BIC-two-dimensional material strong coupling system based on incident angle regulation and dynamic tuning method thereof

Abstract

The application provides a BIC-two-dimensional material strong coupling system based on incident angle regulation and a dynamic tuning method thereof, and belongs to the technical field of nano photonics and light-matter interaction. In the photonic crystal plate heterostructure, a single-layer two-dimensional material exciton (WS2) is coupled to obtain a BIC-two-dimensional material strong coupling system based on incident angle regulation. Then, by changing the incident angle, the switching of the strong coupling system from true BIC to quasi-BIC mode, the continuous, reversible and lossless dynamic regulation of the coupling strength and the polariton energy level are realized, and the dynamic tuning in a pure optical mode is realized. The application provides a reliable implementation path for the active manipulation of BIC topological properties and the dynamic regulation of light-matter strong coupling. The BIC-WS2 heterostructure constructed has the advantages of high quality factor, strong field localization and room temperature regulation, and has guiding significance for application fields such as high-performance nano photonics devices, room temperature polariton devices, ultra-sensitive sensing and low-power coherent light sources.

Description

Technical Field

[0001] This application relates to the fields of nanophotonics and light-matter interaction technology, specifically to a BIC-two-dimensional material strong coupling system based on incident angle modulation and its dynamic tuning method. Background Technology

[0002] Strong coupling between light and matter is a core physical mechanism for realizing quantum state manipulation, low-power lasers, room-temperature polariton devices, and ultrasensitive sensing. Excitons in two-dimensional transition metal sulfides (such as WS2 and MoS2) possess enormous binding energies and room-temperature stability, making them ideal carriers for achieving strong coupling in solid-state applications. However, their atomic-level thickness leads to weak optical absorption and low interaction strength, severely limiting practical applications.

[0003] Continuous domain bound states (BICs) offer an effective approach to solving the aforementioned problems due to their theoretically infinitely high quality factor (Q value) and extremely strong optical field localization capabilities. Existing technologies have already integrated BIC structures with two-dimensional materials, achieving strong coupling at room temperature.

[0004] However, existing research only verifies the strong coupling phenomenon itself and lacks the ability to actively and dynamically control the strong coupling state. Furthermore, traditional control methods require changes to device geometric parameters (such as etching width and depth), making it difficult to achieve real-time and reversible control.

[0005] Therefore, there is an urgent need for a technical solution that can achieve efficient BIC-exciton strong coupling and dynamically, reversibly, and losslessly control the coupling strength. Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides a BIC-two-dimensional material strong coupling system based on incident angle control and its dynamic tuning method. By optimizing the BIC structure, efficient strong coupling is achieved, and the incident angle is used as an external degree of freedom to realize continuous, reversible, and lossless dynamic control of the switching between true BIC and quasi-BIC modes, coupling strength and polariton energy levels.

[0007] This application provides a BIC-two-dimensional material strongly coupled system based on incident angle control, including: Photonic crystal plate heterostructures are used to generate continuous domain bound state modes; A single-layer WS2 material layer is attached to the surface of the heterostructure of the photonic crystal plate, forming a strong coupling with the BIC mode; The heterostructure of the photonic crystal plate includes a silicon nitride plate, a grating array disposed on the upper surface of the silicon nitride plate, a silver film and an aluminum oxide layer disposed on the lower surface of the silicon nitride plate; the aluminum oxide layer is disposed between the silver film and the silicon nitride plate; the material of the grating array is silicon nitride, the thickness hg of the grating array is 90-180 nm, the slab period a is 300-500 nm, and the etching width d is 80-150 nm.

[0008] This application also provides a dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control, comprising the following steps: S1, the threshold incident angle θ0 for the formation of the true BIC of the system is determined by the angle-resolved reflectance spectrum; S2, continuously change the angle θ of the incident light relative to the heterostructure surface of the photonic crystal plate; When θ = θ0, the system is in true BIC mode, and the coupling strength reaches its maximum value; θ0 is the threshold incident angle. When θ deviates from the threshold incident angle θ0, the system is in quasi-BIC mode, and the coupling strength decreases continuously as |θ - θ0| increases; By continuously changing the angle θ, dynamic tuning of coupling strength, Rabi splitting energy, and polariton energy levels can be achieved.

[0009] Furthermore, in step S1, broadband fixed-angle light source technology is used to select a plane wave source with transverse magnetic mode polarization, which is obliquely incident on the surface of the structure at an incident angle θ in the xz plane of the BIC-two-dimensional material strongly coupled system, and the reflection spectrum at different angles is collected.

[0010] Furthermore, in the quasi-BIC mode, the Q factor at different incident angles is obtained by the following formula: ; Where λ0 is the resonant wavelength. λ is the full width at half maximum (FWHM) of the resonant mode.

