Photonic crystal wavelength division multiplexer based on high-order topological two-angle state

Abstract

The application discloses a photonic crystal wavelength division multiplexer based on high-order topology double-angle state, which comprises a first strip waveguide, a second strip waveguide, a third strip waveguide, a first defect waveguide, a second defect waveguide, a third defect waveguide, a first photonic crystal dielectric plate and a second photonic crystal dielectric plate. The first photonic crystal dielectric plate and the second photonic crystal dielectric plate are in the same horizontal plane, the first defect waveguide and the second defect waveguide are arranged on the first photonic crystal dielectric plate, the first defect waveguide is connected to the first strip waveguide, and the second defect waveguide is connected to the second strip waveguide. The third defect waveguide is arranged on the second photonic crystal dielectric plate, and the third defect waveguide is connected to the third strip waveguide. Compared with the prior art, the application has the advantages of simple design method, novel design idea and low crosstalk value of performance index.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-nano and integrated optoelectronic technology, and more particularly, to a photonic crystal wavelength division multiplexer based on high-order topological double angular states. BACKGROUND

[0002] With the development of information technology, more flexible light field regulation and optical information processing methods have attracted widespread attention. Photonic crystals are artificial optical materials formed by periodically arranging two or more different refractive index materials. Due to its unique photonic bandgap property, it can be used to make photonic crystal microcavities, filters, multiplexers and other photonic devices. Among them, the wavelength division multiplexer is used to realize the multiplexing or demultiplexing of two or more different wavelengths of light.

[0003] However, due to the errors and process precision limitations in the device preparation process, there are inevitable problems of energy scattering-induced loss at the device turning points and local microcavities. In addition to constantly improving the preparation process, we can also find a solution from the physical principle, and topological photonics is one of the solutions to overcome this type of energy loss. Current research mainly uses the coupling between waveguide modes and microcavity modes to realize wavelength division multiplexing on a photonic crystal slab. The application of topological photonic crystals in on-chip photonic devices still has some limitations, and the research on photonic devices based on angular state microcavities such as wavelength division multiplexers is less, and less attention is paid to the direction selectivity of angular state excitation, which limits the expansion of topological photonic crystals to more on-chip optical devices.

[0004] Topological photonics uses quantities that remain unchanged under a series of continuous transformations, making the global structure robust to local perturbations or defects, thus providing a new anti-scattering mechanism in physics, which has great potential for improving the performance of photonic devices.

[0005] The prior art discloses a wavelength division multiplexer design method and system based on topological photonic crystals, which comprises the following steps: obtaining three photonic crystal unit cells after topological optimization, the photonic crystal unit cells including PC1 unit cell, PC3 unit cell and PC4 unit cell; combining the three photonic crystal unit cells in pairs to obtain different supercells; determining the boundary state and transmission efficiency of each supercell; designing four directional point sources at the junction of the PC3 unit cell and the PC4 unit cell; verifying whether the structure composed of the three photonic crystal unit cells can produce the combined effect of unidirectional propagation, boundary state and wavelength division multiplexing; obtaining the wavelength division multiplexer; and destroying the structure of each supercell to determine that the overall effect of the wavelength division multiplexer is not affected. The defect of this method is that it uses the unidirectional transmission of the boundary state to realize wavelength division multiplexing, which is not suitable for cases where wavelength division multiplexing is required in two direction waveguides.

[0006] To this end, in combination with the above needs and defects of the prior art, the application provides a photonic crystal wavelength division multiplexer based on high-order topological double-angle states. SUMMARY

[0007] The application provides a photonic crystal wavelength division multiplexer based on high-order topological double-angle states, which changes the coupling efficiency by changing the included angle θ of the waveguide with the horizontal direction, thereby obtaining a wavelength division multiplexer with low crosstalk.

[0008] The primary object of the application is to solve the above technical problems, and the technical solution of the application is as follows:

[0009] The application provides a photonic crystal wavelength division multiplexer based on high-order topological double-angle states, which includes a first strip waveguide, a second strip waveguide, a third strip waveguide, a first defect waveguide, a second defect waveguide, a third defect waveguide, a first photonic crystal dielectric plate, and a second photonic crystal dielectric plate.

