Large-width waveguide wavelength division multiplexer beam splitter based on triangular lattice topology photonic crystal

Abstract

The application provides a large-width waveguide wavelength division multiplexing beam splitter based on a triangular lattice topology photonic crystal, and aims to solve the technical problems of a waveguide beam splitter structure of a honeycomb topology valley photonic crystal, which is complex and has a narrow bandwidth. The application comprises a trivial topology photonic crystal and a non-trivial topology photonic crystal, a region formed by the trivial topology photonic crystal is a trivial region, a region formed by the non-trivial topology photonic crystal is a non-trivial region, the trivial region is provided with the non-trivial region, and the non-trivial region is provided with a waveguide excitation light source. The application takes the middle layer of the non-trivial topology photonic crystal as a tunable "limited width", different working energy band distributions are obtained by changing the lattice layer number of the middle layer, and a large working bandwidth, a large-width waveguide and a wavelength division multiplexing beam splitter are successfully realized. The application can be used for the design and research and development of miniaturized, intelligentized, multifunctional and integrated optical quantum devices.

Description

Technical Field

[0001] This invention relates to the technical fields of topological photonics, waveguide optics and integrated photonic devices, integrated optical path design, etc., and in particular to a wide-width wavelength division multiplexing beamsplitter based on triangular lattice topological photonic crystals. Background Technology

[0002] With the rapid development of the Hall effect in condensed matter physics, scientists have extended it to the quantum realm of light. The discovery of the quantum Hall effect is one of the most significant achievements in the field of quantum light. The quantum Hall effect photonic state is actually a topologically ordered state; its interior does not guide light, but its surface can support special surface waves. These surface waves, due to their intrinsic topological properties, possess strong robustness and can bypass disordered obstacles without reflection. The superior transmission characteristics of the quantum Hall effect photonic ordered state hold promise for providing a new platform for highly integrated chip communication technology.

[0003] Therefore, scientists in related fields are striving to develop ordered photonic states of the quantum Hall effect from different dimensions, structures, and materials. These mainly include unidirectional boundary states of the quantum integer Hall effect based on the magneto-optical effect, unidirectional spiral boundary states of the quantum spin Hall effect protected by time-reversal symmetry, and unidirectional twisted boundary states of the quantum valley Hall effect based on spatial inversion symmetry breaking. Among these, the generation and development of the quantum spin Hall effect has attracted particular attention. Because all-dielectric topological photonic crystals are simple to fabricate and easy to manipulate, waveguide photonic devices based on topological photonic crystals are finding wider applications in topological photonics, nonlinear photonics, and integrated photonic optical circuits.

[0004] In 2015, Professor Hu Xiao and colleagues at the University of Tsukuba proposed constructing a topological photonic crystal using all-dielectric silicon material, realizing a unidirectional spiral boundary state based on the quantum spin Hall effect (Scheme for Achieving a Topological Photonic Crystal by Using Dielectric Material). Subsequently, many scholars abroad have also proposed similar structures, realizing unidirectional spiral boundary states in topological photonic crystals. For example, in 2016, American scholars Sabyasachi Barik et al. constructed unidirectional spiral boundary states in photonic crystals using all-dielectric triangular prism-shaped topological photonic crystals (Two-dimensionally confined topological edge states in photonic crystals). In 2018, American scholars Mikhail I Shalaev et al. proposed reconfigurable topological photonic crystals by changing the refractive index. These are all constructed using honeycomb photonic crystals of all-dielectric material. Although they can realize this unidirectional spiral boundary state, the actual processing and application are quite complex, such as containing 6 dielectric pillars in each lattice.

