Topological photonic crystal waveguide with channel integration function

Abstract

The invention discloses a topological photonic crystal waveguide structure with a channel integration function, the waveguide structure is formed by arranging a plurality of supercells, each supercell comprises a first photonic crystal PC1, a second photonic crystal PC2 and a third photonic crystal PC3, the third photonic crystal PC3 is located on an optical channel, an I-type sandwich splicing strategy PC1-PC3-PC2 is adopted, and the first photonic crystal PC1, the second photonic crystal PC2, the third photonic crystal PC3 and the third photonic crystal PC3 are spliced together. Or an II-type'sandwich 'splicing strategy PC2-PC3-PC1 is adopted, the first photonic crystal PC1 and the second photonic crystal PC2 are a pair of multi-layer photonic crystals which are mirror images of each other and have the topological non-trivialness property, and the third photonic crystal PC3 is a single-layer photonic crystal with the topological trivialness property. Aiming at the defects in the prior art, the invention provides a brand-new topological photonic crystal waveguide structure capable of realizing coexistence of pseudo-spinning and valley-state topology phases, can support unidirectional transmission of a plurality of topological edge states in a single channel at the same time, greatly improves the integration level of a device, and has important application value in the field of integrated optical communication.

Description

Technical Field

[0001] The invention relates to the technical field of integrated optical communication waveguides, and in particular to a topological photonic crystal waveguide with a channel integration function. Background Art

[0002] In the past few decades, topological photonics has flourished under the inspiration of topological states of matter in condensed matter physics, bringing great hope for the robust control of electromagnetic waves. Many phenomena originally discovered in condensed matter physics, such as the quantum Hall effect, quantum spin Hall effect, and quantum valley Hall effect, can be simulated with the help of photonic crystals. This is because the behavior of photons in photonic crystals is similar to the behavior of electrons in quantum systems.

[0003] In photonic systems, the introduction of pseudospin and valley degrees of freedom brings unique advantages to electromagnetic wave transmission. They allow electromagnetic waves to be transmitted in pseudospin and valley modes, thereby achieving unidirectional propagation. This property not only has remarkable unidirectionality, but can also be easily manipulated by selecting the chirality of the excitation source. Therefore, it is very attractive to introduce pseudospin and valley degrees of freedom into photonic systems, which not only greatly expands the manipulation flexibility of electromagnetic energy transmission, but also provides unprecedented opportunities for the design of new functional electromagnetic devices. In order to expand the degrees of freedom of topological edge states in a particular system, valley and pseudospin photonic topological crystals can be combined to produce pseudospin-valley coupled edge states. However, in some cases, once the structure is constructed, the interface channel only supports a single type of edge state, such as valley edge state, pseudospin edge state. To this end, in 2022, Wei Guochao and others from Harbin Institute of Technology conducted research on the coexistence of valley and pseudospin states in distorted Kekulé cell photonic topological insulators (Photonics Research. 2022, 10(4): 999-1010). The study showed that after reasonable design, two-dimensional Kekulé photonic crystals with time-reversal symmetry can simultaneously support topological valley and pseudospin edge states in different frequency bands in the same channel, which lays the foundation for the development of new types of integrated topological photonic crystal functional waveguides. However, the photonic crystal waveguide can only support the transmission of three topological edge states in the same channel. Summary of the invention

[0004] The object of the present invention is to provide a topological photonic crystal waveguide design with channel integration function, which can support multiple topological state transmissions in the same channel.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A topological photonic crystal waveguide structure with channel integration function, the waveguide structure is formed by arranging multiple supercells, each supercell includes a first photonic crystal PC1, a second photonic crystal PC2 and a third photonic crystal PC3, the third photonic crystal PC3 is located on an optical channel, the first photonic crystal PC1 is located above the third photonic crystal PC3, the second photonic crystal PC2 is located below the third photonic crystal PC3, or the first photonic crystal PC1 is located below the third photonic crystal PC3, the second photonic crystal PC2 is located above the third photonic crystal PC3, wherein the first photonic crystal PC1 and the second photonic crystal PC2 are a pair of mutually mirrored multilayer photonic crystals with topological non-trivial properties, and the third photonic crystal PC3 is a single-layer photonic crystal with topological trivial properties.

[0007] Furthermore, the first photonic crystal PC1, the second photonic crystal PC2 and the third photonic crystal PC3 are honeycomb lattice photonic crystals.

[0008] Furthermore, the honeycomb lattice photonic crystal comprises 6 metal pillars placed on the vertices of a regular hexagon and 1 metal pillar placed at the center of the regular hexagon, and the lattice constant is a.

[0009] Furthermore, the metal pillars on the vertices of the regular hexagons of the first photonic crystal PC1 and the second photonic crystal PC2 include three metal pillars with a radius of r A The metal column A and three radii of r B The metal column B, metal columns A and metal columns B are arranged alternately, and the radius of the metal column C at the center of the regular hexagon is r C , r A <r B <r C The vertices and center of the regular hexagon of the third photonic crystal PC3 are D The metal column D, where r A <r B <r C , r B =r D .

