An optical waveguide and a three-channel wavelength division multiplexer

Abstract

This invention discloses an optical waveguide and a three-channel wavelength division multiplexer, including a waveguide interface, a first valley photonic crystal, and a second valley photonic crystal; the first valley photonic crystal is composed of a plurality of first regular hexagonal unit cells arranged periodically with a lattice constant as the period length, and a single first regular hexagonal unit cell has C 3v Rotational symmetry is maintained, with the top and bottom vertices of the first regular hexagonal unit cell forming the first and second silicon dielectric pillars, respectively. The second valley photonic crystal is composed of several second regular hexagonal unit cells arranged periodically with a lattice constant as the period length. A single second regular hexagonal unit cell has C0... 3v The second regular hexagonal cell exhibits rotational symmetry, with its upper and lower vertices forming a second silicon dielectric pillar and a first silicon dielectric pillar, respectively. The side length of the first silicon dielectric pillar is greater than that of the second silicon dielectric pillar, resulting in opposite vortex chirality at point K of the first and second regular hexagonal cells within the same energy band. The valley photonic crystal of this invention possesses C3 symmetry and exhibits higher stability.

Description

Technical Field

[0001] This invention belongs to the field of photonic crystal technology, specifically relating to an optical waveguide and a three-channel wavelength division multiplexer. Background Technology

[0002] In recent years, photonic integrated circuits (PICs) have made significant progress in the field of modern information processing. As a key platform for all-optical communication and quantum computing, their development has driven the research and development of various integrated functional devices, such as light sources, optical modulators, transceivers, wavelength division multiplexing (WDM) devices, and photodetectors. Among these, WDM devices can transmit multi-wavelength optical signals in parallel, playing a crucial role in long-distance communication, data center interconnection, and high-performance computing. However, traditional WDM devices based on dielectric thin films or fiber gratings suffer from problems such as large size, high transmission loss, and low integration density. To overcome these issues, photonic crystals (PCs), due to their unique photonic bandgap modulation capabilities and flexible structural design, have become ideal candidate materials for realizing high-performance WDM devices. Building on this, two-dimensional valley photonic crystals (VPCs) introduce valley topological states, enabling them to simulate the quantum valley Hall effect and further enhance the unidirectionality and robustness of light transmission, providing a new approach for achieving high-precision wavelength-selective separation.

[0003] Traditional wavelength division multiplexing (WDM) devices are primarily designed based on silicon waveguides and optical fibers, but their performance is limited by material properties and manufacturing processes, resulting in typically large sizes that hinder photonic integration. In contrast, two-dimensional valley photonic crystals (WDMs) achieve high forward transmittance based on the spin valley-locking effect, using topologically protected valley states to efficiently control light waves. Compared to traditional photonic crystals, valley photonic crystal WDMs offer significant advantages in interference immunity and transmission efficiency, and typically have larger operating bandwidths. For example, Ruan et al. proposed a three-channel WDM based on a rotating cylindrical array of two-dimensional photonic crystals. The three channels of this device can achieve transmission at frequencies of 9.41 GHz, 10.27 GHz, and 10.79 GHz, respectively, but the optical transmission efficiency of all three channels in experimental verification was low (<65%). Xu et al. reported a method for generating primordial silicon cells based on inverse topology optimization, successfully constructing a high-efficiency topological boundary state WDM. However, this method could only achieve power transfer in the two channels at 6.3 GHz and 12.4 GHz. Wang et al. proposed a dual-channel WDM based on a silicon plate air column unit cell. This device could operate at 1500 nm and 1630 nm in the communication band in demultiplexing mode, but the power transfer efficiency in both boundary states was less than 80%. Guo et al., based on their team's topological power divider design, precisely controlled the lattice constant and size characteristics of VPCs to achieve dual-channel wavelength division multiplexing (WDM) decomposition (5.9 GHz, 6.2 GHz), but this method could only divide the wavelengths into two channels. Xu et al. used a metal tripod photonic crystal with rotational degrees of freedom to construct a three-channel multi-angle WDM (10.08 GHz, 9.97 GHz, 9.92 GHz) using an "ABA" arrangement. This WDM had advantages such as low crosstalk and low scattering, but it could not achieve complete demultiplexing of the three frequencies. In summary, for valley photonic crystal WDM, the above studies have designed various device architectures based on different cell construction methods, but there are few studies on WDM that simultaneously have the three characteristics of fully multiplexed / demultiplexed three channels, high transmission efficiency and adjustable transmission bandwidth. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes an optical waveguide and a three-channel wavelength division multiplexer. The valley photonic crystal in the optical waveguide has C3 symmetry, which makes the optical waveguide more stable.

