A dynamic optical switch based on phase-change metasurface bic state, driving method and application thereof

Abstract

The application provides a dynamic optical switch based on a phase change super surface BIC state and a driving method and application thereof. The dynamic optical switch based on the phase change super surface BIC state comprises, from top to bottom, a super surface layer, a silica upper isolation layer, a phase change functional layer, a silica lower isolation layer and a reflection layer. The device drives the phase change functional layer to reversibly change the crystal state through an electric pulse or a laser pulse, realizes the rapid switching of a BIC high reflection off state and a QBIC critical coupling high absorption on state, ensures that a high Q value and a narrow linewidth resonance can be maintained in different states, and has nanosecond switching speed, micro-joule energy consumption and non-volatile retention advantages. The application effectively overcomes the problems of slow speed, high power consumption, unstable state and Q value reduction in the prior art, and has a broad application prospect in optical communication core devices such as optical modulators, wavelength selection switches and optical path switches.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical communication and metasurface photonics, in particular to a dynamic optical switch based on a phase-change metasurface BIC state and a driving method and application thereof. BACKGROUND

[0002] Narrowband, high-Q light absorbers have important application value in the fields of optical communication, precision spectroscopy, and high-sensitivity sensing, and the core technical challenge is how to achieve high-selectivity light energy capture and utilization at a specific wavelength (such as the 1550 nm communication band). Traditional metal structures based on plasmonic resonance have a large intrinsic loss, and the quality factor (Q value) is usually difficult to break through 400, which is difficult to meet the strict requirements of modern optical systems for ultra-narrow linewidth (<0.1 nm) and ultra-high absorption efficiency (>95%). At the same time, metal devices also have certain limitations in integrability and process compatibility.

[0003] In recent years, the development of all-dielectric metasurfaces has provided a new way to break through the above limitations. Based on the design principle of Bound States in the Continuum (BIC), by introducing topologically protected modes that cancel out radiation in a symmetric structure, an infinitely large Q value can be theoretically obtained. However, BIC is essentially a non-radiative mode and cannot directly achieve light energy absorption. Through precise control of the structural symmetry or lattice parameters, BIC can be converted into Quasi-BIC (QBIC), which introduces a controllable radiation channel while still maintaining a very high quality factor. Existing experiments have shown that the Q value under the QBIC mode can reach 10 4 –10 5 orders of magnitude. This mechanism provides an ideal platform for realizing high-performance narrowband absorption, which can maintain ultra-high Q value characteristics close to BIC and effectively couple light fields and absorbing materials.

[0004] Currently, the static narrowband absorber based on QBIC has made some progress in the fields of filtering and sensing, but if it is to be further used in reconfigurable optical switches (such as optical path switches in optical communication systems), its dynamic regulation capability is still seriously insufficient. The existing regulation technology generally faces the following bottlenecks: first, the switching speed is slow, for example, the response time of mechanical or liquid crystal schemes is usually above the millisecond level; second, the energy efficiency is low, and all-optical regulation schemes often rely on pump power above the milliwatt level; third, the state retention is insufficient, and some liquid crystal devices are obviously dependent on the ambient temperature; fourth, the Q value is prone to decrease in the dynamic regulation process, for example, devices based on some two-dimensional materials introduce large loss. The above problems make it difficult for the existing technology to meet the application requirements of high switching contrast, high speed, low power consumption and long time retention at the same time, thereby limiting the practical application of the BIC principle in dynamic optical switches.

[0005] In view of the above challenges, researchers have begun to focus on low-loss chalcogenide phase change materials. Such materials can undergo reversible transition between amorphous and crystalline states, and exhibit significant refractive index change in the near-infrared communication band, with large refractive index modulation amplitude and low loss. More importantly, such materials have non-volatile characteristics, that is, they can maintain the optical state without continuous power supply after transition between crystalline and amorphous states; at the same time, the switching speed can reach nanoseconds, and the driving energy is in the microjoule level, which is significantly better than liquid crystal or thermo-optic devices. Existing researches have pointed out that if such phase change materials can be combined with the QBIC mechanism, it is expected to realize dynamic regulation of the radiation channel of the resonant system, thereby providing a potential path for realizing reconfigurable optical switches. In view of its high compatibility with CMOS technology, such chalcogenide phase change materials are generally considered as important candidate materials for building a new generation of reconfigurable optical switches (such as wavelength selective switches, optical modulators, and optical path switches); however, how to realize stable, fast and maintainable dynamic switching while maintaining ultra-high Q value still lacks mature technical solutions. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a dynamic optical switch based on phase change metasurface BIC state, so as to overcome the problems of Q value decrease, slow switching speed, high energy consumption and poor state retention in the prior art.

