A topological photonic crystal structure, optical waveguide and optical beam splitter

Abstract

The present invention relates to a topological photonic crystal structure, an optical waveguide and an optical beam splitter. The topological photonic crystal structure described in the present invention can realize a topological phase change by rotating three dielectric columns in a unit cell to form two topological photonic crystal structures. Stacking the obtained two unit cell structures with opposite topological characteristics and arranging them in an array can construct an optical waveguide with different boundary states, including a straight waveguide and a waveguide with bending angles of 60°, 90° and 120° respectively. Since the two unit cell structures have opposite topological characteristics, a light beam carrying orbital angular momentum can be transmitted unidirectionally on the interface of the two photonic crystals without being disturbed by local impurities or defects. The photonic crystal structure constructed with quasi-circular dielectric columns proposed by the present invention can not only realize the beam splitting function, but also the two output waveguides are 90° with the input waveguide, and the frequency division function can be realized in the same photonic crystal device.

Description

Technical Field

[0001] The present invention relates to the technical field of topological photonic crystals, and in particular to a topological photonic crystal structure, an optical waveguide and an optical beam splitter. Background Art

[0002] The heating characteristics associated with traditional circuit transmission restrict the development of ultra-high computing in integrated units. With the development of integrated optics, photonic integrated circuits (PICs) based on topological insulators have shown great potential. Topological insulators are considered to be highly promising materials because of their own insulation but transmission characteristics at the boundary. The existence of topological insulators makes it possible to overcome these obstacles. Based on the extensive study of the band theory of topological insulators, scholars have realized the quantum Hall effect (QHE), quantum spin Hall effect (QSHE) and quantum valley Hall effect (QVHE). In the quantum Hall effect system, an external magnetic field acts on the system, causing the time reversal symmetry (TRS) to be destroyed. QSHE is achieved by constructing pseudospins, that is, simulating the spin freedom of electrons in the working system, relying on spin-orbit coupling. QVHE can be achieved by introducing valley freedom. QVHE is easier to construct and realize than QHE and QSHE, so the structural shape has a richer diversity.

[0003] Various photonic crystals based on QVHE, namely valley photonic crystals (VPCs), have been studied and described. By breaking the spatial inversion symmetry of the hexagonal unit cell lattice, the double degeneracy of K or K' points can be achieved. Because they not only have the inherent properties of traditional PCs, but also have the characteristics of valley polarization, they have attracted great interest. There are many models and methods to realize VPC, such as lattice deformation, the use of tunable dielectric materials, and the use of topological edge states to design optical waveguides, optical beam splitters, optical filters, optical resonators and other devices based on various transmission channels. However, stable cell structure and properties, and larger band gap width are still the anchor points and goals of research, so new structures and topological phase transitions need to be studied to realize VPC. At the same time, due to the robustness of valley topological protection transport, 120° and 60° sharp bends are widely used in beam splitters and frequency dividers, but topological photonic crystal beam splitters or frequency dividers with 90° sharp bends and high transmission efficiency need to be explored. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a topological photonic crystal structure, an optical waveguide and an optical beam splitter.

[0005] A topological photonic crystal structure is formed by arranging a plurality of regular hexagonal unit cells, wherein the distance between the centers of adjacent regular hexagonal unit cells is a lattice constant a; a single regular hexagonal unit cell comprises three dielectric columns arranged in parallel in the air and having a C3 symmetric structure, wherein the cross-sections of the three dielectric columns are fan rings with an outer diameter of R1, an inner diameter of R2, and a center angle of 60°, and the deflection angle of the three dielectric columns rotating counterclockwise around their axes is -30°≤θ≤30°, and the deflection angle of the three dielectric columns when symmetrical about the line connecting the midpoints of the regular hexagonal unit cells is defined as θ=0°.