[0005] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0006] An optical waveguide includes a waveguide interface and a first valley photonic crystal and a second valley photonic crystal distributed on both sides of the waveguide interface.

[0007] The first valley photonic crystal is composed of a number of first regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a; a single first regular hexagonal unit cell has C 3v Rotational symmetry, with the first and second silicon dielectric pillars arranged alternately at its six vertices, the upper and lower vertices of the first regular hexagonal cell being the first and second silicon dielectric pillars, respectively;

[0008] The second valley photonic crystal is composed of a number of second regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a; a single second regular hexagonal unit cell has C 3v Rotational symmetry, with the first and second silicon dielectric pillars arranged alternately at its six vertices, and the second silicon dielectric pillar and the first silicon dielectric pillar at the upper and lower vertices of the second regular hexagonal cell, respectively.

[0009] Both the first and second silicon dielectric pillars have hexagonal cross-sections, and the side length of the first silicon dielectric pillar is greater than that of the second silicon dielectric pillar, so that the first regular hexagonal cell and the second regular hexagonal cell have opposite vortex chirality at point K in the same energy band.

[0010] In conjunction with the first aspect, optionally, when the waveguide interface is a small Z-shaped boundary, the optical waveguide is an input waveguide;

[0011] The small Z-shaped boundary is formed by the staggered arrangement of the second silicon dielectric pillars of the first regular hexagonal cell and the second silicon dielectric pillars of the second regular hexagonal cell.

[0012] In conjunction with the first aspect, optionally, the moving distance of two adjacent second silicon dielectric pillars in the small Z-shaped boundary along the waveguide interface extension direction is t=0.33a.

[0013] In conjunction with the first aspect, optionally, when the waveguide interface is a large Z-shaped boundary, the optical waveguide is an output waveguide;

[0014] The large Z-shaped boundary is formed by the staggered arrangement of the first silicon dielectric pillars of the first regular hexagonal cell and the first silicon dielectric pillars of the second regular hexagonal cell.

[0015] In conjunction with the first aspect, optionally, the moving distance of two adjacent first silicon dielectric pillars in the large Z-shaped boundary along the waveguide interface extension direction is t=0.143a, or t=0.3125a, or t=0.5a.

[0016] In conjunction with the first aspect, optionally, the lattice constant a = 575 nm.

[0017] Secondly, the present invention provides a three-channel wavelength division multiplexer, including an excitation source, an input waveguide connected to the excitation source, and a first output waveguide, a second output waveguide, and a third output waveguide respectively connected to the input waveguide. The operating frequency band of the first output waveguide is concentrated in 183~191 THz, the operating frequency band of the second output waveguide is concentrated in 194~200 THz, and the operating frequency band of the third output waveguide is concentrated in 203~212 THz.

[0018] The input waveguide, the first output waveguide, the second output waveguide, and the third output waveguide each include a waveguide interface, and a first valley photonic crystal and a second valley photonic crystal distributed on both sides of the waveguide interface.

[0019] The first valley photonic crystal is composed of a number of first regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a; each first regular hexagonal unit cell has C 3v Rotational symmetry, with the first and second silicon dielectric pillars arranged alternately at its six vertices, the upper and lower vertices of the first regular hexagonal cell being the first and second silicon dielectric pillars, respectively;

[0020] The second valley photonic crystal is composed of a number of second regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a; a single second regular hexagonal unit cell has C 3v Rotational symmetry, with the first and second silicon dielectric pillars arranged alternately at its six vertices, and the second silicon dielectric pillar and the first silicon dielectric pillar at the upper and lower vertices of the second regular hexagonal cell, respectively.

[0021] The cross-sections of the first silicon dielectric pillar and the second silicon dielectric pillar are both regular hexagonal, and the side length of the first silicon dielectric pillar is greater than that of the second silicon dielectric pillar, so that the K point of the first regular hexagonal unit cell and the second regular hexagonal unit cell have opposite vortex chirality in the same energy band.

[0022] The waveguide interface of the input waveguide is a small Z-shaped boundary, which is formed by the second silicon dielectric pillars of the first regular hexagonal cell and the second silicon dielectric pillars of the second regular hexagonal cell arranged in a staggered manner.

[0023] The waveguide interfaces of the three output waveguides are all large Z-shaped boundaries. The large Z-shaped boundaries are formed by the staggered arrangement of the first silicon dielectric pillars of the first regular hexagonal unit cell and the first silicon dielectric pillars of the second regular hexagonal unit cell. The movement distance between two adjacent second silicon dielectric pillars in the waveguide interfaces of the three waveguides is different.

