Topological vertical coupler

Abstract

To provide a topological vertical coupler capable of substantially improving vertical coupling efficiency.SOLUTION: A topological vertical coupler 30 includes: a photonic structure 11 being an insulator in which a bulk has an energy gap; a topological photonic structure 12 in which the edge of an insulator having an energy gap in the inside is in a gapless metallic state; a topological edge 13 exhibiting a topological edge state allowing the propagation of an optical vortex on a boundary between the photonic structure 11 and the topological photonic structure 12; and a cavity 40 capable of removing structures in one or a plurality of lattice unit cells from the photonic structure 11 or the topological photonic structure 12.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a topological vertical coupler that can be integrated onto a silicon optical circuit. [Background technology]

[0002] The various optical elements used in optical networks include lasers, modulators, multiplexing elements, optical switches, etc. Optical integrated circuits integrate various functions essential for optical communication on a single chip. Compared to single-function optical devices, they can reduce mounting costs, power consumption, size, etc., so numerous modules have been put to practical use and are currently dominating the optical market. In general optical integrated circuits, the mode of propagating light is fixed to the TE mode (Transverse Electric mode) or TM mode (Transverse Magnetic mode). Therefore, various devices integrated on the optical circuit are designed to operate in those modes.

[0003] In recent years, there has been growing interest in communication methods that proactively utilize the degrees of freedom of light. In particular, research into optical vortices (the orbital angular momentum of light) has been active, as there are still many unexplored areas. Optical vortices theoretically enable infinite channel multiplexing by encoding information onto the spiral period of the wavefront, and are considered to have excellent compatibility with optical communications.

[0004] Patent Document 1 describes an optical element that includes a first layer and a second layer facing the first layer, the first layer including a plurality of first structures each having optical anisotropy, and the second layer reflects light incident from the first layer while maintaining the polarization state of the light at the time of incidence and at the time of reflection. Paragraph

[0258] of Patent Document 1 states: "Light LT2 is emitted as an optical vortex. An optical vortex is light that has a singular point and whose equiphase surface forms a helical surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-84679 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in general optical circuits, the waveguide devices that make up the circuits only operate with TE / TM mode light, so their compatibility with optical vortices is not very high. For example, optical integrated circuits that can only handle TE / TM modes and operate in TE / TM modes cannot control optical vortices.

[0007] By replacing part of conventional optical circuits with topological photonics systems, the goal is to perform various controls, including optical vortex propagation, within optical circuits (TPICs: Topological Photonic Integrated Circuits). One of the key challenges in TPICs is to achieve efficient coupling to topological photonic systems in both horizontal and vertical directions.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a topological vertical coupler capable of significantly improving the vertical coupling efficiency. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the topological vertical coupler according to the present invention comprises a photonic structure (Trivial photonic structure) whose bulk is an insulator having an energy gap, a topological photonic structure (Topological photonic structure) whose interior is an insulator having an energy gap and whose edge is in a gapless metallic state, a topological edge (Topological edge) which expresses a topological edge state in which optical vortex propagation is possible at the boundary between the photonic structure and the topological photonic structure, and a cavity obtained by removing one or a plurality of intra-lattice structures from the photonic structure or the topological photonic structure. In the cavity, a structure in one lattice unit cell that is one lattice unit cell away from the topological edge is removed on the photonic structure. It is characterized by: Other solutions are described later in the detailed description of the invention. Effect of the Invention

