Flat panel structure based on topological photonic crystal and infrared sensor

Abstract

The application provides a flat plate structure based on a topological photonic crystal, comprising a plurality of super units, the plurality of super units are arranged in an array along a first direction and a second direction, and form a matrix; the super unit comprises a topological non-trivial structure and a topological trivial structure, the topological trivial structure is arranged on the outer circumferential side of the topological non-trivial structure; the topological non-trivial structure comprises a plurality of topological non-trivial units, the plurality of topological non-trivial units are arranged in an array along the first direction and the second direction, and form a matrix; the topological trivial structure comprises a plurality of topological trivial units, and the plurality of topological trivial units form a matrix. The application also provides an infrared sensor, comprising the flat plate structure and a sensor body, and the flat plate structure is arranged on the sensor body. The flat plate structure based on the topological photonic crystal can interact with air, and therefore the resonance characteristics of the topological corner state are sensitive to the environmental refractive index.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology, specifically relating to a planar structure based on a topological photonic crystal and an infrared sensor. Background Technology

[0002] Photonic crystals introduce the concept of photonic bandgap by incorporating a periodic dielectric constant to mimic the periodic potential of atoms in solids. Through the photonic bandgap, photonic crystals can construct waveguides and microcavity structures, enabling the transmission and localization of light at the microscale, and can be applied to on-chip integrated optical paths and devices.

[0003] As the integration density of topological photonic systems continues to increase, the spacing between topological waveguides (microcavities) will inevitably decrease. This will lead to mode-field coupling between optical topological states through evanescent fields, thereby altering some of the physical properties of the topological states. Furthermore, most work based on photonic crystal topological states focuses on realizing on-chip optical device applications, i.e., introducing, transmitting, and processing optical waveguide modes within a plane. In related technical fields, due to the different arrangement of topological photonic crystals, the planar structures composed of topological photonic crystals are insensitive to changes in the refractive index of the environment, thus reducing the applicability of topological photonic crystals. Summary of the Invention

[0004] The purpose of this application is to provide a planar structure and infrared sensor based on a topological photonic crystal, so as to solve the technical problem in the prior art that the topological photonic crystal is not sensitive to changes in the refractive index of the environment.

[0005] To achieve the above objectives, the technical solution adopted in this application is: to provide a planar structure based on a topological photonic crystal, comprising:

[0006] Multiple supercells are arranged in an array along a first direction and a second direction to form a matrix; each supercell includes a topologically nontrivial structure and a topologically trivial structure, with the topologically trivial structure surrounding the outer periphery of the topologically nontrivial structure; each topologically nontrivial structure includes multiple topologically nontrivial cells, arranged in an array along the first direction and a second direction to form a matrix; each topologically trivial structure includes multiple topologically trivial cells, which form a matrix.

[0007] Optionally, the number of topological nontrivial units is set to nine, and the number of topological trivial units is set to sixteen.

[0008] Optionally, the matrix formed by a plurality of the topologically nontrivial units is set as a square; the matrix formed by a plurality of the topologically trivial units is set as a square.

[0009] Optionally, every four of the topologically nontrivial units are enclosed to form a first air hole; each of the topologically trivial units has a second air hole.

[0010] Optionally, the topologically nontrivial unit includes a first body and a second body, the second body being fixedly connected to the first body, the first body and the second body being distributed intersectingly and forming four slots; wherein each of the four adjacent slots encloses and forms the first air hole.

[0011] Optionally, the cross-sections of the first air hole and the second air hole perpendicular to a third direction are set to be square or circular.

[0012] Optionally, the cross-sectional side length of the first air hole and the second air hole perpendicular to the third direction is 1.37 micrometers to 1.39 micrometers; the cross-sectional diameter of the first air hole and the second air hole perpendicular to the third direction is 1.37 micrometers to 1.39 micrometers.

[0013] Optionally, the lattice constant of the topological nontrivial unit and the lattice constant of the topological trivial unit are both 2.03 micrometers.

[0014] Optionally, the thickness of the topological nontrivial cell along the third direction and the thickness of the topological trivial cell along the third direction are both 4.2 micrometers to 4.3 micrometers.

[0015] This application embodiment also provides an infrared sensor, including the aforementioned flat plate structure and a sensor body, wherein the flat plate structure is disposed on the sensor body.