[0011] Furthermore, when the incident angle θ is θ0, the reflectivity trough disappears, the resonance linewidth approaches zero, and the quality factor Q approaches infinity.

[0012] Furthermore, the threshold incident angle θ0 is 19.4°.

[0013] Furthermore, the Rabi splitting value of the system in true BIC mode ≈192 meV, the coupling strength g satisfies the following formula: ; Where, τ Exciton τ is the energy half-linewidth of the WS2 exciton.Q-BIC The energy half-width for BIC mode.

[0014] The beneficial effects of this application are as follows: This application proposes a dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control. This method achieves strong coupling of BIC and two-dimensional materials at room temperature, utilizing the incident angle as the degree of freedom for adjustment. Without altering the device structure or introducing additional material losses, the method achieves continuous, reversible, and lossless dynamic control of the strong coupled system's switching between true BIC and quasi-BIC modes, coupling strength, and polariton energy levels by changing the incident angle (external degree of freedom). This enables purely optical dynamic tuning. The incident angle can be continuously varied and is completely reversible, allowing for continuous adjustment of coupling strength, Rabi splitting energy, and polariton energy levels. Throughout the tuning range, the coupling strength consistently meets the strong coupling criterion, ensuring the system remains within the strongly coupled operating region.

[0015] This application separates the efficient coupling implementation (through structural design) from the dynamic control implementation (through incident angle), reducing design complexity and improving system reliability.

[0016] This application achieves full-process control of the BIC mode of the system from generation, evolution to annihilation by continuously changing parameters (etch width and etch depth). The method is simple and fast.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0019] Figure 1 This is a schematic diagram of the BIC-two-dimensional material strong coupling system based on incident angle control in this application; where (a) is a three-dimensional view and (b) is a cross-sectional view.

[0020] Figure 2 The reflection spectra of the nanograting surface at different incident angles θ are shown.

[0021] Figure 3 The relationship between the Q factor of the quasi-BIC mode and different incident angles.

[0022] Figure 4 The electric field amplitude distribution in the xz plane of the quasi-BIC mode at θ=19.4°.

[0023] Figure 5 The graph shows the relationship between the wavelengths of the HEHM and LEHM hybrid states and the asymmetric parameters.

[0024] Figure 6 The proportions of Q-BIC and excitons in LEHM and HEHM are shown. Detailed Implementation

[0025] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0027] BIC model construction: Please see Figure 1 As shown, the BIC-two-dimensional material strong coupling system based on incident angle control in this application includes a photonic crystal plate heterostructure and a single-layer WS2 material layer attached to the surface of the photonic crystal plate heterostructure.

[0028] The photonic crystal plate heterostructure includes a high-refractive-index plate, a grating array disposed on the upper surface of the high-refractive-index plate, a silver film and an aluminum oxide layer disposed on the lower surface of the high-refractive-index plate. The aluminum oxide layer is disposed between the silver film and the high-refractive-index plate.

[0029] In this application, the high refractive index plate and the grating array are both made of silicon nitride (Si3N4).

[0030] The thickness of the high refractive index plate is h = 350 nm.

[0031] The thickness hg of the grating array is 90-180 nm, the slab period a is 300-500 nm, and the etching width d is 80-150 nm.

[0032] The thickness t of the silver film a With a wavelength of 250 nm, it can be used as a reflector to further reduce the thickness of the entire structure.

[0033] In this application, an aluminum oxide (Al₂O₃) layer is introduced between the silver film and the silicon nitride plate to prevent the silver film from oxidizing. The thickness t of the silver film... b It is 25nm.

[0034] Because the Si3N4 array is periodic, the waveguide mode bands in the silicon nitride grating array are folded into the continuous spectrum region, thus radiating into free space.

[0035] This application provides a dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control, comprising the following steps: S1, the threshold incident angle θ0 for the formation of the true BIC of the system is determined by the angle-resolved reflectance spectrum; Specifically, using broadband fixed-angle light source technology, a plane wave source with transverse magnetic mode polarization is selected and obliquely incident on the surface of the structure at an incident angle θ in the xz plane of the BIC-two-dimensional material strong coupling system based on incident angle control, and the reflection spectrum at different angles is collected.

[0036] In this application, the incident angle θ was set to 18°, 19°, 19.4°, 20°, 21°, 22°, and 23° to obtain the reflection spectrum of the nanograting surface at different incident angles θ, such as... Figure 2 As shown in the figure. The evolution of the BIC mode relative to the angle change is shown by the green dashed line, and the evolution of the reflectivity trough is shown by the red dashed line.