[0006] Preferably, the outer diameter is R1=0.5*a, the inner diameter is R2=a / 3, and the frequency range of the topological band gap is 0.2583c / a to 0.3364c / a, where a is the lattice constant and c is the speed of light in free space.

[0007] Preferably, the distance between the centers of two adjacent unit cells is lattice constant a=1 μm; the dielectric constant of air is ε0=1; the material of the dielectric column is silicon, and its dielectric constant is ε1=11.7.

[0008] Preferably, a topological photonic crystal unit cell with a deflection angle θ=30° is marked as VPC1; a topological photonic crystal unit cell with a deflection angle θ=0° is marked as VPC3; and a topological photonic crystal unit cell with a deflection angle θ=-30° is marked as VPC2.

[0009] An optical waveguide, consisting of the topological photonic crystal structure as described above, comprising:

[0010] The first crystal unit includes a group of unit cells VPC1 with a deflection angle θ=30°, wherein the unit cells VPC1 diverge from the center of their cross sections to six directions around them and are arranged in an array;

[0011] The second crystal unit includes a group of unit cells VPC2 with a deflection angle θ=-30°, wherein the unit cells VPC2 diverge from the center of their cross sections to six directions around them and are arranged in an array;

[0012] Among them, the boundary formed by the unit cell VPC2 being located above the unit cell VPC1 is an edge1 type edge state, and the boundary formed by the unit cell VPC1 being located above the unit cell VPC2 is an edge2 type edge state; the interface between the first crystal unit and the second crystal unit is one or both of the edge1 type and edge2 type boundary states.

[0013] Preferably, the optical waveguide has a 60° bend and / or a 120° bend.

[0014] Preferably, the optical waveguide has a zipper-type boundary state, which is composed of edge1 type and edge2 type boundary states distributed at intervals; the axes of the unit cells VPC1 and VPC2 located on both sides of the interface are located on the same plane, and the electromagnetic waves transmitted in the optical waveguide having the zipper-type boundary state are entangled and advanced in a cross manner.

[0015] Preferably, the optical waveguide has a 90° bend.

[0016] Preferably, the optical waveguide has four quadrants, the first crystal unit is located in two opposite quadrants, and the second crystal unit is located in the other two opposite quadrants; wherein the interface between the second quadrant and the third quadrant is the input end, and the interface between the first quadrant and the second quadrant and between the third quadrant and the fourth quadrant is a zipper boundary state.

[0017] A beam splitter, comprising an optical waveguide as described in any one of claims 5 to 9, the beam splitter having an input channel and three output channels; the three output channels are respectively a first output channel, a second output channel and a third output channel, the first channel and the second channel are perpendicular to the input channel and are located on both sides of the input channel; the input channel is an edge1 type boundary state, the first output channel and the second output channel are zipper type boundary states, and the third output channel is an edge2 type boundary state.

[0018] The above technical solution of the present invention has the following advantages compared with the prior art:

[0019] 1. The topological photonic crystal structure described in the present invention can realize topological phase change by rotating three dielectric columns in the unit cell to form two topological photonic crystal structures.

[0020] 2. Stacking the two unit cell structures with opposite topological characteristics and arranging them in an array can construct an optical waveguide with different boundary states. The electromagnetic wave in the zipper boundary state has two transmission paths, and the electromagnetic wave is intertwined and advances in a cross manner at the upper and lower edges of the zipper boundary state. Since the two unit cell structures have opposite topological characteristics, the light beam carrying orbital angular momentum can be transmitted unidirectionally on the interface of the two photonic crystals without being interfered by local impurities or defects.

[0021] 3. By utilizing the boundary states of the optical waveguide for different arrangements, a straight waveguide or a waveguide with 60°, 90°, or 120° bend angles can be obtained.

[0022] 4. The optical beam splitter proposed by the present invention has an input channel of edge1 type boundary state, the first output channel and the second output channel are zipper type boundary state, and the third output channel is edge2 type boundary state. Since the transmission rate of the third output channel is lower than 0.05 in the range of 78THz to 86.5THz, the frequency division function can be realized in the same photonic crystal device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0024] Figure 1 Schematic diagram of the topological photonic crystal structure.

