Topological defect cavity based on valley photonic crystal and multi-channel logic device comprising topological defect cavity

Abstract

According to the topological defect cavity based on the valley photonic crystal and the multi-channel logic device comprising the topological defect cavity, an edge mode, protected by topology, in the topological photonic crystal can resist the influence of backscattering, and a brand new thought is provided for solving the problem of high reflection loss of a defect cavity-waveguide direct coupling system under non-resonant frequency. The topological defect cavity is designed based on the valley photonic crystal, and compared with a traditional photonic crystal defect cavity, low reflection loss can be achieved when the topological defect cavity is directly coupled with the waveguide. Besides, the resonant frequency and mode symmetry of the topological defect cavity have flexible tunability, and the multi-channel logic device based on the topological defect cavity and the harpoon type energy beam splitter is provided by utilizing the characteristics of low reflection loss and tunable resonant frequency of the topological defect cavity. According to the logic device, the output result of the harpoon beam splitter can be reserved, meanwhile, more diversified output results are achieved, and the important application value of the topological defect cavity in the integrated micro-nano photonics is reflected.

Description

Technical Field

[0001] The present invention belongs to the field of applications of topological photonic crystals, and particularly relates to a topological defect cavity based on valley photonic crystals and a multi-channel logic device including the topological defect cavity. Background Art

[0002] Due to its ability to efficiently transmit light, photonic crystal waveguides have become an effective carrier for realizing on-chip integrated optical communication. How to control the light transmission in waveguides is the core research content in the field of optical communication. Resonant cavities, with their ability to efficiently control light transmission by coupling with optical waveguides, have become the main tool for people to manipulate light and have been widely used in integrated photonic devices such as filters, lasers, and sensors. There are many types of resonant cavities, among which defect cavities have advantages such as high quality factor and compact structure, and have received extensive attention. The coupling methods between defect cavities and waveguides are divided into two types: side coupling and direct coupling. Among them, the side coupling method has been widely used. The direct coupling method can make the structure of the device more compact and improve the integration degree compared with the side coupling method, but it is rarely used. The important reason is that the direct coupling between the defect cavity and the photonic crystal waveguide will bring large reflection losses, resulting in a significant decrease in the transmission efficiency of the photonic crystal waveguide at non-resonant frequencies, restricting the application of photonic devices, as shown in Figure 1 (a).

[0003] The emergence of topological photonic crystals provides a new idea for solving the above problems. Topological photonic crystal waveguides can resist backscattering and defect interference. When a topological defect cavity is directly coupled with a topological photonic crystal waveguide, the topological photonic crystal waveguide can be immune to the reflection losses brought by the defect cavity, thereby ensuring the transmission efficiency of the waveguide at non-resonant frequencies ( Figure 1 (b)), which brings a wider application range for photonic devices based on defect cavity-waveguide coupling. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of large reflection losses in the direct coupling between traditional photonic crystal waveguides and defect cavities, and to provide a topological defect cavity based on valley photonic crystals (VPC) and a multi-channel logic device including the topological defect cavity. Valley photonic crystals have recently become a powerful platform for integrated micro-nano photonics due to their ability to achieve stable and efficient light transmission with all-dielectric materials. Based on valley photonic crystals with a honeycomb lattice and equilateral triangular air holes, the present invention designs a topological defect cavity. Its direct coupling with a topological waveguide can achieve extremely low reflection losses, and at the same time allows changing the internal air hole size and distribution to adjust the resonant frequency and symmetry of the cavity mode. And this kind of structure can be extended to other types of structures. Finally, a multi-channel logic gate combining a harpoon-shaped power splitter and a topological defect cavity-topological waveguide direct coupling system is designed, demonstrating the application value of the topological defect cavity-topological waveguide direct coupling system.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A topological defect cavity based on valley photonic crystal, the topological defect cavity has a honeycomb lattice, and the unit cell consists of an Si substrate (substrate refractive index n = 3.42) and two equilateral triangle air holes with side lengths of l 1 and l 2 respectively. The unit cell is a rhombus, the lattice constant a = 360 nm, and the VPC unit cell is divided into A-type (l 1 = 0.7a > l 2 = 0.3a) and B-type (l 1 = 0.3a < l 2 = 0.7a) units.

[0007] Further, the A-type and B-type unit cell structures are spliced to construct two boundary states of AB and BA, and their energy bands are as Figure 1 shown in b.

