A high-gain backward brillouin amplifier based on suspended medium valley photonic crystal

Abstract

The application discloses a high-gain backward Brillouin amplifier based on suspended medium valley photonic crystal. The amplifier comprises a substrate, a supporting area and a suspended medium plate, a periodic air hole array is formed in the suspended medium plate, the periodic air hole array respectively constitutes a first valley photonic crystal and a second valley photonic crystal with different valley Chern numbers, and a domain wall supporting propagation of an optical topological boundary state is formed at the junction of the two. The medium reserved between the adjacent air holes at the domain wall forms a periodic suspended medium thin arm structure, and the thin arm structure supports an elastic wave squeezing mode. The optical topological boundary state generates a radiation pressure at the air medium interface near the domain wall, and a displacement vector field of the elastic wave squeezing mode is overlapped with a radiation pressure vector field in a spatial position and is matched in a vector direction; pump light and Stokes light are reversely propagated along the domain wall and satisfy phase matching with the elastic wave squeezing mode, so that backward stimulated Brillouin scattering is enhanced and Stokes light amplification is realized.

Description

Technical Field

[0001] This invention relates to the field of optoelectronics technology, specifically to a high-gain back-facing Brillouin amplifier based on a suspended medium valley photonic crystal. Background Technology

[0002] Stimulated Brillouin scattering (SBS) exhibits narrowband selectivity and coherent photoacoustic nonlinear gain characteristics, making it suitable for on-chip optical signal amplification, microwave photonic filtering, and narrowband signal processing.

[0003] While traditional fiber optic Brillouin devices can achieve high overall gain, their large acousto-optic interaction length and device size hinder chip-level integration. Existing on-chip Brillouin devices can enhance radiation pressure at the air-medium interface through suspended micro / nano structures, but simultaneously improving photomechanical interaction, elastic wave mode compliance, and spatial and directional matching of the photomechanical vector field and elastic wave displacement vector field is often difficult. Therefore, a relatively long acousto-optic interaction length is still required to achieve high net gain. Increasing the back-facing Brillouin gain coefficient and shortening the acousto-optic interaction length can reduce the waveguide length and on-chip footprint of the Brillouin amplifier unit while achieving the target net gain, improving device integration density and cascadability, and providing a foundation for constructing compact microwave photonic signal processing chips and photoacoustic functional circuits. Therefore, an on-chip structure capable of synergistically enhancing the above factors is needed. Summary of the Invention

[0004] To address the challenges of existing on-chip Brillouin devices in simultaneously enhancing optical force, improving elastic wave mode compliance, and enhancing the matching of optical force and elastic wave displacement fields, this invention provides a high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal.

[0005] This amplifier utilizes optical topological boundary states to localize the optical field at the air-medium interface near the domain walls. It leverages the periodic suspended medium arm structure at the domain walls to support highly flexible elastic wave pinching modes, and matches the radiation pressure vector field with the elastic wave displacement vector field in spatial position and direction, thereby improving the photoacoustic coupling efficiency and Brillouin gain coefficient of back-stimulated Brillouin scattering. The technical solution is as follows: A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal includes a substrate, a support region, and a suspended dielectric plate. The suspended dielectric plate is connected to the substrate through the support region and forms an air gap or release cavity between the plate and the substrate. A periodic air hole array is formed in the suspended dielectric plate. The periodic air hole array constitutes a first valley photonic crystal and a second valley photonic crystal with different valley numbers. The boundary between the two forms a domain wall that supports the propagation of optical topological boundary states. The medium retained between adjacent air holes at the domain wall forms a suspended medium arm. The suspended medium arms are periodically staggered along the propagation direction of the optical topological boundary state, forming a periodic suspended medium arm structure that supports the elastic wave pinching mode. The elastic wave pinching mode causes the air medium interface adjacent to the suspended medium arm to undergo an anti-phase periodic displacement along the interface normal. The optical field of the optical topological boundary state generates radiation pressure perpendicular to the air medium interface at the air medium interface adjacent to the suspended medium arm. Its vector field overlaps with the displacement vector field of the elastic wave pinch mode in spatial position and the vector direction matches. The pump light and the Stokes light propagate in opposite directions along the domain wall, and the pump light, the Stokes light and the elastic wave pinch mode satisfy phase matching to enhance the energy transfer of the pump light to the Stokes light and realize back-side stimulated Brillouin amplification.

