the S-polarized light component and P-polarized light component with respect to the incident surface 106, respectively. Also, θbo represents the angle of incidence of ordinary light 131, θbe represents the angle of incidence of extraordinary light 132, and θceme represents the refraction angle of extraordinary light 132.

[0044] Total reflection is a phenomenon that can occur when light is incident on a medium with a smaller refractive index. Therefore, total reflection can occur when ordinary light 131 is incident on the adhesive layer (total reflection surface 106) from the birefringent crystal member 101b, and when extraordinary light 132 is incident on the birefringent crystal member 101a from the adhesive layer. Whether total reflection occurs depends on whether the angle of incidence is greater than the critical angle. Note that if the angle of incidence is equal to the critical angle, an evanescent field is generated along the total reflection surface 106. Here, it is assumed that total reflection does not occur in this case. The critical angle θco corresponding to ordinary light 131 and the critical angle θce corresponding to extraordinary light 132 are calculated by the following equations (1) and (2), respectively. θco = arcsin(ncem / no) ... (1) θce = arcsin(ne / ncem) ... (2)

[0045] In order for the adhesive layer (total reflection surface 106) to reflect ordinary light 131 while transmitting extraordinary light 132, it is necessary to satisfy θbo > θco and θbe < θce. θbo and θbe depend on θi and θoo. Here, the reason why θbo and θbe depend not only on θi but also on θoo is because the orientation of the total reflection surface 106 (normal vector b), which is the basis for θbo and θbe, depends on θoo. Therefore, it is necessary to know whether θbo > θco and θbe < θce are satisfied for the pair of θi and θoo.

[0046] Here, for example, a case will be described in which the wavelength of the incident light 121 is 1550 nm, the birefringent crystal members 101a and 101b are calcite, and the adhesive is Canada balsam. In this case, no = 1.6584, ne = 1.4864, and ncem = 1.55 hold.

[0047] FIG. 13 is a contour chart showing the angle of incidence θbo of ordinary ray 131 on total reflection surface 106 versus the angle of incidence θi (horizontal axis) of incident light 121 on birefringent crystal member 101b and the angle of emergence θoo (vertical axis) of reflected ordinary ray 133 from birefringent crystal member 101b. It can be seen that θbo tends to decrease as θi or θoo increases. The critical angle θco corresponding to ordinary ray 131, calculated using equation (1) above, is 69.2 degrees, and FIG. 13 shows the total reflection region where θbo > θco is satisfied in gray. The boundary of the total reflection region (the region where θbo = θco is satisfied) is essentially a smooth curve, but is represented by a combination of vertical and horizontal lines for ease of drawing.

[0048] Figure 14 is a contour graph showing the angle of incidence θbe of extraordinary ray 132 on the total reflection surface 106 for the set of the angle of incidence θi of incident light 121 on the birefringent crystal member 101b and the angle of emergence θoo of reflected ordinary light 133 from the birefringent crystal member 101b. As in Figure 13, it can be seen that θbe tends to decrease as θi or θoo increases. The critical angle θce corresponding to extraordinary ray 132, calculated using equation (2) above, is 73.5 degrees, and Figure 14 shows in gray the total reflection region where θbe > θce is satisfied. As in Figure 13, the boundaries of the total reflection region are represented by a combination of vertical and horizontal lines.

[0049] The region where θbo > θco and θbe < θce are satisfied (selective reflection region) is the intersection of the total reflection region in FIG. 13 and the non-total reflection region in FIG. 14. Referring to FIGS. 13 and 14, it can be seen that a selective reflection region exists. The selective reflection region is shown in black in FIG. 15. For example, when θi is set to 20 degrees, the attitude (orientation) of the total reflection surface 106 can be adjusted so that θoo is approximately 60 degrees or greater.