[0024] In conjunction with the second aspect, optionally, the distance between two adjacent second silicon dielectric pillars at the waveguide interface of the input waveguide is t=0.33a along the extension direction of the waveguide interface; the distance between two adjacent first silicon dielectric pillars at the waveguide interface of the first output waveguide is t=0.143a along the extension direction of the waveguide interface; the distance between two adjacent first silicon dielectric pillars at the waveguide interface of the second output waveguide is t=0.3125a along the extension direction of the waveguide interface; and the distance between two adjacent first silicon dielectric pillars at the waveguide interface of the third output waveguide is t=0.5a along the extension direction of the waveguide interface.

[0025] In conjunction with the second aspect, optionally, the input waveguide is a linear waveguide; the first output waveguide, the second output waveguide, and the third output waveguide are linear waveguides or Z-shaped waveguides.

[0026] In conjunction with the second aspect, optionally, the lattice constant a = 575 nm.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention proposes a valley photonic crystal (VPC) with a structure different from existing technologies. This valley photonic crystal has C3 symmetry, which makes the optical waveguide more stable.

[0029] This invention provides a three-channel wavelength division multiplexer (WDM), employing the optical waveguide structure proposed in this invention. An input waveguide and three output waveguides are constructed. The input waveguide uses a small Z-shaped boundary with t=0.33a, while the three output waveguides use large Z-shaped boundaries with t=0.143a, t=0.3125a, and t=0.5a, respectively. This achieves three non-overlapping transmission channels (i.e., the operating frequency band of the first output waveguide is concentrated in 183~191 THz, the second output waveguide in 194~200 THz, and the third output waveguide in 203~212 THz). The transmission efficiency of this three-channel WDM exceeds 98% in all three channels. Furthermore, even after introducing defects such as cavities, misalignments, disorder, and impurities, the transmission efficiency remains close to 99%, demonstrating its high robustness. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0031] Figure 1 This is a schematic diagram of the valley photonic crystal structure of the present invention; wherein, Figure 1 (a) Schematic diagram of a photonic crystal structure consisting of regular hexagonal silicon dielectric pillars with side length s; Figure 1 (b) To obtain the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2 by enlarging and shrinking the side lengths of the regular hexagonal silicon dielectric pillars respectively; Figure 1 (c) is C 6v Schematic diagram of a symmetrical unit cell band structure; Figure 1 (d) is a schematic diagram of the band structure of the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2. The gray area represents the photonic band gap.

[0032] Figure 2 The diagram shows the phase distribution of the intrinsic mode fields of the first valley photonic crystal VPC1 and the second valley photonic crystal VPC1 at point K(K') according to an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of different boundaries at the waveguide interface; where, Figure 3 (a) is a schematic diagram of the structure of different waveguide interfaces; Figure 3 (b) Band diagrams of supercell structures at different waveguide interfaces; Figure 3 (c) shows the transmission efficiency of straight waveguides at different waveguide interfaces;

[0034] Figure 4 These are schematic diagrams of the band structure under different boundary conditions; where, Figure 4 (a) Schematic diagram of a large Z-shaped boundary structure with displacement parameter t introduced; Figure 4 (b) shows the standard large Z-shaped topological interface configuration formed when t=0 and the sliding surface symmetrical structure formed when t=0.5a; Figure 4 (c) shows the supercell band structure diagrams corresponding to different t values ​​at the large Z-shaped boundary; Figure 4 (d) shows the variation of the operating frequency of the topological boundary state center of the small Z-shaped boundary with the value of t;

[0035] Figure 5 A schematic diagram of an optical waveguide structure with introduced defects; wherein, Figure 5 (a) Schematic diagram of a Z-defect waveguide structure that introduces four types of defects: cavity, misalignment, disorder, and impurities; Figure 5 (b) is the energy distribution diagram of the Z-defect waveguide electric field; Figure 5 (c) shows the transmission efficiency of Z-type waveguide and Z-defect waveguide structures;

[0036] Figure 6 This is a schematic diagram of the structure of a three-channel wavelength division multiplexer according to an embodiment of the present invention;

[0037] Figure 7 The diagram shows the energy, transmission frequency, and transmission efficiency of different output waveguides; among them, Figure 7 (a) is a diagram showing the electric field energy distribution of the output waveguide of WG2 at the corresponding frequency; Figure 7 (b) is a diagram showing the electric field energy distribution of the WG3 output waveguide at the corresponding frequency; Figure 7 (c) is the electric field energy distribution diagram of the WG4 output waveguide at the corresponding frequency; Figure 7 (d) shows the transmission frequency range and transmission efficiency of the output waveguides WG2, WG3, and WG4;