[0008] Further, in the waveguide, the value of the side length l of the inner small hole air hole can be flexibly tuned within the range of 0 to 0.36a.

[0009] Further, by destroying the geometric symmetry of the topological defect cavity with respect to the waveguide interface, the resonant mode H z distribution is changed, thereby destroying the even symmetry of the H z distribution with respect to the waveguide interface.

[0010] Further, the equilateral triangle air holes are replaced with circular air holes, that is, the structure of this topological defect cavity is not limited to the BA-type waveguide, and it can also be extended to valley photonic crystals with air holes of different shapes and AB-type waveguides.

[0011] A multi-channel logic device including the above topological defect cavity, two topological defect cavities with different sizes of the inner triangular small holes l are directly coupled to two waveguides of a harpoon-type beam splitter respectively to construct a multi-channel logic device, and its structure is as Figure 5 shown in a. By tuning the value of l, the resonant frequency of the topological defect cavity embedded in the harpoon-type beam splitter is changed, and then different output results of the multi-channel logic device are tuned.

[0012] The beneficial effects of the present invention compared with the prior art are as follows: The present invention designs a topological defect cavity that can be directly coupled to a topological waveguide to achieve low reflection loss. Its resonant frequency and mode symmetry have flexible tunability, and this design method can also be extended to similar structures with circular air holes. The present invention also demonstrates the construction of a multi-channel logic device by combining a topological defect cavity and a harpoon-type power splitter. This logic device can achieve more diverse output results while retaining the output results of the harpoon-type splitter, reflecting the important application value of this topological defect cavity in integrated micro-nano photonics. Description of the Drawings

[0013] Figure 1 , (a) Reflection loss diagram of the direct coupling of the defect cavity and the photonic crystal waveguide; (b) Reflection loss diagram of the direct coupling of the topological defect cavity and the topological photonic crystal waveguide;

[0014] Figure 2 , (a) Schematic diagrams of the A-type and B-type unit cell structures; (b) Band diagrams of the AB and BA edge modes and the simulated H z distribution diagram, where the black solid line in the middle of the simulated H z distribution diagram is the interface of the edge state; (c) Schematic diagram of the structure of the direct coupling of the topological defect cavity and the BA-type waveguide, and the black dashed line is the waveguide interface; (d) Simulated |E| distribution diagram of the structure in (c) at different frequencies for the input signal, where the yellow arrow represents the transmission direction of the reflected light;

[0015] Figure 3 , (a) Time-coupling mode theory model of the topological defect cavity-topological photonic crystal waveguide direct coupling system; (b) Transmission spectrum of the topological defect cavity-topological photonic crystal waveguide direct coupling system, where the red dots represent the simulated data and the black curve represents the theoretical calculation result;

[0016] Figure 4 Transmission spectrum of the topological defect cavity-topological photonic crystal waveguide direct coupling system when the simulation l is tuned between 0.294a and 0.306a. The leftmost curve corresponds to l = 0.294a, the rightmost curve corresponds to l = 0.306a, and the l difference between adjacent curves is 0.001a;

[0017] Figure 5 (a) and (b) are the simulated transmittances of the structure when l takes 0 and 0.36a respectively.

[0018] Figure 6 , (a) Schematic diagrams of the A-type and B-type unit cell structures; (b) Band diagrams of the AB and BA edge modes and the simulated H z distribution diagram, where the simulated H z distribution diagram, and the black solid line in the middle is the interface of the edge state;

[0019] Figure 7 , (a) Schematic structural diagram, where the black dashed line represents the waveguide interface, and the inside of the red dashed box is the structure of the topological defect cavity; (b) Transmission spectrum of the structure simulated in (a).

[0020] Figure 8 , (a) and (c) are respectively schematic structural diagrams of direct coupling between the topological defect cavity and the AB-type waveguide when the geometric structure of the topological defect cavity has and does not have symmetry with respect to the waveguide interface, where the black dashed line represents the waveguide interface, and the inside of the red dashed box is the structure of the topological defect cavity; (b) and (d) are respectively the simulated H z distribution diagrams of the resonance modes in (a) and (c), where the black solid circles represent the positions where the topological defect cavities are located.

[0021] Figure 9 , (a) Figure 8 (c) Simulated transmission spectra of the structures in; (b) Schematic structural diagram of direct coupling between the topological defect cavity and the AB-type waveguide in a VPC with triangular air holes; (c) Simulated transmission spectrum of the structure in (b).