[0050] Due to the near-field effect, the phase of light changes when total reflection occurs. The amount of phase change of the S-polarized component differs from the amount of phase change of the P-polarized component. As a result, components other than the x-component are generated in the polarization direction of the reflected ordinary light 133, reducing the coupling efficiency of the output light 141 to the grating coupler 102. Figure 16 is a contour graph showing the proportion of the S-polarized component in the output light 141 relative to the grating coupler 102 for the set of the incident angle θi of the incident light 121 to the birefringent crystal member 101b and the exit angle θoo of the reflected ordinary light 133 from the birefringent crystal member 101b. It can be seen that a minimum of approximately 80% S-polarized component can be obtained, but a small θi may be used to maximize the coupling efficiency.

[0051] Furthermore, if the incident light 121 of the birefringent crystal 101D is not collimated light but convergent light that has passed through a condensing lens, the output light 141 and 142 will also be convergent light. In order to focus the output light 141 and 142 at desired positions, the optical path length difference between the ordinary light 131, 133, and 141 and the extraordinary light 132 and 142 can be important.

[0052] 17 is a contour graph showing the optical path length difference between the ordinary rays 131, 133, and 141 and the extraordinary rays 132 and 142 for a set of the incident angle θi of the incident light 121 onto the birefringent crystal member 101b and the exit angle θoo of the reflected ordinary ray 133 from the birefringent crystal member 101b. It can be seen that there is a region where the optical path length difference is zero. When the optical path length difference is positive, the optical path lengths of the ordinary rays 131, 133, and 141 are longer, and when the optical path length difference is negative, the optical path lengths of the extraordinary rays 132 and 142 are longer. However, the thickness of the birefringent crystal 101D in the z-axis direction is 500 μm, ordinary light 131 is reflected within a plane 250 μm away from the upper surface (lower surface) of the birefringent crystal 101D in the z-axis direction, the thickness of the adhesive layer is zero, and the distance in the z-axis direction between the lower surface of the birefringent crystal 101D and the grating couplers 102 and 103 is zero.

[0053] In addition, if the optical path length difference is not zero, it may happen that, for example, the focus of the output light 141 is on the grating coupler 102, while the focus of the output light 142 is not on the grating coupler 103. In such a case, for example, the grating coupler that is not located at the focus may be a grating coupler suitable for out-of-focus light, or a lens or the like may be inserted in the optical path to adjust the focus. This is also true for the optical coupling systems 100A to 100C. Furthermore, even if the optical path lengths do not exactly match, no problem occurs as long as the difference between them is sufficiently small.

[0054] The optical coupling system 100D can achieve highly efficient optical coupling, similar to the optical coupling systems 100A to 100C. Furthermore, in the illustrated optical coupling system 100D, similar to the optical coupling systems 100B and 100C, the grating couplers 102 and 103 are arranged on the same plane (the xy plane), making it possible to easily form the grating couplers 102 and 103 using silicon photonics. Furthermore, the optical coupling system 100D has a polarization direction adjustment unit (total reflection surface 106) inside the birefringent crystal 101D, making it superior in terms of integration and cost.

[0055] Note that, as long as the emitted beams 141 and 142 are S-polarized with respect to the grating couplers 102 and 103, respectively, an arrangement different from that illustrated is also possible. For example, the grating couplers 102 and 103 may be arranged on two different planes. That is, the positions of the grating couplers 102 and / or 103 may be moved along the optical paths of the emitted beams 143 and / or 142 while maintaining their posture (orientation). Furthermore, for example, the plane on which the grating coupler 102 is arranged and / or the plane on which the grating coupler 103 is arranged may be tilted about the y-axis and / or the x-axis from the xy plane, respectively.

[0056] Furthermore, if the emitted light 141 becomes S-polarized with respect to the grating coupler 102, the attitude of the total reflection surface 106 may be changed. In this case, the optical path (originally in the yz plane) and polarization direction (originally parallel to the x-axis) of the emitted light 141 change, so the position and attitude of the grating coupler 102 can be changed accordingly. Conversely, the attitude of the total reflection surface 106 may be changed depending on the position of the grating coupler 102, or the polarization direction of the emitted light 141 may be adjusted using a polarization rotation element or the like depending on the attitude of the grating coupler 102.