[0038] Figure 8 The graphs show the energy, transmission frequency, and transmission efficiency for different input waveguides; among them, Figure 8 (a) is the electric field energy distribution diagram of the input waveguide of WG2 at the corresponding frequency; Figure 8 (b) is the electric field energy distribution diagram of the WG3 input waveguide at the corresponding frequency; Figure 8 (c) is the electric field energy distribution diagram of the WG4 input waveguide at the corresponding frequency; Figure 8 (d) shows the transmission frequency range and transmission efficiency of the input waveguides WG2, WG3, and WG4. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may include different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0041] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0042] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0043] The application principle of the present invention will be described in detail below with reference to the accompanying drawings.

[0044] Example 1

[0045] An optical waveguide is provided in this embodiment of the invention, such as Figure 6 As shown, it includes a waveguide interface, and a first valley photonic crystal and a second valley photonic crystal distributed on both sides of the waveguide interface.

[0046] The first valley photonic crystal is composed of a number of first regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a (i.e., the first valley photonic crystal is composed of a number of first regular hexagonal unit cells arranged periodically and symmetrically in a hexagonal grid with a period of lattice constant a). Each first regular hexagonal unit cell has C 3v The unit cell exhibits rotational symmetry, with alternating first and second silicon dielectric pillars at its six vertices. The first silicon dielectric pillar is located at the upper vertex of the first regular hexagonal cell, and the second silicon dielectric pillar is located at its lower vertex. For the specific structure of the first regular hexagonal cell, please refer to [link to relevant documentation]. Figure 1 (b).

[0047] The second valley photonic crystal is composed of a number of second regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a. Each second regular hexagonal unit cell has C 3vThe second regular hexagonal unit cell exhibits rotational symmetry, with alternating first and second silicon dielectric pillars at its six vertices. The upper vertex of the second regular hexagonal unit cell is a second silicon dielectric pillar, and its lower vertex is a first silicon dielectric pillar. Both the first and second silicon dielectric pillars have hexagonal cross-sections, with the side length of the first silicon dielectric pillar being greater than that of the second. This results in the first and second regular hexagonal unit cells exhibiting opposite vortex chirality at point K within the same energy band. The specific structure of the second regular hexagonal unit cell is described in [reference needed]. Figure 1 (b).

[0048] The above scheme provides a valley photonic crystal (VPC) with a structure different from the existing technology. The valley photonic crystal has C3 symmetry, which makes the optical waveguide more stable.

[0049] In one specific embodiment of the present invention, when the waveguide interface is a small Z-shaped boundary, the optical waveguide is an input waveguide;

[0050] The small Z-shaped boundary is formed by the staggered arrangement of the second silicon dielectric pillars of the first regular hexagonal cell and the second silicon dielectric pillars of the second regular hexagonal cell.

[0051] In one specific embodiment of the present invention, the moving distance of two adjacent second silicon dielectric pillars in the small Z-shaped boundary along the waveguide interface extension direction is t=0.33a.

[0052] In one specific embodiment of the present invention, when the waveguide interface is a large Z-shaped boundary, the optical waveguide is an output waveguide;

[0053] The large Z-shaped boundary is formed by the staggered arrangement of the first silicon dielectric pillars of the first regular hexagonal cell and the first silicon dielectric pillars of the second regular hexagonal cell.

[0054] In one specific embodiment of the present invention, the moving distance of two adjacent first silicon dielectric pillars in the large Z-shaped boundary along the waveguide interface extension direction is t=0.143a, or t=0.3125a, or t=0.5a.

[0055] In one specific embodiment of the present invention, the lattice constant a = 575 nm.

[0056] Example 2

[0057] This invention provides a three-channel wavelength division multiplexer, such as... Figure 6As shown, it includes an excitation source, an input waveguide WG1 connected to the excitation source, and a first output waveguide WG2, a second output waveguide WG3, and a third output waveguide WG4 respectively connected to the input waveguide WG1; the boundary state transmission bandwidths formed by the three output waveguides do not intersect each other. Specifically, the operating frequency band of the first output waveguide WG2 is concentrated in 183~191 THz, the operating frequency band of the second output waveguide WG3 is concentrated in 194~200 THz, and the operating frequency band of the third output waveguide WG4 is concentrated in 203~212 THz.

[0058] The input waveguide WG1, the first output waveguide WG2, the second output waveguide WG3 and the third output waveguide WG4 each include a waveguide interface, and a first valley photonic crystal and a second valley photonic crystal distributed on both sides of the waveguide interface.