[0022] Figure 10 , (a) Schematic structural diagram of a multi-channel logic device; (b), (c), and (d) are respectively the simulated |E| distribution diagrams of the logic device when the input signal frequencies are 190 THz, 191.791 THz, and 193.828 THz, where the yellow arrows indicate the transmission directions of the reflected signals. Detailed implementation manners

[0023] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0024] The topologically protected edge modes in topological photonic crystals can be immune to the influence of backscattering, which provides a new idea for solving the high reflection loss problem of the defect cavity-waveguide direct coupling system at non-resonant frequencies. Here, the present invention designs a topological defect cavity based on valley photonic crystals. Compared with the traditional photonic crystal defect cavity, the topological defect cavity can achieve low reflection loss when directly coupled with the waveguide. In addition, the resonant frequency and mode symmetry of the topological defect cavity have flexible tunability. Using the low reflection loss and resonant frequency tunability characteristics of the topological defect cavity, a multi-channel logic device based on the topological defect cavity and the harpoon-type power splitter is proposed. This logic device can achieve more diverse output results while retaining the output results of the harpoon-type splitter, reflecting the important application value of the topological defect cavity in integrated micro-nano photonics.

[0025] Example 1:

[0026] The present invention constructs a VPC with a honeycomb lattice. The rhombic unit cell of the VPC is as shown in Figure 2 (a). The unit cell consists of a Si substrate (n = 3.42) and two equilateral triangular air holes with side lengths of l 1 and l 2 respectively, and the lattice constant a = 360 nm. The VPC unit cell is divided into type A (l 1 = 0.7a > l 2 = 0.3a) and type B (l 1 = 0.3a < l 2 = 0.7a) unit cells. Type A and type B unit cells have different topological phases. Due to the bulk-boundary correspondence, connecting them will generate two topological edge states, AB and BA, and the energy bands are as shown in Figure 2 (b). At the same time, Figure 2 (b) also shows the simulated H z distribution of the two edge states. The simulation results show that the H z distribution of the AB-type edge mode shows odd symmetry along the interface, while the BA-type shows even symmetry. This difference in symmetry will affect the coupling effect between the waveguide and the topological defect cavity.

[0027] First, take the direct coupling of the topological defect cavity and the BA-type waveguide as an example. The structure is as shown in Figure 2 (c). The inside of the red dashed box is the structure of the topological defect cavity, which is mainly composed of six identical large air holes (side length 0.7a) in the outer layer and six small air holes with the same shape and size in the inner layer. A key parameter is defined here: the side length l of the small air holes in the inner layer, which is crucial for tuning the resonant frequency of the topological defect cavity. The inside of the blue dashed box is the waveguide without the introduction of the topological defect cavity. By comparing the structures inside the two dashed boxes, it can be found that introducing the topological defect cavity into the BA-type waveguide only needs to change the sizes of four air holes at least. At this time, the side length l of the small air holes inside the topological defect cavity is 0.3a, and the six small air holes are symmetrically distributed about the geometric center of the topological defect cavity. The cavity has C 6 symmetry, and the geometric structure of the topological defect cavity is symmetric about the waveguide interface. This geometric symmetry will affect the symmetry of the resonant mode, and thus affect the coupling effect between the waveguide and the topological defect cavity. The present invention simulates the |E| distribution of the input signal in the structure in Figure 2 (c) at different frequencies, as shown in Figure 2 (d). The results show that when the input signal is at the resonant frequency (198.8667 THz), total reflection occurs in the structure, T = 0.05%; when the input signal is at a non-resonant frequency (199 THz), extremely low reflection loss is achieved in the structure, T = 99.81%.

[0028] To explain Figure 2Based on the results in (d), the time-coupled mode theory is introduced to analyze the transmission characteristics of the cavity-waveguide direct coupling system. Assume a system where a resonant cavity is connected to two identical waveguides, and the system is completely symmetric on both the left and right sides. For non-topological systems, it has been proven that the transmittance is as shown in Equation (1), which will not be discussed in detail here.

[0029]

[0030] where the resonant frequency of the cavity mode is ω 0 , and the lifetime is τ. The result of Equation (1) shows that when the frequency of the input signal is far from the resonant frequency, T ∼ 0, which corresponds to the situation in Figure 1 (a 1 ); when the frequency of the input signal is equal to the resonant frequency, T = 1, which corresponds to the situation in Figure 1 (a 2 ).