[0007] In order to overcome the defects of the above prior art, the present application provides a dynamic optical switch based on phase change metasurface BIC state, comprising, from top to bottom, a metasurface layer composed of periodically arranged all-dielectric nanocolumns, a top isolation layer, a phase change layer, a bottom isolation layer and a substrate.

[0008] The metasurface layer is composed of periodically arranged all-dielectric nanocolumns.

[0009] The top isolation layer is arranged below the metasurface layer.

[0010] A phase change functional layer is arranged below the upper isolation layer, and the material of the phase change functional layer is a thin film material that can reversibly change between amorphous state and crystalline state, and the phase change functional layer satisfies the extinction coefficient k<0.1 in the amorphous state and the refractive index change Δn≥0.5 between the crystalline state and the amorphous state in the 1550 nm wave band;

[0011] A lower isolation layer is arranged below the phase change functional layer;

[0012] A reflective layer is arranged below the lower isolation layer to block the transmitted light and form a single-port optical cavity.

[0013] Compared with the prior art, the dynamic optical switch based on the phase change metasurface BIC state has the following advantages: the present application provides a dynamic optical switch device with reasonable structure and controllable parameters, which includes a metasurface layer, an upper isolation layer, a phase change functional layer, a lower isolation layer and a reflective layer arranged from top to bottom, wherein the metasurface layer is composed of periodically arranged all-dielectric nanocolumns for generating and maintaining BIC / QBIC resonance modes; the upper isolation layer is arranged below the metasurface layer; the phase change functional layer is arranged below the upper isolation layer and is selected from a reversible changeable chalcogenide phase change film between amorphous state and crystalline state, and satisfies the extinction coefficient k<0.1 in the amorphous state and the refractive index change Δn≥0.5 between the crystalline state and the amorphous state in the 1550 nm communication wave band; the lower isolation layer is arranged below the phase change functional layer; and the reflective layer is arranged at the bottom to block the transmitted light and form a single-port optical cavity; the dynamic optical switch based on the phase change metasurface BIC state of the present application introduces a low-loss phase change functional layer into the all-dielectric metasurface structure, so that the device can reversibly switch between the BIC mode corresponding to the amorphous state and the QBIC critical coupling mode corresponding to the crystalline state. In this process, the refractive index jump of the phase change functional layer, the optical thickness of the upper and lower isolation layers, the geometric parameters of the metasurface layer and the total reflection boundary of the reflective layer work together to form a dynamic balance between radiation loss and non-radiation loss. The above-mentioned synergistic relationship not only ensures that the device can maintain high Q value characteristics in different states, but also enables the switched state to be stably maintained without additional power consumption. At the same time, nanosecond switching speed and microjoule level energy driving are realized. Through the above design, the present application effectively solves the problems of slow switching speed, insufficient state retention and Q value degradation in the background art, and provides a dynamic optical switch with high contrast, high speed, low power consumption and maintainability. It is highly compatible with the 1550 nm communication platform and CMOS process, and has a wide application prospect in optical modulators, wavelength selection switches and optical path switches and other optical communication devices.

[0014] In a possible implementation, the material of the phase-change functional layer is Sb2Se3, Sb2S3, or AgInSbTe.

[0015] Compared with the prior art, by further introducing the low-loss chalcogenide phase-change material Sb2Se3, Sb2S3, or AgInSbTe, reversible optical property regulation between the amorphous state and the crystalline state can be achieved, the crystalline state transition of the phase-change material can cause a significant mutation of the dielectric constant, thereby changing the effective optical thickness in the resonant cavity, driving the system to switch between the bound state and the quasi-bound state, and further enabling the device to obtain a dynamically controllable resonant mode, thereby changing the coupling state of the incident light, and the optical switch can break through the limitation of the traditional fixed dielectric layer regulation, and finally realize the dynamic optical regulation function of reversible state switching, lower power consumption, and compatibility with the integrated process.

[0016] In a possible implementation, the extinction coefficient k of the Sb2Se3 is less than 0.05 in the amorphous state at a wavelength of 1550 nm, and the change amount Δn of the refractive index between the crystalline state and the amorphous state is greater than or equal to 0.77.