[0016] The beneficial effects of the planar structure based on topological photonic crystal provided in this application are as follows:

[0017] The planar structure based on topological photonic crystals provided in this application utilizes different photonic crystal unit configurations to enable superunits to possess both topologically nontrivial and topologically trivial units. Furthermore, by arranging the superunits, each superunit becomes a second-order topological insulator, supporting topological corner states. The periodic arrangement allows these topological corner states to couple with each other, enabling them to extend infinitely within the plane formed by the first and second directions. Since these topological corner states can interact with air, their resonance characteristics are sensitive to the environmental refractive index.

[0018] The advantages of the infrared sensor provided in this application are as follows:

[0019] The infrared sensor provided in this application embodiment utilizes the characteristic that topological corner states are sensitive to the refractive index of the environment, and has advantages such as high sensitivity compared to other types of photonic sensors. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A perspective view of a planar structure based on a topological photonic crystal provided in an embodiment of this application;

[0022] Figure 2 A first data diagram of a planar structure based on a topological photonic crystal provided for an embodiment of this application;

[0023] Figure 3 A second data diagram of a planar structure based on a topological photonic crystal provided for an embodiment of this application;

[0024] Figure 4 A third data diagram of a planar structure based on a topological photonic crystal provided for an embodiment of this application;

[0025] Figure 5 A fourth data diagram of a planar structure based on a topological photonic crystal provided for an embodiment of this application;

[0026] Figure 6 A planar diagram of the topological trivial unit of a planar structure based on a topological photonic crystal provided in the embodiments of this application;

[0027] Figure 7 A topological nontrivial unit planar diagram of a planar structure based on a topological photonic crystal provided in the embodiments of this application;

[0028] Figure 8 The fifth data diagram of the planar structure based on topological photonic crystal provided for the embodiments of this application.

[0029] The following are the labeling elements in the figure:

[0030] 1. Supercell; 11. Topologically nontrivial structure; 111. Topologically nontrivial cell; 1111. First main body; 1112. Second main body; 1113. Slot; 112. First air hole; 12. Topologically trivial structure; 121. Topologically trivial cell; 122. Second air hole. Detailed Implementation

[0031] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0032] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0033] It should be understood that the terms "length", "width", "upper", "lower", "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 for the convenience of describing this application and simplifying 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 limitations on this application.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0035] Based on this, the present invention provides a planar structure and an infrared sensor based on a topological photonic crystal, which has excellent properties such as high sensitivity.

[0036] like Figures 1 to 7 As shown, this application provides a planar structure based on a topological photonic crystal, including multiple supercells 1, which are arranged in an array along a first direction and a second direction to form a matrix; the supercells 1 include a topologically nontrivial structure 11 and a topologically trivial structure 12, with the topologically trivial structure 12 surrounding the outer periphery of the topologically nontrivial structure 11; the topologically nontrivial structure 11 includes multiple topologically nontrivial units 111, which are arranged in an array along the first direction and the second direction to form a matrix; the topologically trivial structure 12 includes multiple topologically trivial units 121, which form a matrix.

[0037] It should be noted that the first direction mentioned above and below refers to a bidirectional direction along its axial direction, specifically as follows: Figure 1 The X direction is shown. The second direction above and below refers to the bidirectional direction along its axis, specifically as shown in the figure. Figure 1 Y direction shown in .

[0038] It should also be noted that, according to the topological invariant two-dimensional Zach phase, that is, according to the formula:

[0039]

[0040] Where, P = (P x ,P y ) represents the two-dimensional polarization intensity, k = (k x ,k y ) represents the wave vector. Contact on behalf of Pele, |ψ k > represents the eigenstate of the first ground state band. Tr[A] is a mathematical symbol, representing the trace operation on the target matrix A; dk is part of the integration operation, representing the integration of the wave vector within the first Brillouin zone.

