Photonic crystal plate combining continuous domain bound state at non-gamma point
By introducing cylindrical holes on the photonic crystal plate to break the symmetry, the merger of BICs in the non-Γ-point photonic crystal plate is achieved, and the diffraction and diffusion of the beam at the non-Γ-point is solved, and the focus and transmission stability of the beam is improved. , promotes the flexibility and application diversity of optical systems.
Patent Information
- Application Number
- CN202411458160.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-18
- Publication Date
- 2024-12-10
AI Technical Summary
The combined bound states in existing photonic crystal panels are mainly concentrated at the Γ point in the center of the Brillouin area, which is difficult to achieve at non-Γ points, limiting the application of beam focusing and beam guidance, especially during long-distance transmission.
Design a photonic crystal plate that combines continuous domain bound states at non-Γ points. By introducing multiple uniformly distributed cylindrical holes on the photonic crystal plate, the original symmetry is broken, so that the higher-order topological load BIC splits at non-Γ points. And merged with accidental BIC, and numerical simulation is used to calculate the thickness and pore position of the photonic crystal plate to achieve BIC merge.
The perfect binding and focusing of the beam at non-Γ points is achieved, which significantly improves the spatial resolution and transmission stability of the beam, enhances the focusing ability of the beam, and provides a more flexible and efficient optical system design.
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Figure CN119105116A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of optics, and in particular to a photonic crystal plate that combines continuous domain bound states at a non-Γ point. Background Art
[0002] Bound states in the continuum (BIC) are localized states with infinite lifetimes that exist in a continuous spectrum of extended states, and they remain perfectly localized in space even in the presence of a continuous spectrum with matching energy and momentum. BICs are generally divided into two categories: symmetry-protected and accidental. Symmetry-protected BICs are usually fixed at a high-symmetry point in the Brillouin zone, the Γ point, where the state is completely decoupled from the continuous spectrum due to the incompatible symmetry with the outgoing wave in the radiation channel. Accidental BICs arise from leakage being canceled by interference. Therefore, accidental BICs, which usually exist at non-high-symmetry points, no longer depend on the structural symmetry, but are sensitive to their spatial and geometric parameters.
[0003] BICs provide a new way to achieve high-quality factor (Q factor) resonances, and in theory, resonances with infinitely high Q factors can be achieved. In practical applications, scattering losses caused by inevitable manufacturing defects affect the Q factor of BICs. An effective strategy to solve this problem is to exploit the topological properties of BICs. In optical systems with uncertain far-field polarization directions, BICs are proven to be polarization singularities in momentum space, called eigenmodes. BICs, as linearly polarized momentum space vortex centers, have integer topological charges (q). As long as the system symmetry is maintained, the topological properties of BICs guarantee their robustness, making accidental BICs tunable under structural parameter changes. Based on this, multiple separate BICs can be tuned to the same wave vector to construct a merged BIC, and the Q factor of the states near the merged BIC can be enhanced over a wide range of wave vectors. Due to their ultra-high Q values, the merged BICs can significantly enhance the interaction of light and provide extremely high local beam focusing capabilities.
[0004] However, most of the research on merging BICs on photonic crystals is focused on the Γ point at the center of the Brillouin zone. On the other hand, many potential applications of BICs on photonic crystals require momentum selection, which cannot be achieved by merging BICs at Γ. These applications include but are not limited to beam steering, directional vector beams, non-diffraction beams, optical fibers, modulators, and sensors based on angular selectivity. Therefore, merging BICs at non-Γ points is of great significance for many applications related to the wave vector k. For example, in terms of beam steering, existing beam steering technologies may face beam diffraction and diffusion, especially when the beam is transmitted over long distances, the beam cannot maintain a high degree of focus. Merging BICs at non-Γ points can achieve perfect confinement of the beam in a specific non-Γ point momentum region, effectively focus the beam even during propagation, reduce diffraction effects, achieve stronger beam focusing, and improve the spatial resolution and transmission stability of the beam. Summary of the invention
[0005] The object of the present invention is to provide a photonic crystal plate that merges continuous domain bound states at non-Γ points, which can realize merging BIC at non-Γ points, thereby achieving stronger beam focusing.
