CN115616704A - Waveguide-topological photonic crystal coupling structure based on transverse spin matching mechanism - Google Patents
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Abstract
The invention discloses a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism, which comprises an input waveguide, a topological photonic crystal plate and an output waveguide, wherein incident light is input along the + x direction, is coupled into the topological photonic crystal plate through the input waveguide and then is coupled into the output waveguide from the topological photonic crystal plate, the input waveguide is composed of a strip waveguide and a coupling optimization region, the coupling optimization region is divided into square grids, each grid is filled with two materials, namely air and silicon, 1 represents a filled silicon material, 0 represents filled air, the whole coupling optimization region is represented by a matrix of 0 and 1, and the coupling optimization region is optimized through a genetic optimization algorithm, so that the waveguide-topological photonic crystal high-efficiency coupling is realized. The invention maintains high-efficiency coupling, and simultaneously combines the immune defect and the backscattering characteristic of the topological photonic crystal, thereby providing powerful support for the realization of the integrated optical chip.
Description
Technical Field
The invention belongs to the technical field of micro-nano photonics, and relates to a waveguide-topological photonic crystal plate efficient coupling structure based on a transverse spin matching mechanism.
Background
In recent years, the implementation of topological photonic crystal waveguides has opened new sections to the optical field, as these systems have drastically changed the awareness of the propagation and manipulation of light. In particular, the discovery of quantum spin hall effect and quantum valley hall effect, which rely on spin-orbit coupling rather than external magnetic field, makes the topological transmission mode have one more adjustable degree of freedom than the traditional waveguide device. Another particularly attractive property of topological photonic crystal waveguides is that they can be immune backscattered, with unparalleled tolerance to any bending and manufacturing defects. Based on these advantages, topological photonic crystal waveguides provide an efficient method for on-chip integration of optical devices because they enable dense integration and high fidelity lossless transmission compared to conventional waveguides.
The interconnection between optical devices is particularly important for integrated optical chips, and the premise of wide application of topological photonic crystal waveguides in integrated optical chips is perfect coupling between light and the topological photonic crystal waveguides. Unfortunately, coupling between light and a topological photonic crystal waveguide is fraught with challenges. The existing coupling theory based on the mode matching technology is not suitable for coupling the waveguide with the topological photonic crystal waveguide. Therefore, it is a urgent need in the art to explore new mechanisms for coupling waveguides to topological photonic crystals and to design efficient coupling structures.
Disclosure of Invention
In order to solve the existing problems, the invention provides a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism, provides a novel waveguide and topological photonic crystal waveguide coupling mechanism-the transverse spin matching mechanism, and designs that light is perfectly coupled into the topological photonic crystal waveguide from an input waveguide according to the mechanism, thereby greatly improving the input and output efficiency of an integrated optical chip.
The purpose of the invention is realized by the following technical scheme:
a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism comprises an input waveguide, a topological photonic crystal plate and an output waveguide, wherein incident light is input along the + x direction, is coupled into the topological photonic crystal plate through the input waveguide and is then coupled into the output waveguide from the topological photonic crystal plate, and the waveguide-topological photonic crystal coupling structure comprises:
the input waveguide is composed of a strip waveguide and a coupling optimization region, the coupling optimization region is divided into square grids, each grid is filled with two materials of air and silicon, 1 represents a filled silicon material, 0 represents filled air, the whole coupling optimization region is represented by a matrix of 0 and 1, the coupling optimization region is optimized through a genetic optimization algorithm, the matrixes of 0 and 1 are randomly obtained to obtain the corresponding transmission rate of the output waveguide and the transverse spin matching distribution of the input waveguide, the optimal coupling optimization region is obtained through multiple iterations, and the efficient coupling of the waveguide-topological photonic crystal is realized;
the specific steps of the genetic optimization algorithm for optimizing the coupling optimization region are as follows: firstly, randomly generating 200 populations as a first generation population, then evaluating the first generation population, calculating the transmittance of an output waveguide through numerical simulation in the evaluation process, taking the transmittance as an optimization coefficient (FOM), and meanwhile, calculating corresponding coupling efficiency through recording transverse spin distribution on a coupling plane and comparing the coupling efficiency with the transmittance; then selecting a proper population as a parent, recombining the parent to generate a filial generation through genetic hybridization and gene mutation, and circulating for multiple times until the target is reached, wherein the circulation is finished, and the requirement that the FOM is not further promoted after 5 generations is met;
the topological photonic crystal plate is formed by splicing two Valley Photonic Crystals (VPCs) with different topological ages, the topological ages of the two VPCs are opposite numbers (+/-1) and are marked as VPC1 and VPC2, and a unidirectional topological transmission mode is formed on a splicing boundary;
the output waveguide is a strip waveguide.