[0006] Furthermore, the first valley photonic crystal and the second valley photonic crystal are valley photonic crystal structures that are mirror-symmetric about the domain wall and have a common bulk band gap in the operating frequency range. The optical topological boundary states are located within the bulk band gap and propagate along the domain wall.

[0007] Furthermore, the cells of both the first valley photonic crystal and the second valley photonic crystal include pairs of air triangular holes formed in the suspended dielectric plate; the pairs of air triangular holes include a first equilateral triangular air hole and a second equilateral triangular air hole, both of which penetrate the suspended dielectric plate along the thickness direction of the suspended dielectric plate, and the side lengths of the first equilateral triangular air hole and the second equilateral triangular air hole are different.

[0008] Furthermore, in the centering of the air triangular holes, the side length of the first equilateral triangular air hole is... l 1 is 0.2a to 0.3a, the side length of the second equilateral triangle air hole. l 2 is 0.6a ~ 5 a / 6, and l 2 is greater than l 1; The thickness h of the suspended dielectric plate is 0.4a to 0.75a, where a is the lattice constant.

[0009] Furthermore, the side length of the first equilateral triangular air hole l 1 = 0.3a, the side length of the second equilateral triangular air hole l 2 = 5 a / 6, the thickness h of the suspended medium plate is 0.535a.

[0010] Furthermore, the domain wall comprises a row of domain wall cells periodically arranged along the propagation direction of the optical topological boundary state. Each domain wall cell is a parallelogram and includes two equilateral triangular air holes penetrating along the thickness direction of the suspended dielectric plate. The size of the two equilateral triangular air holes is the same as the size of the relatively larger equilateral triangular air hole in the cells of the first valley photonic crystal and the second valley photonic crystal. The domain wall cells are located at the boundary between the first valley photonic crystal and the second valley photonic crystal and are periodically repeated along the propagation direction of the optical topological boundary state. The dielectric material retained between adjacent large equilateral triangular air holes forms the suspended dielectric arm. The suspended dielectric arms are periodically staggered along the propagation direction of the optical topological boundary state and constitute the periodic suspended dielectric arm structure. The periodic suspended dielectric arm structure constitutes a phononic crystal in acoustic properties and supports elastic wave pinching mode.

[0011] Furthermore, the suspended dielectric plate is formed through a sacrificial layer release process.

[0012] Furthermore, the first valley photonic crystal and the second valley photonic crystal are located on opposite sides of the domain wall, and are connected to the corresponding support region after extending at least 6 cell cycles away from the domain wall.

[0013] Furthermore, the first valley photonic crystal and the second valley photonic crystal are located on opposite sides of the domain wall, and are connected to the corresponding support region after extending 8 to 20 cell periods away from the domain wall.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Enhanced radiation pressure: The optical topological boundary states are located within the band gap of the common band and evanescently decay towards the valley photonic crystal regions on both sides, causing the light field to concentrate at the air medium interface near the domain wall, thereby enhancing the radiation pressure at the interface.

[0015] 2. High-compliance elastic wave mode: The periodically staggered suspended medium arm structure at the domain wall supports the elastic wave pinching mode, so that the elastic displacement is concentrated in the suspended medium arm and its adjacent air medium interface, and the structural compliance of the elastic wave mode is improved by geometric softening.

[0016] 3. Improved photoacoustic field matching: The direction of radiation pressure is perpendicular to the air medium interface. The elastic wave pinch mode causes the adjacent air medium interface to undergo an anti-phase periodic displacement along the interface normal, thereby matching the radiation pressure vector field and the elastic wave displacement vector field in spatial position and direction.

