Waveguide-topological photonic crystal coupling structure based on transverse spin matching mechanism

Abstract

The present invention discloses a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism. The structure comprises an input waveguide, a topological photonic crystal slab, and an output waveguide. Incident light is input along the +x direction, coupled into the topological photonic crystal slab via the input waveguide, and then coupled from the topological photonic crystal slab into the output waveguide. The input waveguide consists of a strip waveguide and a coupling optimization region. The coupling optimization region is divided into a square grid, each filled with air and silicon. "1" represents silicon filling, and "0" represents air filling. The entire coupling optimization region is represented by a "0", "1" matrix. The coupling optimization region is optimized using a genetic optimization algorithm to achieve efficient waveguide-topological photonic crystal coupling. While maintaining high-efficiency coupling, the present invention combines the immune deficiency and backscattering properties of topological photonic crystals, providing strong support for the implementation of integrated optical chips.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano photonics and relates to, in particular to, a waveguide-topological photonic crystal plate high-efficiency coupling structure based on a transverse spin matching mechanism. Background Art

[0002] In recent years, the realization of topological photonic crystal waveguides has opened a new chapter in the field of optics, as these systems have revolutionized our understanding of the propagation and manipulation of light. In particular, the discovery of the quantum spin Hall effect and the quantum valley Hall effect, which rely on spin-orbit coupling rather than an external magnetic field, has given topological transmission modes an additional adjustable degree of freedom compared to traditional waveguide devices. Another particularly attractive feature of topological photonic crystal waveguides is that they are immune to backscattering and have unparalleled tolerance to arbitrary bends and fabrication defects. Based on these advantages, topological photonic crystal waveguides provide an effective approach for on-chip integration of optical devices, as they enable dense integration and high-fidelity lossless transmission compared to traditional waveguides.

[0003] For integrated optical chips, interconnection between optical devices is particularly important. The widespread application of topological photonic crystal waveguides in integrated optical chips requires perfect coupling between light and the topological photonic crystal waveguide. Unfortunately, coupling between light and the topological photonic crystal waveguide is fraught with challenges. Existing coupling theories based on mode matching techniques are not applicable to the coupling between waveguides and topological photonic crystal waveguides. Therefore, exploring new mechanisms for coupling between waveguides and topological photonic crystals and designing efficient coupling structures are urgent issues in this field. Summary of the Invention

[0004] In order to solve the above existing problems, the present invention provides a waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism, and proposes a new mechanism for coupling waveguide and topological photonic crystal waveguide - the transverse spin matching mechanism. According to this mechanism, light is designed to be perfectly coupled from the input waveguide into the topological photonic crystal waveguide, greatly improving the input and output efficiency of the integrated optical chip.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism includes an input waveguide, a topological photonic crystal slab, and an output waveguide. Incident light is input along the +x direction, coupled into the topological photonic crystal slab through the input waveguide, and then coupled from the topological photonic crystal slab into the output waveguide, wherein:

[0007] The input waveguide is composed of a strip waveguide and a coupling optimization region. The coupling optimization region is divided into a square grid. Each grid is filled with two materials, air and silicon. "1" represents silicon filling and "0" represents air filling. The entire coupling optimization region is represented by a "0", "1" matrix. The coupling optimization region is optimized by a genetic optimization algorithm. The "0", "1" matrix is ​​randomly obtained to obtain the corresponding output waveguide transmittance and input waveguide transverse spin matching distribution. After multiple iterations, the optimal coupling optimization region is obtained to achieve efficient coupling between waveguide and topological photonic crystal.

[0008] The specific steps of optimizing the coupling optimization region using the genetic optimization algorithm are as follows: first, 200 populations are randomly generated as the first generation population, and then the first generation population is evaluated. During the evaluation process, the transmittance of the output waveguide is calculated through numerical simulation and used as the optimization factor (FOM). At the same time, the corresponding coupling efficiency is calculated by recording the transverse spin distribution on the coupling plane and compared with the transmittance. Then, a suitable population is selected as the parent generation, and the parent generation is recombined to produce offspring through genetic hybridization and gene mutation. After multiple cycles, until the target is achieved, the cycle ends. The requirement for stopping is that the FOM does not further improve after 5 generations.

[0009] The topological photonic crystal plate is composed of two valley photonic crystals (VPCs) with different topological Chern numbers, the topological Chern numbers of the two VPCs are opposite to each other (±1), and are recorded as VPC1 and VPC2, forming a unidirectional topological transmission mode on the splicing boundary;

[0010] The output waveguide is a strip waveguide.