[0041] like Figure 2 As shown, the integration is performed in the first Brillouin zone (FBZ). When the Zach phase value is (0,0), it represents that the system is in a topologically trivial phase. When the Zach phase value is (π,π), it represents that the system is in a topologically nontrivial phase. To calculate the two-dimensional Zach-Zach phase, the band structure of the photonic crystal unit in the first Brillouin zone must first be calculated. Each k-point of each band corresponds to an eigenstate, and its electromagnetic field distribution contains all the information of this eigenstate, which can be substituted into the above equation for calculation. Here, only the transversely electric (TE-like) modes in the photonic crystal are considered. The band structures of the topologically trivial and nontrivial units are as follows: Figure 2As shown. Based on the ground-state band structure, it can be found that the ground-state band structure of the two units is the same, and a ground-state band gap exists in the range of 6.5 micrometers to 7.74 micrometers. The above equation can be used to calculate that the topologically trivial unit 121 and the topologically non-trivial unit 111 have different phase values ​​of (0,0) and (π,π), respectively, i.e., they have topologically trivial and non-trivial phases, thus forming a topologically trivial region and a topologically non-trivial region. The topologically trivial region and the topologically non-trivial region can constitute a classic two-dimensional second-order topological insulator. Multiple topologically non-trivial units 111 are arranged in a 3×3 manner to form a square matrix, and multiple topologically non-trivial units 111 are arranged to form a topologically non-trivial region. Multiple topologically trivial units 121 surround the outer perimeter of the 3×3 square matrix, forming a new square matrix, and multiple topologically trivial units 121 are arranged to form a topologically trivial region. In this embodiment, the topologically non-trivial region and the topologically trivial region constitute a classic two-dimensional second-order topological insulator, which can support zero-dimensional topological states, i.e., topological corner states, i.e., superunit 1. This second-order topological insulator is considered as a superunit 1, and periodically arranged in a plane to form the planar structure of a topological photonic crystal. Topological corner states within adjacent superunit 1s couple with each other, allowing their optical fields to extend infinitely within the plane. Since these corner states are located within the optical cone of the photonic crystal planar plate at point Γ (corresponding to the direction of perpendicular incident light), their modes leak, enabling them to couple with and be simultaneously excited by external electromagnetic fields. For example... Figure 3 As shown, a full-wave simulation of the structure was performed using the finite-difference time-domain method. A vertically incident plane wave was introduced above the plate structure to achieve far-field excitation, and an energy monitor was placed below the plate structure to calculate the normalized transmission spectrum. Simulation results showed a sharp transmission valley at the resonant wavelength of 7.21 μm in the corner state on the infinitely extended plate structure, which is a characteristic of optical resonance, with a transmittance of 0.51. Due to the C4 rotational symmetry of the structure, the polarization angle φ of the rotating plane wave does not change its resonant wavelength. The distribution of the magnetic field z-component of superunit 1 at the resonant wavelength under different polarization angles is shown in the figure. Figure 3The inset is shown in the figure. The results show that the two corner states are excited at φ = 135° and φ = 45° respectively; furthermore, when φ = 90°, the magnetic field is concentrated at the four corners, showing a superposition of the two corner states. The interference between the corner states and the plate state results in a Fano line shape in the transmission spectrum (an asymmetric line shape, a classic Fano line shape. The Fano line shape is an asymmetric line shape produced by the interference between the continuous-state scattering amplitude and the discrete-state scattering amplitude. In this structure, the plate state and the corner state play the roles of continuous and discrete states, respectively. The asymmetric characteristics of the Fano line shape mean that even a slight drift can cause a large change in transmittance within a certain wavelength range, which is beneficial for improving the sensing effect). This line shape of the transmission spectrum can be theoretically fitted by the following Fano formula:

[0042]

[0043] In the formula, a1, a2, and b are fitting constants, ω0 is the resonant frequency, γ is the resonant attenuation rate, i is the imaginary unit, ω is the frequency to be fitted, and T... Fano This is the transmittance obtained from the fitting. The quality factor can be obtained from the following relationship:

[0044] Q=ω0 / 2γ

[0045] By fitting the Fano formula, the quality factor of this state was found to be 3022. It should be noted that a higher value indicates a longer time the corner state can confine light within the plate, resulting in a longer interaction time between the corner state and its surroundings. This makes it more sensitive to changes in the environment and improves sensing sensitivity.

[0046] like Figure 4 As shown in the optical field distribution diagram of superunit 1, the resonant electromagnetic field of the corner state is mainly distributed inside the micropore, thus enabling it to fully interact with the environment surrounding the micropore and the plate. Its characteristics are also highly sensitive to changes in the refractive index of the environment. Therefore, we investigated the changes in the normalized transmission spectrum under different refractive indices (from 1 to 1.1), as shown... Figure 4 As shown, the resonant transmission valley caused by the corner state shifts significantly with increasing environmental refractive index, indicating that an increase in environmental refractive index leads to an increase in the resonant wavelength of the corner state. Therefore, by examining the shift in the transmission spectrum, the sensing function of the environmental refractive index can be achieved. The sensing sensitivity S is defined as follows:

[0047]

[0048] S is defined as the resonant wavelength shift caused by each unit change in ambient refractive index. The resonant wavelength changes with the ambient refractive index as follows: Figure 5As shown, the resonant wavelengths at ambient refractive indices of 1, 1.025, 1.05, 1.075, and 1.1 are 7.21 μm, 7.23 μm, 7.25 μm, 7.27 μm, and 7.29 μm, respectively, exhibiting a linear relationship with the change in ambient refractive index. Therefore, the slope of the fitted line represents the sensing sensitivity. Calculations show that the sensing sensitivity of this structure is 800 nm / unit refractive index, or 800 nm / RIU, indicating high sensing sensitivity.

