Chiral ultra-slow light all-dielectric metasurface based on continuous domain bound state and implementation method thereof
By designing periodic metasurface unit structures on a high-refractive-index dielectric substrate and breaking the symmetry, a chiral ultraslow light all-dielectric metasurface based on continuous domain bound states was realized. This solved the complexity problem of the interaction between chiral quasi-BIC and other modes, and achieved efficient spin-dependent slow light effect and strong chirality control, which is suitable for a variety of optical devices.
Patent Information
- Application Number
- CN202610028256.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-09
- Publication Date
- 2026-02-24
AI Technical Summary
In existing technologies, the complex interactions between chiral quasi-BIC and other coexisting modes have not been fully explored, making it difficult to achieve efficient spin-dependent slow light effects and failing to meet the needs of polarization multiplexing and quantum information processing.
A chiral ultraslow light all-dielectric metasurface based on continuous domain bound states is designed. By periodically arranging metasurface unit structures on a high-refractive-index dielectric substrate, the in-plane and out-of-plane symmetry is broken to transform BIC into quasi-BIC, thereby forming a chiral optical response and spin-dependent slow light effect.
It achieves a significant spin-dependent slow light effect, with group delays reaching the nanosecond level and circular dichroism values close to 1. It is suitable for devices such as optical delay lines, optical switches, polarization beam splitters, and quantum information processors, and uses all-dielectric materials to reduce losses.
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Figure CN121559643A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metamaterials and photonics technology, specifically relating to a chiral ultraslow light all-dielectric metasurface based on continuous domain bound states and its realization method. Background Technology
[0002] Light-matter interaction is central to modern optics, and its intensity directly influences many important physical phenomena such as spontaneous emission, high-sensitivity sensing, and cavity quantum electrodynamics. However, in conventional homogeneous media, the speed of light is extremely fast (approaching the speed of light *c* in a vacuum), resulting in brief and weak interactions between light and matter. Therefore, effectively reducing the group velocity of light (i.e., achieving "slow light") to enhance light-matter interaction has been a focus of research.
[0003] In existing technologies, various mechanisms have been proposed to achieve slow light, such as utilizing flat-band dispersion in photonic crystals, electromagnetically induced transparency in cold atom systems, and plasma-induced transparency in metamaterials. Through these methods, the speed of light has been reduced to [a certain value]. arrive The magnitude of light is on the order of magnitude and it has been applied to devices such as optical delay lines, optical switches, and optical buffers. However, most research focuses on the slow light effect of linearly polarized light, while less attention is paid to the spin-dependent (i.e., chiral-dependent) slow light effect, which has important application value.
[0004] In recent years, a special type of optical state known as "Bound States in the Continuum" (BICs) has attracted widespread attention. BICs are special bound states existing in the radiation continuum, theoretically possessing an infinitely large quality factor (Q-factor) and zero radiative loss. When the symmetry is slightly broken, an ideal BIC transforms into a "quasi-BIC" with an ultra-high Q-factor, exhibiting extremely narrow resonance lines. This ultra-high Q-factor characteristic makes quasi-BICs an ideal platform for enhancing light-matter interactions, showing great potential in lasers, nonlinear optics, and high-sensitivity sensing.
[0005] Recent studies have shown that metasurfaces supporting quasi-BICs can serve as powerful platforms for achieving chiral control. However, the complex interactions between chiral quasi-BICs and other coexisting modes remain largely unexplored in current technologies. In particular, how to leverage the unique properties of BICs to achieve efficient, spin-dependent slow light effects remains a pressing technical problem.
[0006] Therefore, there is an urgent need in this field for a new technical solution that can utilize the BIC mechanism to achieve significant chiral response and efficient spin-dependent slow light effect, in order to meet the needs of cutting-edge applications such as polarization multiplexing and quantum information processing. Summary of the Invention
[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a chiral, ultraslow-light all-dielectric metasurface based on continuous domain bound states (BIC) and its realization method. This metasurface, through specific structural design and symmetry breaking, utilizes the unique physical properties of BIC to efficiently achieve enormous external and internal chirality, thereby generating a significant spin-dependent slow-light effect.
[0008] A chiral ultraslow-light all-dielectric metasurface based on continuous-domain bound states, characterized in that it comprises:
[0009] A substrate made of a high-refractive-index dielectric material;
[0010] The metasurface unit structures arranged periodically on the substrate form a two-dimensional lattice.