[0005] In China, within a year of Professor Hu Xiao's proposal of topological photonic crystal structures, in 2016, Professor Jiang Jianhua of Soochow University proposed a triangular crystalline toroidal topological photonic crystal that could realize unidirectional helical boundary states based on the quantum spin Hall effect (Accidental degeneracy in photonic bands and topological phase transitions in two-dimensional core-shell dielectric photonic crystals). Triangular lattice topological photonic crystals have only one hollow dielectric pillar in each lattice, making them simple in structure and easy to fabricate, thus attracting considerable attention. In 2018, Professor Jiang Jianhua and others verified the "Hu Xiao model" (Visualization of a Unidirectional Electromagnetic Waveguide Using Topological Photonic Crystals Made of Dielectric Materials) in the laboratory. This experiment also demonstrated that unidirectional helical boundary states based on the quantum spin Hall effect can be verified and obtained under laboratory conditions. Topological photonic crystals based on the "Hu Xiao model" have been constructed and proposed by scholars in many related fields with different structures, materials, and methods, which has also promoted the rapid development of topological photonics, quantum optical devices, and communications.

[0006] In 2022, Professor Hang Zhihong of Soochow University constructed a "finite-width" sandwich structure based on an all-dielectric honeycomb topological photonic crystal, realizing a tunable optical switch (Observation and control of pseudospin switching in a finite-width topological photonic crystal). He proposed that the "finite width" of the topological photonic crystal can serve as a degree of freedom for light manipulation, providing a theoretical basis for the research of micro / nano quantum optical devices and photonic waveguide transmission. While honeycomb lattices are complex, triangular lattices are simpler and more conducive to fabrication. "Finite width" is a concept and method for tunable optical waveguides. This invention combines honeycomb lattices and "finite width" to achieve shifting of the photonic operating bandwidth, based on which a wavelength division multiplexing waveguide structure is constructed. Furthermore, Professor Hang's article uses a trivial topological structure as the intermediate layer of the "finite width," enabling electromagnetic wave coherence.

[0007] Based on the above research, this invention proposes to construct a sandwich structure using an all-dielectric triangular lattice toroidal topological photonic crystal. By changing the "finite width" of the middle layer of the nontrivial topological photonic crystal, a wavelength division multiplexing beamsplitter for a wide-width waveguide can be realized. Summary of the Invention

[0008] To address the technical challenges of complex structures and narrow bandwidth in waveguide beamsplitters constructed from honeycomb topological valley photonic crystals, this invention proposes a wide-width waveguide wavelength division multiplexing beamsplitter based on triangular lattice topological photonic crystals. Compared to other waveguide beamsplitters, it offers advantages such as simple structure, low R&D cost, wide-width waveguide, large operating bandwidth, and wavelength division multiplexing capability. This significantly improves the transmission characteristics of waveguide photonic devices and promotes their development towards miniaturization, intelligence, multifunctionality, and integration.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: a wide-width waveguide wavelength division multiplexing beamsplitter based on a triangular lattice topological photonic crystal includes a trivial topological photonic crystal and a non-trivial topological photonic crystal. The region composed of the trivial topological photonic crystal is a trivial region, and the region constructed by the non-trivial topological photonic crystal is a non-trivial region. A non-trivial region is provided within the trivial region, and a waveguide-excited light source is provided within the non-trivial region.

[0010] Preferably, the non-trivial region includes a first non-trivial region, a second non-trivial region, and a third non-trivial region, which are interconnected; the first non-trivial region is constructed from a single layer of continuously arranged non-trivial topological photonic crystals, the second non-trivial region is constructed from two layers of continuously arranged non-trivial topological photonic crystals, and the third non-trivial region is constructed from three layers of continuously arranged non-trivial topological photonic crystals; a light source is provided within the third non-trivial region.

[0011] Preferably, the non-trivial region has a Y-shaped structure, the third non-trivial region is horizontally arranged, one end of the third non-trivial region is provided with a light source, and the other end is connected to the first non-trivial region and the second non-trivial region respectively.

[0012] Preferably, the third non-trivial region is set horizontally, and the first and second non-trivial regions extend towards the boundary, respectively.