A design method of the waveguide-topological photonic crystal high-efficiency coupling structure comprises the following steps:
(1) Determining the optimum offset y of the center center : when the input waveguide is coupled with the topological photonic crystal plate, the optimization is carried out in the y direction of the topological photonic crystal plate by changing the center of the input waveguideRelative position y of center in y direction center While monitoring the transmittance at the output waveguide end, and taking the y of the highest transmittance center As the best matching position;
(2) Input waveguide width W in determining optimal lateral spin matching d : monitoring the transmissivity at the output waveguide end by changing the width of the coupling waveguide, and taking the W with the highest transmissivity d AsAn optimal waveguide width, wherein:
the transverse spin matching is the matching degree of the transverse spin distribution of the coupling surface of the input waveguide and the topological photonic crystal plate and the transverse spin distribution of the topological transmission mode;
(3) Determining an optimal coupling tangent plane of the input waveguide and the topological photonic crystal: the topological photonic crystal plate is periodically arranged in the x direction, the input waveguide is coupled with the topological photonic crystal plate to form a plurality of sections, the coupling efficiency of the output waveguide is monitored by coupling the input waveguide with the topological photonic crystal plate with different coupling sections, and the coupling section with the highest transmissivity is taken as the optimal coupling section, wherein:
the coupling efficiency β is defined as:
wherein, the first and the second end of the pipe are connected with each other,
and
the transverse spin angular momentum of the waveguide and the topological photonic crystal on the coupling surface and the topological transmission mode respectively; e W (y, z) and E TPC And (y, z) are the electric field distribution of the waveguide on the coupling surface with the topological photonic crystal and the topological transmission mode respectively.
(4) Determining an optimal coupling optimization area structure: according to the characteristic that the coupling efficiency in the coupling of the input waveguide and the topological photonic crystal plate depends on a transverse spin matching mechanism, the structure of a coupling optimization region is randomly changed by utilizing a genetic optimization algorithm, the transverse spin distribution of a coupling surface is changed, the transverse spin distribution matching degree of the coupling surface and the transverse spin distribution of a topological transmission mode is higher, and the optimal coupling efficiency is obtained.
Compared with the prior art, the invention has the following advantages:
the invention adopts a strip waveguide structure which is easy to integrate on chip and is coupled with a topological photonic crystal plate, wherein the topological photonic crystal plate is formed by splicing two valley photonic crystals with different topological numbers, and light realizes one-way transmission of a topological boundary mode on an interface of the two valley photonic crystal structures. The invention provides a novel mechanism of waveguide-topological photonic crystal plate coupling, namely a transverse spin matching mechanism, by researching the coupling efficiency of a topological transmission mode when waveguides have different widths and coupling positions. By utilizing a transverse spin matching mechanism, the coupling region of the waveguide-topological photonic crystal plate is optimized to enable transverse spin distribution at the input end of the waveguide to be matched with topological transmission mode distribution, so that high-efficiency coupling of the waveguide-topological photonic crystal plate is realized. The invention improves the coupling efficiency of the waveguide-topological photonic crystal plate, the highest coupling efficiency can reach more than 95 percent, and the invention is suitable for other types of topological photonic crystal structures. The invention maintains high-efficiency coupling, and simultaneously combines the immune defect and the backscattering characteristic of the topological photonic crystal, thereby providing powerful support for the realization of the integrated optical chip.