[0031] For example, for the topological system in Figure 2 (c), first only consider the cavity mode with no incident power. Due to weak coupling, it can be assumed that the mode decays exponentially with time with a lifetime of τ 0 , and the amplitude A satisfies the equation dA / dt = -iω 0 A - A / τ 0 , and its solution is Now introduce the waveguides. Since the system is completely immune to reflection loss, ideally, the energy input from waveguide 1 can be coupled into the cavity and directly transmitted to the output energy of waveguide 2, but cannot be reflected into the output energy of waveguide 1. The same applies to the energy input from waveguide 2. The energy of the resonant cavity will flow into the output energy of waveguide 1 and waveguide 2, and since the system is symmetric on both the left and right sides, the values of the energy flowing into waveguide 1 and waveguide 2 are equal. In the case of weak coupling, the equations satisfied by the system are

[0032]

[0033] s 1- = βs 2+ + γA (3)

[0034] s 2- = βs 1+ + γA (4)

[0035] where α, β, and γ are proportionality constants, α and γ are the coupling coefficients between the resonant cavity and the waveguides, and β is the transmission coefficient. It should be noted that α and γ are actually functions of frequency, but in the case of weak coupling and assuming that the quality factor Q of the resonant cavity is large enough, it can be considered that coupling only occurs near the resonance frequency ω 0 , so it can be approximately considered that α(ω) = α(ω 0) = α. The same applies to the case of β.

[0036] Next, the constant γ is determined by energy conservation. Assume that neither waveguide 1 nor waveguide 2 has input energy. At this time, the cavity mode decays exponentially to Without considering radiative decay, this part of the energy can only flow to waveguide 1 and waveguide 2. And because the system is symmetric, there is s 1- = s 2- = s. So there is the formula

[0037]

[0038] It can be solved that

[0039] For α, β is determined by time-reversal symmetry. From the previous derivation, it can be known that when s 1+ = s 2+ = 0, there is From time-reversal symmetry, it can be known that running the original solution backward in time and taking the conjugate to maintain the time dependence, another valid solution of the equation must be obtained. This solution must be in the form of and should also satisfy and s 1- = s 2- = 0. Substituting this result into equations (3) and (4) immediately gives β = -1. When τ → ∞, that is, when the resonator is not coupled to the waveguide, the resonator is equivalent to a defect introduced in the topological waveguide at this time. Ideally, because the system is robust, the defect does not affect the normal transmission of the waveguide, and the transmittance is 100%, which is also consistent with the calculation result s 2- = -s 1+ of the present invention (the negative sign here is a human convention, that is, the input resonator is positive and the output resonator is negative). Substituting the solution into equation (2) again, there is the equation

[0040]

[0041] It is solved that And due to weak coupling, the high-order effects of τ on α and γ can be ignored.

[0042] For the case where only waveguide 1 has input, since the frequency is constant in a linear system, the incident wave oscillates at a fixed frequency ω. Then all electromagnetic waves must oscillate in the form of e -iωt and dA / dt = -iωA holds. Substituting the previously obtained coefficients and s 2+ = 0 into equations (2), (3), and (4) can obtain the final equation

[0043]

[0044] The above equation can be solved to obtain

[0045]

[0046] The result of Equation (10) shows that when the frequency of the input signal is far from the resonance frequency, T~0; when the frequency of the input signal is equal to the resonance frequency, T = 1, which is consistent with Figure 2 the result in (d).

[0047] In the previous text, the present invention defines the key parameter - the side length l of the inner small air hole for tuning the resonance frequency of the topological defect cavity. As Figure 4 shown, the present invention simulates the transmission spectra of the direct coupling system of the topological defect cavity - topological photonic crystal waveguide when l takes different values. The results show that when l decreases, the resonance frequency becomes lower; when l increases, the resonance frequency becomes higher, and the resonance frequency of the topological defect cavity has continuous tunability. In addition, the value range of l is not limited to Figure 4 as shown in, the value of l can be flexibly tuned in the range of 0 - 0.36a. Due to the continuous tunability of the resonance frequency, only two extreme values are demonstrated here in the present invention. When l takes the minimum value of 0, the present invention simulates the transmittance of the structure at different frequencies, as Figure 5 (a) shows, and the results show that the structure can still achieve a relatively low reflection loss at non-resonance frequencies. When l = 0.36a, the present invention also simulates the transmittance of the structure at different frequencies, as Figure 5 (b) shows, and at this time the structure can still achieve a relatively low reflection loss at non-resonance frequencies. It should be noted that 0.36a is not a strict maximum value, but when l takes a larger value, the resonance frequency of the topological defect cavity will be too high to be within the frequency range where the BA-type waveguide can achieve robust transmission, resulting in too large a reflection loss of the structure. Therefore, 0.36a is a relatively large value selected in the present invention to ensure a relatively low reflection loss.