[0013] Preferably, the light source is a chiral polarization source; the chiral polarization source consists of 4 antennas perpendicular to the z-axis, with linear polarization sources added to the antennas, and the phases of adjacent linear polarization sources are distributed in increments or decreases of π / 2.

[0014] Preferably, the chiral polarization source is chiral circularly polarized, and the antennas are arranged in a square with a side length of 0.2a, where a is the lattice constant of the triangular lattice.

[0015] Preferably, both the trivial topological photonic crystal and the non-trivial topological photonic crystal are triangular lattice ring-shaped topological photonic crystals, and both are composed of all-dielectric silicon ring pillars with a relative permittivity of 11.7 and an air background.

[0016] Preferably, the lattice unit of the trivial topological photonic crystal has an outer radius r1 = 0.4a and an inner radius r2 = 0.26a; the lattice unit of the non-trivial topological photonic crystal has an outer radius r1 = 0.45a and an inner radius r2 = 0.35a; wherein the lattice constant a has a value of 1µm.

[0017] Preferably, in the photonic band distribution of the first Brillouin zone, the pseudospin photonic states p and d are separated, then undergo double degeneracy of the Dirac cone, and finally band separation; the pseudospin photonic states p and d achieve mode inversion.

[0018] Preferably, in the projection photonic bulk-side bandgap diagram of the sandwich structure containing the first nontrivial region, the second nontrivial region, and the third nontrivial region, two boundary mode dispersion curves appear in the photonic bulk bandgap. By changing the number of layers of the nontrivial topological photonic crystal lattice in the middle layer of the sandwich structure, the working bandwidth waveguide of the unidirectional boundary mode is continuously increased until the region of the total internal reflection bandwidth of the boundary mode disappears.

[0019] Electromagnetic waves in the sandwich structure are mainly concentrated in the middle nontrivial region of the sandwich structure, and the transmission mode is uniformly distributed over a wide area in the nontrivial region. When the middle layer is a sandwich structure with the first nontrivial region, the second nontrivial region, and the third nontrivial region, the waveguide widths are a, 2a, and 3a lattice constants, respectively, and the energy is uniformly distributed at 95%, 75%, and 75% respectively.

[0020] The distribution of band dispersion curves along the first Brillouin Kx direction in the sandwich structure containing the first, second, and third nontrivial regions shows that different structural layer waveguides can be excited at different frequencies; if the frequency f A The band dispersion curve intersects the band dispersion curve of the sandwich structure containing the first, second, and third nontrivial regions, with frequency f. A The light source produces unidirectional wideband waveguides in different lattice layers of three nontrivial regions; if the frequency f B The band dispersion curve intersects the sandwich structure containing the second and third nontrivial regions, with frequency f. B The light source generates a unidirectional wide-width waveguide in a sandwich structure composed of two or three layers of nontrivial topological photonic crystals, and is a cutoff in a sandwich structure composed of a single layer of nontrivial topological photonic crystals; if the frequency f CThe band dispersion curve intersects the sandwich structure containing the third nontrivial region at frequency f. C The excitation source generates a unidirectional wide-width waveguide only in three nontrivial topological layers, and is a cutoff in sandwich structures composed of one or two nontrivial topological photonic crystals; such as the frequency f D The band dispersion curve intersects the band dispersion curve of the sandwich structure containing the first and third nontrivial regions, with frequency f. D The light source generates a unidirectional wide-width waveguide in a sandwich structure composed of one or three layers of nontrivial topological photonic crystals, and is a cutoff in a sandwich structure composed of two layers of nontrivial topological photonic crystals.