[0037] As can be seen, the decrease in reflectance gradually decreases as the incident angle θ increases, and the spectral linewidth of the resonance gradually narrows. When the incident angle θ is 19.4°, the decrease in reflectance completely disappears, indicating the formation of a true BIC mode. When the incident angle θ continues to increase, the decrease in reflectance occurs again, indicating that a transition from a true BIC mode to a quasi-BIC mode has occurred in the system.

[0038] S2, set the incident angle control unit to continuously change the angle θ of the incident light relative to the heterostructure surface of the photonic crystal plate; When θ = θ0, the system is in true BIC mode, and the coupling strength reaches its maximum value; When θ deviates from θ0, the system is in quasi-BIC mode, and the coupling strength decreases continuously as |θ - θ0| increases; By continuously changing the angle θ, dynamic tuning of coupling strength, Rabi splitting energy, and polariton energy levels can be achieved.

[0039] When the incident angle θ is θ0, the reflectivity trough disappears, the resonance linewidth approaches zero, and the quality factor Q approaches infinity.

[0040] Specifically, in quasi-BIC mode, the Q factor at different incident angles is obtained by the following formula: ; Where λ0 is the resonant wavelength. λ is the full width at half maximum (FWHM) of the resonant mode.

[0041] Figure 3 The relationship between the Q factor of the quasi-BIC mode and different incident angles.

[0042] As the incident angle increases, the position of the Rabi splitting peak in the reflection spectrum of the simulation graph shifts, and the splitting amplitude changes. From an incident angle of 23° to 18°, the positions of the two peaks change from "obvious" to "insignificant" to "obvious." Due to the change in incident angle, the corresponding Rabi splitting energy changes positively, and the interaction between photons and excitons also changes accordingly.

[0043] As can be seen from the figure, when the incident angle is close to 19.4°, the Q factor is close to infinity, and when the incident angle is far from 19.4°, the Q factor decreases. Therefore, 19.4° is the threshold incident angle θ0.

[0044] Figure 4 The electric field amplitude distribution in the xz plane of the quasi-BIC mode at θ=19.4°.

[0045] It can be seen that the electric field enhancement is located at the upper corner of the grating and in the WS2 gap.

[0046] Figure 5 The graph shows the relationship between the wavelengths of the HEHM and LEHM hybrid states and the asymmetric parameters.

[0047] As can be seen, the presence of the exciton peak causes a significant anti-crossing behavior in the transmission spectrum, with the Q-BIC splitting into an upper branch (UB) and a lower branch (LB). This indicates that the energy exchange rate between excitons and photons exceeds their respective decay rates, causing the initial energy level to split into two new energy levels. This phenomenon can be qualitatively explained using the Hamiltonian coupled oscillator model, with the following eigenvalue equation: (1) Among them, E Q-BIC and E Exciton These are the energies of the uncoupled Q-BIC and the exciton, respectively; γ Q-BIC and γ Exciton These are the half-widths of the uncoupled Q-BIC and the exciton, respectively; E ±Let be the eigenenergy of the high-energy hybrid mode (HEHM) and the low-energy hybrid mode (LEHM); g is the coupling strength between the Q-BIC and the exciton; α and β represent the weights of the Q-BIC and the exciton in the hybrid mode, respectively, and are the Hopfield coefficients, satisfying . .

[0048] Those skilled in the art will know that when Q-BIC matches exciton resonance ( When ), there are (2) (3) (4) The simulation results were fitted using formulas (2) and (3) to obtain two branch dispersion curves. The numerical simulation results were highly consistent with the theoretical results.

[0049] Based on formula (1), the proportions of Q-BIC and WS2 excitons in LEHM and HEHM are derived respectively, and we have: (5) (6) (7) Figure 6 The proportions of Q-BIC and excitons in LEHM and HEHM are shown.

[0050] When the Q-BIC energy shifts from a high energy level across the exciton level to a lower energy level, the exciton proportion decreases and the Q-BIC proportion increases in the LEHM; the HEHM shows the opposite trend. This result directly confirms the energy exchange dynamics between Q-BIC and excitons, providing strong evidence for the anti-crossover behavior caused by their strong coupling.

[0051] Calculations show that when the incident angle θ = 19.4°, Rabi splits. ≈192 meV.

[0052] Continue to verify through data calculations.