[0048] Meanwhile, the realization of such a topological defect cavity is not limited to the BA-type waveguide. The present invention also extends it to the AB-type waveguide and the valley photonic crystal with a honeycomb lattice and circular air holes. The present invention constructs a valley photonic crystal with a honeycomb lattice and circular air holes. The rhombic unit cell of the VPC is as Figure 6 (a) shows, and the unit cell consists of a Si substrate (n = 3.42) and two circular air holes with diameters d 1 and d 2 respectively, and the lattice constant a = 360 nm. The VPC unit cell is divided into type A (d 1 = 0.5a > d 2 = 0.3a) and type B (d 1 = 0.3a < d 2= 0.5a), similar to the triangular air-hole VPC, connecting the A-type and B-type unit cells will generate two topological edge states, AB and BA. The energy bands are as Figure 6 (b) shows, and at the same time Figure 6 (b) also shows the simulated H z distribution of the two edge states. The results show that the H z distribution of the AB-type edge mode shows odd symmetry along the interface, while the BA-type shows even symmetry, which is consistent with the triangular air-hole VPC.

[0049] The present invention first realizes the construction of a topological defect cavity in the BA-type waveguide. The topological defect cavity is mainly composed of six large air holes of the same size in the outer layer and six small air holes of the same size in the inner layer. The structure is as Figure 7 (a) shows. A key parameter for tuning the resonant frequency of the topological defect cavity is also defined: the diameter d of the small air holes in the inner layer. It should be noted that in order to ensure that the resonant frequency of the topological defect cavity is within the frequency range where robust transmission can be achieved in the BA-type waveguide, the present invention sets d = 90 nm. Simulate Figure 7 the transmittance of the structure in (a) at different frequencies. The results are as Figure 7 (b) shows. The results show that at this time, the topological defect cavity-topological waveguide coupling system can achieve low-reflection-loss transmission under non-resonant conditions.

[0050] Next, how to tune the symmetry of the cavity mode and realize the construction of a topological defect cavity in the AB-type waveguide will be introduced. As mentioned above, the H z distribution of the AB-type edge mode is odd-symmetric with respect to the waveguide interface. For a topological defect cavity with a geometric structure symmetric with respect to the waveguide interface directly coupled to the AB-type waveguide, its structure is as Figure 8 (a) shows, where d = 0.3a at this time. The H z distribution of the resonant mode is as Figure 8 (b) shows. It can be found that since the resonant mode is a monopole mode and the geometric structure of the topological defect cavity is symmetric with respect to the waveguide interface, the H z distribution of the resonant mode is even-symmetric with respect to the waveguide interface. At this time, the mode symmetry of the resonant mode of the topological defect cavity does not match that of the AB-type waveguide mode, resulting in extremely low coupling efficiency between the topological defect cavity and the AB-type waveguide.

[0051] To solve this problem, the present invention proposes to change the H z distribution of the resonant mode by destroying the geometric symmetry of the topological defect cavity with respect to the waveguide interface, thereby destroying the even symmetry of the H z distribution with respect to the waveguide interface, and finally achieving the purpose of improving the coupling efficiency between the topological defect cavity and the AB-type waveguide. The present invention removes two air holes above the waveguide interface and one air hole below the waveguide interface in the topological defect cavity. The structure is as Figure 8(c), the geometric symmetry of the topological defect cavity with respect to the waveguide interface is broken at this time. The H z distribution of the resonant mode of the simulated structure is shown in Figure 8 (d). The results show that the even symmetry of the cavity mode with respect to the waveguide interface is broken at this time, so the cavity mode and the waveguide mode can be matched, and the coupling efficiency between the topological defect cavity and the AB-type waveguide is greatly improved. Then, the present invention simulates the transmittance of the input signal at different frequencies in the structure of Figure 8 (c), and the results are shown in Figure 9 (a). The results show that the topological defect cavity-topological waveguide coupling system can also achieve low-reflection-loss transmission under non-resonant conditions at this time.