[0011] A method for designing the above-mentioned waveguide-topological photonic crystal high-efficiency coupling structure comprises the following steps:

[0012] (1) Determine the optimal center offset y center :When the input waveguide is coupled with the topological photonic crystal slab, the optimization is sought in the y direction of the topological photonic crystal slab by changing the relative position y between the center of the input waveguide and the center of the topological photonic crystal slab in the y direction. center , while monitoring the transmittance of the output waveguide end, taking the highest transmittance y center As the best matching position;

[0013] (2) Determine the input waveguide width W for optimal transverse spin matching d :By changing the width of the coupled waveguide, monitoring the transmittance at the output waveguide end, and taking the highest transmittance W d As Optimal waveguide width, where:

[0014] The transverse spin matching is the matching degree between the transverse spin distribution of the coupling surface between the input waveguide and the topological photonic crystal slab and the transverse spin distribution of the topological transmission mode;

[0015] (3) Determine the optimal coupling section between the input waveguide and the topological photonic crystal: The topological photonic crystal plate is periodically arranged in the x-direction. There are multiple sections for coupling the input waveguide and the topological photonic crystal plate. By coupling the input waveguide with the topological photonic crystal plate with different coupling sections, the coupling efficiency of the output waveguide is monitored. The coupling section with the highest transmittance is taken as the optimal coupling section, where:

[0016] The coupling efficiency β is defined as:

[0017]

[0018]

[0019]

[0020] in, and are the transverse spin angular momentum on the coupling surface between the waveguide and the topological photonic crystal and the topological transmission mode, respectively; E W (y,z) and E TPC (y,z) are the electric field distribution on the coupling surface between the waveguide and the topological photonic crystal and the topological transmission mode, respectively.

[0021] (4) Determine the optimal coupling optimization region structure: Based on the fact that the coupling efficiency between the input waveguide and the topological photonic crystal plate depends on the characteristics of the transverse spin matching mechanism, the genetic optimization algorithm is used to randomly change the coupling optimization region structure, change the transverse spin distribution of the coupling surface, and make it more closely matched with the transverse spin distribution of the topological transmission mode, thereby obtaining the optimal coupling efficiency.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention couples a strip waveguide structure, easily integrated on-chip, with a topological photonic crystal slab. The topological photonic crystal slab is constructed by splicing two valley photonic crystals with different topological Chern numbers. Light propagates unidirectionally along the interface between the two valley photonic crystal structures, achieving topological boundary modes. By studying the coupling efficiency of topological transmission modes at different waveguide widths and coupling positions, the invention proposes a new mechanism for waveguide-topological photonic crystal slab coupling, namely the transverse spin matching mechanism. Leveraging this transverse spin matching mechanism, the coupling region between the waveguide and the topological photonic crystal slab is optimized to match the transverse spin distribution at the waveguide input to the distribution of the topological transmission mode, thereby achieving high-efficiency coupling between the waveguide and the topological photonic crystal slab. This invention improves the coupling efficiency between the waveguide and the topological photonic crystal slab, achieving a maximum coupling efficiency exceeding 95%, and is applicable to other types of topological photonic crystal structures. While maintaining high coupling efficiency, the invention combines the immune deficiency and backscattering properties of topological photonic crystals, providing strong support for the realization of integrated optical chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism of the present invention.

[0025] Figure 2 Schematic diagram of the coupling optimization area;

[0026] Figure 3 Schematic diagram of a topological photonic crystal slab;

[0027] Figure 4 The electric field diagram of the coupling between the waveguide and the topological photonic crystal slab;

[0028] Figure 5 The coupling mechanism between the basic transverse spin-matched waveguide and the topological photonic crystal waveguide.

[0029] Figure 6 Schematic diagram and design ideas for optimizing the coupling efficiency between waveguide and topological photonic crystal waveguide using genetic algorithm. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0031] The present invention provides a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism, such as Figure 1-4 As shown, the coupling structure includes an input waveguide, a topological photonic crystal plate, and an output waveguide, wherein:

[0032] The input waveguide is composed of a strip waveguide and a coupling optimization area. The coupling optimization area is divided into a square grid. Each grid is filled with two materials, air and silicon. "1" represents silicon filling and "0" represents air filling. The entire coupling optimization area is represented by a "0", "1" matrix. The "0", "1" matrix is ​​randomly obtained through a genetic optimization algorithm to obtain the corresponding output waveguide transmittance and input waveguide transverse spin matching distribution. After multiple iterations, the final result is obtained to realize a waveguide-topological photonic crystal efficient coupling structure.