[0010] According to the present invention, it is possible to provide a topological vertical coupler capable of significantly improving the vertical coupling efficiency. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a structure of a topological edge state waveguide used in a topological vertical coupler according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a Brillouin Zone diagram showing a structure of a nanohole having C6v symmetry in the topological vertical coupler according to the first embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic diagram illustrating the case where light is perpendicularly incident on the topological edge transmission line of FIG. [Figure 4] 2 is a diagram for explaining the vertical coupling (incidence) position dependency in the topological edge transmission line of FIG. [Diagram 5] 5 is a diagram showing an analysis result of the output intensity versus wavelength at Port1 when circularly polarized light is perpendicularly incident on each of the vertical coupling positions A, B, C, and D of the topological edge transmission line in FIG. 4. FIG. [Figure 6] This shows the output intensity versus wavelength at Port 1 and Port 2 when circularly polarized light is perpendicularly incident on the vertical coupling position A of the topological edge transmission line in FIG. [Figure 7] 1 is a diagram showing a structure having a cavity at a vertical coupling position A of a topological vertical coupler according to a first embodiment of the present invention. FIG. [Figure 8] 1 is a diagram showing a structure having a cavity at a vertical coupling position B of the topological vertical coupler according to the first embodiment of the present invention. FIG. [Figure 9] 1 is a diagram showing a structure having a cavity at a vertical coupling position C of the topological vertical coupler according to the first embodiment of the present invention. FIG. [Figure 10] 1 is a diagram showing a structure having a cavity at a vertical coupling position D of the topological vertical coupler according to the first embodiment of the present invention. FIG. [Figure 11] FIG. 8 is a diagram showing an analysis result of the output intensity versus wavelength at Port 1 when right-handed circularly polarized light is perpendicularly incident on the topological vertical coupler of FIG. 7. [Figure 12] FIG. 8 is a diagram showing a mode distribution at each wavelength in a band in which a topological edge state occurs when right-handed circularly polarized light is perpendicularly incident on the topological vertical coupler of FIG. 7. [Figure 13] FIG. 11 is a diagram showing a structure of a topological vertical coupler according to a second embodiment of the present invention. [Figure 14] FIG. 14 is a diagram showing an analysis result of the output intensity versus wavelength at Port 1 when right-handed circularly polarized light is perpendicularly incident on the topological vertical coupler of FIG. 13. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. (Explanation of the principle) Attempts to trace the topology of electronic systems in topological insulators and Weyl semimetals to photon systems are called topological photonics, and have been rapidly progressing in recent years. A topological insulator is a material in which the bulk is an insulator with an energy gap, but a gapless metallic state occurs at the edge (edge ​​in a two-dimensional system, surface in a three-dimensional system).

[0013] In particular, C 6v The emergence of Z2 topology (a class in the classification of topological structures of electronic wave functions) in a structure in which dielectrics with symmetry (which overlaps when rotated by 60 degrees) are arranged in a honeycomb lattice pattern makes it possible to realize a topological edge state capable of transmitting optical vortices.

[0014] <Design of topological edge transmission lines> FIG. 1 is a diagram illustrating the structure of a topological edge state waveguide 20 used in a topological vertical coupler according to an embodiment of the present invention (Si-based topological edge state waveguide used in simulation). As shown in FIG. 1, the topological edge transmission line 20 has a photonic structure (Trivial photonic structure) 11 whose bulk is an insulator with an energy gap, a topological photonic structure (Topological photonic structure) 12 whose interior is an insulator with an energy gap and whose edge is in a gapless metallic state, and a topological edge (Topological edge) 13 that expresses a topological edge state capable of optical vortex propagation at the boundary between the photonic structure 11 and the topological photonic structure 12.

[0015] <Photonic Structure> Photonic Structure (Trivial Ph.C.) 11 is C6v The structure is such that first dielectric layers 111 having symmetry are arranged in a honeycomb lattice pattern (for example, with a period a=800 nm). Topological Photonic Structure (Topological Ph.C.) 12 is a 6v The structure is such that the second dielectric layers 112 having symmetry are arranged in a honeycomb lattice pattern (for example, with a period a=800 nm).

[0016] The first dielectric 111 is a silicon-on-insulator (SOI) wafer. 6v The nanoholes 111a are arranged in a honeycomb lattice (period a=800 nm) unit cell 121. -9 m) Using structure. The second dielectric 112 is a C 6v A nanostructure is used in which symmetrical nanoholes 112a are arranged in cells 122 in a honeycomb lattice pattern (period a=800 nm). Nanoholes 111a of first dielectric 111 and nanoholes 112a of second dielectric 112 have different parameters, namely, distance r from the center of honeycomb cells 121, 122 to the center of nanoholes 111a, 112a and length l of one side of the nanohole (described later).

[0017] In a topological photonics system, a topological edge state occurs at the interface between two types of photonic structures where the length of one side of the triangle in the honeycomb dielectric part and the distance from the center of the cell are slightly different, and light propagates through it. Depending on the direction of rotation of the optical vortex, light propagates in only one direction, either left or right. In Figure 1, a topological edge mode is manifested at the topological edge 13 at the boundary between the photonic structure 11 and the topological photonic structure 12. The optical state (topological edge state) that arises at the interface between the two regions created by the topological photonic structure 12 only allows light with specific polarizations and optical vortices, and these specific polarizations and optical vortices have propagation direction dependence.