[0059] The first valley photonic crystal is composed of a number of first regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a. Each first regular hexagonal unit cell has C 3v Rotational symmetry, with a first silicon dielectric pillar and a second silicon dielectric pillar arranged alternately at its six vertices, the first silicon dielectric pillar being at the upper vertex of the first regular hexagonal cell and the second silicon dielectric pillar being at its lower vertex;

[0060] The second valley photonic crystal is composed of a number of second regular hexagonal unit cells arranged in a honeycomb array with a period of lattice constant a. Each second regular hexagonal unit cell has C 3v Rotational symmetry is achieved by alternating first and second silicon dielectric pillars at their six vertices. The upper vertex of the second regular hexagonal cell is the second silicon dielectric pillar, and the lower vertex is the first silicon dielectric pillar. The cross-sections of the first and second silicon dielectric pillars are both regular hexagonal, and the side length of the first silicon dielectric pillar is greater than that of the second silicon dielectric pillar. This results in the first and second regular hexagonal cells having opposite vortex chirality at point K in the same energy band.

[0061] The waveguide interface of the input waveguide WG1 is a small Z-shaped boundary, which is formed by the staggered arrangement of the second silicon dielectric pillars of the first regular hexagonal cell and the second silicon dielectric pillars of the second regular hexagonal cell.

[0062] The waveguide interfaces of the first output waveguide WG2, the second output waveguide WG3, and the third output waveguide WG4 are all large Z-shaped boundaries. The large Z-shaped boundaries are formed by the staggered arrangement of the first silicon dielectric pillars of the first regular hexagonal unit cell and the first silicon dielectric pillars of the second regular hexagonal unit cell, and the moving distance between two adjacent second silicon dielectric pillars in the waveguide interfaces of the three waveguides is different.

[0063] In one specific embodiment of the present invention, the moving distance of two adjacent second silicon dielectric pillars along the waveguide interface extension direction in the waveguide interface of the input waveguide WG1 is t=0.33a; the moving distance of two adjacent first silicon dielectric pillars along the waveguide interface extension direction in the waveguide interface of the first output waveguide WG2 is t=0.143a; the moving distance of two adjacent first silicon dielectric pillars along the waveguide interface extension direction in the waveguide interface of the second output waveguide WG3 is t=0.3125a; and the moving distance of two adjacent first silicon dielectric pillars along the waveguide interface extension direction in the waveguide interface of the third output waveguide WG4 is t=0.5a.

[0064] In one specific embodiment of the present invention, the input waveguide WG1 is a linear waveguide; the first output waveguide WG2, the second output waveguide WG3 and the third output waveguide WG4 are linear waveguides or Z-shaped waveguides.

[0065] In one specific embodiment of the present invention, the lattice constant a = 575 nm.

[0066] The following is combined Figure 1 (a)- Figure 8 (d), and a specific embodiment thereof, will be described in detail to illustrate the three-channel wavelength division multiplexer in the present invention.

[0067] To realize the three-channel wavelength division multiplexer proposed in this embodiment of the invention, the structure of a two-dimensional valley photonic crystal is first designed, such as... Figure 1 As shown in (a), hexagonal silicon dielectric pillars are uniformly placed in air with a period of lattice constant a (lattice constant a = 575 nm). The dielectric constant of the hexagonal silicon dielectric pillars is ℇ1 = 11.7, and the dielectric constant of air is ℇ0 = 1. Figure 1 The hexagonal region in (a) is a hexagonal unit cell (i.e., a photonic crystal unit cell), which can be considered as a composite of two triangular lattices, each of which is composed of two triangular lattices with the same side length. Composed of regular hexagonal silicon dielectric pillars, forming a C 6v A rotationally symmetric honeycomb photonic crystal structure. The photonic band structure of a regular hexagonal unit cell was calculated using COMSOL software. In this embodiment, only the TM mode of electromagnetic wave propagation was considered. It was found that the first and second bands of the regular hexagonal unit cell exhibit double degeneracy at point K(K'), which is a high-symmetry point in reciprocal space. Figure 1 As shown in (c). To study the topological properties of a regular hexagonal unit cell, the spatial inversion symmetry of the regular hexagonal silicon dielectric pillars is broken by changing the side lengths of the pillars. The side lengths of the regular hexagonal silicon dielectric pillars located in the same triangular lattice are enlarged or reduced by the same scale. ), will C 6vRotational symmetry decreases to C 3v Rotational symmetry yields the first regular hexagonal unit cell VPC1, and exchange yields the second regular hexagonal unit cell VPC2, as follows. Figure 1 As shown in (b).