[0011] Each of the metasurface unit structures contains at least two subwavelength holes, and the geometric parameters of the holes are designed such that, in a undisturbed state, the metasurface unit structure has sufficiently high symmetry to support at least one symmetry-protected continuous domain bound state at the center of the Brillouin zone.
[0012] By perturbing one or more of the at least two holes, the symmetry of the metasurface unit structure is broken, the BIC is transformed into a quasi-BIC, and two polarization singularities with opposite chirality are formed in momentum space, thereby generating chiral optical response and spin-dependent slow light effect in the metasurface.
[0013] The structural disturbances include in-plane symmetry breaking and out-of-plane symmetry breaking;
[0014] The in-plane symmetry breaking is achieved by changing the size of one of the at least two holes, and the out-of-plane symmetry breaking is achieved by rotating one or more of the at least two holes about their center by a non-zero tilt angle α.
[0015] The chiral optical response is characterized by a circular dichroism value close to 1, and the spin-dependent slow light effect is characterized by a significantly higher group delay at the quasi-BIC resonance frequency for incident light of one spin state than for incident light of another spin state.
[0016] The high refractive index dielectric material is one of silicon (Si), germanium (Ge), silicon nitride (Si3N4), or titanium dioxide (TiO2), and the metasurface operates in the terahertz band.
[0017] To achieve the above objectives, the present invention adopts the following technical solution in terms of method:
[0018] A method for realizing chiral ultraslow light in an all-dielectric metasurface, characterized by comprising the following steps:
[0019] (a) Provide an all-dielectric metasurface comprising a unit cell structure periodically arranged on a substrate, each unit cell containing at least two subwavelength holes, the unit cell structure having sufficiently high symmetry in an undisturbed state to support at least one symmetry-protected continuous domain bound state (BIC) at the center of the Brillouin zone.
[0020] (b) Introduce a structural perturbation into at least one hole in the unit structure to break the symmetry of the unit structure, so that the BIC is transformed into a quasi-BIC and two polarization singularities with opposite chirality are formed in momentum space;
[0021] (c) Excite the metasurface treated in step (b) with an optical field to achieve chiral optical response and spin-dependent slow light effect.
[0022] Preferably, the hole is a rectangular hole.
[0023] Furthermore, the in-plane symmetry breaking is achieved by changing the size of one of the at least two holes, for example, by reducing the length of one hole from L1 to L2, forming a length difference Y = L1 - L2 (Y > 0).
[0024] Furthermore, the out-of-plane symmetry breaking is achieved by rotating one or more of the at least two holes about their center by a non-zero tilt angle α.
[0025] According to one aspect of the invention, step (c) specifically includes: achieving significant external chirality by introducing in-plane symmetry breaking and exciting the metasurface with oblique incidence. Chirality reversal can be achieved by changing the direction of the incident angle.
[0026] According to another aspect of the invention, step (c) specifically includes: by simultaneously introducing in-plane symmetry breaking and out-of-plane symmetry breaking, causing the chiral singularity in momentum space to move to the vicinity of the Γ point, and then exciting the metasurface in a normal incidence manner, thereby achieving a large intrinsic chirality under normal incidence.
[0027] The metasurface of this invention produces a huge chiral optical response exhibiting a circular dichroism (CD) value close to 1. Simultaneously, due to the drastic phase change at the resonant frequency of the quasi-BIC, the group velocity of one spin state (such as left-handed circularly polarized light LCP) is significantly reduced, while the other spin state (such as right-handed circularly polarized light RCP) remains almost unaffected. This results in a significant spin-dependent slow light effect, with a group delay reaching nanosecond levels or higher.
[0028] The beneficial effects of this invention are as follows:
[0029] (1) High efficiency chiral control and slow light effect: This invention utilizes the topological properties of BIC and the principle of symmetry breaking to achieve near-perfect circular dichroism and significant spin-dependent slow light effect.
[0030] (2) Novel structure and ingenious method: The proposed metasurface structure design is unique and the implementation method is logically clear, providing a new physical mechanism and technical approach for realizing spin photonics functions.