Drawings
FIG. 1 is a schematic diagram of a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism.
FIG. 2 is a schematic diagram of a coupling optimization region;
FIG. 3 is a schematic diagram of a topological photonic crystal slab;
FIG. 4 is a graph of the electric field of the waveguide coupled to a topological photonic crystal slab;
FIG. 5 is a substantially transverse spin-matched waveguide and topological photonic crystal waveguide coupling mechanism.
FIG. 6 is a schematic diagram and design concept for optimizing the coupling efficiency of a waveguide and a topological photonic crystal waveguide using a genetic algorithm.
Detailed Description
The technical solutions of the present invention are further described below with reference to the drawings, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
The invention provides a waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism, which comprises an input waveguide, a topological photonic crystal plate and an output waveguide as shown in figures 1-4, wherein:
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 of air and silicon, a '1' represents a filled silicon material, a '0' represents filled air, the whole coupling optimization area is represented by a '0' matrix and a '1' matrix, the '0' matrix and the '1' matrix are obtained randomly through a genetic optimization algorithm to obtain corresponding output waveguide transmissivity and input waveguide transverse spin matching distribution, a final result is obtained through multiple iterations, and a waveguide-topology photonic crystal efficient coupling structure is achieved;
the topological photonic crystal plate is of a silicon-based energy valley topological photonic crystal structure based on a valley quantum Hall effect, and is formed by splicing two valley photonic crystals 1 (VPC 1) and valley photonic crystals 2 (VPC) with different topological numbers, and a unidirectional topological transmission mode is formed on a splicing boundary;
the output waveguide is a strip waveguide.
The design steps of the waveguide-topological photonic crystal high-efficiency coupling structure are as follows:
(1) Determining the optimum offset y of the center center . The topological photonic crystal slab is structurally asymmetric in the y direction, and therefore the lateral 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, so that the coupling efficiency is highest. By changing the relative position y of the center of the input waveguide and the center of the topological photonic crystal plate in the y direction center While monitoring the output waveguide end transmittance, taking y of the highest transmittance center As the best matching position.
(2) Input waveguide width W in determining optimal lateral spin matching d . Monitoring the transmissivity at the output waveguide end by changing the width of the coupling waveguide, and taking the W with the highest transmissivity d As an optimal waveguide width.
(3) And determining the optimal coupling tangent plane of the input waveguide and the topological photonic crystal. The topological photonic crystal plates are periodically arranged in the x direction, so that a plurality of sections exist for the coupling of the input waveguide and the topological photonic crystal plates, the coupling efficiency of the output waveguide is monitored by coupling the input waveguide and the topological photonic crystal plates with different coupling sections, and the coupling section with the highest transmissivity is taken as the optimal coupling section.
(4) And determining an optimal coupling optimization area structure. According to the characteristic that the coupling efficiency in the coupling of the waveguide and the topological photonic crystal plate depends on a transverse spin matching mechanism, the structure of the coupling optimization region is randomly changed by utilizing an optimization algorithm, the transverse spin distribution of the coupling surface is changed, the matching degree of the transverse spin distribution of the coupling surface and the transverse spin distribution of a topological transmission mode is higher, and the optimal coupling efficiency is obtained. When the coupling efficiency did not further increase after 5 generations, the structure was considered as the optimal coupling optimized region structure.
In the present invention, the input waveguide and the output waveguide have widths of W d The thicknesses are all h =220nm.
In the invention, the size of the coupling optimization area is L multiplied by W d The size of each square grid is S multiplied by S, L is the length of the optimized area and is an integral multiple of S; w d Is the optimized region width and is an integral multiple of S.