[0006] To achieve the above object, the present invention provides the following solutions:
[0007] A photonic crystal plate for merging continuous domain bound states at a non-Γ point, characterized in that the photonic crystal plate comprises: a photonic crystal plate body and a plurality of target holes penetrating the photonic crystal plate body;
[0008] The photonic crystal plate body has a plurality of evenly distributed cylindrical holes;
[0009] The position of each target hole is set on the diagonal line of a parallelogram formed by the line connecting the center points of four adjacent cylindrical holes; the four sides of the parallelogram are equal and the internal angle is 60 degrees.
[0010] Optionally, the material of the photonic crystal plate body is silicon nitride.
[0011] Optionally, the photonic crystal plate body has C 6v Symmetrical structure.
[0012] Optionally, the radius of the cylindrical hole is 80 nm.
[0013] Optionally, the diameter of the target pore is 40 nm.
[0014] Optionally, the thickness of the photonic crystal slab is determined according to a BIC merging condition in a far-field polarization vector generated by a lowest TE band energy band of the photonic crystal slab.
[0015] Optionally, the lowest TE band energy band structure is calculated by applying a numerical simulation method by immersing the photonic crystal plate in a liquid with a refractive index of 1.46.
[0016] Optionally, the thickness of the photonic crystal slab is 335.2 nm.
[0017] Optionally, the distance between the center point of the target hole and the target vertex of the parallelogram is 270 nm; the target vertex is the vertex corresponding to the inner angle of 60 degrees in the parallelogram.
[0018] Optionally, the photonic crystal plate body is an optical structure capable of generating a high-order topological charge BIC at the Γ point.
[0019] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:
[0020] The present invention discloses a photonic crystal plate for merging continuous domain bound states at non-Γ points, including: designing an optical structure based on a high-order topological charge BIC at the Γ point; calculating the energy band of the photonic crystal plate, and generating a far-field polarization vector diagram from the energy band structure; breaking the original symmetric structure by introducing a circular hole, so that the high-order topological charge BIC at the Γ point is split; and by changing the structural parameters of the photonic crystal plate, the split BIC and the accidental BIC can be merged at the non-Γ point. The introduction of the non-Γ point merging BIC provides a new way and possibility for the application of beam steering and directional vector beams, making the optical system more flexible and efficient in design and application, and promoting the development of more optical technologies. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0022] Figure 1 C 6v Schematic diagram of a symmetric photonic crystal slab;
[0023] Figure 2 C 6v Simulated TE band diagram of a symmetric photonic crystal slab;
[0024] Figure 3 is the far-field polarization vector calculated from the lowest TE band;
[0025] Figure 4 Schematic diagram of the photonic crystal plate after the circular hole is introduced;
[0026] Figure 5 The simulated TE band diagram of the photonic crystal slab after the circular hole is introduced;
[0027] Figure 6 The far-field polarization vector calculated for the lowest TE band of the photonic crystal slab after the circular hole is introduced;
[0028] Figure 7 The polarization vector around the lowest TE band when the plate thickness is t1 = 336 nm with the Q factor as the background color;
[0029] Figure 8 The polarization vector around the lowest TE band when the plate thickness is t2 = 335.2nm with the Q factor as the background color;
[0030] Fig. 9 Schematic diagram of simulating Q factor in three photonic crystal plates with different thicknesses at the lowest TE band;
[0031] Fig.10 Schematic diagram of the Q factor as a function of the wave vector away from the BIC along the ΓM direction;
[0032] Fig.11 Schematic diagram of the simulated evolution of the Q factor along the M-Γ direction with the thickness of the photonic crystal slab;
[0033] Fig.12 A partial top view of the photonic crystal plate with circular pinholes initially introduced;
[0034] Fig.13 It is a local top view of the initial small hole position rotated 60 degrees counterclockwise around point o;
[0035] Fig.14 It is a local top view of the initial hole position rotated 60 degrees clockwise around point o;
[0036] Fig.15 The polarization vector around the lowest TE sample band of the circular aperture is initially introduced;
[0037] Fig.16 is the polarization vector around the lowest TE sample band after the initial aperture position is rotated 60 degrees counterclockwise around point o;
[0038] Fig.17 is the polarization vector around the lowest TE sample band after the initial aperture position is rotated 60 degrees clockwise around point o. DETAILED DESCRIPTION
[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0040] The object of the present invention is to provide a photonic crystal plate for merging continuous domain bound states at a non-Γ point, aiming to achieve merging BIC at a non-Γ point, thereby achieving stronger beam focusing.