[0031] (3) Flexible control and wide application: This invention can realize external chirality under oblique incidence and internal chirality under normal incidence. The intensity and sign of chirality can be flexibly controlled by adjusting structural parameters (such as length difference Y, tilt angle α) and incident conditions (such as incident angle θ). It is applicable to various devices such as optical delay lines, optical switches, polarization beam splitters, and quantum information processors.
[0032] (4) Low loss of all dielectric materials: The design of all dielectric materials avoids the ohmic loss inherent in metal plasma structures, which is conducive to obtaining high Q factor and high efficiency in actual devices. Attached Figure Description
[0033] Figure 1 (a) Schematic diagram of a unit cell of a chiral metasurface; (b) Far-field polarization distribution of BIC; (c) Calculated band structure and Q factor for two bands: s=0 nm and α1=α2=0°.
[0034] Figure 2 The evolution of the far-field polarization state distribution in momentum space under different perturbations;
[0035] Figure 3 (a) Transmission spectra of two circularly polarized states where Y or θ is non-zero, (b) Transmission spectra of two circularly polarized states where s and θ are non-zero, (c)-(d) Transmission spectra of two circularly polarized states where s = 20 nm is non-zero and the tilt angle is normal incident.
[0036] Figure 4 (a) Transmission spectra of LCP wave and (b) RCP wave as incident angle; (c) CD spectrum of structure as incident angle.
[0037] Figure 5 (a) Reflection phase and (c) group delay at θ=-1.5°, (b) Reflection phase and (d) group delay at θ=1.5°;
[0038] Figure 6(a)-(b) Evolution and enhancement of intrinsic chirality: (a) Schematic diagram of the shift of polarization state distribution in momentum space toward the central Γ point after the introduction of tilt angle α; (b) LCP and RCP transmission spectra corresponding to different tilt angles α under normal incidence;
[0039] Figure 7 (a) Transmission spectra of LCP wave and (b) RCP wave as tilt angle changes; (c) Relationship between CD spectrum of structure and perturbation parameter Y.
[0040] Figure 8 The ultraslow light effect under intrinsic chirality, the spin-dependent reflection phase spectrum corresponding to the tilt angles (a)-(b); the spin-dependent chiral slow light group delay spectrum corresponding to (c)-(d). Detailed Implementation
[0041] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the concept of the invention, they should all fall within the protection scope of the present invention.
[0042] The preparation method of the present invention will be described below through specific embodiments and comparative examples.
[0043] Example 1: Spin-dependent slow light under extrinsic chirality and oblique incidence
[0044] This embodiment aims to achieve a large external chirality and spin-dependent slow light effect by combining in-plane symmetry breaking and oblique incidence.
[0045] (1) Metasurface preparation: such as Figure 1 As shown in (a), the metasurface system of the present invention consists of a square lattice with a period constant of a = 400 μm, and its unit cell structure consists of two rectangular holes drilled into a dielectric silicon substrate. The hole width w = 75 μm, and in the unperturbed configuration, the lengths L1 = L2 = 75 μm, maintaining C4ᵥ rotational symmetry. A perturbation, defined as the arm length reduction Y, is introduced by reducing the arm length L2 of one of the holes.
[0046] (2) BIC characteristic verification: Figure 1 (b) and Figure 1(c) shows the photon band structure and Q-factor distribution in momentum space at Y=0 μm and α=0° (i.e., the perturbation-free configuration). At the Γ point (center of the Brillouin zone), a symmetry-protected BIC with a near-infinite Q-factor is observed at the normalized frequency ωa / 2πc of 0.652. The Q-factor decreases sharply as the momentum moves away from the Γ point, demonstrating the sensitivity of this BIC to momentum space perturbations.
[0047] (3) Spectral evolution under in-plane symmetry breaking: To verify the effect of in-plane symmetry breaking on BIC, we calculated the reflection spectra of TE polarized waves with different asymmetry parameters Y under normal incidence, such as... Figure 2 As shown in (a), as Y decreases from 40 μm to 0 μm, the resonance linewidth narrows significantly, while the Q factor increases rapidly. At Y = 0 μm, the resonance completely disappears, indicating the formation of a perfect BIC. The continuous variation of the reflectance spectrum with Y is shown in Figure (a). Figure 2 As shown in (b), it can be seen that as Y increases, the line width gradually widens and the Q factor decreases significantly.