[0010] The first photonic crystal dielectric plate and the second photonic crystal dielectric plate are in the same horizontal plane and are connected to each other by two connecting boundaries, and the intersection of the two connecting boundaries constitutes a corner structure with high-order topological double-angle states; the first defect waveguide and the second defect waveguide are arranged on the first photonic crystal dielectric plate, one end of the first defect waveguide is L1 away from the corner structure, the other end extends outward from the first photonic crystal dielectric plate and is connected to the first strip waveguide, one end of the second defect waveguide is L2 away from the corner structure, the other end extends outward from the first photonic crystal dielectric plate and is connected to the second strip waveguide; the third defect waveguide is arranged on the second photonic crystal dielectric plate, one end of the third defect waveguide is L3 away from the corner structure, and the other end extends outward from the second photonic crystal dielectric plate and is connected to the third strip waveguide.

[0011] Further, the first photonic crystal dielectric plate is composed of a first unit cell arranged periodically, and the second photonic crystal dielectric plate is composed of a second unit cell arranged periodically; the first unit cell and the second unit cell are both Kagome lattice photonic crystals and have an initial shape of a regular hexagon, a first air hole is arranged at the center of the first unit cell, and a second air hole is arranged at three non-adjacent apex angles of the second unit cell.

[0012] Further, part of the first air holes of the first photonic crystal dielectric plate are filled with photonic crystal dielectric to obtain the first defect waveguide and the second defect waveguide, and part of the second air holes of the second photonic crystal dielectric plate are filled with photonic crystal dielectric to obtain the third defect waveguide.

[0013] Further, the first air hole of the first unit cell is arranged as a regular hexagon, and the second air hole of the second unit cell is arranged as a rhombus.

[0014] Further, the side length of the first air hole and the second air hole is 0.28a, wherein a represents a lattice constant.

[0015] Further, the overall size of the first photonic crystal dielectric slab and the second photonic crystal dielectric slab is

[0016] Further, the width of the first defect waveguide is The length of the first defect waveguide is 38a; the width of the second defect waveguide is The width of the third defect waveguide is a, and the length is

[0017] Further, the width of the first strip waveguide is The length of the first strip waveguide is 20a; the width of the second strip waveguide is The width of the third strip waveguide is 2a, and the length is 20a.

[0018] Further, the input port of the first strip waveguide is used to receive light containing two wavelengths and transmit to the first defect waveguide, then excite two local corner state modes at the corner structure, and separate the light of two wavelengths, wherein the light of the first wavelength enters the third defect waveguide through boundary coupling with a length of L3, and is output from the output port of the third strip waveguide, and the light of the second wavelength enters the second defect waveguide through boundary coupling with a length of L2, and is output from the output port of the second strip waveguide.

[0019] Further, by adjusting the included angle θ of the second strip waveguide and the second defect waveguide with the horizontal direction, the transmission peak efficiency is changed, so as to adjust the demultiplexing effect of the wavelength division multiplexer, and the optimal coupling angle is θ=30°.

[0020] Compared with the prior art, the beneficial effects of the technical scheme of the present application are:

[0021] The present application provides a photonic crystal wavelength division multiplexer based on high-order topological double-angle state, which uses topological optical principle to predict topological double-angle state local mode, and designs a topologically protected photonic crystal wavelength division multiplexer; by changing the included angle θ of the waveguide with the horizontal direction, the coupling efficiency is changed, so as to obtain a wavelength division multiplexer with low crosstalk. It has the advantages of simple design principle, novel design idea, etc., and is expected to provide a new idea for guiding the design of topological photonic wavelength division multiplexer, and has potential application in wavelength division multiplexing system. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1A schematic diagram of a photonic crystal wavelength division multiplexer based on high-order topology double-angle state according to an embodiment of the present application.

[0023] Figure 2 A schematic diagram of an xy cross section of a photonic crystal wavelength division multiplexer according to an embodiment of the present application.

[0024] Figure 3 A magnetic field energy distribution diagram when a photonic crystal wavelength division multiplexer according to an embodiment of the present application transmits.

[0025] Figure 4 A transmission spectrum diagram of a photonic crystal wavelength division multiplexer with a rotation angle θ=0° according to an embodiment of the present application.

[0026] Figure 5 A transmission spectrum diagram of a photonic crystal wavelength division multiplexer with a rotation angle θ=30° according to an embodiment of the present application.

[0027] Figure 6 A transmission spectrum diagram of a photonic crystal wavelength division multiplexer with a rotation angle θ=45° according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to more clearly understand the above objectives, features and advantages of the present application, the following further specifically describes the present application with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0029] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, however, the present application can also be implemented in other manners different from those described herein, and therefore, the protective scope of the present application is not limited by the specific embodiments disclosed below.