[0053] Strong coupling requires the following conditions to be met: (8) To achieve mode separation in the spectrum, the minimum splitting value must be greater than the sum of the half-widths of the two resonances. Strong coupling also requires the following: (9) In this application, the energy half-linewidth of the WS2 exciton is taken as τ. Exciton =25 meV (corresponding to a bus width of 50 meV), the energy half-width in BIC mode is τ. Q-BIC=11 meV. According to the strong coupling criterion, the coupling strength must satisfy: In this system, the coupling strength g = 96 meV, which is much greater than the threshold, thus satisfying the strong coupling condition. Therefore, it can be determined that strong coupling does indeed occur in the WS2 material system based on the BIC structure, and that changing the incident angle adjusts the effective refractive index of the light-structure interaction, thereby altering the mode's resonant frequency and coupling efficiency. Precise modulation of the optical response of the strongly coupled system can be achieved by controlling the incident angle.

[0054] In summary, this application successfully constructed a strongly coupled BIC-exciton system at room temperature and observed significant spectral anti-crossing and Rabi splitting behavior. This application utilizes the incident angle as a simple, lossless external control degree of freedom to achieve dynamic and reversible tuning of the strongly coupled system.

[0055] In this application, the incident angle θ = 19.4° is the threshold angle of the system, at which point a true BIC mode is formed and the measured Rabi splitting value reaches 192 meV; when the angle deviates from the threshold, a mode transition occurs from true BIC to quasi-BIC, and the reflectance spectrum, linewidth and quality factor show regular evolution.

[0056] Theoretical verification based on the coupled oscillator model and strong coupling criterion shows that stable strong coupling occurs between light and matter. By changing the effective refractive index and mode resonant frequency, the incident angle can be precisely modulated to achieve coupling strength and polariton energy, verifying the feasibility of the two-level scheme of "efficient coupling through structural design and dynamic control through external angle".

[0057] This application provides a reliable path for the active manipulation of BIC topological properties and the dynamic control of strong light-matter coupling. The constructed BIC-WS2 heterostructure has the advantages of high quality factor, strong field localization and room temperature tunability. It has important theoretical reference and technical support value for applications such as high-performance nanophotonic devices, room temperature polariton devices, ultrasensitive sensing and low-power coherent light sources. It also has important guiding significance for the development of low-power lasers, programmable quantum light sources and ultrasensitive sensors.

[0058] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A BIC-two-dimensional material strongly coupled system based on incident angle control, characterized in that, include: Photonic crystal plate heterostructures are used to generate continuous domain bound state modes; A single-layer WS2 material layer is attached to the surface of the heterostructure of the photonic crystal plate, forming a strong coupling with the BIC mode; The heterostructure of the photonic crystal plate includes a silicon nitride plate, a grating array disposed on the upper surface of the silicon nitride plate, a silver film and an aluminum oxide layer disposed on the lower surface of the silicon nitride plate; the aluminum oxide layer is disposed between the silver film and the silicon nitride plate; the material of the grating array is silicon nitride, the thickness hg of the grating array is 90-180 nm, the slab period a is 300-500 nm, and the etching width d is 80-150 nm.

2. A dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control as described in claim 1, characterized in that, Includes the following steps: S1, the threshold incident angle θ0 for the formation of the true BIC of the system is determined by the angle-resolved reflectance spectrum; S2, continuously change the angle θ of the incident light relative to the heterostructure surface of the photonic crystal plate; When θ = θ0, the system is in true BIC mode, and the coupling strength reaches its maximum value; θ0 is the threshold incident angle. When θ deviates from the threshold incident angle θ0, the system is in quasi-BIC mode, and the coupling strength decreases continuously as |θ - θ0 increases; By continuously changing the angle θ, dynamic tuning of coupling strength, Rabi splitting energy, and polariton energy levels can be achieved.

3. The dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control according to claim 2, characterized in that, In step S1, broadband fixed-angle light source technology is used to select a plane wave source with transverse magnetic mode polarization. The source is obliquely incident on the surface of the structure at an incident angle θ in the xz plane of the BIC-two-dimensional material strongly coupled system, and the reflection spectrum at different angles is collected.

4. The dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control according to claim 2, characterized in that, In quasi-BIC mode, the Q factor at different incident angles is obtained by the following formula: ； Where λ0 is the resonant wavelength. λ is the full width at half maximum (FWHM) of the resonant mode.

5. The dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control according to claim 2, characterized in that, When the incident angle θ is the threshold incident angle θ0, the reflectivity trough disappears, the resonance linewidth approaches zero, and the quality factor Q approaches infinity.

6. The dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control according to claim 2, characterized in that, The threshold incident angle θ0 is 19.4°.

7. The dynamic tuning method for a BIC-two-dimensional material strongly coupled system based on incident angle control according to claim 2, characterized in that, The Rabi splitting value of the system in true BIC mode ≈192 meV, the coupling strength g satisfies the following formula: ； Where, τ Exciton τ is the energy half-linewidth of the WS2 exciton. Q-BIC The energy half-width for BIC mode.

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