[0041] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.
[0042] Example 1
[0043] like Figures 1 to 17 As shown, the photonic crystal plate for merging continuous domain bound states at non-Γ points in this embodiment includes: a photonic crystal plate body and a plurality of target holes penetrating the photonic crystal plate body; the photonic crystal plate body has a plurality of evenly distributed cylindrical holes; the position of each of the target holes is set on the diagonal line of a parallelogram formed by connecting the center points of four adjacent cylindrical holes; the four sides of the parallelogram are equal and the internal angle is 60 degrees. The distance between the center point of the target hole and the target vertex of the parallelogram is 270nm; the target vertex is the vertex corresponding to the internal angle of 60 degrees in the parallelogram.
[0044] Specifically, the material of the photonic crystal plate body is silicon nitride. 6v Symmetrical structure. The photonic crystal plate body is an optical structure capable of generating a high-order topological charge BIC at the Γ point.
[0045] The thickness of the photonic crystal plate is 335.2 nm. The radius of the cylindrical hole is 80 nm. The diameter of the target hole is 40 nm. The thickness of the photonic crystal plate is determined according to the split BIC and accidental BIC merging conditions in the far-field polarization vector diagram generated by the lowest TE band energy band of the photonic crystal plate.
[0046] Furthermore, the lowest TE band energy band structure is calculated by applying a numerical simulation method by immersing the photonic crystal plate in a liquid with a refractive index of 1.46.
[0047] The method for preparing a photonic crystal plate that merges continuous domain bound states at a non-Γ point specifically includes:
[0048] S1. Design an optical structure that generates a high-order topological charge BIC at the Γ point; the present invention uses a C formed by drilling holes in silicon nitride 6v Symmetric photonic crystal plate, and the C 6v The symmetric photonic crystal plate serves as the photonic crystal plate body.
[0049] Specifically, the process of generating BIC in the photonic crystal slab is as follows: Figure 1 The photonic crystal plate is composed of silicon nitride (n = 2.02) and cylindrical holes with C 6v Symmetrical structure, the photonic crystal plate body is immersed in a liquid with a refractive index n=1.46; the C 6v The symmetrical structure is composed of parallelograms with equal sides and a small angle of 60 degrees arranged periodically in all directions. The period a = 336nm, the thickness t = 340nm, and the radius of the circular hole r = 80nm. The structure of the photonic crystal plate is composed of parallelograms arranged in all directions. In other words, the parallelogram structure is the unit cell structure of the photonic crystal plate, and this photonic crystal plate is composed of such parallelogram structures. The thickness t = 340nm is the initial thickness. After the small hole is introduced, the high-order topological charge is split. In order to operate the split BIC and the surrounding accidental BIC to merge, the thickness of the plate is adjusted.
[0050] S2. By using numerical simulation software (COMSOL Multiphysics simulation), the medium around the photonic crystal plate body is set to n=1.46, the band structure of the photonic crystal plate body is calculated, and then the far-field polarization vector is generated from the band structure to see the BIC topological charge distribution.
[0051] Specifically, the TE band structure is as follows: Figure 2 As shown, Figure 2 The arrow in the middle shows the lowest TE band. Because it is in the light cone and below the diffraction limit, it can only radiate into the free space through zero-order diffraction. Use this lowest TE band to find the far-field polarization vector and observe the BIC topological charge distribution. Since the mode at Γ belongs to C 6v point group, so it exhibits a charge q = -2 symmetry-protected BIC with a divergent Q factor, as can be seen from the far-field polarization vector, Figure 3 As shown. The topological charge related formula is:
[0052]
[0053] Where q represents the topological charge of the BIC, which quantifies the winding of the polarization vector around the BIC; k represents the wave vector; c is a closed loop in the counterclockwise direction around the vortex center; φ(k) = arg[C x (k)+iC y (k)] is the polarization angle, where Cx and C x represent the electric field along the x and y directions respectively; It is the gradient operator in momentum space, describing the change in momentum space.