[0025] Figure 2 (a) is a topological photonic crystal unit cell with a deflection angle θ=30°, marked as VPC1; (b) is a topological photonic crystal unit cell with a deflection angle θ=0°, marked as VPC3; (c) is a topological photonic crystal unit cell with a deflection angle θ=-30°, marked as VPC2.

[0026] Figure 3 (a) is the energy band structure of a topological photonic crystal composed of unit cells (VPC3) with a deflection angle of θ = 0°; (b) is the energy band structure of a topological photonic crystal composed of unit cells (VPC2) with a deflection angle of θ = -30°; (c) is the energy band structure of a valley topological photonic crystal composed of unit cells (VPC1) with a deflection angle of θ = 30°.

[0027] Figure 4 (a) is the phase distribution of a topological photonic crystal composed of unit cells (VPC2) with a deflection angle of θ = -30° at K (K'); (b) is the electric field distribution of a topological photonic crystal composed of unit cells (VPC2) with a deflection angle of θ = -30° at K (K').

[0028] Figure 5 Schematic diagram of optical waveguide.

[0029] Figure 6 (a) is a schematic diagram of the edge1 type boundary state; (b) is a schematic diagram of the edge2 type boundary state; (c) is a schematic diagram of the energy band of the edge1 type boundary state; (d) is a schematic diagram of the energy band of the edge2 type boundary state.

[0030] Figure 7 are the electric field distributions of the two edge states and the Poynting vector diagram.

[0031] Figure 8(a)-(d) construct three different defects in the optical waveguide structure: disorder, cavity, Z-bend, and multiple sharp bends, and plot the corresponding electric field distribution. (e) is a comparison of the transmission rate of the defect-free structure and the transmission rate of the structure with disorder, cavity, Z-bend, and multiple sharp bend defects.

[0032] Fig. 9 (a) is a zipper-like boundary state and its simulated electric field; (b) is a schematic diagram of the zipper-like boundary state structure; (c) is the Poynting vector diagram when electromagnetic waves are transmitted in the zipper-like boundary state; (d) is the way in which edge1 boundary state and edge2 boundary state form a zipper-like boundary; (e) is a comparison of the transmittance of the zipper-like boundary state and the transmittance of the edge2 boundary state.

[0033] Fig.10 (a) is a schematic diagram of the optical beam splitter structure; (b) is the transmittance of the first output channel, the second output channel and the third output channel; (c) is the electric field diagram with a frequency of 80.045 THz; (d) is the electric field diagram with a frequency of 81.544 THz; (e) is the electric field diagram with a frequency of 77.946 THz.

[0034] Explanation of the reference numerals in the specification: 1, unit cell; 101, dielectric column; 201, first crystal unit; 202, second crystal unit; 203, interface. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0036] like Figure 1 As shown, the present invention provides a topological photonic crystal structure, which is composed of a plurality of regular hexagonal unit cells 1 arranged in parallel, and the distance between the centers of adjacent regular hexagonal unit cells is a lattice constant a; a single regular hexagonal unit cell includes three dielectric columns 101 arranged in parallel in the air and having a C3 symmetric structure, the cross-section of the three dielectric columns is a fan ring with an outer diameter of R1, an inner diameter of R2, and a center angle of 60°, and the deflection angle of the three dielectric columns rotating counterclockwise around their axes is -30°≤θ≤30°, and the deflection angle of the three dielectric columns when symmetrical about the line connecting the midpoints of the regular hexagonal unit cells is defined as θ=0°.

[0037] The distance between the centers of two adjacent unit cells of the topological photonic crystal structure of the present invention is lattice constant a=1 μm; the dielectric constant of air ε0=1; the material of the dielectric column is silicon, and its dielectric constant is ε1=11.7.