[0033] The topological photonic crystal plate is a silicon-based valley topological photonic crystal structure based on the valley quantum Hall effect, which is composed of two valley photonic crystals 1 (VPC1) and valley photonic crystal 2 (VPC) with different topological Chern numbers, forming a unidirectional topological transmission mode on the splicing boundary;

[0034] The output waveguide is a strip waveguide.

[0035] The design steps of the above-mentioned waveguide-topological photonic crystal efficient coupling structure are as follows:

[0036] (1) Determine the optimal center offset y center The topological photonic crystal slab is asymmetric in the y direction, so the transverse spin distribution of the topological transmission mode is also asymmetric in the y direction. When the input waveguide is coupled with the topological photonic crystal slab, there is an optimal matching position in the y direction, which makes the coupling efficiency the highest. By changing the relative position y between the center of the input waveguide and the center of the topological photonic crystal slab in the y direction center , while monitoring the transmittance of the output waveguide end, taking the highest transmittance y center as the best matching position.

[0037] (2) Determine the input waveguide width W for optimal transverse spin matching d By changing the width of the coupled waveguide, monitoring the transmittance of the output waveguide end, and taking the highest transmittance W d as the optimal waveguide width.

[0038] (3) Determine the optimal coupling facet between the input waveguide and the topological photonic crystal. The topological photonic crystal slab is periodically arranged in the x-direction. Therefore, there are multiple facets for coupling the input waveguide and the topological photonic crystal slab. By coupling the input waveguide with topological photonic crystal slabs with different coupling facets, the coupling efficiency of the output waveguide is monitored, and the coupling facet with the highest transmittance is taken as the optimal coupling facet.

[0039] (4) Determine the optimal coupling optimization region structure. Since the coupling efficiency between the waveguide and the topological photonic crystal plate depends on the characteristics of the transverse spin matching mechanism, an optimization algorithm is used to randomly change the coupling optimization region structure, changing the transverse spin distribution of the coupling surface to make it more closely matched with the transverse spin distribution of the topological transmission mode, thereby obtaining the optimal coupling efficiency. When the coupling efficiency does not improve further after 5 generations, the structure is considered to be the optimal coupling optimization region structure.

[0040] In the present invention, the width of the input waveguide and the output waveguide are both W d , the thickness is h = 220nm.

[0041] In the present invention, the size of the coupling optimization area is L×W d , the size of each square grid is S×S, L is the length of the optimization area, which is an integer multiple of S; W d is the width of the optimization region, which is an integer multiple of S.

[0042] In this invention, the topological photonic crystal slab is constructed by splicing two types of valley photonic crystals. Changing the diameter of the dielectric pillars in the VPC unit cell disrupts spatial inversion symmetry, opening a Dirac point in the energy band and achieving a topological phase transition. When the diameter difference between the air holes in the VPC unit cells is Δd > 0 and Δd < 0, the topological Chern numbers of the two VPCs are opposite (±1), denoted as VPC1 and VPC2. A topological transmission mode can form at the interface between the two structures.

[0043] In the present invention, the valley photonic crystal (VPC) is a two-dimensional orthorhombic restoration cell structure made by etching air holes in a silicon substrate. The lattice constant is a, and the original cell contains two circular air holes with diameters d1 and d2, respectively. The photonic crystal plate has a thickness of h. The air holes are arranged in a graphene structure.

[0044] In the present invention, the diameters of the two air holes in the two valley photonic crystals VPC1 and VPC2 are opposite.

[0045] In the present invention, the input waveguide, output waveguide and topological photonic crystal plate are all made of silicon material.

[0046] In the present invention, the transverse spin matching is the matching degree between the transverse spin distribution of the input waveguide and the coupling surface of the topological photonic crystal slab and the transverse spin distribution of the topological transmission mode, and the coupling efficiency β is defined as:

[0047]

[0048]

[0049]

[0050] in, and are the transverse spin angular momentum on the coupling surface between the waveguide and the topological photonic crystal and the topological transmission mode, respectively; E W (y,z) and E TPC (y,z) are the electric field distribution on the coupling surface between the waveguide and the topological photonic crystal and the topological transmission mode, respectively.

[0051] In the present invention, the transverse spin matching mechanism can be applied to the efficient coupling of other types of topological photonic crystal plates, including topological photonic crystal plates based on quantum spin Hall effect and quantum valley Hall effect.