[0057] The wavelength of the incident light 121, the material of the birefringent crystal 101D (birefringent crystal members 101a and 101b), and the material of the adhesive are not limited to those shown in the examples. For example, the wavelength of the incident light 121 may be 1064 nm, the birefringent crystal 101D may be α-BBO, and the adhesive may be Canada balsam. In this case, n = 1.6579, n = 1.5203, and n = 1.55. The total reflection surface 106 may also be realized by means other than adhesive. For example, only the ordinary ray 131 may be reflected by a mirror or a total reflection surface inserted in the birefringent crystal at a position on the optical path of the ordinary ray 131 but not on the optical path of the extraordinary ray 132. Furthermore, the materials (refractive indexes) of the birefringent crystal members 101a and 101b may be different, or the birefringent crystal member 101a may be omitted. An anti-reflection film may also be provided between the adhesive layer and the birefringent crystal member 101a. This makes it possible to prevent the extraordinary light 132 in the adhesive layer from being reflected by the birefringent crystal member 101a and returning to the birefringent crystal member 101b.

[0058] "1-5. Application Examples of Optical Coupling System" "1-5-1. Receiving System" A receiving system using the optical coupling system of the present technology will be described. Fig. 18 shows an optical coupling optical system. This optical coupling optical system includes an optical fiber 201, a resin connector 202, a polarization separation member 203, and a grating coupler 205 and a silicon waveguide 206 formed on an SOI substrate 204.

[0059] The output end of optical fiber 201 is connected to resin connector 202. An optical signal output from a transmitter is input to the input end of optical fiber 201. The polarization state of the optical signal traveling through optical fiber 201 changes due to, for example, stress or vibration applied to optical fiber 201. Therefore, even if a linearly polarized wave is input to the input end, an optical signal having any polarization state can be output from the output end.

[0060] An optical signal output from the output end of optical fiber 201 is reflected by reflecting surface 202a of resin connector 202 and transformed into collimated light by lens 202b formed integrally with resin connector 202. The collimated light incident on lens 203a of polarization separation member 203 is transformed into converging light having a focus on grating coupler 205.

[0061] The polarization splitter 203 and the grating coupler 205 may be any of the optical coupling systems 100A to 100D described above. The grating coupler 205 may be the grating couplers 102 and 103. A silicon waveguide 206 is connected to each of the grating couplers 205. The polarization splitter 203 is fixed to the grating coupler 205 using an adhesive or the like after alignment, for example.

[0062] FIG. 19 shows an example of the configuration of an optical unitary converter 207 that combines (restores) optical signals separated into two branches using an appropriate algorithm. Optical signals are input to this optical unitary converter 207 from each of the silicon waveguides 206. This optical unitary converter 207 includes two phase modulators 207a and two 2×2 fiber-optic couplers 207b. Note that the configuration of the optical unitary converter 207 is not limited to the example shown. Instead of or in addition to the upstream phase modulator 207a, a phase modulator may be inserted in the optical path upstream of the grating coupler 205. For example, a phase modulator may be inserted in at least one of the optical paths of the lights 131 to 133 and 141 to 144. In addition, the phase of the light can be adjusted by changing the angle of incidence of the incident light 121, the dimensions of the birefringent crystals 101 and 101D, the positions of the grating couplers 102 and 103, the position and attitude (orientation) of the mirror 105, the position, attitude (orientation) and thickness of the total reflection surface 106, etc.

[0063] It should be noted that this receiving system can also utilize polarization-division multiplexing, in which case, by performing an appropriate optical unitary transformation in the optical unitary converter 207, two output signals corresponding to two input signals having orthogonal polarization states input to the optical fiber 201 can be obtained from the two outputs of the downstream optical coupler 207b.