[0038] In a specific embodiment, the outer diameter is R1=0.5*a, the inner diameter is R2=a / 3, and the frequency range of the topological band gap is 0.2583c / a to 0.3364c / a, where a is the lattice constant and c is the speed of light in free space. The unit cell formed under this condition has a wide band gap of 0.087c / a, and the unit cell properties have stronger anti-interference properties.

[0039] Figure 2 Shown is the unit cell of the topological photonic crystal structure of the present invention. Figure 2 (a) is a topological photonic crystal unit cell with a deflection angle θ = 30°, marked as VPC1; Figure 2 (b) is a topological photonic crystal unit cell with a deflection angle θ = 0°, marked as VPC3; Figure 2 (c) is a topological photonic crystal unit cell with a deflection angle θ = -30°, labeled VPC2.

[0040] Figure 3 The band structures of the topological photonic crystals when the deflection angles are θ = 0°, -30°, and 30° respectively. Figure 3 As shown in (a), the band structure of a topological photonic crystal composed of a unit cell (VPC3) with a deflection angle of θ = 0°, the corresponding band gap has a degenerate Dirac cone (Dirac cone), i.e., an energy valley, at K and K′. If the lattice symmetry is broken and the deflection angle is increased or decreased, the degenerate energy valley will be opened and a photonic band gap will appear. Figure 3 (b) shows the band structure of a topological photonic crystal composed of a unit cell (VPC2) with a deflection angle of θ = -30°, and the photonic band gap is open. Figure 3 (c) shows the band structure of a valley topological photonic crystal composed of a unit cell (VPC1) with a deflection angle of θ = 30°, and the photonic band gap is open.

[0041] Figure 4 are the phase and electric field distribution of the topological photonic crystal composed of a unit cell (VPC2) with a deflection angle of θ = -30° at K (K'). Figure 4 As shown in (a), in the phase distribution diagram of the VPC2 unit cell structure, in the same frequency band, K and K' have opposite vortex chirality (indicated by black arrows in the figure), which are respectively manifested as right-hand circular polarization (RCP) and left-hand circular polarization (LCP) orbital angular momentum, indicating that there is band inversion in its energy band and a topological phase transition exists in this topological photonic crystal. Figure 4 The amplitude of the Ez component in (b) shows a phase reversal, indicating a topological phase transition.

[0042] The topological photonic crystal structure of the present invention adjusts the photonic band gap width only by rotating the dielectric column without changing the size and material of the dielectric column. Compared with the previous structure, it has a higher degree of freedom and is easier to prepare.

[0043] like Figure 5 As shown, the present invention also provides an optical waveguide, which is composed of the topological photonic crystal structure as described above, including:

[0044] The first crystal unit 201 includes a group of unit cells VPC1 with a deflection angle θ=30°, wherein the unit cells VPC1 are arranged in an array and radiate from the center of their cross sections to six directions around them;

[0045] The second crystal unit 202 includes a group of unit cells VPC2 with a deflection angle θ=-30°, wherein the unit cells VPC2 diverge from the center of the cross section to six directions around the unit cells and are arranged in an array;

[0046] The interface 203 between the first crystal unit and the second crystal unit is one or both of edge1 type and edge2 type boundary states.

[0047] The unit cells VPC1 and VPC2 are stacked in different ways as follows Figure 5 The supercell structure shown in the figure has perfect conductor boundary conditions at the upper and lower boundaries of the supercell, and periodic boundary conditions at the left and right boundaries. Figure 6 As shown in , there are three main types of edge states: edge1 type and edge2 type. The boundary formed by the unit cell VPC2 being located above the unit cell VPC1 is called the edge1 type edge state, as shown in Figure 6 (a); the boundary formed by the unit cell VPC1 being located above the unit cell VPC2 is called the edge2 type edge state, as shown in Figure 6 (b) as shown. Figure 6 (c) and (d) are schematic diagrams of the energy bands of edge1 and edge2 boundary states, respectively. The dotted lines represent the body states, and the edge states formed at the boundary can be observed between the body states. Figure 6 The edge mode shown by the solid line in (c) has two different valley pseudospin states, namely Φ +12 and Φ -12 ; Figure 6 The two edge modes represented by the solid lines in (d) also have two different valley pseudo-spin states, namely Φ -21 and Φ +21 .