[0010] Furthermore, 0.1a <r A <0.28a,0.1a <r B <0.28a,0.1a <r C <0.28a.

[0011] Furthermore, the metal pillar A, the metal pillar B, the metal pillar C and the metal pillar D in the first photonic crystal PC1, the second photonic crystal PC2 and the third photonic crystal PC3 are embedded in a dielectric background material.

[0012] Furthermore, the materials of the metal pillar A, the metal pillar B, the metal pillar C and the metal pillar D are copper, gold, silver or aluminum, and the dielectric background material is polytetrafluoroethylene.

[0013] Compared with the prior art, the present invention has the following technical effects: the present invention adopts a waveguide structure design in which a single-layer photonic crystal with topologically trivial properties is inserted in the middle of a multi-layer photonic crystal with topologically non-trivial properties, thereby achieving simultaneous support for unidirectional transmission of multiple (3 or 4) topological edge states in a single channel, greatly improving the integration of the device and having important application value in the field of integrated optical communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the topological photonic crystal waveguide structure with channel integration function of the present invention.

[0015] Figure 2 This is a simulation diagram of the topological photonic crystal waveguide structure with channel integration function of the present invention.

[0016] Figure 3 The energy band diagram and mode diagram corresponding to PC1 and PC2 in the first embodiment of the present invention.

[0017] Figure 4 In the first embodiment of the present invention, supercell projection energy bands corresponding to type I and type II splicing strategies are adopted.

[0018] Figure 5 Schematic diagram of full-field simulation of topological edge states corresponding to the I-type splicing strategy adopted in Example 1 of the present invention.

[0019] Figure 6 Schematic diagram of full-field simulation of each topological edge state corresponding to the type II splicing strategy adopted in Example 1 of the present invention.

[0020] Figure 7 Schematic diagram of full-field simulation of topological edge states corresponding to the I-type splicing strategy adopted in the second embodiment of the present invention.

[0021] Figure 8 Schematic diagram of full-field simulation of each topological edge state corresponding to the type II splicing strategy adopted in the second embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention proposes a topological photonic crystal waveguide structure with channel integration function, wherein the waveguide structure is formed by arranging a plurality of supercells, each supercell comprising a first photonic crystal PC1, a second photonic crystal PC2 and a third photonic crystal PC3, and Figure 1-2, adopting a type I "sandwich" splicing strategy PC1-PC3-PC2, that is, the third photonic crystal PC3 is located on the optical channel, the first photonic crystal PC1 is located above the third photonic crystal PC3, and the second photonic crystal PC2 is located below the third photonic crystal PC3, or adopting a type II "sandwich" splicing strategy PC2-PC3-PC1, that is, the third photonic crystal PC3 is located on the optical channel, the first photonic crystal PC1 is located below the third photonic crystal PC3, and the second photonic crystal PC2 is located above the third photonic crystal PC3, wherein the first photonic crystal PC1 and the second photonic crystal PC2 are a pair of mirror-image multilayer photonic crystals with topological non-trivial properties, and the third photonic crystal PC3 is a single-layer photonic crystal with topological trivial properties.

[0023] Furthermore, the first photonic crystal PC1, the second photonic crystal PC2 and the third photonic crystal PC3 are honeycomb lattice photonic crystals.

[0024] Furthermore, the honeycomb lattice photonic crystal comprises 6 metal pillars placed on the vertices of a regular hexagon and 1 metal pillar placed at the center of the regular hexagon, and the lattice constant is a.

[0025] Furthermore, the metal pillars on the vertices of the regular hexagons of the first photonic crystal PC1 and the second photonic crystal PC2 include three metal pillars with a radius of r A The metal column A and three radii of r B The metal column B, metal columns A and metal columns B are arranged alternately, and the radius of the metal column C at the center of the regular hexagon is r C , r A <r B <r C The vertices and center of the regular hexagon of the third photonic crystal PC3 are D The metal column D, where r A <r B <r C , r B =r D .

[0026] Preferably, 0.1a <r A <0.28a,0.1a <r B <0.28a,0.1a <r C <0.28a. The design of the above size range takes into account that if the radius of the metal column is too small, the band gap will be too small, which is not conducive to the design of the waveguide. If the radius of the metal column is too large, it will be not conducive to the design of the waveguide mechanism.

[0027] Furthermore, the metal pillar A, the metal pillar B, the metal pillar C and the metal pillar D in the first photonic crystal PC1, the second photonic crystal PC2 and the third photonic crystal PC3 are embedded in a dielectric background material.

[0028] Furthermore, the materials of the metal pillar A, the metal pillar B, the metal pillar C and the metal pillar D are copper, gold, silver or aluminum, and the dielectric background material is polytetrafluoroethylene.