[0064] "1-5-3. Measurement System" A measurement system utilizing the optical coupling system of the present technology will be described. This measurement system can be used, for example, as a LiDAR. FIG. 20 shows an optical coupling optical system. In FIG. 20, parts corresponding to those in FIG. 18 are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate. The optical coupling optical system on the transmitting side includes a silicon waveguide 306 and a grating coupler 305 formed on an SOI substrate 304, and a lens support member 303. The optical coupling optical system on the receiving side includes a polarization separation member 203, a grating coupler 205 and a silicon waveguide 206 formed on the SOI substrate 204.

[0065] The measurement light is sent from the silicon waveguide 306 to the grating coupler 305 and emitted there. The light emitted from the grating coupler 305 is transformed into collimated light by the lens 303b supported by the lens support member 303, and is then irradiated onto the measurement target 400. Note that the lens support member 303 is fixed to the grating coupler 304 using, for example, an adhesive after alignment. The light reflected by the measurement target 400 (return light) is incident on the lens 203b of the polarization separation member 203.

[0066] The light incident on lens 203b is transformed into converging light that is focused on grating coupler 205. The polarization state of the light (return light) incident on lens 203b changes depending on the state of measurement object 400 and the optical path. Therefore, even if linearly polarized light is emitted from grating 305, light with any polarization state can be incident on lens 203b. The light incident on each of grating couplers 205 is combined by optical unitary converter 207, so the received light intensity can be ensured.

[0067] 2. Modifications For convenience of explanation, in the above-described embodiment, the optical path of the incident light 121 is assumed to lie within a certain xz plane, the birefringent crystals 101 and 101D have a rectangular parallelepiped shape, and the output lights 141 and 142 are assumed to be emitted from the bottom surface of the birefringent crystal. However, as long as each output light ultimately becomes S-polarized with respect to the corresponding grating coupler, the optical path of the incident light 121 may lie within a plane tilted about the z-axis from the xz plane, the birefringent crystal may have a different shape, and at least one of the output lights 141 and 142 may be emitted from a side surface of the birefringent crystal. Furthermore, even if the polarization direction of the light incident on the grating coupler is not strictly parallel to the direction of each slit in the grating coupler, sufficiently high coupling efficiency can be achieved as long as the angle between these directions is sufficiently small. Therefore, an arrangement in which each output light is not strictly S-polarized with respect to the corresponding grating coupler is also permissible. Furthermore, the polarization splitter may be realized by an optical module other than a birefringent crystal, such as a liquid crystal, an optical modulator using the Pockels effect, or a metamaterial.