[0052] In the present invention, the highly efficient coupling structure of the waveguide and topological photonic crystal based on the transverse spin matching mechanism can operate within any wavelength and frequency range by changing the structural dimensions.

[0053] Example:

[0054] This embodiment provides a waveguide-topological photonic crystal high-efficiency coupling structure based on a transverse spin matching mechanism, including an input waveguide, a topological photonic crystal slab, and an output waveguide, wherein: the input waveguide is divided into a strip waveguide and a coupling optimization region, and the topological photonic crystal slab is composed of a valley photonic crystal 1 (VPC1) and a valley photonic crystal 2 (VPC) spliced ​​together.

[0055] Specifically, the coupling optimization region is divided into a square grid with a side length of 50 nm × 50 nm, and silicon and air are selected as filling materials, such as Figure 2 As shown. The VPC1 and VPC2 are both composed of a silicon-based dielectric plate with two air holes of diameters d1 and d2 respectively. Their lattice constants are both a. The difference is that the diameters of the two air holes in the unit cell are reversed, as shown in Figure 3 Taking VPC1 as an example, the structural parameters are: a=385nm, d1=195nm, d2=95nm.

[0056] Finite element simulation is used to calculate the electric field diagram and coupling efficiency of the waveguide coupled with the topological photonic crystal slab. The incident light is input along the +x direction, coupled into the topological photonic crystal slab through the input waveguide, and then coupled from the topological photonic crystal slab into the output waveguide. Here, the coupling optimization area is filled with silicon material, the incident light wavelength is 1433nm, and the input waveguide and output waveguide widths are W. d =0.8μm. The structure can be divided into three regions, where regions I and III are input waveguide structure and output waveguide structure, and region II is a topological photonic crystal plate, thus forming two different coupling planes I-II and II-III, as shown in the following example: Figure 4As shown. For the first coupling plane (I-II), the incident light is reflected back to the input waveguide and interferes with the incident light (R1~36%) and part of the light is scattered (T sca ~0.19), only part of the light is coupled into the topological photonic crystal waveguide (coupling efficiency β Ⅰ-Ⅱ For the second coupling plane (Ⅱ-Ⅲ), almost all the light is coupled from the topological photonic crystal waveguide to the output waveguide (coupling efficiency β Ⅱ-Ⅲ ~97.3%). Therefore, the optical coupling from the input waveguide to the topological photonic crystal waveguide (coupling plane I-II) is the first problem to be solved.

[0057] To solve the above problems, the present invention proposes a new mechanism for efficient coupling between waveguide and topological photonic crystals - transverse spin matching mechanism. The present invention is analogous to the mode matching technology and defines the coupling efficiency β as:

[0058]

[0059]

[0060]

[0061] like Figure 5 (a), where and They are the transverse spin angular momentum distribution on the coupling surface between the waveguide and the topological photonic crystal and the transverse spin angular momentum distribution in the topological transmission mode, respectively. Here, the transverse spin angular momentum is defined as S z ∝(Re(E x )Im(E y )-Im(E x )Re(E y )) / E 2 , where E x and E y are the x-component and y-component of the electric field in the transmission plane, and E is the electric field.

[0062] Next, we verify the accuracy of the coupling mechanism between topological photonic crystal waveguides and waveguides based on transverse spin matching. Two key parameters are the input waveguide width (W d ) and different coupling facets (type A and type B) of topological photonic crystal structures, such as Figure 5 (a) is shown. d Taking the 0.8μm A-type coupling structure as an example, Figure 5 (b). When y center =-0.17μm, S w and S TPC Partial matching, the transmittance is low (T = 27.7%). In contrast, when ycenter =0.21 μm, the transmittance is increased to a higher level (T=44.7%) due to the improvement of transverse spin matching.

[0063] The coupling characteristics based on the transverse spin matching mechanism can be extended to different coupling sections and different W d In the coupled structure ( Figure 6 (a)). Here, light is incident from the input waveguide into the topological photonic crystal slab, and the y center changes, and the transmittance of the output waveguide is measured. Figure 6 In (c) and 6(d), the effects of these parameters on the coupling efficiency are investigated. The results show that the numerically calculated transmittance agrees well with the coupling efficiency, with only small deviations. This is because light is scattered during the coupling process between the waveguide and the topological photonic crystal waveguide, and small deviations can be expected. The coupling efficiency is affected by W d The effect is small, as W d The maximum transmission rate is 52.8% (Type B, W d =1μm,y center The next step in this research is to explore how to achieve perfect coupling of topological transport modes using the transverse spin matching mechanism.