[0021] Compared with existing technologies, the beneficial effects of this invention are as follows: using a nontrivial topological photonic crystal as the intermediate layer, a wide-width, high-capacity waveguide can be obtained. Furthermore, changing the "finite width of the nontrivial layer" allows for the shifting of the operating band, thereby achieving wavelength division multiplexing (WDM). This invention is based on constructing a sandwich structure using an all-dielectric toroidal triangular lattice topological photonic crystal. By changing the thickness of the toroidal wall, photonic band separation and mode inversion are achieved, thus realizing the formation of unidirectional helical boundary states at different topological interface structures. In addition, this invention uses the nontrivial topological photonic crystal intermediate layer as a tunable "finite width," and by changing the lattice width of the intermediate layer, different operating band distributions are successfully achieved. Finally, a large-bandwidth, wide-width waveguide with WDM capability is realized. This invention can be used for the design and development of miniaturized, intelligent, multifunctional, and integrated optical quantum devices. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0024] Figure 2This diagram shows the triangular lattice toroidal topological photonic crystal and its corresponding photonic band distribution in this invention. (a) is a schematic diagram of the triangular lattice topological photonic crystal structure; (b) is a trivial topological photonic crystal lattice unit; (c) is the most primitive trivial topological photonic crystal lattice unit; (d) is a non-trivial topological photonic crystal lattice unit; and (e) corresponds sequentially to the distribution of the photonic bandgap in the first Brillouin zone and the distribution of the photonic eigenmode fields of the pseudospin p-state and d-state of the topological photonic crystal lattice units (b)-(d).

[0025] Figure 3 This is a schematic diagram of a sandwich structure of a triangular lattice topological photonic crystal. In the diagram, (a) shows the sandwich structure, where L1, L2, and L3 represent one, two, and three layers of nontrivial topological photonic crystal in the middle layer, respectively; (b) shows the projected photonic volume-side band diagrams calculated based on the supercells of the three structures; (c) shows the electric field (Ez) energy distribution in the three topological sandwich structures; and (d) shows the normalized electric field amplitude distribution along the y-axis in the three topological sandwich structures.

[0026] Figure 4 The following is a simulation example diagram of the present invention. Among them, (a) is the projected band dispersion curve along the Kx direction in the present invention; (be) are the waveguide transmission modes at different frequencies A, B, C, and D, respectively.

[0027] In the figure, 1 is a trivial topological photonic crystal, 2 is a non-trivial topological photonic crystal, 3 is a trivial region, 4 is a non-trivial region, 5 is the first non-trivial region, 6 is the second non-trivial region, 7 is the third non-trivial region, 8 is a chiral polarization source, 9 is the antenna for constructing the chiral polarization source, and 10 is an enlarged schematic diagram of the chiral polarization source. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1As shown, a wavelength division multiplexing beamsplitter based on a triangular lattice topological photonic crystal includes a trivial topological photonic crystal 1 and a nontrivial topological photonic crystal 2. The region formed by the trivial topological photonic crystal 1 is the trivial region 3, and the region constructed by the nontrivial topological photonic crystal 2 is the nontrivial region 4. The nontrivial region 4 includes a first nontrivial region 5, a second nontrivial region 6, and a third nontrivial region 7. The intermediate layer is constructed by one layer of nontrivial topological photonic crystal 2, forming the first nontrivial region 5; the intermediate layer is constructed by two layers of nontrivial topological photonic crystal 2, forming the second nontrivial region 6; and the intermediate layer is constructed by three layers of nontrivial topological photonic crystal 2, forming the third nontrivial region 7. The waveguide-excited light source is a chiral polarization source 8, which is located within the third nontrivial region 7. Figure 10 shows an enlarged schematic diagram of the chiral polarization source 8. The chiral polarization source includes four antennas 9 perpendicular to the z-axis. Linear polarization sources are added to the antennas 9, and the phases of adjacent linear polarization sources are distributed in an increasing or decreasing order of π / 2, thus realizing a chiral polarization light source. The antennas 9 are arranged in a square, with a side length of 0.2a, where a is the lattice constant of the triangular lattice. The antennas 9 are perfectly symmetrical, and this chiral polarization source is chiral circularly polarized.