[0068] By adjusting the side lengths (s1 and s2) of the regular hexagonal silicon dielectric pillars, the dual valley degeneracy at point K (K') of the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2 is opened, thereby forming a topologically nontrivial bandgap with a width of approximately Δω≈0.141c / a in the normalized frequency range of 0.3251~0.4659c / a. Figure 1 The gray shaded area in (d) is shown. The phase distribution of the first regular hexagonal cell VPC1 and the second regular hexagonal cell VPC2 at points K(K′) in the first and second energy bands is analyzed as follows: Figure 2 As shown in the figure, observing the black arrows reveals that within the same energy band, the K(K′) points of the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2 exhibit opposite vortex chirality. Furthermore, the K(K′) points of the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2 also exhibit opposite vortex chirality in different energy bands. This indicates that band reversal has occurred in the unit cell energy bands of the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2, indicating a topological phase transition.

[0069] To further analyze its topological properties, the Berry curvature distribution was calculated in this embodiment of the invention. Berry curvature is an important quantity describing the topological properties of the band structure, and its calculation formula is as follows:

[0070] ,

[0071] in, Contact Berry. Let be the Bloch state wavefunction at point k. The valley Chern number can be obtained by integrating the Berry curvature over the first Berry zone, defined as:

[0072] ,

[0073] in, For the number of grains, It refers to the Brillon area.

[0074] To quantify its topological properties, the valley Chern numbers of the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2 were calculated respectively. The valley Chern number of the first regular hexagonal unit cell VPC1 at point K(K′) was obtained as follows: The valley Chern number at point K(K′) of the second regular hexagonal unit cell VPC2 is It can be seen that the two have opposite valley Chern numbers. This result indicates that the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2 belong to opposite topological phases with topological Chern numbers of ±1, respectively, satisfying the boundary state existence condition of the quantum valley Hall effect.

[0075] Next, we study the topological boundary states by splicing the first regular hexagonal unit cell VPC1 and the second regular hexagonal unit cell VPC2 to form a supercell structure, such as... Figure 3 As shown in (a), the red dielectric bar represents VPC1, and the blue dielectric bar represents VPC2. There are four possible types of boundary splicing methods: small straight bar, large straight bar, small Z-shape, and large Z-shape, corresponding to... Figure 3 (a) A, B, C, and D. Calculate the supercell band structure diagrams for these four boundary types, as shown below. Figure 3 As shown in (b), four topological boundary states are represented by purple, green, blue, and red lines, respectively, with transmission band ranges of 0.403–0.412 c / a (small stripe type), 0.325–0.353 c / a (large stripe type), 0.358–0.440 c / a (small Z-type), and 0.313–0.369 c / a (large Z-type), where c is the speed of light, and gray represents the topological state. Comparison reveals that the zigzag boundary has a wider transmission bandwidth than the bread boundary, and the bandwidth of the small Z-type boundary edge state is wider than that of the large Z-type boundary edge state. Combined with… Figure 3 (c) The frequency-transmission efficiency relationship curves of the straight waveguides composed of the four boundary splicing methods are used. The small Z-shaped boundary is selected as the input waveguide of the wavelength division multiplexing device, and the large Z-shaped boundary is selected as the output waveguide of the wavelength division multiplexing device.

[0076] The following study examines the impact of interface changes on the operating band of the topological edge state, such as... Figure 4 As shown in (a), the red dielectric pillar represents VPC1, and the blue dielectric pillar represents VPC2. The variable t is set as the distance the regular hexagonal dielectric pillar moves along the interface (i.e., the waveguide interface). When t=0, the boundary shape is a common zigzag type; when t=0.5a, the boundary shape becomes a sliding symmetry, as shown... Figure 4 As shown in (b), calculate the supercell band structure formed after the large Z-shaped boundary and small Z-shaped boundary hexagonal dielectric cylinders are moved by different distances, as shown in [example]. Figure 4 (c)- Figure 4 As shown in (d), it can be seen that as the value of t increases, the boundary states of the large Z-shaped boundary and the small Z-shaped boundary undergo blue shift and red shift respectively, and the transmission bandwidth changes. Analysis Figure 4 (c) When t=0.143a, t=0.3125a, and t=0.5a, the boundary state transmission bandwidths formed are mutually exclusive and can be used to form the three output waveguides of a wavelength division multiplexing device. Simultaneously, analysis... Figure 4(d) When t=0.33a, the transmission range of the small Z boundary covers all or part of the transmission range of the three large Z boundaries when t=0.143a, t=0.3125a and t=0.5a. Therefore, the small Z boundary with t=0.33a is selected as the input waveguide of the wavelength division multiplexer.