[0064] In order to obtain higher coupling efficiency, the input waveguide needs to be reshaped to achieve transverse spin redistribution on the coupling plane. In recent years, the design of intelligent photonic devices using mathematical optimization algorithms has been widely studied. Among them, genetic algorithms, as a method that is good at global optimization, have attracted much attention in the design of various nanophotonic devices. Therefore, genetic algorithms are used to design the coupling optimization area of ​​the input waveguide. Figure 6 As shown in (a), the coupling optimization area is discretized into a 20×12 square array with a side length of 50nm, and the optimization area is 1×0.6μm 2 . First, 200 populations are randomly generated as the first generation population, and then the first generation population is evaluated. During the evaluation process, the transmittance of the output waveguide is calculated by numerical simulation, and the transmittance is used as the optimization factor (FOM). At the same time, by recording the transverse spin distribution on the coupling plane, the corresponding coupling efficiency is calculated and compared with the transmittance. Then a suitable population is selected as the parent generation, and the parent generation is recombined to produce offspring through genetic hybridization and gene mutation. After multiple cycles, until the goal is achieved, the cycle ends, and the stopping requirement is that the FOM has not been further improved after 5 generations.

[0065] To achieve higher coupling efficiency, select Figure 5 The optimal transmittance in (d) is optimized, and the corresponding parameters are type B, Wd =1.0μm,y center =-0.11μm. Figure 6 (b) is the optimized result of transmittance when the number of iterations (N) increases, where N = 0 corresponds to the unoptimized structure. It can be found that the transmittance increases rapidly at the beginning, then gradually tends to be flat, and finally remains unchanged when N = 15. The optimized transmittance increases from 52.8% (N = 0) to 95.1% (N = 15), which is the highest level reported so far. At the same time, the optimal structure can maintain perfect coupling (T ≥ 90%) of the topological transmission mode within a wide bandwidth (1427 ~ 1441nm), as shown in Figure 2. Figure 6 (b) shown.

[0066] To verify the accuracy of the transverse spin matching mechanism during the optimization process, the coupling efficiency of each generation of optimized structures was calculated and compared with the transmittance. The results show that the optimized transmittance and coupling efficiency are in good agreement, especially at high transmittance (N ≥ 4). At low transmittance (N < 4), the calculated coupling efficiency is slightly lower than the transmittance due to strong scattering of the incident light at the coupling plane and coupling of the scattered light with the topological photonic crystal waveguide. In addition, the lower the transmittance, the stronger the scattering, resulting in a larger deviation between the two results. At high transmittance, the two results are almost completely consistent.

[0067] Taking the unoptimized structure (N=0) and the optimized structure (N=15) as examples, the properties of the transverse spin matching mechanism are analyzed. According to the transverse spin matching mechanism, it can be known that the coupling efficiency is determined by S W and S TPC Decide. Figure 6 (c) is the S of the topological transmission mode corresponding to the coupling plane TPC For the unoptimized structure, the S W distributed( Figure 6 (d1)) and S TPC There is a large difference in the distribution, resulting in lower coupling efficiency, more light reflected back to the input waveguide and generating interference fringes (Figure 6(d2)). In contrast, for the optimal structure, the S W distributed( Figure 6 (e1)) and S TPC The distribution is perfectly matched, and the waveguide and the topological photonic crystal structure have extremely high coupling efficiency ( Figure 6 (e1)).

[0068] In summary, the coupling mechanism between the waveguide and the topological photonic crystal is determined by the transverse spin matching between the input waveguide and the topological photonic crystal waveguide. According to the proposed transverse spin matching mechanism, it means that the topological transmission mode can achieve perfect coupling (transmittance is close to 1). By introducing a genetic algorithm to optimize the coupling optimization area, the coupling efficiency is controlled by controlling the transverse spin matching, and the maximum transmittance can reach 95.1%. Although this new coupling mechanism is only demonstrated in topological photonic crystal structures based on the quantum valley Hall effect, it is applicable to a wider range of topological photonic crystal structures. The perfect coupling of the waveguide and the topological photonic crystal waveguide reported in this invention, combined with the advantages of unidirectional transmission and immune defects, makes it an ideal platform for realizing integrated optical chips, which will be used in the next generation of optical communication systems.