[0017] The three effects mentioned above work together to improve the coupling efficiency between the pump light, the back Stokes light and the elastic wave, thereby increasing the back stimulated Brillouin gain coefficient and shortening the acousto-optic interaction length required to obtain the target amplification.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] Figure 1 This is a schematic diagram of the overall structure of a suspended medium valley photonic crystal according to an exemplary embodiment. Figure 1 (a) in the diagram is a schematic diagram of the transverse cross-section of the suspended structure. Figure 1 (b) is a top view of the suspended medium valley photonic crystal.

[0021] Figure 2 This is a schematic diagram illustrating the back-stimulated Brillouin scattering process and the cell structure parameters of a valley photonic crystal according to an exemplary embodiment. Figure 2 (a) in the diagram is a schematic diagram of the back-stimulated Brillouin scattering process in a valley photonic crystal. Figure 2 (b) is a schematic diagram of the valley photonic crystal cell and its structural parameters, where a is the lattice constant. l 1 and l 2 represents the side lengths of the first and second equilateral triangle air holes, respectively, and h represents the thickness of the suspended medium plate.

[0022] Figure 3 This is an illustrative diagram illustrating optical topological boundary states, radiation pressure, and elastic wave pinch modes according to an exemplary embodiment. Figure 3 (a) in the diagram is the optical topological boundary state dispersion map. Figure 3 (b) in the figure is the dispersion plot of the elastic wave pinch mode. Figure 3 (c) in the figure is a power-normalized radiation pressure distribution map. Figure 3 (d) in the figure is the distribution diagram of the elastic wave displacement field.

[0023] Figure 4 This is a schematic diagram illustrating the variation of the net Stokes wave gain with the acousto-optic interaction length, calculated theoretically according to an exemplary embodiment. Detailed Implementation

[0024] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0025] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0026] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0027] To clearly illustrate the technical solutions provided in the embodiments of this application, some concepts that may appear in subsequent embodiments will be introduced first.

[0028] In this application, a valley photonic crystal (VPC) refers to a periodic dielectric structure possessing valley-related optical topological properties. The first valley photonic crystal and the second valley photonic crystal can be abbreviated as VPC1 and VPC2, respectively. The first valley photonic crystal and the second valley photonic crystal form domain walls at their interface, where a domain wall refers to the interface region between two valley photonic crystals with different valley Chern numbers.

[0029] In this application, a unit cell refers to the basic periodic structural unit constituting the first valley photonic crystal, the second valley photonic crystal, or the domain wall. In this embodiment, both the first valley photonic crystal unit cell and the second valley photonic crystal unit cell include two unequal equilateral triangular air holes of different sizes; the domain wall unit cell refers to the structural unit located at the boundary between the first valley photonic crystal and the second valley photonic crystal and periodically arranged along the TES propagation direction, and it includes two large equilateral triangular air holes. A lattice refers to the overall periodic structure formed by multiple units cells arranged periodically according to a lattice constant.

[0030] In this application, a topological edge state (TES) refers to an optical mode supported by a domain wall between a first valley photonic crystal and a second valley photonic crystal, propagating along the domain wall, and having its light field distribution concentrated near the domain wall.

[0031] In this application, the elastic wave pinch mode refers to the elastic wave deformation mode localized at the domain wall, which can also be called the pinch mode in related phononic crystal research. Specifically, the elastic wave pinch mode is characterized by periodic vibrations, mainly lateral displacement, generated by the periodically staggered suspended dielectric arm structure at the domain wall. This causes the adjacent air-medium interfaces at the domain wall to undergo anti-phase periodic displacements along the interface normal, resulting in the adjacent air-medium interfaces alternately approaching and moving away from each other.