[0077] To verify that the structure still possesses strong robustness after changing the boundary interface, Z-shaped no-defect waveguides formed by VPC1 and VPC2 at t=0.33a and Z-shaped defective waveguides formed by simultaneously introducing four types of defects were constructed, as follows: Figure 5 As shown in (a), green represents the Z-shaped waveguide transmission channel, and yellow pentagrams represent the excitation source. Defects such as cavities, misalignments, disorder, and impurities are introduced sequentially along the transmission path of the Z-shaped waveguide. Figure 5 The Ez electric field intensity (i.e., the electric field intensity in the z-direction) distribution in (b) sufficiently demonstrates that the structure can maintain stable transmission capability under the influence of large-angle sharp bends, defects, and other interferences, exhibiting strong anti-interference characteristics. Boundary probes are inserted into the Z-shaped waveguide transmission channel to calculate the transmission efficiency of the defect-free Z-shaped waveguide and the Z-shaped waveguide after introducing defects, such as... Figure 5 As shown in (c), the transmission efficiency of the two waveguides is close to 99% in the frequency range of 179~195THz and remains consistent, which verifies that the structure still has strong transmission capability and high robustness after changing the t value.

[0078] In this invention, VPC1 and VPC2 are spliced ​​together to form a three-channel wavelength division multiplexer, such as... Figure 6 As shown. Figure 6 In the diagram, the red dielectric pillar represents VPC1, the blue dielectric pillar represents VPC2, and the yellow pentagram represents the excitation source. This three-channel wavelength division multiplexer contains four transmission waveguides. The input waveguide WG1 is formed by splicing small Z-shaped boundaries, with a boundary shift distance of t=0.33a. The first output waveguide WG2, the second output waveguide WG3, and the third output waveguide WG4 are formed by splicing large Z-shaped boundaries, with boundary shift distances of t=0.143a, t=0.3125a, and t=0.5a, respectively.

[0079] Figure 7 (a)- Figure 7 (c) The electric field intensity distribution diagrams for WG2, WG3, and WG4 are shown respectively. As can be seen from the diagrams, after the incident light enters through the input waveguide WG1 channel, it can selectively propagate to the corresponding output waveguide according to different frequency ranges. The transmission efficiency diagrams for different output waveguides are shown below. Figure 7As shown in (d), WG2's transmission range is concentrated in the 183–191 THz range, WG3's range is concentrated in the 194–200 THz range, and WG4's range is concentrated in the 203–212 THz range. These frequency bands are independent of each other and do not overlap, and the transmission efficiency of the three output waveguides exceeds 98% within their respective transmission ranges. This indicates that the device has good channel isolation and signal purity in terms of wavelength selectivity.

[0080] Meanwhile, the device design not only supports wavelength division multiplexing of optical signals, but also has a high-efficiency wavelength multiplexing function. To verify this feature, the original three output terminals (WG2, WG3, WG4) were used as new input terminals, and an excitation source was placed at each port; at the same time, the original input waveguide (WG1) was used as the output channel after multiplexing. Figure 8 (a)- Figure 8 (c) shows the electric field intensity distribution under excitation at each port, where the yellow pentagrams indicate the location of the excitation source. It can be seen that various optical signals of different frequencies from WG2, WG3, and WG4 can be efficiently transmitted in the device and finally combined and output at the WG1 channel. The quantitative results of the transmission efficiency are as follows: Figure 8 As shown in (d), the output efficiency of the multiplexed optical signal can reach over 95%, further confirming the excellent performance of the three-channel wavelength division multiplexer in the present invention in combining multi-wavelength optical signals.

[0081] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of the present invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of the present invention.