According to the invention, the topological photonic crystal plate is formed by splicing two valley photonic crystals, when the diameter of a dielectric column in a VPC primitive cell is changed, the space inversion symmetry is destroyed, a Dirac point in an energy band is opened, and topological phase change is realized. When the diameter difference delta d of the VPC original cell air holes is greater than 0 and delta d is less than 0, the topological numbers of the two VPCs are opposite to each other (+ -1) and are marked as VPC1 and VPC2. A topological transmission mode can be formed at the interface of the two structures.
In the invention, the valley photonic crystal VPC is a two-dimensional orthorhombic system restored cell structure formed by etching air holes on a silicon substrate, the lattice constant is a, two circular air holes with the diameters of d are contained in an original cell 1 And d 2 And the thickness h of the photonic crystal plate. The whole air holes are arranged in a graphene structure.
In the invention, the two air holes of the two valley photonic crystals VPC1 and VPC2 are opposite in diameter.
In the invention, the input waveguide, the output waveguide and the topological photonic crystal plate are all made of silicon materials.
In the invention, the transverse spin matching is the matching degree of the transverse spin distribution of the coupling surface of the input waveguide and the topological photonic crystal slab and the transverse spin distribution of the topological transmission mode, and the coupling efficiency beta is defined as:
wherein the content of the first and second substances,
and
the transverse spin angular momentum of the waveguide and the topological photonic crystal on the coupling surface and the topological transmission mode respectively; e W (y, z) and E TPC (y, z) are waveguide and topological photonic crystal respectivelyElectric field distribution on the coupling surface and in the topological transmission mode.
In the invention, the transverse spin matching mechanism can be suitable for the high-efficiency coupling of other types of topological photonic crystal plates, including the topological photonic crystal plates based on the quantum spin Hall effect and the quantum valley Hall effect.
In the invention, the waveguide and topological photonic crystal high-efficiency coupling structure based on the transverse spin matching mechanism can work in any wavelength and frequency range through the change of the structure size.
Example (b):
the waveguide-topological photonic crystal efficient coupling structure based on the transverse spin matching mechanism provided by the embodiment comprises an input waveguide, a topological photonic crystal plate and an output waveguide, wherein: the input waveguide is divided into a strip waveguide and a coupling optimization region, and the topological photonic crystal plate is formed by splicing a valley photonic crystal 1 (VPC 1) and a valley photonic crystal 2 (VPC).
Specifically, the coupling optimization area is divided into square grids with the side length of 50nm × 50nm, and silicon and air are selected as filling materials, as shown in fig. 2. The VPC1 and the VPC2 are both silicon-based dielectric plates with the diameters of d 1 And d 2 The difference between the two air holes is that the diameters of the two air holes in the original cells are reversed, as shown in fig. 3. Taking VPC1 as an example, the structural parameters are: a =385nm, d 1 ＝195nm， d 2 ＝95nm。
And calculating the coupling electric field diagram and the coupling efficiency of the waveguide and the topological photonic crystal plate by using a finite element simulation method. Incident light is input in 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 coupling optimization area is completely filled with silicon material, the wavelength of incident light is 1433nm, and the widths W of the input waveguide and the output waveguide d =0.8 μm. The structure can be divided into three regions, wherein the I region and the III region are an input waveguide structure and an output waveguide structure, the II region is a topological photonic crystal plate, and therefore two different coupling planes I-II and II-III are formed, and the structure is shown in figure 4. For the first coupling planeFacets (I-II) which reflect incident light back into the input waveguide and interfere with the incident light (R) 1 36%) and partial light scattering (T) sca 0.19) with only a partial coupling into the topological photonic crystal waveguide (coupling efficiency β) Ⅰ-Ⅱ 44.7%). For the second coupling plane (II-III), almost all light is coupled from the topological photonic crystal waveguide into the output waveguide (coupling efficiency beta) Ⅱ-Ⅲ 97.3%). Therefore, optical coupling (coupling surfaces i-ii) from an input waveguide to a topological photonic crystal waveguide is the first problem to be solved.