[0032] This application improves the Brillouin gain coefficient through the synergistic effect of enhanced photodynamic action, improved elastic wave mode compliance, and matching of photodynamic distribution with elastic wave displacement field. In this embodiment, the domain walls of the suspended medium valley photonic crystal support TES propagating along the domain walls and evanescently attenuating towards the two bulk regions, concentrating the light field and radiation pressure at the air-medium interface at the domain walls; the periodically staggered suspended medium thin-arm structure at the domain walls supports a highly compliant elastic wave pinching mode; the direction of the radiation pressure is perpendicular to the air-medium interface, and the elastic wave pinching mode causes adjacent air-medium interfaces to undergo anti-phase periodic displacement along the interface normal, thereby matching the radiation pressure vector field with the elastic wave displacement vector field in spatial position and direction, and improving the coupling efficiency between the pump light, the back-stokes light, and the elastic wave.

[0033] like Figure 1 as well as Figure 2As shown in (a), this application provides a high-gain back-facing Brillouin amplifier based on a suspended medium valley photonic crystal. The back-facing Brillouin amplifier is composed of the suspended medium valley photonic crystal, which includes a substrate, a support region, and a suspended dielectric plate. An air gap or release cavity is formed between the suspended dielectric plate and the substrate through the support region, thereby placing the photoacoustic interaction region in a suspended state. A periodic array of air triangular holes is formed in the suspended dielectric plate, which constitutes a first valley photonic crystal (VPC1) and a second valley photonic crystal (VPC2) with different valley cell numbers. A domain wall supporting the propagation of optical topological boundary states is formed at the boundary between the two. The dielectric material retained between adjacent air holes at the domain wall forms a suspended dielectric arm. The suspended medium arms are periodically staggered along the propagation direction of the optical topological boundary states, forming a periodic suspended medium arm structure that supports elastic wave pinching modes. The elastic wave pinching modes cause the air medium interface adjacent to the suspended medium arms to undergo an anti-phase periodic displacement along the interface normal. The optical field of the optical topological boundary states generates radiation pressure perpendicular to the air medium interface at the air medium interface adjacent to the suspended medium arms. Its vector field overlaps spatially with the displacement vector field of the elastic wave pinching modes, and their vector directions match. The pump light and Stokes light propagate in opposite directions along the domain walls, and the pump light, the Stokes light, and the elastic wave pinching modes satisfy phase matching to enhance the energy transfer from the pump light to the Stokes light and achieve back-side stimulated Brillouin amplification.

[0034] Specifically, such as Figure 1 As shown in (b), the periodic air triangular aperture array can be considered as being composed of three types of parallelogram cells, including a first valley photonic crystal cell, a second valley photonic crystal cell, and domain wall cells. Both the first and second valley photonic crystal cells include a relatively large equilateral triangular air aperture and a relatively small equilateral triangular air aperture, and are arranged in a mirror-symmetric manner about the domain wall. The domain wall is composed of a row of domain wall cells periodically arranged along the TES propagation direction at the boundary between the first and second valley photonic crystals; each domain wall cell includes two large equilateral triangular air apertures, the size of which is the same as the size of the relatively large equilateral triangular air aperture in the first and second valley photonic crystal cells. The medium retained between adjacent large equilateral triangular air holes forms suspended medium arms. These suspended medium arms are periodically staggered along the TES propagation direction to form a periodic suspended medium arm structure, thereby supporting elastic wave pinch mode.

[0035] Specifically, VPC1 and VPC2 are valley photonic crystal structures that are mirror-symmetric about the domain walls and share a common bulk bandgap within the operating frequency range. VPC1 and VPC2 have different valley Chern numbers and form an interface at the domain walls that supports TES propagation, allowing the TES to be located within the bulk bandgap and propagate along the domain walls. Since the TES evanescently decays in the direction perpendicular to the domain walls into the first and second valley photonic crystals, the light field distribution of the TES is concentrated near the domain walls, generating radiation pressure at the air-medium interface at the domain walls. The periodically staggered suspended dielectric arm structures at the domain walls support the elastic wave pinching mode and concentrate the displacement distribution of the elastic wave pinching mode at the domain walls. The elastic wave pinching mode causes the adjacent air-medium interfaces at the domain walls to undergo anti-phase periodic displacement along the interface normal, causing the adjacent air-medium interfaces to alternately approach and move away from each other, matching the radiation pressure, thereby achieving stimulated Brillouin scattering.