[0048] Figure 7 The electric field diagram and Poynting vector of the two boundary states are shown. It can be seen from the figure that the energy flow directions of the upper valley pseudo-spin states Φ+12 and Φ-12 of the edge state formed by the edge1 type boundary are opposite; the upper valley pseudo-spin state Φ of the edge state formed by the edge2 type boundary is opposite. -21 With Φ +21 The energy flow is in the opposite direction.

[0049] In order to verify the valley chirality of the Valley Hall Effect, a harmonic source (OAM) is placed at the interface of VPC1 and VPC2. The harmonic source consists of four line sources with a phase of π / 2, and the orbital angular momentum is positive or negative, which can excite the valley chirality, and the electromagnetic waves are transmitted along the interface of VPC1 and VPC2. By using a harmonic source and controlling its polarization direction, the quantum Valley Hall effect can be realized. A perfect electric conductor boundary condition is also set around the model to prevent electromagnetic waves from scattering outward. Figure 5 As shown in the figure, when the harmonic source carries positive OAM (L=-1) and is left-handed circular polarization (LCP), it can be seen from the electric field distribution that the electromagnetic wave propagates to the right along the interface without obvious backscattering. The electromagnetic wave is confined near the interface and will not scatter into the two VPC domains, showing good light localization. When the harmonic source carries negative OAM (L=1) and is right-handed circular polarization (RCP), it can be observed that the electromagnetic wave propagates in the opposite direction with the same properties and state. Through simulation studies on supercells of two boundary structures, it is found that for the boundary, the valley polarized edge state located at the K or K' point only propagates in a single direction, which shows the valley chirality characteristics of the Valley Hall effect.

[0050] In a specific embodiment, the optical waveguide has a 60° bend and / or a 120° bend.

[0051] In order to verify the robustness of the designed waveguide structure, cavities, disordered structures, and the like are introduced into the optical waveguide structure by exchanging the positions of two adjacent topological photonic crystal units. Figure 8 As shown in (a) and (b), it can be seen from the figure that the light is not disturbed by the cavity and disordered defects, but continues to propagate forward. In order to verify the robustness of the waveguide at the bend, a z-bend and a domain wall with multiple sharp bends are constructed, such as Figure 8 As shown in (c) and (d), there is no scattering loss of light at the 60° and 120° bends, and good transmission is still maintained. This application places probes at the beginning and end of several waveguides to further test the transmission performance and robustness of the waveguide; the transmission rate of electromagnetic waves along these boundaries can be calculated based on the energy intensity at the beginning and end of the waveguide. The calculated transmission coefficient does not include the coupling loss from the source to the waveguide. This application only captures the transmission rate in the main working frequency band (77.2~87THz), which is obtained by Figure 8(e) It can be seen that the transmission rate of the straight waveguide is extremely high, up to 99.9%. Cavity defects and disorder defects have almost no effect on the transmission rate. Only at high frequencies (greater than 86.3THz), the efficiency decreases compared to the straight waveguide, that is, the frequency range of efficient transmission is reduced. The Z-type and multiple sharp bend waveguides have a decrease in efficiency in the entire working frequency band, especially at Figure 8 (e) shows a sharp decline. Figure 4 In the shadow band (78.05-86.3 THz) in (e), the transmission efficiency of the Z-waveguide is still above 99%, and that of the multiple sharp bend waveguide is above 97.5%, and the transmission efficiency still maintains a very high level.