[0018] <C 6v Symmetrical nanohole structure> Figure 2 shows the C 6v 1 is a Brillouin zone diagram (schematic image of a unit cell in the reciprocal space) showing the structure of a symmetric nanohole. Take the nanohole 111a in the first dielectric 111 of the photonic structure 11 as an example. The nanohole 112a in the second dielectric 112 of the topological photonic structure 12 also has a similar structure. As shown in the right diagram of Fig. 2, the center of the honeycomb lattice cell 121 is set as the center (origin) Γ point of the Brillouin zone. In addition, the highly symmetrical points of the Brillouin zone include point M (center of a rectangular surface), point K (center of an edge connecting two rectangular surfaces), point A (center of a hexagonal surface), point H (end point), and point L (center of an edge connecting a hexagonal surface and a rectangular surface).

[0019] As shown in the left diagram of FIG. 2, the Si film 133 is made up of honeycomb lattice cells 121 and C 6v A symmetrical nanohole 111a is formed. A photonic structure consisting of the remaining Si film 133 and the nanohole 111a opened in the Si film 133 forms the first dielectric 111 of the photonic structure 11. The left diagram in Fig. 2 is a diagram of the cell 121 of the photonic structure 11 viewed obliquely from above in front of the upper surface, and the SiO2 insulating film 132 below the opened nanohole 111a is exposed. 2, the parameters of the nanohole 111a are the distance r from the center (Γ point) of the honeycomb lattice cell 121 to the center of the nanohole 111a and the length l of one side of the nanohole 111a. The central angle between the cells 121 of adjacent nanoholes 111a is π / 3. In the case of the nanohole 111a of the photonic structure 11, for example, r=240 nm and l=240 nm. In the case of the nanohole 112a of the topological photonic structure 12, for example, r=290 nm and l=250 nm. Furthermore, as shown in the left diagram of FIG. 2, the distances a1, a2 between the centers (Γ points) of adjacent cells 121 of the honeycomb lattice are the same (here, a1=a2=800 nm≡a).

[0020] <Vertical coupling to topological systems> FIG. 3 is a schematic diagram of a case where light 10 is perpendicularly incident on the topological edge transmission line 20 of FIG. The light 10 is a plane wave (orthogonal to the direction in which the electric field E and the magnetic field H propagate) when it is perpendicularly incident on the topological edge transmission line 20. The polarization is circular polarization.

[0021] 4 is a diagram for explaining the vertical coupling (incidence) position dependency in the topological edge transmission line 20. FIG. 4 shows a case where spots of the plane wave (circularly polarized light 10) shown in FIG. 3 are vertically incident on each of the vertical coupling positions A, B, C, and D of the topological edge transmission line 20. For example, when spots of plane waves are vertically incident on each of the vertical coupling positions A, B, C, and D of the topological edge transmission line 20, looking at the output of Port1, the output is largest when light is vertically incident on the vertical coupling position A. For this reason, when vertically coupled light is output to Port1, it is desirable to provide a cavity 40 (described later) at the vertical coupling position A of the topological edge transmission line 20.

[0022] The inventors have found that, on the photonic structure 11 side, the incidence of light at vertical coupling position A, which is one cell away from the topological edge 13, has a higher vertical coupling efficiency than that at vertical coupling position B, which is closer to the topological edge 13. Also, on the topological photonic structure 12 side, the inventors have found that the vertical coupling efficiency at vertical coupling position C, which is closer to the topological edge 13, is higher than that at vertical coupling position D, which is one cell away from the topological edge 13. Furthermore, in the structural example of FIG. 4, it has been found that, among the vertical coupling positions A, B, C, and D, the vertical coupling position A has the highest vertical coupling efficiency.

[0023] <Port branching when circularly polarized light is input> FIG. 5 shows the output intensity (magnetic field component intensity distribution Hy in the perpendicular (y-axis) direction) versus wavelength at Port 1 when circularly polarized light is perpendicularly incident on each of the vertical coupling positions A, B, C, and D of the topological edge transmission line 20 in FIG. 2 ) (Output power of port 1 as a function of wavelength of vertical incident light.) The horizontal axis is wavelength (μm), and the vertical axis is the magnetic field component strength distribution Hy 2 However, the intensity of the circularly polarized incident light is Hy 2 It states that:

[0024] As shown in Fig. 5, circularly polarized light is vertically incident on the topological edge transmission line 20. Even when the light is incident at the vertical coupling position A where the output (vertical axis) of Port 1 is maximized, the vertical coupling efficiency is less than 10%. In other words, when a topological vertical coupler is configured using the topological edge transmission line 20 shown in Fig. 4, it is expected that the vertical coupling efficiency will be poor.