[0036] like Figure 2 As shown in (a), the pump light, the back-stokes light, and the elastic wave pinch mode satisfy the energy matching and phase matching conditions. The seed signal shown in the figure is an unamplified Stokes wave. The beat frequency of the pump light and the back-stokes light excites the elastic wave pinch mode, and the periodic perturbation of the interface caused by the elastic wave pinch mode promotes the coherent energy transfer from the pump light to the Stokes light, thereby realizing the stimulated amplification of the Stokes light. The direction of the radiation pressure is perpendicular to the air medium interface, and the displacement of the elastic wave pinch mode is mainly distributed along the normal of the air medium interface, thereby improving the directional matching degree between the radiation pressure vector field and the elastic wave displacement vector field.

[0037] like Figure 2 As shown in (b), the cells of the valley photonic crystals VPC1 and VPC2 both include pairs of air triangles formed in the suspended dielectric plate; the pairs of air triangles include a first equilateral triangular air hole and a second equilateral triangular air hole, both of which penetrate the suspended dielectric plate along its thickness direction, and the side lengths of the first and second equilateral triangular air holes are different. In the figure, a is the lattice constant. l 1 and l 2 represents the side length of the first equilateral triangular air hole and the second equilateral triangular air hole, respectively, and h represents the thickness of the suspended medium plate.

[0038] In this application, the elastic wave pinching mode corresponds to the periodic elastic deformation of the suspended medium arm and its adjacent air medium interface in the domain wall cell. This mode causes the adjacent air medium interfaces at the domain wall to undergo antiphase periodic displacement along the interface normal, which manifests as the adjacent air medium interfaces alternately approaching and moving away from each other, thus matching the radiation pressure direction at the domain wall air medium interface.

[0039] The periodic length of the domain wall cell along the TES propagation direction is the lattice constant a, and the minimum width of the suspended dielectric arm is determined by the side length of the second equilateral triangular air hole. l 2. The spacing between adjacent air holes is determined and set to a minimum feature size close to that achievable in nanofabrication, while satisfying both fabrication feasibility and structural integrity, to balance enhanced acousto-optic coupling and practical fabrication. For valley photonic crystal cells, increasing the difference in side length between the first and second equilateral triangular air holes is beneficial for enhancing spatial inversion symmetry breaking, expanding the valley topological bandgap, and enhancing the localization of TES at domain walls; for domain wall structures, reducing the width of the suspended dielectric arm between adjacent large equilateral triangular air holes is beneficial for improving the structural flexibility of elastic wave pinching modes.

[0040] In specific implementations, the lattice constant α can be scaled according to the target optical wavelength and the material of the suspended dielectric substrate. In an embodiment using silicon as the suspended dielectric substrate material and operating in the near-infrared communication band, the lattice constant α can be selected from 400 nm to 600 nm, where α can be 467 nm. The side length of the first equilateral triangular air hole... l 1. The side length of the second equilateral triangular air hole can be selected as 0.2a to 0.3a. l 2 can be selected from 0.6a to 5a. a / 6, and l 2 is greater than l 1. By breaking the spatial inversion symmetry through two unequal equilateral triangular air holes, a bulk bandgap is opened near the K / K′ valley, resulting in different valley Chern numbers for the first and second valley photonic crystals. Typically, l 1 and l The greater the difference between 2 and 3, the stronger the spatial inversion symmetry breaking, resulting in a larger valley topological bandgap. This leads to stronger evanescent attenuation of the TES in the valley photonic crystal regions perpendicular to the domain walls, thus making it more advantageous to concentrate the TES's light field distribution near the domain walls. In a preferred embodiment, the side length of the first equilateral triangular air hole... l 1. Take 0.3a as the side length of the second equilateral triangle air hole. l 2 is taken as 5 a / 6, the thickness h of the suspended dielectric substrate is taken as 0.535a. For the valley photonics crystal cell, under the premise of satisfying fabrication feasibility, l 1. Smaller and l 2. A larger value is beneficial for increasing the inequivalence of the two air holes, expanding the bulk band gap near the K / K′ valley, and enhancing the localization of TES at the domain wall; simultaneously, l 2. Increasing the width of the suspended dielectric arm between adjacent large equilateral triangular air holes at the domain wall also reduces the structural flexibility of the elastic wave pinch mode. Therefore, in this embodiment, the following is selected: l 1 = 0.3a、 l 2 = 5 a / 6 and h = 0.535a are used as a combination of parameters that take into account valley topological bandgap, TES localization, elastic wave pinch mode compliance, and the feasibility of actual nanofabrication.