[0017] Compared with the prior art, by using the technical solution, the low k value is helpful to inhibit non-radiative loss and maintain a high Q value, and the large Δn can destroy the original symmetry and introduce a controllable radiation channel, thereby ensuring that the loss is extremely low in the amorphous state, and a large enough refractive index contrast is provided in the crystalline state, so that the device can maintain a narrow linewidth resonance and achieve significantly different absorption and reflection characteristics in different phase-change states.

[0018] In a possible implementation, the thickness of the phase-change functional layer is 155±5 nm.

[0019] Compared with the prior art, by controlling the thickness of the phase-change functional layer to be 155±5 nm, the optical thickness of the phase-change functional layer can be matched with the interference condition in the cavity while ensuring that the phase-change functional layer has a sufficient refractive index contrast, when the thickness of the phase-change functional layer is within 155±5 nm, the coupling relationship between the phase condition in the cavity and the BIC / QBIC mode can accurately meet the critical coupling requirement; if the thickness deviates from the above range, the resonant condition will not be matched, and the Q value will be reduced or the absorption rate will be reduced, thereby enabling the device to obtain a significant distinction when switching between the crystalline state and the amorphous state, and maintaining a high switching contrast and stable narrowband absorption performance.

[0020] In a possible implementation, the material of the all-dielectric nanopillar of the metasurface layer is germanium, and the period of the all-dielectric nanopillar is 0.873±0.02 μm, the diameter is 400±20 nm, and the height is 170±10 nm.

[0021] Compared with the prior art, the above technical scheme ensures the strong coupling relationship between the super surface structure and the incident wavelength, in the application, the ratio of the period, the diameter and the height determines the interference condition between the guided mode supported by the nanocolumn and the radiation mode, only in the above range of the application, stable BIC can be formed, and QBIC is converted when the symmetry is broken, when the parameter combination deviates from the above range, mode leakage or mismatch will occur, which will significantly reduce the switching contrast and the control ability.

[0022] In a possible implementation, the material of the upper isolation layer and the lower isolation layer is silicon dioxide, and the thickness of the upper isolation layer and the lower isolation layer is 470±20 nm.

[0023] Compared with the prior art, the above technical scheme can form stable Fabry-Perot interference conditions in the cavity, effectively isolate the coupling loss between the phase change functional layer and the reflection layer, and the thickness of the isolation layer determines the optical length and the phase distribution of the cavity. Within the above range, the resonant frequency can be accurately matched with the 1550 nm communication waveband, and the balance between radiation loss and non-radiation loss can be maintained.

[0024] In a possible implementation, the reflection layer is a metal silver film with a thickness of not less than 0.2 μm or a distributed Bragg reflector.

[0025] Compared with the prior art, the above technical scheme can ensure near-full reflection characteristics in the target waveband by using a silver film with a thickness of not less than 0.2 μm, and the distributed Bragg reflector can also achieve high reflection performance comparable to the silver film through the Bragg interference effect of multiple layers of media. The above scheme can provide a high-reflection interface at the bottom of the device to block the transmission channel, so that the entire structure forms a single-port optical cavity, restricts the incident light field energy in the cavity area, and enhances the localization and coupling between the super surface layer and the phase change functional layer.

[0026] In summary, the application further realizes the synergistic optimization of cavity phase matching and mode coupling by precisely controlling the thickness and structure parameters of the super surface layer, the super surface layer, the upper isolation layer, the lower isolation layer and the reflection layer, thereby ensuring the effective switching of the device between BIC and QBIC states, and thereby obtaining high Q value, high contrast and stable controllable dynamic optical switch performance.

[0027] The second technical problem to be solved by the application is to provide a driving method of the above dynamic optical switch to solve the problems of slow switching speed, high energy consumption and insufficient state retention in the prior art.

[0028] To solve the above technical problems, the application provides a driving method of the dynamic optical switch, comprising the following steps: driving the phase change functional layer to reversibly transform between amorphous state and crystalline state by applying an energy pulse to the phase change functional layer, so that the optical switch reversibly converts between high-reflection off state and high-absorption on state.

[0029] Compared with the prior art, the driving method of the dynamic optical switch has the following advantages: the application uses solid-state phase change as the driving mechanism, replacing the traditional liquid crystal or thermal-optical regulation mode, and after the phase change material absorbs the energy of an electric pulse or a laser pulse, the crystal lattice structure of the phase change material is transformed, resulting in a sudden change in dielectric constant, thereby changing the effective optical thickness of the resonant cavity, realizing dynamic switching of BIC and QBIC modes, and the dynamic optical switch based on the phase change metasurface BIC state has fast switching speed, low driving energy consumption, and no need for continuous power supply after switching is completed to maintain the state, effectively solving the problem that speed, energy consumption and stability are difficult to balance in the prior art dynamic optical switch.