[0030] Before the specific embodiments are described, the following explains the specific terms involved in the present application as shown below:

[0031] Bandwidth (BW): defined as the frequency band width when the transmittance of a wavelength division multiplexer reduces to half of the transmission signal. It is used to represent the frequency width occupied by the transmission signal, and within the bandwidth, half of the power is concentrated. In logarithmic coordinates, the half-power point corresponds to the position of-3dB, and the bandwidth defined in the present application can be considered as a 3dB bandwidth. In optical fiber transmission, the size of the bandwidth is used to represent the ability of the line to transmit data.

[0032] Free Spectral Range (FSR): Defined as the wavelength difference between the output signals at the two output ports of a wavelength division multiplexer. It refers to the wavelength interval between two adjacent resonant modes in a resonant cavity and serves as an important indicator of wavelength selectivity. Its magnitude determines whether different wavelengths of light can be selectively transmitted. FSR is a key parameter in laser and fiber optic communication; a larger free spectral range can improve the communication performance of optical devices.

[0033] Crosstalk is defined as the degree of influence of interfering light on transmitted light in a transmission channel. It is calculated by taking the logarithm of the ratio of the transmittance of interfering light to the transmittance of transmitted light in the transmission channel and then multiplying it by a coefficient of 10. This can be understood as the smaller the channel crosstalk, the smaller the ratio of interfering light to transmitted light, and the better the WDM multiplexing effect.

[0034] Example 1

[0035] like Figure 1 As shown, the present invention provides a photonic crystal wavelength division multiplexer based on a high-order topological biangular state, comprising: a first strip waveguide 1, a second strip waveguide 2, a third strip waveguide 3, a first defect waveguide 4, a second defect waveguide 5, a third defect waveguide 6, a first photonic crystal dielectric plate 8, and a second photonic crystal dielectric plate 9.

[0036] The first photonic crystal dielectric plate 8 and the second photonic crystal dielectric plate 9 are on the same horizontal plane and are connected to each other by two connecting boundaries. The intersection of the two connecting boundaries forms a corner structure 7 with a higher-order topological biangular state. A first defect waveguide 4 and a second defect waveguide 5 are provided on the first photonic crystal dielectric plate 8. One end of the first defect waveguide 4 is at a distance L1 from the corner structure 7, and the other end extends outward from the first photonic crystal dielectric plate 8 and is connected to the first strip waveguide 1. One end of the second defect waveguide 5 is at a distance L2 from the corner structure 7, and the other end extends outward from the first photonic crystal dielectric plate 8 and is connected to the second strip waveguide 2. A third defect waveguide 6 is provided on the second photonic crystal dielectric plate 9. One end of the third defect waveguide 6 is at a distance L3 from the corner structure 7, and the other end extends outward from the second photonic crystal dielectric plate 9 and is connected to the third strip waveguide 3.

[0037] like Figure 2 As shown, the first photonic crystal dielectric plate 8 is composed of a periodically arranged first unit cell 10, and the second photonic crystal dielectric plate 9 is composed of a periodically arranged second unit cell 11; the first unit cell 10 and the second unit cell 11 are both Kagome lattice photonic crystals with an initial shape of regular hexagon. A first air hole is provided at the center of the first unit cell 10, and a second air hole is provided at the three non-adjacent vertices of the second unit cell 11.

[0038] The first defect waveguide 4 and the second defect waveguide 5 are obtained by filling the first air holes of the first photonic crystal dielectric slab 8 with photonic crystal dielectric, and the third defect waveguide 6 is obtained by filling the second air holes of the second photonic crystal dielectric slab 9 with photonic crystal dielectric.

[0039] The first air holes of the first unit cell 10 are arranged as regular hexagons, and the second air holes of the second unit cell 11 are arranged as rhombuses. The side length of the first air holes and the second air holes is 0.28a, where a represents the lattice constant.

[0040] In a specific embodiment, the lattice constant a = 407 nm. The two-dimensional Zak phase of the first unit cell 10 is (0, 0), i.e., the first unit cell 10 is in a trivial topological phase, and the two-dimensional Zak phase of the second unit cell 11 is (π, π), i.e., the second unit cell 11 is in a non-trivial topological phase.

[0041] The overall size of the first photonic crystal dielectric slab 8 and the second photonic crystal dielectric slab 9 is The width of the first defect waveguide 4 is The length of the first defect waveguide 4 is 38a; the width of the second defect waveguide 5 is The width of the third defect waveguide 6 is a, and the length is The width of the first strip waveguide 1 is The length of the first strip waveguide 1 is 20a; the width of the second strip waveguide 2 is The width of the third strip waveguide 3 is 2a, and the length is 20a.