[0041] The thickness h of the suspended dielectric plate can be selected from 0.4a to 0.75a, and in one embodiment h is 0.535a. This thickness range is beneficial for ensuring that the elastic wave pinch-down mode at the domain wall is within the frequency range suitable for stimulated Brillouin scattering while ensuring the optical field is confined in the vertical direction. The first valley photonic crystal and the second valley photonic crystal are located on opposite sides of the domain wall, and extend from the domain wall away from the domain wall for at least 6 cell periods, preferably 8 to 20 cell periods, before connecting with the corresponding support region. This allows the TES and elastic wave mode to be sufficiently attenuated before reaching the support region, and reduces the influence of the support region on the photoacoustic interaction region of the domain wall, thereby forming a structure in which the two sides are mechanically anchored by the support region and the photoacoustic interaction region in the middle is suspended.

[0042] In one embodiment, reference is made to Figure 1 and Figure 2 In (b) of the above, the high-gain back-facing Brillouin amplifier based on a suspended-medium valley photonic crystal includes a suspended-medium valley photonic crystal. The suspended-medium valley photonic crystal is composed of two types of mirror-symmetric valley photonic crystal lattices (VPC1 and VPC2), with domain walls forming at their interface that simultaneously support the propagation of TES and elastic wave pinch-down modes. The cell adopts an equilateral triangular air-hole pair structure with a lattice constant of [missing information]. a The wavelength is set to 467 nm. Each cell of the valley photonic crystal contains two unequal equilateral triangular air holes with side lengths of 167 nm and 167 nm respectively. l 1 = 0.3 a and l 2 = 5 a / 6, the thickness of the suspended medium plate is h = 0.535 a ,in ais the lattice constant. This unequal side length design breaks the spatial inversion symmetry, thereby generating topologically protected TES at the domain walls. Simultaneously, the geometry of the periodic suspended dielectric slender arm structure induces highly flexible elastic wave pinching modes.

[0043] In one embodiment, the suspended dielectric plate is made of silicon. It should be noted that silicon is used to illustrate a specific implementation and its technical effects of the present invention and does not constitute a limitation on the material of the suspended dielectric plate; in other embodiments, the suspended dielectric plate may also be made of silicon nitride, silicon carbide, gallium arsenide, indium phosphide, or other dielectric materials suitable for forming suspended photoacoustic interaction structures. When using other dielectric materials, the lattice constant, air hole size, and thickness of the suspended dielectric plate can be adjusted accordingly based on the optical and mechanical parameters of the material.

[0044] In one embodiment, the suspended dielectric plate can be formed using a sacrificial layer release process. For example, an on-chip material system comprising a substrate, a sacrificial layer, and a dielectric thin film layer can be used, wherein the dielectric thin film layer uses the aforementioned dielectric material, and the sacrificial layer can be a silicon oxide layer or other selectively removable material layer. First, a pattern corresponding to the first valley photonic crystal, the second valley photonic crystal, and the domain walls is formed on the dielectric thin film layer; then, the pattern is transferred to the dielectric thin film layer by an etching process, allowing air triangular holes to penetrate the dielectric thin film layer; subsequently, the sacrificial layer located below the suspended dielectric plate is selectively removed to form an air gap or release cavity between the suspended dielectric plate and the substrate, while retaining the substrate support below the support region. Thus, a suspended dielectric valley photonic crystal structure supported by the support region and with the photoacoustic interaction region suspended is formed.