[0052] like Fig. 9 (a), (b), in an optional embodiment, the axes of the unit cells VPC1 and VPC2 located on both sides of the interface are located on the same plane, forming a zipper-type boundary state. The zipper-type boundary state is formed by the edge1 type and edge2 type boundary states being distributed alternately, the edge2 type boundary state is located on the hypotenuse path, and the edge1 type boundary state is located on the turning angle, such as Figure 6 (d) As shown. A light source is placed on the left side of the interface, and the light is transmitted along the Poynting vector, as shown in Fig. 9 As shown in (c), it can be seen from the figure that light has two electromagnetic wave transmission paths in the zipper-type domain wall. The electromagnetic waves transmitted in the zipper-type boundary state are entangled and moved forward in a cross manner. However, after multiple bends, the electromagnetic waves are actually transmitted along a straight line (as shown in the Poynting vector diagram), which can be regarded as a straight waveguide. Fig. 9 As shown in (e), even though the waveguide structure of this embodiment is a waveguide formed by multiple sharp bends, the zipper-type boundary state still maintains an extremely high transmission rate in the frequency band of 79THZ to 90THz, and the transmission rate drops rapidly in the frequency band less than 79THz and greater than 90THz.

[0053] Although the working frequency band of the zipper edge is reduced compared with edge2, due to its special propagation performance, it can propagate at the 90° bend constructed in the transmission waveguide. Compared with the generally known 60° or 120° bends widely used in photonic crystal beam splitters, the 90° bend transmission that can be achieved by the optical waveguide of the present invention can increase the diversity of the photonic crystal waveguide path. When the device needs to bend the waveguide, the 90° bend shortens the transmission distance.

[0054] In a specific embodiment, the optical waveguide has a 90° bend, and the optical waveguide has four quadrants, the first crystal unit is located in two opposite quadrants, and the second crystal unit is located in the other two opposite quadrants; wherein, the interface between the second quadrant and the third quadrant is the input end, and the interface between the first quadrant and the second quadrant and between the third quadrant and the fourth quadrant is a zipper boundary state.

[0055] like Fig.10 As shown, the present invention also provides an optical beam splitter, which includes the optical waveguide as described above, and has an input channel and three output channels; the three output channels are respectively a first output channel, a second output channel and a third output channel, the first channel and the second channel are perpendicular to the input channel and are separated on both sides of the input channel; the input channel is an edge1 type boundary state, the first output channel and the second output channel are zipper type boundary states, and the third output channel is an edge2 type boundary state.

[0056] These three edge states can be realized within the device operating frequency band (76THZ ~ 92THz). A light source is placed at the input channel as the input end, and probes are set at the four ports. Then, the power flow plane density of each reference plane at the operating frequency is calculated, and the transmission coefficient is derived. The transmission rate of the beam splitter at the three output ports is measured as follows: Fig. 9 (b) As shown. The transmission rate of the third output channel is less than 0.05 in the range of 78THz to 86.5THz. In this frequency domain, it is considered that the beam splitter mainly splits the beam through the first output channel and the second output channel. Energy balancing is one of the objective criteria for evaluating the performance of a topological beam splitter, that is, the first output channel and the second output channel of the beam splitter reach approximately 1:1, such as 1:1.05 and 1:1.03 splitting ratios at 80.045 and 81.544THz, respectively. The electric field is shown in Figure 7 As shown in (c) and (d), at 76THz~77.5THz and 86.5THz~90THz, the third output channel has a relatively obvious transmission, and the transmission rate is between 0.05 and 0.41, so three-channel output can be achieved. And because the domain wall structure and working frequency band of the third output channel path are different from those of the first and second output channels, their transmission frequencies are also different. Figure 7 (b) It can be seen that the transmission rate of the third output channel is almost 0 in the range of 78.2THz to 86THz. By utilizing this property, the third output channel effectively isolates the electromagnetic waves in this frequency band and achieves the frequency division effect. Therefore, the optical beam splitter of the present application can also be used as a filter.