[0068] Furthermore, while the preferred embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0069] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0070] The present technology can also be configured as follows. (1) An optical processing device including an optical processing unit that separates light incident on an incident surface into a first linearly polarized wave and a second linearly polarized wave, and outputs a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave, wherein the first linearly polarized wave has a first polarization plane, the second linearly polarized wave has a second polarization plane orthogonal to the first polarization plane, and the polarization plane of the first final output light is different from the first polarization plane. (2) The optical processing device described in (1), wherein the polarization direction of the first final output light and the polarization direction of the second final output light are parallel to a predetermined plane. (3) The optical processing device described in (2), wherein the polarization direction of the first final output light is parallel to the polarization direction of the second final output light. (4) The optical processing device according to (1) or (2), wherein the first final output light is orthogonal to the second final output light. (5) The optical processing device according to any of (2) to (4), wherein at least one of a first grating coupler onto which the first final output light is incident and a second grating coupler onto which the second final output light is incident is disposed on the predetermined plane. (6) The optical processing device according to (5), wherein the first grating coupler and the second grating coupler are disposed on the predetermined plane. (7) The optical processing device according to (6), wherein the first grating coupler and the second grating coupler are identical. (8) The optical processing device according to any of (1) to (7), wherein the optical processing section includes: a polarization splitter that splits the incident light into the first linearly polarized wave and the second linearly polarized wave; and a polarization direction adjuster that adjusts the polarization direction of the first linearly polarized wave. (9) The light processing device according to (8), wherein the polarization splitter includes a birefringent crystal. (10) The light processing device according to (9), wherein the birefringent crystal is a uniaxial negative crystal. (11) The light processing device according to (10), wherein the optical axis of the polarization splitter is orthogonal to the incident light, the first linearly polarized wave is ordinary light having the first polarization plane perpendicular to the optical axis, and the second linearly polarized wave is extraordinary light having the second polarization plane parallel to the optical axis.(12) The optical processing device according to any one of (8) to (11), wherein the polarization direction adjustment unit includes a polarization rotation element. (13) The optical processing device according to (12), wherein the polarization rotation element rotates the polarization direction of the first linearly polarized wave by 90 degrees around the optical path of the first linearly polarized wave. (14) The optical processing device according to any one of (8) to (12), wherein the polarization direction adjustment unit includes a mirror. (15) The optical processing device according to (14), wherein the mirror reflects the first linearly polarized wave. (16) The optical processing device according to any one of (8) to (12), wherein the polarization direction adjustment unit includes a reflective surface that reflects the first linearly polarized wave into the polarization separation unit. (17) The optical processing device according to (16), wherein the reflective surface transmits the second linearly polarized wave. (18) The optical processing device according to (16), wherein the reflective surface does not intersect with the second linearly polarized wave. (19) The light processing device according to (17) or (18), wherein the reflective surface is an adhesive layer in contact with the polarization separation unit. (20) The light processing device according to (19), wherein the reflective surface is an adhesive layer sandwiched between the polarization separation units. (21) The light processing device according to (19) or (20), wherein an anti-reflection film is provided on the surface of the adhesive layer from which the second linearly polarized light is emitted. (22) The light processing device according to any of (19) to (21), wherein the refractive index of the adhesive layer is between the ordinary refractive index and extraordinary refractive index of the polarization separation unit. (23) The light processing device according to any of (19) to (22), wherein the wavelength of the incident light is 1550 nm, the polarization separation unit contains calcite, and the adhesive contains Canada balsam. (24) The light processing device according to any of (19) to (22), wherein the wavelength of the incident light is 1064 nm, the polarization separation unit contains α-BBO, and the adhesive contains Canada balsam. (25) The optical processing device according to any one of (1) to (24), wherein an optical path length of the first linearly polarized wave from the incident surface to the first grating coupler is equal to an optical path length of the second linearly polarized wave from the incident surface to the second grating coupler. (26) The optical processing device according to any one of (1) to (25), wherein the incident light is light output from an optical fiber.(27) An optical processing method having the steps of: separating incident light into a first linearly polarized wave and a second linearly polarized wave; and outputting a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave, wherein the first linearly polarized wave has a first polarization plane; the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane; and the polarization plane of the first final output light is different from the first polarization plane. (28) An optical coupling system comprising: an optical fiber; an optical processing section that separates incident light from the optical fiber into a first linearly polarized wave and a second linearly polarized wave and outputs a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave; a first grating coupler onto which the first final output light is incident; and a second grating coupler onto which the second final output light is incident, wherein the first linearly polarized wave has a first polarization plane, the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane, and the polarization plane of the first final output light is different from the first polarization plane. (29) A receiving system comprising: the optical coupling system according to (28); a first waveguide connected to the first grating coupler; a second waveguide connected to the second grating coupler different from the first grating coupler; and an optical unitary converter connected to the first waveguide and the second waveguide. (30) An optical coupling system comprising: an optical fiber; an optical processing section that separates incident light from the optical fiber into a first linearly polarized wave and a second linearly polarized wave and outputs a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave; a first grating coupler to which the first final output light is coupled; and a second grating coupler to which the second final output light is coupled, wherein the first linearly polarized wave has a first polarization plane, and the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane, and the first grating coupler and the second grating coupler are different.