[0054] S3. Introduce a circular hole into the photonic crystal plate to break the original system symmetry and split the high-order topological charge BIC.
[0055] Specifically, Figures 4 to 6 As shown in , the value of diameter D and the value of d are determined little by little based on the observation of the splitting of higher-order topological charges. Figure 4 As shown, the circular hole is located on the diagonal line of the parallelogram, with a diameter of D = 40nm and a horizontal distance of d = 270nm from one corner of the parallelogram. At this time, the TE band structure of the photonic crystal plate is as follows Figure 5 As shown. Due to the conservation of topological charge, the symmetry of the original system is reduced, and the topological charge of the high-order BIC before symmetry reduction will not disappear suddenly, but should be split into two separate topological charges at the non-Γ point. Select the lowest TE band to generate the corresponding far-field polarization vector. Figure 6 As shown, a high-order topological charge splitting into two q=-1 BICs is observed.
[0056] In the present invention, Figures 1 to 6 A BIC schematic diagram is generated for the photonic crystal plate body and the photonic crystal plate according to the embodiment of the present invention. Figure 1 C 6v Schematic diagram of a symmetrical photonic crystal plate, where the inset in the upper right corner is the unit cell structure of the photonic crystal plate, and the inset in the lower right corner is the first Brillouin zone; Figure 2 is the simulated TE band diagram of the photonic crystal slab body, with the lowest TE band highlighted by an arrow; Figure 3 is the far-field polarization vector calculated from the lowest TE band, with the Q factor as the background, showing the polarization vortex appearing around the BIC; Figure 4 Schematic diagram of the photonic crystal plate after the circular hole is introduced; Figure 5 The simulated TE band diagram of the photonic crystal slab after the introduction of the circular hole, the lowest TE band is highlighted by an arrow; Figure 6 The far-field polarization vector calculated for the lowest TE band of the photonic crystal slab after the introduction of a circular hole, with the Q factor as the background, showing the polarization vortex that appears around the high-order topological charge BIC splitting.
[0057] S4. By changing the structural parameters of the system, that is, changing the thickness of the photonic crystal plate, the split BIC is merged with the surrounding accidental BICs.
[0058] Specifically, through the far-field polarization vector, Figure 6As shown in Figure 1, there are accidental BICs around. Then, keeping other parameters unchanged, only changing the thickness of the board, calculating the corresponding far-field polarization vector, and observing the change in the position of the BIC. By reducing the thickness, the accidental BIC is adjusted to be close to Γ, while the split BIC is adjusted to be away from Γ, as shown in Figure 1. Fig.11 As shown in the figure, point 0 is the Γ point, the left side is the accidental BIC, and the right side is the split BIC. It can be seen that one BIC is getting closer and the other is getting farther away from the Γ point. Finally, the two BICs merge at a thickness of about 335nm. In this example, the thickness is 336nm and 335.2nm, as shown in Figure 7 and Figure 8 As shown in Figure 2, the BIC that breaks the original symmetry split merges with the accidental BIC at the non-Γ point, and the Q factor of the state near the merged BIC can be enhanced in a wider wave vector range. Figure 7 and Figure 8 In the figure, t = 340 nm (just split), t1 = 336 nm (two BICs approaching each other), t2 = 335.2 nm (two BICs merged), and they are at equal distances (kk BIC ), the combined Q factor significantly enhances the other two, where the nearby state means the wave vector scanning range.
[0059] Compared with the separated BIC, the combined BIC (t2 = 335.2 nm) significantly improves the Q factor of the neighboring state, which can be seen from the quality factor Q obtained by scanning the Brillouin zone, such as Fig. 9 and Fig.10 In addition, this example also simulates the evolution of the Q factor along the M-Γ direction with the thickness of the photonic crystal plate. It is found that the split BIC and the accidental BIC gradually approach each other until they merge when the plate thickness decreases. Then the accidental BIC and the split BIC with opposite topological charges annihilate each other and finally evolve into a quasi-BIC, as shown in Fig.11 shown.