[0082] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An optical waveguide, characterized by: The waveguide interface includes a waveguide interface, and a first energy valley photonic crystal and a second energy valley photonic crystal distributed on both sides of the waveguide interface; The first energy valley photonic crystal is arranged in a honeycomb array with a lattice constant a as a period length by a plurality of first regular hexagonal unit cells; a single first regular hexagonal unit cell has C 3v rotational symmetry, the first regular hexagonal unit cell is arranged with first silicon dielectric columns and second silicon dielectric columns at six vertices thereof, the upper vertices and the lower vertices of the first regular hexagonal unit cell are respectively provided with the first silicon dielectric columns and the second silicon dielectric columns; The second energy valley photonic crystal is arranged in a honeycomb array with a lattice constant a as a period length by a plurality of second regular hexagonal unit cells; a single second regular hexagonal unit cell has C 3v rotational symmetry, the first silicon dielectric column and the second silicon dielectric column are arranged at six vertices thereof alternately, the upper vertex and the lower vertex of the second regular hexagonal unit cell are respectively the second silicon dielectric column and the first silicon dielectric column; The cross sections of the first and second silicon medium columns are both regular hexagons, and the side length of the first silicon medium column is greater than that of the second silicon medium column, so that the K points of the first and second regular hexagonal unit cells have opposite vortex chirality in the same energy band; When the waveguide interface is a small Z-type boundary, the moving distance of the two adjacent second silicon medium columns in the small Z-type boundary along the extension direction of the waveguide interface is t=0.33a; When the waveguide interface is a large Z-type boundary, the moving distance of the two adjacent first silicon medium columns in the large Z-type boundary along the extension direction of the waveguide interface is t=0.143a, or t=0.3125a, or t=0.5a.

2. An optical waveguide according to claim 1, wherein: The optical waveguide is an input waveguide. The small Z-type boundary is formed by staggered arrangement of the second silicon medium column of the first regular hexagonal unit cell and the second silicon medium column of the second regular hexagonal unit cell.

3. An optical waveguide according to claim 1, wherein: The optical waveguide is an output waveguide. The large Z-type boundary is formed by staggered arrangement of the first silicon medium column of the first regular hexagonal unit cell and the first silicon medium column of the second regular hexagonal unit cell.

4. The optical waveguide of claim 1, wherein: The lattice constant a=575nm.

5. A triplexer, characterized by: The excitation source, the input waveguide connected with the excitation source, and the first output waveguide, the second output waveguide and the third output waveguide connected with the input waveguide respectively, the working frequency band of the first output waveguide is concentrated in 183-191 THz, the working frequency band of the second output waveguide is concentrated in 194-200 THz, and the working frequency band of the third output waveguide is concentrated in 203-212 THz; The input waveguide, the first output waveguide, the second output waveguide and the third output waveguide all include a waveguide interface, and a first energy valley photonic crystal and a second energy valley photonic crystal distributed on both sides of the waveguide interface; The first energy valley photonic crystal is arranged in a honeycomb array with a lattice constant a as a period length by a plurality of first regular hexagonal unit cells; a single first regular hexagonal unit cell has C 3v rotational symmetry, the first regular hexagonal unit cell is arranged with first silicon dielectric columns and second silicon dielectric columns at six vertices thereof, the upper vertices and the lower vertices of the first regular hexagonal unit cell are respectively provided with the first silicon dielectric columns and the second silicon dielectric columns; The second energy valley photonic crystal is arranged in a honeycomb array with several second regular hexagonal cells as the period length with a lattice constant a; a single second regular hexagonal cell has C 3v rotational symmetry, the first silicon dielectric column and the second silicon dielectric column are arranged alternately at six vertices thereof, the upper vertex and the lower vertex of the second regular hexagonal cell are respectively the second silicon dielectric column and the first silicon dielectric column; The cross sections of the first and second silicon medium columns are both regular hexagons, and the side length of the first silicon medium column is greater than that of the second silicon medium column, so that the K points of the first and second regular hexagonal unit cells have opposite vortex chirality in the same energy band; The waveguide interface of the input waveguide is a small Z-type boundary, and the small Z-type boundary is formed by staggered arrangement of the second silicon medium column of the first regular hexagonal unit cell and the second silicon medium column of the second regular hexagonal unit cell; The waveguide interfaces of the three output waveguides are all large Z-type boundaries, the large Z-type boundaries are formed by staggered arrangement of the first silicon medium column of the first regular hexagonal unit cell and the first silicon medium column of the second regular hexagonal unit cell, and the moving distances between the two adjacent second silicon medium columns in the waveguide interfaces of the three output waveguides are different. The distance between two adjacent second silicon dielectric pillars at the waveguide interface of the input waveguide is t=0.33a; the distance between two adjacent first silicon dielectric pillars at the waveguide interface of the first output waveguide is t=0.143a; the distance between two adjacent first silicon dielectric pillars at the waveguide interface of the second output waveguide is t=0.3125a; and the distance between two adjacent first silicon dielectric pillars at the waveguide interface of the third output waveguide is t=0.5a.

6. The triplexer of claim 5, wherein: The input waveguide is a linear waveguide; the first output waveguide, the second output waveguide, and the third output waveguide are linear waveguides or Z-shaped waveguides.

7. The triplexer of claim 5, wherein: The lattice constant a = 575 nm.

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