[0030] like Figure 2 As shown, (a) is a triangular lattice toroidal topological photonic crystal with a lattice constant of a, which has a value of 1 μm. (a) The lattice vector direction of the triangular lattice. Triangular lattice topological photonic crystals 1 and 2 are composed of all-dielectric silicon toroidal pillars with a relative permittivity of 11.7. The background is air, and c is the speed of light in vacuum. (b) is the lattice unit of the trivium topological photonic crystal 1, with an outer radius r1 = 0.4a and an inner radius r2 = 0.26a. (c) is the lattice unit of the most primitive trivium photonic crystal, with an outer radius r1 = 0.45a and an inner radius r2 = 0.2656a. (d) is the lattice unit of the non-trivium topological photonic crystal 2, with an outer radius r1 = 0.45a and an inner radius r2 = 0.35a. This radii setting achieves the separation of pseudospin photonic states and mode inversion. Figure (e) shows the photonic band distributions in the first Brillouin zone of the three triangular lattice topological photonic crystals mentioned above. It can be observed that the pseudospin photonic p-state and d-state transition from separation to double degeneracy of the Dirac cone, and then to band separation. More importantly, the pseudospin photonic p-state and d-state achieve mode inversion, as can be seen from the intrinsic mode distribution of the electric fields in the pseudospin photonic p-state and d-state.

[0031] like Figure 3As shown, (a) is a schematic diagram of a triangular lattice topological photonic crystal sandwich structure, where L1, L2, and L3 represent one, two, and three layers of nontrivial topological photonic crystals in the middle, and the two sides are composed of trivial topological photonic crystals. (b) are the projected photonic bulk-edge band diagrams calculated based on the three structures, respectively. Two dispersion curves for boundary modes appear in the photonic bulk bandgap, where the light gray rectangular area represents the unidirectional boundary mode bandwidth, and the dark gray rectangular area represents the boundary mode total internal reflection bandwidth, which does not support unidirectional transmission. Therefore, it can be seen that by changing the number of lattice layers of the nontrivial topological photonic crystal in the middle layer of the sandwich structure, the unidirectional boundary mode working bandwidth continuously increases until the dark gray rectangular area disappears. This is sufficient to demonstrate that the design in this invention results in a continuous increase and a certain shift in the working bandwidth of the unidirectional boundary mode waveguide.

[0032] (c) shows the electric field (Ez) energy distribution in the three sandwich structures, with the white circular arrows indicating the palm-biased source direction. Observation reveals that the electromagnetic waves are mainly concentrated in the middle nontrivial layer of the sandwich structure, rather than at the boundary between the topologically trivial and nontrivial structures. This indicates that the waveguide of this invention is not a traditional unidirectional spiral boundary mode, but rather a transmission mode with a large, uniformly distributed energy distribution in the nontrivial layer. (d) shows the normalized electric field amplitude distribution along the y-axis in the three topological sandwich structures. As shown by the dashed line in (c), quantitative measurements of the normalized electric field distribution along the y-axis in different sandwich structures reveal that the electric field energy is mainly concentrated in the nontrivial topological photon layer. When the middle layer is one, two, or three layers of nontrivial topological photons, the waveguide width is approximately one lattice constant a, 2a, and 3a, respectively, and the energy is uniformly distributed, approximately 95%, 75%, and 75%, respectively. Therefore, this invention can obtain a unidirectional transmission waveguide with a large waveguide width and uniform amplitude distribution.