In order to solve the existing problems, the invention provides a novel waveguide-topological photonic crystal efficient coupling mechanism-transverse spin matching mechanism. The present invention, similar to the pattern matching technique, defines the coupling efficiency β as:
as shown in FIG. 5 (a), wherein
And
respectively the transverse spin angular momentum distribution on the coupling surface of the waveguide and the topological photonic crystal and the transverse spin angular momentum distribution of the topological transmission mode, wherein the transverse spin angular momentum is defined as S z ∝(Re(E x )Im(E y )-Im(E x )Re(E y ))/E 2 In which E x And E y The x-and y-components of the transmission plane electric field, respectively, and E is the electric field.
The accuracy of the coupling mechanism between the lateral spin matching based topological photonic crystal waveguide and the waveguide is verified below. Two of the key parameters are the input waveguide width (W) d ) And different coupling facets (type a and type B) of the topological photonic crystal structure, as shown in fig. 5 (a). With W d An A-type coupling structure of 0.8 μm is exemplified as shown in FIG. 5 (b). When y is center When = -0.17. Mu.m, S w And S TPC Partially matched, the transmission was lower (T = 27.7%). In contrast, when y center When =0.21 μm, the transmittance is improved to a higher level (T = 44.7%) due to the improvement of the lateral spin matching.
The coupling characteristics based on the transverse spin matching mechanism can be extended to have different coupling facets and different W d The coupling structure of (1) (FIG. 6 (a)). Here, light is guided from an input waveguide into the topological photonic crystal slab, input waveguide y center The change occurs and the transmittance of the output waveguide is measured. In fig. 6 (c) and 6 (d), the effect of these parameters on coupling efficiency was investigated. The results show that the numerically calculated transmittance is in good agreement with the coupling efficiency with only minor deviations. This is because the light is scattered during coupling of the waveguide to the topological photonic crystal waveguide, and small deviations can be expected. Coupling efficiency is influenced by W d Has a small influence with W d The position of the maximum of the coupling efficiency is only slightly shifted. The maximum transmission obtained was 52.8% (type B, W) d ＝1μm，y center = 0.11 μm), still at a lower level. How to realize perfect coupling of topological transmission modes by utilizing a transverse spin matching mechanism is the primary objective of the next research.
To achieve higher coupling efficiency, the input waveguide needs to be reshaped to achieve lateral spin redistribution in the coupling plane. In recent years, the design of intelligent photonic devices using mathematical optimization algorithms has been extensively studied. Among them, genetic algorithm is a good global optimization method, and is drawing attention in the design of various nanophotonic devices. Therefore, a genetic algorithm is employed to design the coupling optimization region of the input waveguide. As shown in fig. 6 (a), the coupling optimization area is discretized into 20 tabs12 square arrays with side length of 50nm and optimized area of 1 × 0.6 μm 2 . First, 200 populations were randomly generated as first generation populations, and then the first generation populations were evaluated. In the evaluation, the transmittance of the output waveguide was calculated by numerical simulation, and the transmittance was taken as an optimization coefficient (FOM). Meanwhile, by recording the transverse spin distribution on the coupling plane, the corresponding coupling efficiency is calculated and compared with the transmittance. Suitable populations are then selected as parents, and progeny are generated by genetic crossing and genetic mutation to recombine the parents. After a number of cycles until the target is reached, the cycle ends, stopping with the requirement that the FOM is not further lifted after 5 generations.
To obtain higher coupling efficiency, the optimal transmittance in FIG. 5 (d) is selected for optimization, corresponding to the parameters B, W d ＝1.0μm，y center = 0.11 μm. Fig. 6 (b) is the optimized result of transmittance when the number of iterations (N) increases, where N =0 corresponds to the unoptimized structure. It was found that the transmittance increased rapidly initially, then gradually leveled off, and finally remained constant at N = 15. The transmission after optimization increased from 52.8% (N = 0) to 95.1% (N = 15), the highest level reported so far. Meanwhile, the optimal structure can keep the perfect coupling (T is more than or equal to 90 percent) of the topological transmission mode in a wider bandwidth (1427-1441 nm), as shown in FIG. 6 (b).