[0029] Embodiment 1

[0030] The metal column material is copper, the background medium material is polytetrafluoroethylene, and the PC1 and PC2 parameters are r A =0.1a, r B =0.15a, r C =0.18a; PC3 parameter is r D =0.15a. a is 10√3mm.

[0031] Figure 3 The energy band diagram and mode diagram corresponding to PC1 and PC2 are shown in Figure (a) and Figure (b) respectively. Figure 3 It can be seen that two band gaps appear between the first and second energy bands and between the fifth and sixth energy bands in PC1 and PC2 at the K point in the Brillouin zone. The eigenmodes at the edges of the band gaps exhibit typical valley topological phases, and the valley states of PC1 and PC2 are mirror images of each other.

[0032] Figure 4 Figures (a) and (b) in the figure are the supercell projection energy bands corresponding to the type I and type II splicing strategies, respectively. Figure 4 As shown in the figure, if the Type I splicing strategy is adopted, two pseudospin topological edge state energy bands (1 and 2) and one valley topological edge state energy band (3) can be found in the projected energy band, with a total of three topologically protected edge states. If the Type II splicing strategy is adopted, two pseudospin topological edge state energy bands (2 and 3) and two valley topological edge state energy bands (1 and 4) can be found in the projected energy band, with a total of four topologically protected edge states.

[0033] Figure 5 and Figure 6 The full-field simulation results of each topological edge state corresponding to the type I and type II splicing strategies are given. It can be clearly seen that both the three topological edge states in the type I splicing strategy and the four topological edge states in the type II splicing strategy exhibit unidirectional transmission characteristics.

[0034] Embodiment 2

[0035] The metal column material is silver, the background medium material is polytetrafluoroethylene, and the PC1 parameter is r A=0.11a, r B =0.16a, r C =0.19a; PC3 parameter is r D =0.16a. a is 10√3mm.

[0036] Figure 7 and Figure 8 The full-field simulation results of each topological edge state corresponding to the type I and type II splicing strategies are given. It can be clearly seen that both the three topological edge states in the type I splicing strategy and the four topological edge states in the type II splicing strategy exhibit unidirectional transmission characteristics.

[0037] The above embodiments demonstrate that the topological photonic crystal waveguide implementation scheme with channel integration function of the present invention is feasible and can simultaneously support unidirectional transmission of multiple topological edge states in a single channel.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A topological photonic crystal waveguide structure with channel integration function, characterized in that: The waveguide structure is formed by arranging a plurality of supercells, each supercell comprising a first photonic crystal PC1, a second photonic crystal PC2 and a third photonic crystal PC3, the third photonic crystal PC3 being located on an optical channel, the first photonic crystal PC1 being located above the third photonic crystal PC3, the second photonic crystal PC2 being located below the third photonic crystal PC3, or the first photonic crystal PC1 being located below the third photonic crystal PC3, the second photonic crystal PC2 being located above the third photonic crystal PC3, wherein the first photonic crystal PC1 and the second photonic crystal PC2 are a pair of mutually mirrored multilayer photonic crystals having topologically non-trivial properties, and the third photonic crystal PC3 is a single-layer photonic crystal having topologically trivial properties.

2. The topological photonic crystal waveguide structure with channel integration function according to claim 1, characterized in that: The first photonic crystal PC1, the second photonic crystal PC2 and the third photonic crystal PC3 are honeycomb lattice photonic crystals.

3. The topological photonic crystal waveguide structure with channel integration function according to claim 2, characterized in that: The honeycomb lattice photonic crystal comprises six metal columns placed on the vertices of a regular hexagon and one metal column placed at the center of the regular hexagon, and the lattice constant is a.

4. The topological photonic crystal waveguide structure with channel integration function according to claim 3, characterized in that: The metal pillars on the vertices of the regular hexagons of the first photonic crystal PC1 and the second photonic crystal PC2 include three A The metal column A and three radii of r B The metal column B, metal columns A and metal columns B are arranged alternately, and the radius of the metal column C at the center of the regular hexagon is r C , r A <r B <r C The vertices and center of the regular hexagon of the third photonic crystal PC3 are D The metal column D, where r A <r B <r C , r B =r D .

5. The topological photonic crystal waveguide structure with channel integration function according to claim 4, characterized in that: Of which 0.1a <r A <0.28a,0.1a <r B <0.28a,0.1a <r C <0.28a.

6. The topological photonic crystal waveguide structure with channel integration function according to claim 5, characterized in that: The metal pillars A, B, C and D in the first photonic crystal PC1, the second photonic crystal PC2 and the third photonic crystal PC3 are embedded in a dielectric background material.

7. The topological photonic crystal waveguide structure with channel integration function according to claim 6, characterized in that: The materials of the metal pillar A, the metal pillar B, the metal pillar C and the metal pillar D are copper, gold, silver or aluminum, and the dielectric background material is polytetrafluoroethylene.

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