Claims

1. A waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism, characterized in that The waveguide-topological photonic crystal coupling structure includes an input waveguide, a topological photonic crystal plate, and an output waveguide. Incident light is input along the +x direction, coupled into the topological photonic crystal plate through the input waveguide, and then coupled from the topological photonic crystal plate into the output waveguide. The input waveguide is composed of a strip waveguide and a coupling optimization area. The coupling optimization area is divided into square grids, each grid is filled with two materials, air and silicon. "1" represents silicon filling, and "0" represents air filling. The entire coupling optimization area is represented by a "0" and "1" matrix. The coupling optimization area is optimized by a genetic optimization algorithm, and the "0" and "1" matrices are randomly obtained to obtain the corresponding output waveguide transmittance and input waveguide transverse spin matching distribution. After multiple iterations, the optimal coupling optimization area is obtained to achieve efficient coupling between the waveguide and the topological photonic crystal. The topological photonic crystal plate is a topological photonic crystal plate based on the quantum spin Hall effect or the quantum valley Hall effect.

2. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1 is characterized in that The specific steps of optimizing the coupled optimization area using the genetic optimization algorithm are as follows: First, 200 populations are randomly generated as the first generation population, and then the first generation population is evaluated. During the evaluation process, the transmittance of the output waveguide is calculated through numerical simulation, and the transmittance is used as the optimization coefficient FOM. At the same time, by recording the transverse spin distribution on the coupling plane, the corresponding coupling efficiency is calculated and compared with the transmittance; then a suitable population is selected as the parent generation, and the parent generation is recombined to produce the offspring through genetic hybridization and gene mutation. After multiple cycles, until the goal is achieved, the cycle ends. The stopping requirement is that the FOM does not further improve after 5 generations.

3. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1 is characterized in that The topological photonic crystal plate is composed of two valley photonic crystals (VPCs) with different topological Chern numbers. The topological Chern numbers of the two VPCs are opposite to each other, and are denoted as VPC1 and VPC2. A unidirectional topological transmission mode is formed on the splicing boundary.

4. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1 or 3, characterized in that The topological photonic crystal plate is a silicon-based valley topological photonic crystal structure based on the valley quantum Hall effect.

5. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 3 is characterized in that The valley photonic crystal (VPC) is a two-dimensional orthorhombic restoration cell structure in which air holes are etched from a silicon substrate. The lattice constant is a. The original cell contains two circular air holes with diameters of d1 and d2, d1≠d2. The thickness of the photonic crystal plate is h, and the air holes are arranged in a graphene structure as a whole.

6. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 5 is characterized in that The two air holes of VPC1 and VPC2 have opposite diameters.

7. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1 is characterized in that The output waveguide is a strip waveguide.

8. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1 is characterized in that The input waveguide, output waveguide and topological photonic crystal plate are all made of silicon.

9. A design method for a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism according to any one of claims 1 to 8, characterized in that The method comprises the following steps: (1) Determine the optimal center offset y center :When the input waveguide is coupled with the topological photonic crystal slab, the optimization is sought in the y direction of the topological photonic crystal slab by changing the relative position y between the center of the input waveguide and the center of the topological photonic crystal slab in the y direction. center , while monitoring the transmittance of the output waveguide end, taking the highest transmittance y center As the best matching position; (2) Determine the input waveguide width W for optimal transverse spin matching d :By changing the width of the coupled waveguide, monitoring the transmittance at the output waveguide end, and taking the highest transmittance W d as the optimal waveguide width; (3) Determine the optimal coupling section between the input waveguide and the topological photonic crystal: The circular air holes in the topological photonic crystal plate are periodically arranged in the x direction, and the period is the lattice constant a. There are multiple sections for coupling the input waveguide and the topological photonic crystal plate. By coupling the input waveguide with the topological photonic crystal plate with different coupling sections, the coupling efficiency of the output waveguide is monitored, and the coupling section with the highest transmittance is taken as the optimal coupling section; (4) Determine the optimal coupling optimization region structure: Based on the fact that the coupling efficiency between the input waveguide and the topological photonic crystal plate depends on the characteristics of the transverse spin matching mechanism, the genetic optimization algorithm is used to randomly change the coupling optimization region structure, change the transverse spin distribution of the coupling surface, and make it more closely matched with the transverse spin distribution of the topological transmission mode, thereby obtaining the optimal coupling efficiency.

10. The design method of the waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 9, characterized in that The coupling efficiency β is defined as: ； ； ； in, and are the transverse spin angular momentum on the coupling surface between the waveguide and the topological photonic crystal and the topological transmission mode, E W (y,z) and E TPC (y,z) are the electric field distribution on the coupling surface between the waveguide and the topological photonic crystal and the topological transmission mode, respectively.

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