[0052] This method of tuning the mode symmetry is also applicable to the VPC with triangular air holes. For example, in the present invention, an air hole below the waveguide interface is removed from the topological defect cavity and directly coupled to the AB-type waveguide, and the structure is shown in Figure 9 (b). The parameters are the same as those set in the main text at this time, l = 0.3a. The transmittance of the simulated input signal at different frequencies in the structure of Figure 9 (b) is shown in Figure 9 (c), and the results show that the topological defect cavity-topological waveguide coupling system can also achieve low-reflection-loss transmission under non-resonant conditions at this time.

[0053] The advantages of the topological defect cavity such as low reflection loss, compact structure, and tunable resonant frequency enable it to be used as a compact low-reflection-loss logic element, providing more abundant functions for traditional integrated photonic devices based on waveguide bifurcation. As a demonstration, the present invention directly couples the topological defect cavity 1 with the side length l of the internal small air hole being 0.18a and the topological defect cavity 2 with l being 0.08a to the waveguide 1 at the top and the waveguide 2 at the bottom of the harpoon-type power splitter respectively to construct a multi-channel logic device, and its structure is shown in Figure 10 (a). This logic device has one input and three output ports. By controlling the frequency of the input signal, different output ports can be realized. For example, when the frequency of the input signal is 191.791 THz (the resonant frequency of the topological defect cavity 2) ([[]] Figure 10 (c)), the input signal is split and transmitted into the waveguide 1 and the waveguide 2. Due to the low reflection loss characteristic of the topological defect cavity under non-resonant conditions, the signal input into the waveguide 1 can be normally transmitted, while the signal input into the waveguide 2 is completely reflected due to resonance. Due to valley locking and vortex matching, the reflected signal will propagate into the waveguide where the input port and the output port 3 are located, so the ports 1 and 3 are opened at this time; similarly, when the frequency of the input signal is 193.828 THz (the resonant frequency of the topological defect cavity 1) ([[]] Figure 10(d)), ports 2 and 3 are opened; while when the frequency of the input signal is far from the resonance frequencies of the topological defect cavities 1 and 2 (e.g., 190 THz), ports 1 and 2 are opened, and at this time the logic device is consistent with the output ports of the fishbone beam splitter ( Figure 10 (b)). The above analysis results show that the multi-channel logic device can achieve more diverse output ports than the fishbone beam splitter, which reflects the application value of the topological defect cavity in compact integrated photonic devices.

Claims

1. A topological defect cavity based on valley photonic crystal, characterized in that: The topological defect cavity has a honeycomb lattice, and the unit cell consists of an Si substrate (substrate refractive index n = 3.42) and two equilateral triangular air holes with side lengths of l1 and l2 respectively. The lattice constant a = 360 nm, and the VPC unit cell is divided into type A (l1 = 0.7a > l2 = 0.3a) and type B (l1 = 0.3a < l2 = 0.7a) units.

2. A topological defect cavity based on valley photonic crystal according to claim 1, characterized in that: The type A and type B unit cell structures are spliced to construct two boundary states of AB type and BA type.

3. A topological defect cavity based on valley photonic crystal according to claim 2, characterized in that: In the waveguide, the value of the side length l of the inner small air hole can be flexibly tuned within the range of 0 to 0.36a.

4. A topological defect cavity based on valley photonic crystal according to claim 2 or 3, characterized in that: Changing the resonant mode H by breaking the geometric symmetry of the topological defect cavity about the waveguide interface z distribution, thus destroying H z Even symmetry of the distribution about the waveguide interface.

5. A topological defect cavity based on valley photonic crystal according to any one of claims 1 to 4, characterized in that: The equilateral triangular air holes are replaced by circular air holes.

6. A multi-channel logic device comprising the topological defect cavity according to any one of claims 1 to 5, characterized in that: Two topological defect cavities with different inner triangular small hole sizes l are directly coupled to two waveguides of a harpoon-type energy splitter respectively to construct a multi-channel logic device. By tuning the value of l, the resonant frequency of the topological defect cavity embedded in the harpoon-type splitter is changed, and further the output result of the multi-channel logic device is tuned.

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