[0049] The planar structure based on topological photonic crystals provided in this application utilizes different photonic crystal unit configurations to give superunit 1 topologically nontrivial units 111 and topologically trivial units 121. By arranging the superunits 1, each superunit 1 is made a second-order topological insulator, supporting topological corner states. The periodic arrangement allows the topological corner states to couple with each other, enabling them to extend infinitely within the plane formed by the first and second directions. The topological corner states can interact with air; therefore, their resonance characteristics are sensitive to the environmental refractive index.

[0050] In one embodiment of this application, the number of topological nontrivial units 111 is set to nine, and the number of topological trivial units 121 is set to sixteen.

[0051] This configuration ensures that the sensing sensitivity of the flat plate structure is no less than 800 nanometers per unit refractive index.

[0052] In one embodiment of this application, the matrix formed by a plurality of topologically nontrivial units 111 is set as a square. The matrix formed by a plurality of topologically trivial units 121 is set as a square.

[0053] This configuration ensures that the sensing sensitivity of the flat plate structure is no less than 800 nanometers per unit refractive index.

[0054] In one embodiment of this application, a first air hole 112 is formed by enclosing every four topologically nontrivial units 111. Each topologically trivial unit 121 has a second air hole 122.

[0055] This configuration allows the resonant magnetic field of the topological corner state to be distributed within the first air hole 112 and the second air hole 122, thereby enabling both the first air hole 112 and the second air hole 122 to interact with the external environment.

[0056] In one embodiment of this application, the topological nontrivial unit 111 includes a first body 1111 and a second body 1112. The second body 1112 is fixedly connected to the first body 1111. The first body 1111 and the second body 1112 are distributed intersectingly and form four slots 1113. Each of the four adjacent slots 1113 encloses and forms a first air hole 112.

[0057] It should be noted that in this embodiment, the first main body 1111 extends along the first direction and the second main body 1112 extends along the second direction as an example. The first main body 1111 and the second main body 1112 are intersecting and forming an angle, that is, the first main body 1111 and the second main body 1112 intersect and form an angle.

[0058] With this configuration, the first main body 1111 and the second main body 1112 can cross to form a topological nontrivial unit 111, and the first air hole 112 is formed by the enclosing of each of the four adjacent slots 1113.

[0059] Optionally, both the first body 1111 and the second body 1112 are configured as silicon plates.

[0060] In one embodiment of this application, the cross-section of the first air hole 112 and the second air hole 122 perpendicular to a third direction is set as a square.

[0061] It should be noted that the "above" and "below" third directions refer to bidirectional directions along its axis, that is, directions perpendicular to the plate, specifically as follows: Figure 1 The Z-axis is shown in the figure.

[0062] It should also be noted that this embodiment is illustrated by setting the cross-section of the first air hole 112 and the second air hole 122 perpendicular to a third direction as a square. Of course, in other embodiments, the cross-section of the first air hole 112 and the second air hole 122 perpendicular to a third direction can also be set as a circle.

[0063] With this configuration, the cross-sections of the first air hole 112 and the second air hole 122 perpendicular to the third direction are set to be square or circular, which can ensure that the sensing sensitivity of the flat plate structure is 800 nanometers / unit refractive index.

[0064] In one embodiment of this application, such as Figure 8 As shown, the side length of the cross-section of the first air hole 112 and the second air hole 122 perpendicular to the third direction is 1.37 micrometers to 1.39 micrometers. The diameter of the cross-section of the first air hole 112 and the second air hole 122 perpendicular to the third direction is 1.37 micrometers to 1.39 micrometers.