[0033] like Figure 4 As shown, (a) the band dispersion curves of the three sandwich structures along the first Brillouin Kx direction are displayed. This figure is a representation of... Figure 3 (a) shows the integration of band dispersion curves calculated from the three sandwich structures. The distribution of the three band dispersion curves indicates that waveguides with different structural layers can be excited at different frequencies. In the structure of this invention, optical waveguide beam splitting is achieved by excitation with light sources of different frequencies (A, B, C, D). For example, at frequency f... A Intersecting at L1, L2, L3, indicating that at frequency f A The excitation source produces unidirectional wideband waveguides in three different lattice layers; such as frequency f B Intersecting at L2 and L3, this indicates that at frequency f B The excitation source generates a unidirectional wideband waveguide in two or three layers of nontrivial topology, and is cut off in a single layer of nontrivial topology. For example, at frequency f... CIntersecting at L3 indicates that at frequency f C The excitation source generates a unidirectional wide-width waveguide only in three nontrivial topology layers, and is cut off in one or two nontrivial topology layers. For example, at frequency f... D Intersecting at L1 and L3, this indicates that at frequency f D The excitation source generates a unidirectional wide-width waveguide in one or three nontrivial topology layers, and is cut off in two nontrivial topology layers.

[0034] (b) The electric field energy distribution in this invention, wherein the frequency of the excitation source is f. A Observations revealed that the waveguide transmission was consistent with the theoretical result in (a). (c) The electric field energy distribution in this invention, wherein the frequency of the excitation source is f. B Observations revealed that the waveguide transmission was consistent with the theoretical result in (a). (d) The electric field energy distribution in this invention, wherein the frequency of the excitation source is f. C Observations revealed that the waveguide transmission was consistent with the theoretical result in (a). (e) Electric field energy distribution in this invention, wherein the frequency of the excitation source is f. D Observations revealed that the waveguide transmission was consistent with the theoretical results in (a). Therefore, this invention realizes a waveguide beamsplitter with a wide-width waveguide, a large operating bandwidth, and wavelength division multiplexing capability.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A photonic crystal large-width waveguide wavelength division multiplexing beam splitter based on a triangular lattice topology photonic crystal, characterized in that, It includes a trivial topological photonic crystal (1) and a non-trivial topological photonic crystal (2). The region formed by the trivial topological photonic crystal (1) is a trivial region (3), and the region constructed by the non-trivial topological photonic crystal (2) is a non-trivial region (4). The trivial region (3) contains the non-trivial region (4), and the non-trivial region (4) contains a waveguide-excited light source. The non-trivial region (4) includes a first non-trivial region (5), a second non-trivial region (6), and a third non-trivial region (7), which are connected. The first non-trivial region (5) is constructed from a single layer of non-trivial topological photonic crystal (2), the second non-trivial region (6) is constructed from two layers of non-trivial topological photonic crystal (2), and the third non-trivial region (7) is constructed from three layers of non-trivial topological photonic crystal (2). A light source is provided in the third non-trivial region (7).

2. The photonic crystal large-width waveguide wavelength division multiplexer splitter based on the triangular lattice topology photonic crystal according to claim 1, characterized in that, The third non-trivial region (7) is set horizontally, with a light source at one end and the other end connected to the first non-trivial region (5) and the second non-trivial region (6).

3. The photonic crystal large-width waveguide wavelength division multiplexer splitter based on the triangular lattice topology photonic crystal of claim 2, characterized in that, The third non-trivial region (7) is set horizontally, and the first non-trivial region (5) and the second non-trivial region (6) extend toward the boundary respectively.

4. The wide-width waveguide wavelength division multiplexing beamsplitter based on triangular lattice topological photonic crystal according to any one of claims 1-3, characterized in that, The light source is a chiral polarization source (8); the chiral polarization source (8) consists of four antennas (9) perpendicular to the z-axis, and linear polarization sources are added to the antennas (9). The phases of adjacent linear polarization sources are equal. Increasing or decreasing distribution.

5. The photonic crystal large-width waveguide wavelength division multiplexer splitter based on the triangular lattice topology photonic crystal of claim 4, characterized in that, The chiral polarization source (8) is chiral circularly polarized, and the antennas (9) are arranged in a square, with the side length of the square being... ,in, It is the lattice constant of a triangular lattice.