[0045] the following Figure 3 The model dispersion, radiation pressure distribution, and elastic wave displacement field shown are as follows: Figure 4 The theoretical gain results shown are all calculated based on the above-described embodiments using silicon material for the suspended dielectric substrate.

[0046] Reference Figure 3 , Figure 3 (c) and Figure 3 In the diagram, (d) represents the magnitude of the normalized power radiation pressure and elastic wave displacement field by varying shades of color, and arrows represent the directions of the radiation pressure vector and elastic wave displacement vector, respectively. Figure 3 (a) and Figure 3The solid red lines in (b) represent the dispersion curves of the TES and the elastic wave pinch-down mode, respectively. The TES is located within the common bandgap formed by the bulk bands (gray regions) of the VPC lattice. The first valley photonic crystal and the second valley photonic crystal adopt a mirror-symmetric cell configuration, and they open the bulk bandgap near the K / K′ valley and have different valley chevron numbers. When the two are connected at the domain walls, the difference in valley chevron numbers causes the TES to propagate along the domain walls within the common bandgap. Since the TES evanescently decays towards the valley photonic crystal regions on both sides in a direction perpendicular to the domain walls, its light field is concentrated near the domain walls, and a radiation pressure perpendicular to the interface is generated at the air-medium interface of the domain walls. The elastic wave pinch-down mode is supported by a periodic suspended medium arm structure at the domain walls. Its displacement field is concentrated at the domain walls, and it causes the adjacent air-medium interface to undergo an anti-phase periodic displacement along the interface normal. The geometric softening effect of the suspended medium arm improves the structural compliance of the elastic wave pinch-down mode. Thus, the radiation pressure vector field and the elastic wave displacement vector field are matched in spatial position and direction, providing a basis for improving the optoacoustic coupling efficiency.

[0047] Reference Figure 4 , Figure 4 The figure shows the trend of Stokes wave net gain as the acousto-optic interaction length increases, theoretically calculated under steady-state conditions based on the aforementioned silicon material embodiment. The point corresponding to the maximum net gain is retained in the figure, and a new point corresponding to an acousto-optic interaction length of 1.64 mm and a net gain of 20 dB is added. Theoretical calculation results show that the back-facing Brillouin gain coefficient of the silicon material embodiment is 601566 m. -1 ·W -1 When the pump power is 34 mW and the acousto-optic interaction length is 1.64 mm, the net gain of the Stokes signal reaches 20 dB.

[0048] The acousto-optic interaction length refers to the actual length of the domain wall waveguide along the propagation direction of the TES, i.e., the propagation length through which the pump light, Stokes light, and elastic wave satisfy phase matching and undergo stimulated Brillouin scattering in the suspended medium valley photonic crystal. This acousto-optic interaction length is related to the period length and number of periodic units of the domain wall cells along the propagation direction of the TES, and can be expressed as L = N·a, where N is the number of domain wall cells arranged along the propagation direction of the TES, and a is the lattice constant.

[0049] Therefore, this application does not rely solely on a single geometric parameter to improve Brillouin gain, but rather improves the interaction efficiency between pump light, Stokes light and elastic waves through the synergistic effect of enhanced radiation pressure of optical modes at domain walls, high flexibility of elastic wave pinching modes, and spatial and directional matching of radiation pressure vector field and elastic wave displacement vector field.

[0050] In summary, this invention utilizes the localized optical field of TES at the domain wall air-medium interface to enhance radiation pressure, employs a periodic suspended dielectric slender arm structure to support a highly flexible elastic wave pinching mode, and matches the radiation pressure vector field with the elastic wave displacement vector field in spatial position and direction, thereby improving the photoacoustic coupling efficiency and Brillouin gain coefficient of back-stimulated Brillouin scattering. The amplifier employs a single dielectric material system and a suspended structure, which facilitates shortening the acousto-optic interaction length and enabling on-chip integration.