[0065] Specifically, when the side length of the cross-section of the first air hole 112 and the second air hole 122 perpendicular to the third direction is set to 1.37 micrometers, the resonant wavelengths under different refractive indices are 7.26, 7.28, 7.3, 7.32, and 7.34 micrometers, respectively. When the side length of the cross-section of the first air hole 112 and the second air hole 122 perpendicular to the third direction is set to 1.39 micrometers, the resonant wavelengths under different refractive indices are 7.18, 7.2, 7.22, 7.24, and 7.26 micrometers, respectively.

[0066] In one embodiment of this application, the lattice constant of the topological nontrivial unit 111 and the lattice constant of the topological trivial unit 121 are both 2.03 micrometers.

[0067] This setting ensures that the resonant wavelength is within the mid-infrared band, making it suitable for mid-infrared sensing. It also prevents the resonant wavelength from deviating from the mid-infrared range and thus losing its mid-infrared sensing function if the lattice constant is set to other values.

[0068] In one embodiment of this application, such as Figure 8 As shown, the thickness of the topological nontrivial element 111 along the third direction and the thickness of the topological trivial element 121 along the third direction are both 4.2 μm to 4.3 μm.

[0069] With this configuration, when the thickness of both the topological nontrivial unit 111 and the topological trivial unit 121 along the third direction is set to 4.2 μm, the resonance wavelengths under different refractive indices are 7.2, 7.22, 7.24, 7.26, and 7.28 μm, respectively. When the thickness of both the topological nontrivial unit 111 and the topological trivial unit 121 along the third direction is set to 4.3 μm, the resonance wavelengths under different refractive indices are 7.23, 7.25, 7.27, 7.29, and 7.31 μm, respectively.

[0070] Optionally, the dielectric constant of the plate is 12 and it is set to non-dispersive.

[0071] This application also provides an infrared sensor, including a flat panel structure and a sensor body, wherein the flat panel structure is disposed on the sensor body.

[0072] It should be noted that the sensor body is a mid-infrared refractive index sensor.

[0073] The infrared sensor provided in this application embodiment utilizes the characteristic that topological corner states are sensitive to the refractive index of the environment, and has advantages such as high sensitivity compared to other types of photonic sensors.

[0074] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A planar structure based on a topological photonic crystal, characterized in that, include: Multiple supercells are arranged in an array along a first direction and a second direction to form a matrix. The multiple supercells are periodically arranged in the plane formed by the first direction and the second direction. Each supercell includes a topologically nontrivial structure and a topologically trivial structure. The topologically trivial structure surrounds the outer periphery of the topologically nontrivial structure. Each topologically nontrivial structure includes multiple topologically nontrivial cells, which are arranged in an array along the first direction and the second direction to form a matrix. Each topologically trivial structure includes multiple topologically trivial cells, which form a matrix. Every four topologically nontrivial cells enclose a first air hole. Each topologically trivial cell has a second air hole.

2. The planar structure based on topological photonic crystal as described in claim 1, characterized in that, The number of non-trivial topological units is set to nine, and the number of trivial topological units is set to sixteen.

3. The planar structure based on topological photonic crystal as described in claim 1, characterized in that, The matrix formed by multiple topologically nontrivial units is set as a square; the matrix formed by multiple topologically trivial units is set as a square.

4. The planar structure based on topological photonic crystal as described in claim 1, characterized in that, The topologically nontrivial unit includes a first body and a second body, the second body being fixedly connected to the first body, the first body and the second body being intersected and forming four slots; wherein, each of the four adjacent slots encloses and forms the first air hole.

5. The planar structure based on topological photonic crystal as described in claim 1, characterized in that, The cross-sections of the first air hole and the second air hole perpendicular to a third direction are set as square or circular.

6. The planar structure based on a topological photonic crystal as described in any one of claims 1, 4, and 5, characterized in that, The cross-sectional side lengths of the first and second air holes perpendicular to the third direction are 1.37 micrometers to 1.39 micrometers; the cross-sectional diameters of the first and second air holes perpendicular to the third direction are 1.37 micrometers to 1.39 micrometers.

7. The planar structure based on a topological photonic crystal as described in any one of claims 1-5, characterized in that, The lattice constant of the topological nontrivial unit and the lattice constant of the topological trivial unit are both 2.03 micrometers.

8. The planar structure based on a topological photonic crystal as described in any one of claims 1-5, characterized in that, The thickness of the nontrivial topological element along the third direction and the thickness of the trivial topological element along the third direction are both 4.2 micrometers to 4.3 micrometers.

9. An infrared sensor, characterized in that, It includes the flat plate structure and sensor body as described in any one of claims 1-8, wherein the flat plate structure is disposed on the sensor body.

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