[0048] (4) Evolution of polar singularities in momentum space: In order to explain the emergence of chirality, we explored the evolution of polar singularities in momentum space. Figure 3 (a) schematically illustrates that, when the perturbation parameter Y = 0 μm, the polarization in momentum space is degenerate due to C4ᵥ symmetry. When a finite Y is introduced (in-plane symmetry breaking), the original symmetry of the system is broken, leading to the splitting of the symmetry-protected BIC and the formation of two singularities with opposite circularly polarized chirality (RCP and LCP), as shown in the diagram. Figure 3 As shown in (b).
[0049] (5) Realization and control of extrinsic chirality: It is crucial that changes in Y alone or only the oblique angle of incidence θ alone are insufficient to induce chirality in the system. A chiral optical response will only occur when both parameters are non-zero. Figure 3 (c) This study demonstrates a significant difference in the transmission spectra of LCP and RCP incident light at Y=40 μm and θ=1.5°, indicating that the structure exhibits pronounced chiral behavior. By fixing the perturbation parameter at Y=40 μm and gradually increasing θ, the chirality of the quasi-BIC gradually increases, reaching a maximum at θ=1.5°. When the incident direction is changed to θ=-1.5°, chirality reversal is achieved, as shown in the diagram. Figure 3 As shown in (d).
[0050] (6) Quantitative analysis of extrinsic chirality: Figure 4 (a) and Figure 4 (b) Transmission spectra of LCP and RCP incident light at different incident angles θ with a structural perturbation of Y = 40 μm, respectively. Figure 4In (a), when θ is approximately -1.5°, the resonant linewidth of the LCP light disappears (the Q factor tends to infinity), while the RCP light exhibits broad resonance; conversely, in Figure 4 In (b), the resonant linewidth of the RCP light disappears when θ = 1.5°. This strong polarization-dependent behavior leads to a large circular dichroism (CD). Figure 4 (c) shows the calculated CD value as a function of the incident angle θ. At the quasi-BIC wavelength, the CD value approaches the ideal value of 1 at θ = ±1.5°, indicating near-perfect extrinsic chirality. The inversion of the CD sign with θ reveals the strong tunable chirality of the system.
[0051] (7) Spin-dependent slow light under oblique incidence: We realized the spin-dependent slow light effect by using high Q chirality quasi-BIC. Figure 5 (a) and Figure 5 (b) The reflection phase was calculated for incident angles θ = -1.5° and θ = 1.5°, respectively. It can be seen that under one type of circularly polarized wave excitation, a drastic phase change occurs (e.g., LCP light at θ = -1.5°), while under the other type of circularly polarized wave excitation, only a slower phase change occurs due to broad resonance. This large difference in phase gradient produces a chiral slow-light effect. Figure 5 (c) and Figure 5 As shown in (d), one type of chiral polarized light can achieve a group delay of more than 2500 ps, while the corresponding other type of chiral polarized light has almost no group delay.
[0052] Example 2: Spin-dependent slow light under intrinsic chirality and normal incidence
[0053] This embodiment aims to achieve a large intrinsic chirality and spin-dependent slow light effect under normal incidence by simultaneously introducing in-plane and out-of-plane symmetry breaking.
[0054] (1) Introduction of compound symmetry breaking: Based on Example 1 (Y=40 μm), we further tilted the hole by a non-zero tilt angle α to break the out-of-plane symmetry.
[0055] (2) Realization of intrinsic chirality: By introducing an inclination angle α, the distribution of the circularly polarized state in momentum space can be adjusted, causing it to move towards the center of the Brillouin zone (Γ point). When α = 10°, the circularly polarized state is very close to the Γ point, such as... Figure 6 As shown in (a) (this figure schematically illustrates the shift of the circularly polarized state towards the Γ point), this circularly polarized state near the Γ point imparts significant intrinsic chirality to the structure. We calculated the transmission spectra at different tilt angles when the incident angle θ = 0°, as shown below. Figure 6 As shown in (b), the chirality is weak when α = 4°; when α increases to 10°, a large intrinsic chirality is observed at the resonance wavelength.
[0056] (3) Quantitative analysis of intrinsic chirality: Figure 7 (a) and Figure 7 (b) shows the transmission spectra of LCP and RCP incident light at different tilt angles α, with normal incidence (θ=0°). It can be seen that the resonance linewidths of LCP and RCP incident light disappear at α=10° and α=-10°, respectively, exhibiting the largest and opposite intrinsic chirality. Figure 7 (c) shows the change of CD value with tilt angle α. It can be seen that the CD value is close to ±1 when α=±10° and the sign reverses as α changes, indicating the strong tunability of the system's intrinsic chiral response.