[0051] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal, characterized in that, It includes a substrate, a support region, and a suspended dielectric plate, wherein the suspended dielectric plate is connected to the substrate through the support region and forms an air gap or release cavity with the substrate; A periodic air hole array is formed in the suspended dielectric plate. The periodic air hole array constitutes a first valley photonic crystal and a second valley photonic crystal with different valley numbers. The boundary between the two forms a domain wall that supports the propagation of optical topological boundary states. The medium retained between adjacent air holes at the domain wall forms a suspended medium arm. The suspended medium arms are periodically staggered along the propagation direction of the optical topological boundary state, forming a periodic suspended medium arm structure that supports the elastic wave pinching mode. The elastic wave pinching mode causes the air medium interface adjacent to the suspended medium arm to undergo an anti-phase periodic displacement along the interface normal. The optical field of the optical topological boundary state generates radiation pressure perpendicular to the air medium interface at the air medium interface adjacent to the suspended medium arm. Its vector field overlaps with the displacement vector field of the elastic wave pinch mode in spatial position and the vector direction matches. The pump light and the Stokes light propagate in opposite directions along the domain wall, and the pump light, the Stokes light and the elastic wave pinch mode satisfy phase matching to enhance the energy transfer of the pump light to the Stokes light and realize back-side stimulated Brillouin amplification.

2. The high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 1, characterized in that, The first valley photonic crystal and the second valley photonic crystal are valley photonic crystal structures that are mirror-symmetric about the domain wall and have a common bulk band gap in the operating frequency range. The optical topological boundary states are located within the bulk band gap and propagate along the domain wall.

3. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 1, characterized in that, The cells of both the first valley photonic crystal and the second valley photonic crystal include pairs of air triangular holes formed in the suspended dielectric plate; the pairs of air triangular holes include a first equilateral triangular air hole and a second equilateral triangular air hole, both of which penetrate the suspended dielectric plate along the thickness direction of the suspended dielectric plate, and the side lengths of the first equilateral triangular air hole and the second equilateral triangular air hole are different.

4. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 3, characterized in that, In the pair of air triangular holes, the side length of the first equilateral triangle air hole is... l 1 is 0.2a to 0.3a, the side length of the second equilateral triangle air hole. l 2 is 0.6a ~ 5 a / 6, and l 2 is greater than l 1; The thickness h of the suspended dielectric plate is 0.4a to 0.75a, where a is the lattice constant.

5. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 3, characterized in that, The side length of the first equilateral triangular air hole l 1 = 0.3a, the side length of the second equilateral triangular air hole l 2 = 5 a / 6, the thickness h of the suspended medium plate is 0.535a.

6. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 3, characterized in that, The domain wall comprises a row of domain wall cells periodically arranged along the propagation direction of the optical topological boundary state. Each domain wall cell is a parallelogram and includes two equilateral triangular air holes penetrating along the thickness direction of the suspended dielectric plate. The size of the two equilateral triangular air holes is the same as the size of the relatively larger equilateral triangular air hole in the cells of the first valley photonic crystal and the second valley photonic crystal. The domain wall cells are located at the boundary between the first valley photonic crystal and the second valley photonic crystal and are periodically repeated along the propagation direction of the optical topological boundary state. The dielectric space between adjacent large equilateral triangular air holes forms the suspended dielectric arm. The suspended dielectric arms are periodically staggered along the propagation direction of the optical topological boundary state and constitute the periodic suspended dielectric arm structure. The periodic suspended dielectric arm structure constitutes a phononic crystal in acoustic properties and supports elastic wave pinching mode.

7. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 1, characterized in that, The suspended dielectric plate is formed through a sacrificial layer release process.

8. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 1, characterized in that, The first valley photonic crystal and the second valley photonic crystal are located on opposite sides of the domain wall, and are connected to the corresponding support region after extending at least 6 cell cycles away from the domain wall.

9. A high-gain back-facing Brillouin amplifier based on a suspended dielectric valley photonic crystal according to claim 1, characterized in that, The first valley photonic crystal and the second valley photonic crystal are located on opposite sides of the domain wall, and are connected to the corresponding support region after extending 8 to 20 cell periods away from the domain wall.

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