[0057] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A topological photonic crystal structure, characterized in that: It is composed of a plurality of regular hexagonal unit cells, and the distance between the centers of adjacent regular hexagonal unit cells is a lattice constant a; a single regular hexagonal unit cell includes three dielectric columns arranged in parallel in the air and having a C3 symmetric structure, the cross-section of the three dielectric columns is a fan ring with an outer diameter of R1, an inner diameter of R2, and a center angle of 60°, and the deflection angle of the three dielectric columns rotating counterclockwise around their axes is -30°≤θ≤30°, and the deflection angle of the three dielectric columns when symmetrical about the line connecting the midpoints of the regular hexagonal unit cells is defined as θ=0°.

2. The topological photonic crystal structure according to claim 1, characterized in that: The outer diameter is R1=0.5*a, the inner diameter is R2=a / 3, and the frequency range of the topological band gap is 0.2583c / a~0.3364c / a, where a is the lattice constant and c is the speed of light in free space.

3. The topological photonic crystal structure according to claim 1, characterized in that: The distance between the centers of two adjacent unit cells is a lattice constant a=1 μm; the dielectric constant of air ε0=1; the material of the dielectric column is silicon, and its dielectric constant is ε1=11.

7.

4. The topological photonic crystal structure according to claim 1, characterized in that: The topological photonic crystal unit cell with a deflection angle θ=30° is marked as VPC1; the topological photonic crystal unit cell with a deflection angle θ=0° is marked as VPC3; the topological photonic crystal unit cell with a deflection angle θ=-30° is marked as VPC2.

5. An optical waveguide, characterized in that: Composed of a topological photonic crystal structure as claimed in any one of claims 1 to 4, including: The first crystal unit includes a group of unit cells VPC1 with a deflection angle θ=30°, wherein the unit cells VPC1 diverge from the center of their cross sections to six directions around them and are arranged in an array; The second crystal unit includes a group of unit cells VPC2 with a deflection angle θ=-30°, wherein the unit cells VPC2 diverge from the center of their cross sections to six directions around them and are arranged in an array; Among them, the boundary formed by the unit cell VPC2 being located above the unit cell VPC1 is an edge1 type edge state, and the boundary formed by the unit cell VPC1 being located above the unit cell VPC2 is an edge2 type edge state; the interface between the first crystal unit and the second crystal unit is one or both of the edge1 type and edge2 type boundary states.

6. The optical waveguide according to claim 5, characterized in that The optical waveguide has a 60° bend and / or a 120° bend.

7. The optical waveguide according to claim 5, characterized in that The optical waveguide has a zipper-type boundary state, which is composed of edge1 type and edge2 type boundary states distributed at intervals; the axes of the unit cells VPC1 and VPC2 located on both sides of the interface are located on the same plane, and the electromagnetic waves transmitted in the optical waveguide with the zipper-type boundary state are entangled and advanced in a cross manner.

8. The optical waveguide according to claim 7, characterized in that The optical waveguide has a 90° bend.

9. The optical waveguide according to claim 8, characterized in that The optical waveguide has four quadrants, the first crystal unit is located in two opposite quadrants, and the second crystal unit is located in the other two opposite quadrants; wherein the interface between the second quadrant and the third quadrant is an input end, and the interface between the first quadrant and the second quadrant and between the third quadrant and the fourth quadrant is a zipper boundary state.

10. An optical beam splitter, characterized in that: The optical beam splitter comprises an optical waveguide as described in any one of claims 5 to 9, and the optical beam splitter has an input channel and three output channels; the three output channels are respectively a first output channel, a second output channel and a third output channel, the first output channel and the second output channel are perpendicular to the input channel and are located on both sides of the input channel; the input channel is an edge1 type boundary state, the first output channel and the second output channel are zipper type boundary states, and the third output channel is an edge2 type boundary state.

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