[0057] (4) Spin-dependent slow light under normal incidence: After breaking in-plane and out-of-plane symmetry, the emergence of high-Q chiral resonances provides a possibility for enhancing the slow light effect under normal incidence. We... Figure 8 (a) and Figure 8 (b) calculates the reflection phase at tilt angles α = -10° and α = 10°. When α = -10°, the reflection phase under LCP excitation changes significantly, while the reflection phase under RCP excitation remains flat; the opposite is true when α = 10°. This large difference in phase gradient produces a significant chiral slow light effect, such as... Figure 8 (c) and Figure 8 As shown in (d). One type of chiral polarized light can achieve a polarization exceeding 8 × 10⁻⁶. 4 ps has a group delay, while the corresponding chiral polarized light has almost no group delay.
[0058] In summary, this invention, through a cleverly designed all-dielectric metasurface structure and a dual symmetry breaking mechanism, successfully utilizes BIC to achieve efficient external and internal chirality control and a powerful spin-dependent slow light effect. This design provides important technical support for the development of novel polarization devices, optical buffers, and quantum information processors.
Claims
1. A chiral, ultraslow-light all-dielectric metasurface based on continuous-domain bound states, characterized in that, include: A substrate made of a high-refractive-index dielectric material; The metasurface unit structures arranged periodically on the substrate form a two-dimensional lattice. Each of the metasurface unit structures contains at least two subwavelength holes, and the geometric parameters of the holes are designed such that, in a undisturbed state, the metasurface unit structure has sufficiently high symmetry to support at least one symmetry-protected continuous domain bound state at the center of the Brillouin zone. By perturbing one or more of the at least two holes, the symmetry of the metasurface unit structure is broken, the BIC is transformed into a quasi-BIC, and two polarization singularities with opposite chirality are formed in momentum space, thereby generating chiral optical response and spin-dependent slow light effect in the metasurface. The structural disturbances include in-plane symmetry breaking and out-of-plane symmetry breaking; The in-plane symmetry breaking is achieved by changing the size of one of the at least two holes, and the out-of-plane symmetry breaking is achieved by rotating one or more of the at least two holes about their center by a non-zero tilt angle α. The chiral optical response is characterized by a circular dichroism value close to 1, and the spin-dependent slow light effect is characterized by a significantly higher group delay at the quasi-BIC resonance frequency for incident light of one spin state than for incident light of another spin state. The high refractive index dielectric material is selected from silicon, germanium, silicon nitride or titanium dioxide, and the metasurface operates in the terahertz band.
2. A method for realizing chiral ultraslow light in an all-dielectric metasurface, characterized in that, Includes the following steps: (a) Provide an all-dielectric metasurface comprising a unit structure periodically arranged on a substrate, each unit structure containing at least two subwavelength holes, the unit structure having sufficiently high symmetry in an undisturbed state to support at least one symmetry-protected continuous domain bound state at the center of the Brillouin zone. (b) Introduce a structural perturbation into at least one hole in the unit structure to break the symmetry of the unit structure, so that the BIC is transformed into a quasi-BIC and two polarization singularities with opposite chirality are formed in momentum space; as well as (c) Excite the metasurface treated in step (b) with an optical field to achieve chiral optical response and spin-dependent slow light effect.
3. The method according to claim 2, characterized in that, The structural perturbation introduced in step (b) includes in-plane symmetry breaking, and the light field in step (c) illuminates the metasurface in an oblique incidence manner to achieve an external chiral optical response.
4. The method according to claim 2, characterized in that, The structural perturbation introduced in step (b) includes both in-plane symmetry breaking and out-of-plane symmetry breaking. The light field in step (c) irradiates the metasurface in a normal incident manner to achieve an intrinsic chiral optical response.
5. The method according to claim 3 or 4, characterized in that, It also includes the step of reversing the sign of the chiral optical response by changing the angle of the incident light or the direction of the structural perturbation.
6. A chiral optical modulation device, characterized in that, The device comprises an all-dielectric metasurface as described in any one of claims 1, wherein the device is selected from optical delay lines, optical switches, optical buffers, polarization beam splitters, or quantum information processors.