[0025] FIG. 6 is a diagram showing the analysis results of the output intensity (magnetic field distribution (Hz)) versus wavelength at Port 1 and Port 2 when circularly polarized light is perpendicularly incident at vertical coupling position A of the topological edge transmission line 20 in FIG. 4 (Output power of port 1, 2 as a function of wavelength of vertical incident light.) The horizontal axis represents wavelength (μm) and the vertical axis represents magnetic field distribution (Hz).

[0026] As shown in FIG. 6, when circularly polarized light is perpendicularly incident on the topological edge transmission line 20, the output from Port 2 is minimized at a wavelength of 1.54 μm.

[0027] (First embodiment) 7 to 10 are schematic images of a proposed device showing the structure of a topological vertical coupler 30 according to a first embodiment of the present invention. The topological vertical coupler 30A (30) in FIG. 7 shows a structure having a cavity 40 at the vertical coupling position A in FIG. 4, the topological vertical coupler 30B (30) in FIG. 8 shows a structure having a cavity 40 at the vertical coupling position B in FIG. 4, the topological vertical coupler 30C (30) in FIG. 9 shows a structure having a cavity 40 at the vertical coupling position C in FIG. 4, and the topological vertical coupler 30D (30) in FIG. 10 shows a structure having a cavity 40 at the vertical coupling position D in FIG. 4. When the topological vertical couplers 30A to 30D are not to be distinguished from each other, they are referred to as the topological vertical coupler 30. Note that the same components as those in FIG. 1 are denoted by the same reference numerals, and the description of the overlapping parts is omitted.

[0028] As shown in Figures 7 to 10, topological vertical coupler 30 has photonic structure 11 whose bulk is an insulator with an energy gap, topological photonic structure 12 whose interior is an insulator with an energy gap and whose edges are in a gapless metallic state, topological edge 13 that expresses a topological edge state capable of optical vortex propagation at the boundary between photonic structure 11 and topological photonic structure 12, and cavity 40 that removes the structure within one or more lattice unit cells in the topological transmission path (optical vortex transmission path).

[0029] In other words, the topological vertical coupler 30 has a cavity 40 that removes the structure within one or more lattice unit cells near the topological edge transmission line 20 shown in FIG. 1 for vertical coupling.

[0030] The topological vertical coupler 30 has an air bridge structure in which a 300 nm thick Si core layer is sandwiched between air cladding layers. 6vA topological transmission line 20 (see FIG. 1) was constructed in which symmetric triangular nanoholes were arranged in a honeycomb lattice (lattice spacing 775 nm). In the topological transmission line 20, the R / L of the photonic structures in the photonic structure 11 and the topological photonic structure 12 was determined to be 225 / 265 nm and 270 / 265 nm, respectively, by band analysis. The topological vertical coupler 30 has a cavity structure (cavity 40) in which all the dielectric material within one lattice unit cell in the vicinity of the topological transmission line is removed.

[0031] <Cavity> The cavity 40 is a cavity structure obtained by removing the structure within one or more lattice unit cells in the vicinity of the topological transmission line. Here, the cavity 40 has a structure in which the air portion is filled with Si. A topological vertical coupler 30A shown in FIG. 7 has a cavity 40 on the photonic structure 11, in which a structure within one lattice unit cell spaced apart from the topological edge 13 by one lattice unit cell is removed. A topological vertical coupler 30B shown in FIG. 8 has a cavity 40 formed on the photonic structure 11 by removing a structure within one lattice unit cell in contact with the topological edge 13. A topological vertical coupler 30C shown in FIG. 9 has a cavity 40 formed by removing a structure within one lattice unit cell in contact with a topological edge 13 on a topological photonic structure 12. A topological vertical coupler 30D shown in FIG. 10 has a cavity 40 in which a structure within one lattice unit cell one cell away from the topological edge 13 is removed on the topological photonic structure 12.