[0060] Figures 7 to 11 Schematic diagram of merging BIC at non-Γ points. Figure 7 The polarization vector around the lowest TE band when the plate thickness is t1 = 336 nm with the Q factor as the background color; Figure 8 The polarization vector around the lowest TE band when the plate thickness is t2 = 335.2nm with the Q factor as the background color; Fig. 9 Simulated Q factor in the lowest TE band under three photonic crystal slabs with different thicknesses. The inset is the first Brillouin zone. Fig.10 Taking the Q factor as a function of the wave vector away from the BIC along the ΓM direction, it can be seen that the combined BIC (t2 = 335.2nm) significantly improves the Q factor of the neighboring state compared with the separated BIC; Fig.11This is the simulated evolution of the Q factor along the M-Γ direction with the thickness of the photonic crystal slab. It can be seen that the split BIC and the accidental BIC get closer and closer until they merge as the thickness of the slab decreases. Finally, the accidental BIC and the split BIC with opposite topological charges annihilate each other and become quasi-BIC.
[0061] Step S1 is to generate the main body of the photonic crystal plate with high-order topological charges; step S2 is to see the distribution of topological charges, which is specifically achieved through the far-field polarization vector, and the topological charge distribution position can be intuitively seen through the far-field polarization vector diagram; step S3 is to introduce small holes, which is to change the original symmetry structure, because the high-order topological charge at the Γ point (that is, the center point of the polarization diagram) exists due to symmetry, and the introduction of small holes reduces the original symmetry of the plate. Due to the conservation of topological charge, the high-order topological charge will not disappear out of thin air, so it will split. Therefore, each time the thickness is changed on the basis of step S3, it is only necessary to perform step S2 again to observe the change in the topological charge distribution position. As for whether the thickness of the photonic crystal plate becomes thicker or narrower, it is determined based on experimental observations, and the change in the thickness of the photonic crystal plate can be seen. Fig.11 By simulating the evolution, it was found that when the thickness of the plate becomes smaller, the two BICs get closer until they merge. Therefore, the present invention selected two plates with thicknesses of 336nm (two BICs getting closer) and 335.2nm (merging BIC) to observe their far-field polarization vectors and intuitively observe their merging.
[0062] In this example, the position of the small hole was also changed, and it was found that the direction of the high-order topological charge BIC splitting was closely related to the position of the small hole. Fig.12 This is a partial top view after the small hole was first introduced. Fig.13 for Fig.12 The local top view of the small and medium holes is obtained by rotating 60 degrees counterclockwise around point o. Fig.14 for Fig.12 The local top view of the small and medium holes is obtained by rotating 60 degrees clockwise around point o.
[0063] The changing rules are respectively in the C 6v Introducing small holes on the diagonals of a symmetrical photonic crystal plate and introducing small holes on different diagonals will cause the high-order topological charge to split along different directions. It is found that the BIC splitting direction is vertically related to the position of the small holes, that is, the high-order topological charge is split along the symmetry direction.
[0064] By changing the holes to different diagonals, such as Figure 12-14 As shown in the figure, the solid line is the BIC splitting direction. By observing the corresponding far-field polarization vectors at different positions, it is found that the BIC splitting direction is perpendicular to the position of the small hole, as shown in Figure 15-17. Similarly, if the structural parameters of the plate are adjusted, that is, the thickness of the plate is changed, it is also possible to merge BICs at different non-Γ points. In other words, when the small holes are on different diagonals, the high-order topological charges will obtain different splitting directions. At this time, adjusting the thickness of the plate will allow the merged BICs to be at different positions, that is, merging BICs at different non-Γ points. In summary, merging BICs at non-Γ points is of great significance for the application of BICs that require angular selectivity. The present invention realizes the merging of continuous domain bound states at non-Γ points through the preparation process of a photonic crystal plate that merges continuous domain bound states at non-Γ points by breaking the original symmetry, which is of great significance for applications that require momentum selectivity in non-Γ merged BICs, such as beam steering, directional vector beams, and non-diffraction beams.