[0042] In a specific embodiment, the first photonic crystal dielectric slab 8, the second photonic crystal dielectric slab 9, the first strip waveguide 1, the second strip waveguide 2, the third strip waveguide 3, and the first defect waveguide 4, the second defect waveguide 5, and the third defect waveguide 6 are all made of silicon, and the refractive index is 3.464.

[0043] Embodiment 2

[0044] Based on the above embodiment 1, in combination with Figure 3 , this embodiment describes the working principle of the present application in detail.

[0045] As Figure 3As shown, the input port of the first strip waveguide 1 is used to receive light containing two wavelengths λ3 and λ4 and transmit it to the first defect waveguide 4. Then, two local angular modes are excited at the corner structure 7 to separate the two wavelengths of light. The light of the first wavelength λ3 is coupled into the third defect waveguide 6 through a boundary of length L3 and output from the output port of the third strip waveguide 3. The light of the second wavelength λ4 is coupled into the second defect waveguide 5 through a boundary of length L2 and output from the output port of the second strip waveguide 2.

[0046] Example 3

[0047] Based on the above embodiments 1 and 2, as Figures 4-6 As shown, the demultiplexing process of the present invention is illustrated in detail in the embodiments of the present invention.

[0048] The photonic crystal wavelength division multiplexer of the present invention adjusts the transmission peak efficiency by adjusting the angle θ between the second strip waveguide 2 and the second defect waveguide 5 and the horizontal direction, thereby adjusting the demultiplexing effect of the wavelength division multiplexer. The optimal coupling angle is θ = 30°.

[0049] like Figure 4 As shown, when θ = 0° (less than the optimal coupling angle), Port2 can achieve a signal output with a bandwidth of 0.235nm, and Port3 can achieve a signal output with a bandwidth of 0.178nm.

[0050] like Figure 5 As shown, when θ = 30° (equal to the optimal coupling angle), Port2 can achieve a signal output with a bandwidth of 0.235nm, and Port3 can achieve a signal output with a bandwidth of 0.178nm.

[0051] like Figure 6 As shown, when θ = 45° (greater than the optimal coupling angle), Port2 can achieve a signal output with a bandwidth of 0.353nm, and Port3 can achieve a signal output with a bandwidth of 0.297nm.

[0052] It can be seen that when θ = 0° (less than the optimal coupling angle) or θ = 45° (greater than the optimal coupling angle), the transmittance is lower than when θ = 30° (equal to the optimal coupling angle).

[0053] In one specific embodiment, the free spectral range of the output signal of the wavelength division multiplexer based on the higher-order topological biangular state is simulated and calculated, with the following results: Figure 4 , 5When θ = 0° (less than the optimal coupling angle), the free spectral range of the two ports is 7.38 nm; when θ = 45° (greater than the optimal coupling angle), the free spectral range of the two ports is 7.14 nm; when θ = 30° (equal to the optimal coupling angle), the free spectral range of the two ports is 7.38 nm.

[0054] Further, the channel crosstalk of the WDM based on the high-order topology double-angle state is simulated, and the calculation formula is C = 10log(I ′ out / I out When θ = 0° (less than the optimal coupling angle), the crosstalk C = 5.9142; when θ = 45° (greater than the optimal coupling angle), the crosstalk C = -0.9337; when θ = 30° (equal to the optimal coupling angle), the crosstalk C = -12.8038.

[0055] In the embodiments provided by the present application, it should be understood that the disclosed system and method can be implemented in other ways. Those skilled in the art can understand that all or part of the steps of the above-mentioned method embodiments can be completed by a program instructing related hardware, and the foregoing program can be stored in a computer-readable storage medium, and when the program is executed, the steps of the above-mentioned method embodiments are performed. The foregoing storage medium includes mobile storage equipment, read-only memory (ROM), random access memory (RAM), magnetic disk or optical disk, and various media capable of storing program codes.

[0056] Alternatively, the above-mentioned embodiments of the present application can be stored in a computer-readable storage medium if they are realized in the form of software function modules and sold or used as independent products. Based on such understanding, the technical solutions of the embodiments of the present application can be embodied in the form of a software product, and the computer software product is stored in a storage medium, includes several instructions for causing a computer device to execute all or part of the methods described in the embodiments of the present application. The foregoing storage medium includes mobile storage equipment, ROM, RAM, magnetic disk or optical disk, and various media capable of storing program codes.