[0032] [simulation] <Highly efficient coupling through cavity> FIG. 11 is a diagram showing the analysis results of the output power of Port 1 as a function of wavelength of vertical incident light when right-handed circularly polarized light is perpendicularly incident on the topological vertical coupler 30A (30) of FIG. 7 (output power of port 1 as a function of wavelength of vertical incident light). The horizontal axis is wavelength (μm), and the vertical axis is magnetic field component intensity distribution Hy2 in the direction perpendicular to the surface (y axis). 2 Take. The thick solid line in FIG. 11 indicates the analysis result of the output intensity of port 1 when right-handed circularly polarized light is incident, and the thin solid line in FIG. 11 indicates the analysis result of a normal topological transmission line without a cavity (see topological transmission line 20 in FIG. 4).

[0033] By analyzing the output intensity of port 1 when right-handed circularly polarized light is incident, the vertical coupling efficiency of the topological vertical coupler 30A (30) can be determined.

[0034] In the simulation, a focal length lens is placed 1.5 μm above the topological vertical coupler 30A (30) in Fig. 7, and the beam waist diameter is set to 1 μm, so that light is incident on a region centered on the cavity structure (cavity 40 of the topological vertical coupler 30A) shown in Fig. 7. The incident light is a plane wave, and the polarization is changed between two types: left-handed and right-handed circular polarization.

[0035] As shown by the arrow a in Fig. 11, the topological vertical coupler 30 (topological edge transmission line having a cavity 40) exhibited a significant improvement in vertical coupling efficiency compared to a normal topological edge transmission line without a cavity 40, and an improvement in output intensity of up to 876% (wavelength 1540 nm) was confirmed within the band in which the topological edge state occurs. The output of Port 1 (intensity output to Port 1) improved by just under one order of magnitude.

[0036] <Coupling mode distribution due to cavity> FIG. 12 shows the case where right-handed circularly polarized light is perpendicularly incident on the topological vertical coupler 30A (30) of FIG. This figure shows the mode distribution at each wavelength (1540 nm, 1560 nm, 1580 nm) in the band where the topological edge state occurs. The horizontal axis is the Z axis (μm) (the left end of the Z axis is Port 1, and the right end of the Z axis is Port 2), and the vertical axis is the output intensity (magnetic field component intensity distribution Hy in the direction perpendicular to the surface (y axis)) for each wavelength at Port 1 and Port 2. The shading in Figure 12 represents the intensity of the magnetic field component intensity distribution Hy (the darker the intensity, the greater the intensity).

[0037] At the center of the band, the edge states are expected to disappear due to significant spin-spin scattering, and the coupling to the transmission line is completely cut off. As shown in FIG. 12, it was confirmed that at the wavelength (1560 nm) at which spin-spin scattering occurs, scattering (blocking) occurs in both directions. At wavelengths on either side of the wavelength at which spin-spin scattering occurs (1560 nm) (1540 nm, 1580 nm), the optical vortex propagates in only one direction depending on the orientation.

[0038] Second embodiment Fig. 13 is a diagram showing the structure of a topological vertical coupler 30 according to a second embodiment of the present invention. The topological vertical coupler 30A (30) in Fig. 13 has a structure having a cavity 40 at the vertical coupling position A in Fig. 4. The same components as those in Fig. 7 are given the same reference numerals, and explanations of overlapping parts will be omitted. As shown in Fig. 13, the topological vertical coupler 30 has a lattice unit cell 50 in which the arrangement of the dielectric around the cavity 40 is changed. In Fig. 13, the distance a from the center of the cavity 40 to the center of the lattice unit cell of each of the six lattice unit cells 50 surrounding the cavity 40 is changed. By changing the distance a between the centers, the size of each lattice unit cell 50 remains the same, but the positions of the six triangles change.

[0039] FIG. 14 shows the output intensity (magnetic field component intensity distribution in the direction perpendicular to the surface (y-axis) Hy) versus wavelength at Port 1 when right-handed circularly polarized light is perpendicularly incident on the topological vertical coupler 30A (30) in FIG. 2 The figure shows the analysis results of the output power of port 1 as a function of wavelength of vertical incident light. The horizontal axis shows the wavelength (μm) and the vertical axis shows the magnetic field component strength distribution Hy 2 Take. 14 shows the case where the distance a from the center of the cavity 40 to the center of the cell is changed to 775 nm, 800 nm, 805 nm, and 815 nm. For example, by configuring the first dielectric 111 of the photonic structure 11 so that the distance a=775 nm, the peak frequency of the vertical coupling efficiency can be adjusted to 1.54 μm. Also, by changing the distance a=800 nm, the peak frequency of the vertical coupling efficiency can be adjusted to 1.58 μm. In this way, by changing the distance a, the peak frequency of the vertical coupling efficiency can be shifted, and the wavelength can be controlled.