[0065] Figures 12 to 17 The influence of circular holes at different positions on the BIC splitting direction at Γ point. Fig.12 A partial top view of the photonic crystal plate with initially introduced circular pinholes; Fig.13 It is a local top view of the initial small hole position rotated 60 degrees counterclockwise around point o; Fig.14 It is a local top view of the initial hole position rotated 60 degrees clockwise around point o; Figures 15 to 17 They are Figure 12 to Figure 14 Polarization vectors around the lowest TE band for different circular aperture positions.
[0066] The present invention proposes a method of breaking the symmetry to operate a high-order Γ point BIC splitting, so that the split BIC merges with another accidental BIC, thereby enhancing the robustness of the non-Γ point BIC to manufacturing defects. 6v The symmetric photonic crystal plate body can find high-order BICs at the Γ point based on this symmetry. At non-Γ points, some accidental BICs can be formed by adjusting the structural parameters. By introducing circular holes to break the original symmetry, the high-order topological charge BICs will split due to the conservation of topological charge. Then, when the structural parameters change, the separated BICs can be operated to merge with the nearby accidental BICs. In addition, the present invention also discusses the influence of the position of the hole on the direction of BIC splitting.
[0067] Merging BICs with robust Q factors can enhance light-matter interactions, such as nonlinear and quantum effects, and improve the performance of optoelectronic devices. For example, merging BICs can improve the laser performance, nonlinear conversion efficiency and light confinement of zero-refractive index materials. However, it is more difficult to control BICs to merge BICs at non-Γ points, which limits the flexibility and diversity of their application in a wider momentum space. The present invention breaks the symmetry and merges the photonic crystal plates of continuous domain bound states at non-Γ points, which is of great significance for applications that require momentum selectivity in non-Γ merged BICs, such as beam steering, directional vector beams and non-diffraction beams. In beam steering, using momentum selectivity, efficient waveguide coupling can be achieved to ensure that the transmission loss of light between waveguides is minimized, thereby improving the overall performance of the system. In terms of directional vector beams, by optimizing directional vector beams, the directivity of the light beam can be significantly improved, scattering and radiation losses can be reduced, thereby enhancing the signal strength and quality of the optical system. And in terms of non-diffraction beams, high-precision beam manipulation can be achieved.
[0068] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0069] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of the present invention. At the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.
Claims
1. A photonic crystal slab merging continuous domain bound states at a non-Γ point, characterized in that: The photonic crystal plate comprises: a photonic crystal plate body and a plurality of target holes penetrating the photonic crystal plate body; The photonic crystal plate body has a plurality of evenly distributed cylindrical holes; The position of each target hole is set on the diagonal line of a parallelogram formed by the line connecting the center points of four adjacent cylindrical holes; the four sides of the parallelogram are equal and the internal angle is 60 degrees.
2. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The material of the photonic crystal plate body is silicon nitride.
3. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The photonic crystal plate body has C 6v Symmetrical structure.
4. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The radius of the cylindrical pores is 80 nm.
5. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The diameter of the target pore is 40 nm.
6. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The thickness of the photonic crystal slab is determined according to the merging conditions of the split BIC and the accidental BIC in the far-field polarization vector generated by the lowest TE band energy band of the photonic crystal slab.
7. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 6, characterized in that: The lowest TE band energy band structure is calculated by applying a numerical simulation method by immersing the photonic crystal plate in a liquid with a refractive index of 1.
46.
8. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The thickness of the photonic crystal slab is 335.2 nm.
9. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The distance between the center point of the target hole and the target vertex of the parallelogram is 270 nm; the target vertex is the vertex corresponding to the inner angle of 60 degrees in the parallelogram.
10. The photonic crystal slab for merging continuous domain bound states at non-Γ points according to claim 1, characterized in that: The photonic crystal plate body is an optical structure capable of generating a high-order topological charge BIC at the Γ point.