In order to verify the accuracy of the lateral spin matching mechanism in the optimization process, the coupling efficiency of each generation of optimized structures was calculated and compared with the transmittance. The result shows that the optimized transmittance and the coupling efficiency accord well, particularly when the transmittance is high (N is more than or equal to 4), and when the transmittance is low (N is less than 4), the calculated coupling efficiency is slightly less than the transmittance because the incident light has stronger scattering on the coupling plane and the scattered light is coupled with the topological photonic crystal waveguide. Further, the lower the transmittance, the stronger the scattering, resulting in a large deviation of the two results, whereas in the case of high transmittance, the two results almost completely agree.
The properties of the lateral spin matching mechanism were analyzed, taking as an example an unoptimized structure (N = 0) and an optimized structure (N = 15). According to a transverse spin matching mechanism, canKnowing the coupling efficiency as S W And S TPC And (6) determining. FIG. 6 (c) is S of coupling plane corresponding to transmission mode of topology TPC And (4) distribution. For non-optimized structures, coupling the S of the planes W Distribution (FIG. 6 (d) 1 ) And S) TPC There is a large difference in the distribution, resulting in a lower coupling efficiency, and more light is reflected back into the input waveguide and generates interference fringes (fig. 6 (d)) 2 )). In contrast, for an optimal structure, the S of the coupling plane W Distribution (FIG. 6 (e) 1 ) And S) TPC The distribution is perfectly matched, where there is extremely high coupling efficiency of the waveguide to the topological photonic crystal structure (FIG. 6 (e)) 1 ))。
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. The proposed lateral spin matching mechanism means that the topological transmission modes can achieve perfect coupling (transmission close to 1). The coupling optimization area is optimized by introducing a genetic algorithm, the coupling efficiency is controlled by controlling transverse spin matching, and the highest transmittance can reach 95.1%. Although this new coupling mechanism is shown only in a quantum valley hall effect based topological photonic crystal structure, it is applicable to a wider range of topological photonic crystal structures. The perfect coupling of the waveguide and the topological photonic crystal waveguide, which is reported by the invention, combines the advantages of unidirectional transmission and immunodeficiency, so that the waveguide becomes an ideal platform for realizing an integrated optical chip and can be applied to next-generation optical communication systems.
Claims (10)
1. A waveguide-topological photonic crystal coupling structure based on a transverse spin matching mechanism is characterized by comprising an input waveguide, a topological photonic crystal plate and an output waveguide, wherein incident light is input along the + x direction and is coupled into the topological photonic crystal plate through the input waveguide, then is coupled into the output waveguide from the topological photonic crystal plate, the input waveguide is composed of a strip waveguide and a coupling optimization region, the coupling optimization region is divided into square grids, each grid is filled with two materials, namely air and silicon, 1 represents a filled silicon material, 0 represents filled air, the whole coupling optimization region is represented by a matrix of 0 and 1, the coupling optimization region is optimized through a genetic optimization algorithm, the matrixes of 0 and 1 are randomly obtained to obtain corresponding output waveguide transmissivity and input waveguide transverse spin matching distribution, and the optimal coupling optimization region is obtained through multiple iterations to realize waveguide-topological photonic crystal efficient coupling.
2. The waveguide-topology photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1, wherein the genetic optimization algorithm optimizes the coupling optimization region by the following specific steps:
firstly, randomly generating 200 populations as a first generation population, then evaluating the first generation population, calculating the transmissivity of an output waveguide through numerical simulation in the evaluation process, taking the transmissivity as an optimization coefficient FOM, and meanwhile, calculating corresponding coupling efficiency through recording transverse spin distribution on a coupling plane and comparing the corresponding coupling efficiency with the transmissivity; then selecting a proper population as a parent, recombining the parent through genetic hybridization and gene mutation to generate a filial generation, and repeating for multiple times until the target is reached, wherein the circulation is ended, and the requirement that the FOM is not further promoted after 5 generations is met.
3. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism of claim 1, wherein the topological photonic crystal slab is formed by splicing two valley photonic crystals VPCs with different topological indices, the topological indices of the two VPCs are opposite to each other and are denoted as VPC1 and VPC2, and a unidirectional topological transmission mode is formed at the splicing boundary.
4. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1 or 3, wherein the topological photonic crystal plate is a silicon-based energy valley topological photonic crystal structure based on the valley quantum Hall effect.
5. Waveguide-topology photonic crystal based on transverse spin matching mechanism according to claim 3The bulk coupling structure is characterized in that the valley photonic crystal VPC is a two-dimensional orthorhombic system primitive cell structure formed by etching air holes on a silicon substrate, the lattice constant is a, the primitive cell comprises two circular air holes with the diameters of d 1 And d 2 And the thickness h of the photonic crystal plate and the whole air hole are arranged in a graphene structure.
6. The waveguide-topology photonic crystal coupling structure based on the transverse spin matching mechanism of claim 5, wherein the two air holes of VPC1 and VPC2 are opposite in diameter.
7. The waveguide-topology photonic crystal coupling structure based on the transverse spin matching mechanism of claim 1, wherein the output waveguide is a slab waveguide.
8. The waveguide-topological photonic crystal coupling structure based on the transverse spin matching mechanism according to claim 1, wherein the input waveguide, the output waveguide and the topological photonic crystal plate are all made of silicon material.
9. A method for designing a waveguide-topology photonic crystal coupling structure based on a transverse spin matching mechanism according to any one of claims 1 to 8, the method comprising the steps of:
(1) Determining the optimum offset y of the center center : when the input waveguide is coupled with the topological photonic crystal plate, the optimization is carried out in the y direction of the topological photonic crystal plate by changing the relative position y of the center of the input waveguide and the center of the topological photonic crystal plate in the y direction center While monitoring the transmittance at the output waveguide end, and taking the y of the highest transmittance center As the best matching position;
(2) Input waveguide width W in determining optimal lateral spin matching d : monitoring the transmissivity at the output waveguide end by changing the width of the coupling waveguide, and taking the W with the highest transmissivity d As an optimal waveguide width;
(3) Determining an optimal coupling tangent plane of the input waveguide and the topological photonic crystal: the topological photonic crystal plates are periodically arranged in the x direction, the input waveguide is coupled with the topological photonic crystal plates to form a plurality of sections, the coupling efficiency of the output waveguide is monitored by coupling the input waveguide with the topological photonic crystal plates with different coupling sections, and the coupling section with the highest transmissivity is taken as the optimal coupling section;
(4) Determining an optimal coupling optimization area structure: according to the characteristic that the coupling efficiency in the coupling of the input waveguide and the topological photonic crystal plate depends on a transverse spin matching mechanism, the structure of a coupling optimization region is randomly changed by utilizing a genetic optimization algorithm, the transverse spin distribution of a coupling surface is changed, the transverse spin distribution matching degree of the coupling surface and the transverse spin distribution of a topological transmission mode is higher, and the optimal coupling efficiency is obtained.
10. The design method of waveguide-topology photonic crystal coupling structure based on transverse spin matching mechanism according to claim 9, characterized in that the coupling efficiency β is defined as:
wherein the content of the first and second substances,
and
transverse spin angular momentum, E, of the waveguide and the topological photonic crystal coupling plane and the topological transmission mode, respectively W (y, z) and E TPC (y, z) are respectively on the coupling surfaces of the waveguide and the topological photonic crystalAnd electric field distribution of topological transmission mode.
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