[0040] As described above, the topological vertical coupler 30 (see FIG. 7 ) according to the first embodiment has the photonic structure 11 whose bulk is an insulator having an energy gap, the topological photonic structure 12 whose interior is an insulator having an energy gap and whose edges are in a gapless metallic state, the topological edge 13 which expresses a topological edge state capable of optical vortex propagation at the boundary between the photonic structure 11 and the topological photonic structure 12, and the cavity 40 in which the structure within one or more lattice unit cells has been removed from the photonic structure 11 or the topological photonic structure 12.

[0041] This configuration provides a topological vertical coupler that can significantly improve the vertical coupling efficiency, making it possible to realize a topological vertical coupler that can be integrated on topological silicon optical circuits (Topological Photonic Integrated Circuits: T-PICs).

[0042] In the second embodiment, the topological vertical coupler 30 has a wavelength-selecting grating 50 surrounding the cavity 40, and an adjustment means for adjusting the peak frequency of the vertical coupling efficiency by changing the distance a between the centers of the cavity 40 and the wavelength-selecting grating 50. In this way, by changing the distance a, the peak frequency of the vertical coupling efficiency can be shifted, and the wavelength can be controlled.

[0043] The topological vertical coupler 10 can be applied to optical circuits with topological properties. A topological vertical coupler using optical vortex transmission can be formed on a semiconductor substrate (silicon, InP, etc.) and is highly compatible with semiconductor lasers and multicore fibers, which are key components for large-capacity transmission, and is therefore expected to improve compatibility with optical communications.

[0044] The present invention is not limited to the above-described embodiment, and includes other modifications and applications without departing from the gist of the present invention described in the claims. For example, the cavity 40 may be arranged in any manner as long as it is arranged in the topological edge transmission line 20.

[0045] Furthermore, the structure, arrangement, dimensions, number, and material of the cavities 40 are not limited to those in the embodiment and modified examples. There may be two or more cavities 40. The cavity 40 may have a structure in which the air portion is filled with Si, or a structure in which no dielectric is formed. [Explanation of symbols]

[0046] 11 Trivial photonic structure 12 Topological photonic structure 13 Topological edge 20 Topological edge transmission line 30,30A,30B,30C,30D Topological vertical coupler 40 Cavity 50 cells (wavelength selection lattice unit cells) 111 First Dielectric 112 Second Dielectric 121 Photonic Structure Cell 122 Cells of topological photonic structures

Claims

1. A photonic structure in which the bulk is an insulator with an energy gap (Trivial photonic structure), A topological photonic structure is an insulator with an energy gap inside, and its edges are in a gapless metallic state. A topological edge that exhibits a topological edge state in which optical vortex propagation is possible at the boundary between the photonic structure and the topological photonic structure; a cavity formed by removing one or more lattice unit cell structures from the photonic structure or the topological photonic structure, In the cavity, a structure in one lattice unit cell that is one lattice unit cell away from the topological edge is removed on the photonic structure. A topological vertical coupler comprising:

2. A photonic structure (Trivial photonic structure) in which the bulk is an insulator having an energy gap; A topological photonic structure is an insulator with an energy gap inside, and its edges are in a gapless metallic state. A topological edge that exhibits a topological edge state in which optical vortex propagation is possible at the boundary between the photonic structure and the topological photonic structure; a cavity formed by removing one or more lattice unit cell structures from the photonic structure or the topological photonic structure, In the cavity, a structure in one of the lattice unit cells adjacent to the topological edge is removed on the topological photonic structure. A topological vertical coupler comprising:

3. a wavelength-selective grating surrounding the cavity; and an adjustment means for adjusting a peak frequency of the vertical coupling efficiency by changing a distance between the center of the cavity and the wavelength selection grating.

3. The topological vertical coupler according to claim 1 or 2.

4. The cavity receives vertically coupled incident light. The topological vertical coupler according to any one of claims 1 to 3.

5. The topological photonic structure comprises a dielectric material having symmetry within the arranged cells.

3. The topological vertical coupler according to claim 1 or 2.

6. The topological photonic structure is ６ｖ The structure is such that a dielectric material containing symmetric nanoholes is arranged in a honeycomb lattice-like cell.

3. The topological vertical coupler according to claim 1 or 2.

7. The topological photonic structure is Z ２ It is a topological structure that is expressed by topology.

3. The topological vertical coupler according to claim 1 or 2.

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