6. The wide-width waveguide wavelength division multiplexing beamsplitter based on triangular lattice topological photonic crystal according to claim 5, characterized in that, The trivial topological photonic crystal (1) and the non-trivial topological photonic crystal (2) are both triangular lattice ring-shaped topological photonic crystals. Both the trivial topological photonic crystal (1) and the non-trivial topological photonic crystal (2) are composed of all-dielectric silicon ring pillars. The relative permittivity of the all-dielectric silicon ring pillars is 11.7, and the background is air.

7. The photonic crystal large-width waveguide wavelength division multiplexer splitter based on the triangular lattice topology photonic crystal of claim 6, wherein, The lattice unit of the trivial topological photonic crystal (1) has an outer radius r1 = 0.4a and an inner radius r2 = 0.26a; the lattice unit of the nontrivial topological photonic crystal (2) has an outer radius r1 = 0.45a and an inner radius r2 = 0.35a; wherein the lattice constant is... The value is 1µm.

8. The photonic crystal large-width wavelength division multiplexer beam splitter based on the triangular lattice topology of claim 7, wherein, In the photonic band structure of the first Brillouin zone, pseudospin photonic states p and d separate into a double degeneracy of the Dirac cone, and then reopen the Dirac cone; the pseudospin photonic states p and d achieve mode inversion.

9. The large-width photonic crystal wavelength division multiplexer beam splitter based on the triangular lattice topology of claim 3, wherein, The projection photonic body-side bandgap diagram of the sandwich structure containing the first nontrivial region (5), the second nontrivial region (6), and the third nontrivial region (7) shows two boundary mode dispersion curves in the photonic body bandgap. By changing the number of layers of the nontrivial topological photonic crystal lattice in the middle layer of the sandwich structure, the working bandwidth of the unidirectional boundary mode waveguide is continuously increased until the region of the total reflection bandwidth of the boundary mode disappears. Electromagnetic waves in the sandwich structure are mainly concentrated in the middle nontrivial region, and the transmission mode is uniformly distributed over a wide area in the nontrivial region; when the middle layer is a sandwich structure of the first nontrivial region (5), the second nontrivial region (6), and the third nontrivial region (7), the waveguide widths are a, 2a, and 3a lattice constants, respectively, and the energy is uniformly distributed and is 95%, 75%, and 75% respectively; The distribution of band dispersion curves in the first Brillouin Kx direction of the sandwich structure containing the first nontrivial region (5), the second nontrivial region (6), and the third nontrivial region (7) shows that different structural layer waveguides can be excited at different frequencies; if the frequency f A =0.4398(c / a) intersects the band dispersion curve of the sandwich structure containing the first nontrivial region (5), the second nontrivial region (6), and the third nontrivial region (7), with frequency f. A The light source generates unidirectional wideband waveguides in different lattice layers of three nontrivial regions, where c is the speed of light in vacuum; if the frequency f B =0.44431(c / a) intersects the band dispersion curve of the sandwich structure containing the second nontrivial region (6) and the third nontrivial region (7), with frequency f B The light source generates a unidirectional wide-width waveguide in a sandwich structure composed of two or three layers of nontrivial topological photonic crystals (2), and is a cutoff in a sandwich structure composed of a single layer of nontrivial topological photonic crystals (2); if the frequency f C =0.45128(c / a) intersects the band dispersion curve of the sandwich structure containing the third nontrivial region (7), with frequency f C The excitation source generates a unidirectional wide-width waveguide only in the three nontrivial topological layers, and is cut off in the sandwich structure composed of one or two nontrivial topological photonic crystals (2); such as the frequency f D =0.46301(c / a) intersects the band dispersion curve of the sandwich structure containing the first nontrivial region (5) and the third nontrivial region (7), with frequency f D The light source generates a unidirectional wide-width waveguide in a sandwich structure composed of one or three layers of nontrivial topological photonic crystals (2), while the sandwich structure composed of two layers of nontrivial topological photonic crystals (2) is a cutoff.

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