[0071] 100A to 100D... Optical coupling system 101, 101D... Birefringent crystal 101a, 101b... Birefringent crystal member 102, 103, 205, 305... Grating coupler 104... Polarization rotation element 105... Mirror 106... Total reflection surface 111... Optical axis 121... Incident light 131, 133... Ordinary light 132... Extraordinary light 141 to 144... Emitted light 201... Optical fiber 202... Resin connector 202a... Reflection surface 202b, 203a, 203b, 303b... Lens 203... Polarization separation member 204, 304... SOI substrate 206, 306... Silicon waveguide 207... Optical unitary converter 207a... Phase modulator 207b... 2 × 2 optical coupler 303: Lens support member 400: Measurement object

Claims

1. An optical processing device comprising an optical processing unit that separates light incident on an incident surface into a first linearly polarized wave and a second linearly polarized wave, and outputs a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave, wherein the first linearly polarized wave has a first polarization plane, the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane, and the polarization plane of the first final output light is different from the first polarization plane.

2. The optical processing device according to claim 1, wherein the polarization direction of the first final outgoing light and the polarization direction of the second final outgoing light are parallel to a predetermined plane.

3. The optical processing device according to claim 2, wherein the polarization direction of the first final exit light is parallel to the polarization direction of the second final exit light.

4. The optical processing device according to claim 1, wherein the first final exit light is perpendicular to the second final exit light.

5. The optical processing device according to claim 2, wherein at least one of a first grating coupler onto which the first final output light is incident and a second grating coupler onto which the second final output light is incident is disposed on the predetermined plane.

6. The optical processing device according to claim 1, wherein the optical processing section includes a polarization separation section that separates the incident light into the first linearly polarized wave and the second linearly polarized wave, and a polarization direction adjustment section that adjusts the polarization direction of the first linearly polarized wave.

7. An optical processing device according to claim 6, wherein the optical axis of the polarization separation unit is orthogonal to the incident light, the first linearly polarized wave is ordinary light having the first polarization plane perpendicular to the optical axis, and the second linearly polarized wave is extraordinary light having the second polarization plane parallel to the optical axis.

8. The optical processing device according to claim 7, wherein the polarization direction adjustment unit includes a polarization rotation element.

9. The optical processing device according to claim 8, wherein the polarization direction adjustment unit includes a mirror.

10. The optical processing device according to claim 7, wherein the polarization direction adjusting section includes a reflecting surface that reflects the first linearly polarized wave into the polarization separating section.

11. The optical processing device according to claim 10, wherein the reflecting surface transmits the second linearly polarized wave.

12. The optical processing device according to claim 10, wherein the reflecting surface is an adhesive layer in contact with the polarization splitter.

13. The optical processing device according to claim 12, wherein the reflecting surface is an adhesive layer sandwiched between the polarization splitters.

14. The optical processing device according to claim 12, wherein the refractive index of the adhesive layer is between the ordinary refractive index and extraordinary refractive index of the polarization splitter.

15. The light processing device according to claim 12, wherein the wavelength of the incident light is 1550 nm, the polarization separation unit contains calcite, and the adhesive contains Canada balsam.

16. The optical processing device according to claim 12, wherein the wavelength of the incident light is 1064 nm, the polarization separation section contains α-BBO, and the adhesive contains Canada balsam.

17. The optical processing device according to claim 1, wherein the optical path length of the first linearly polarized wave from the incident surface to the first grating coupler is equal to the optical path length of the second linearly polarized wave from the incident surface to the second grating coupler.

18. The optical processing device according to claim 1, wherein the incident light is light output from an optical fiber.

19. An optical processing method comprising the steps of: separating incident light into a first linearly polarized wave and a second linearly polarized wave; and outputting a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave, wherein the first linearly polarized wave has a first polarization plane; the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane; and the polarization plane of the first final output light is different from the first polarization plane.

20. An optical coupling system comprising: an optical fiber; an optical processing section that separates light incident on an incident surface from the optical fiber into a first linearly polarized wave and a second linearly polarized wave, and outputs a first final output light corresponding to the first linearly polarized wave and a second final output light corresponding to the second linearly polarized wave; a first grating coupler onto which the first final output light is incident; and a second grating coupler onto which the second final output light is incident, wherein the first linearly polarized wave has a first polarization plane, the second linearly polarized wave has a second polarization plane that is orthogonal to the first polarization plane, and the polarization plane of the first final output light is different from the first polarization plane.

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