[0057] Obviously, the above embodiments of the present application are merely exemplary and are not intended to limit the embodiments of the present application. The icons in the drawings for describing the positional relationship of the structures are only used for exemplary illustration and should not be understood as a limitation of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A photonic crystal wavelength division multiplexer based on high-order topological two-angle states, characterized in that, The application relates to a photonic crystal waveguide device, which comprises a first strip waveguide (1), a second strip waveguide (2), a third strip waveguide (3), a first defect waveguide (4), a second defect waveguide (5), a third defect waveguide (6), a first photonic crystal dielectric slab (8) and a second photonic crystal dielectric slab (9); the first photonic crystal dielectric slab (8) is composed of periodically arranged first unit cells (10), and the second photonic crystal dielectric slab (9) is composed of periodically arranged second unit cells (11); the first unit cells (10) and the second unit cells (11) are both Kagome lattice photonic crystals and have an initial shape of a regular hexagon; a first air hole is arranged at the center of the first unit cell (10), and a second air hole is arranged at three non-adjacent apex angles of the second unit cell (11); the first air hole of the first unit cell (10) is arranged as a regular hexagonal hole, and the second air hole of the second unit cell (11) is arranged as a rhombic hole. The first photonic crystal dielectric slab (8) and the second photonic crystal dielectric slab (9) are located in the same horizontal plane and are connected with each other through two connecting boundaries, and the intersection of the two connecting boundaries forms a corner structure (7) with high-order topological double-angle states; the first defect waveguide (4) and the second defect waveguide (5) are arranged on the first photonic crystal dielectric slab (8), one end of the first defect waveguide (4) is away from the corner structure (7) by a distance L1, the other end of the first defect waveguide (4) extends out of the first photonic crystal dielectric slab (8) and is connected to the first strip waveguide (1), one end of the second defect waveguide (5) is away from the corner structure (7) by a distance L2, the other end of the second defect waveguide (5) extends out of the first photonic crystal dielectric slab (8) and is connected to the second strip waveguide (2); the third defect waveguide (6) is arranged on the second photonic crystal dielectric slab (9), one end of the third defect waveguide (6) is away from the corner structure (7) by a distance L3, the other end of the third defect waveguide (6) extends out of the second photonic crystal dielectric slab (9) and is connected to the third strip waveguide (3); the input port of the first strip waveguide (1) is used for receiving light containing two wavelengths and transmitting the light to the first defect waveguide (4), then exciting two local angle state modes at the corner structure (7) to separate the light of the two wavelengths, wherein the light of the first wavelength is coupled into the third defect waveguide (6) through a boundary with a length of L3 and is output from the output port of the third strip waveguide (3), and the light of the second wavelength is coupled into the second defect waveguide (5) through a boundary with a length of L2 and is output from the output port of the second strip waveguide (2).

2. The photonic crystal wavelength division multiplexer based on high-order topological two-angle states according to claim 1, characterized in that, The first defect waveguide (4) and the second defect waveguide (5) are obtained by filling photonic crystal dielectric in part of the first air holes of the first photonic crystal dielectric slab (8), and the third defect waveguide (6) is obtained by filling photonic crystal dielectric in part of the second air holes of the second photonic crystal dielectric slab (9). 3.The photonic crystal wavelength division multiplexer based on high-order topological two-angle states according to claim 2, characterized in that, The side length of the first air hole and the second air hole is 0.28a, wherein a represents a lattice constant.

4. The photonic crystal wavelength division multiplexer based on high-order topological two-angle states according to claim 3, characterized in that, The overall dimensions of the first photonic crystal dielectric slab (8) and the second photonic crystal dielectric slab (9) are 5. The photonic crystal wavelength division multiplexer based on high-order topological two-angle states according to claim 4, characterized in that, The width of the first defective waveguide (4) is Length 38a; The width of the second defect waveguide (5) is a The width of the third defect waveguide (6) is a, and the length is 6. The photonic crystal wavelength division multiplexer based on high-order topological two-angle states according to claim 5, characterized in that, The width of the first strip waveguide (1) is The width of the second strip waveguide (2) is The width of the third strip waveguide (3) is 2a and the length is 20a.

7. The photonic crystal wavelength division multiplexer based on high-order topological two-angle states according to any one of claims 1-6, characterized in that, The efficiency of the transmission peak is changed by adjusting the angle θ between the second bar waveguide (2) and the second defect waveguide (5) and the horizontal direction, so that the demultiplexing effect of the wavelength division multiplexer is adjusted, and the optimal coupling angle is θ=30°.

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