[0030] In a possible implementation, the energy pulse is a laser pulse or an electric pulse.

[0031] Compared with the prior art, the above technical solution can flexibly select the driving mode according to different application scenarios: the laser pulse is convenient for remote non-contact triggering, and the electric pulse is more suitable for on-chip circuit integration.

[0032] The application also provides an application of the dynamic optical switch, which comprises applying the dynamic optical switch to an optical device, and the optical device is an optical modulator, a wavelength selection switch or an optical path switch.

[0033] Compared with the prior art, the above technical solution can make full use of the narrowband, high Q value and reversible switching characteristics of the dynamic optical switch of the application, and when the device is in different phase change states, the incident light signal can be controlled in high reflection or high absorption mode, thereby realizing modulation and routing of the light signal, further obtaining high switch contrast and low insertion loss of the optical communication function, so that the dynamic optical switch based on the phase change metasurface BIC state can be effectively applied to high-speed optical modulation, optical path switching and wavelength selection core devices in the 1550nm communication band, meeting the development needs of optical communication and photonic integrated circuits. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a whole structure schematic diagram of the dynamic optical switch based on the phase change metasurface BIC state.

[0035] Figure 2XZ profile and XY plane of the whole dynamic optical switch based on phase change metasurface BIC state;

[0036] Figure 3 Influence of the thickness of the silicon dioxide isolation layer on the resonance quality factor (Q value) relationship diagram;

[0037] Figure 4 Comparison diagram of the absorption characteristics of the dynamic optical switch based on phase change metasurface BIC state in amorphous and crystalline states, wherein, Figure 4 (a) shows the absorption of different wavelengths corresponding to different lattice constants in amorphous and crystalline states, and the white dotted line corresponds to the case where the lattice constant is 0.873 μm; Figure 4 (b) shows the absorption spectrum corresponding to the amorphous and crystalline states when the lattice constant is 0.873 μm;

[0038] Figure 5 Comparison diagram of the influence of different isolation layer and phase change functional layer thicknesses on the absorption performance of the device, wherein, Figure 5 (a) shows the absorption spectrum change corresponding to different isolation layer thicknesses, Figure 5 (b) shows the absorption spectrum change corresponding to different phase change functional layer thicknesses.

[0039] Explanation of reference signs:

[0040] 1, metasurface layer; 2, upper isolation layer; 3, phase change functional layer; 4, lower isolation layer; 5, reflective layer. DETAILED DESCRIPTION

[0041] First of all, those skilled in the art should understand that these embodiments are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can adjust them as needed in order to adapt to specific application occasions.

[0042] In the description of the embodiments of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0043] In the embodiments of the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature is "above", "over" and "on" the second feature, which can be that the first feature is directly above or obliquely above the second feature, or only means that the first feature is higher in horizontal height than the second feature. The first feature is "under", "below" and "underneath" the second feature, which can be that the first feature is directly below or obliquely below the second feature, or only means that the first feature is lower in horizontal height than the second feature.

[0044] The present application provides a dynamic optical switch based on phase change metasurface BIC state, the schematic diagram of the overall structure is shown as Figure 1 The XZ cross-sectional view and XY plane view are shown as Figure 2 Figure 1 In the above, the top cylinder is the incident electromagnetic wave action area, Figure 2 In the above, S1 refers to the thickness of the upper isolation layer 2 and the lower isolation layer 4, and S2 refers to the thickness of the phase change functional layer 3. Figure 2 The circular area of the right figure is the incident electromagnetic wave action area, and the dynamic optical switch comprises, from top to bottom, the following layers:

[0045] The metasurface layer 1 is composed of periodically arranged all-dielectric nanocolumns;

[0046] The upper isolation layer 2 is arranged below the metasurface layer 1;

[0047] The phase change functional layer 3 is arranged below the upper isolation layer 2, and the material thereof is a thin film material that can reversibly transform between amorphous state and crystalline state. The phase change functional layer satisfies the extinction coefficient k < 0.1 in the amorphous state and the refractive index change Δn ≥ 0.5 between the crystalline state and the amorphous state in the 1550 nm wavelength band.

[0048] The lower isolation layer 4 is arranged below the phase change functional layer 3;

[0049] The reflective layer 5 is arranged below the lower isolation layer 4, and is used to block the transmitted light to form a single-port optical cavity.

[0050] As a preferred scheme, the material of the phase change functional layer 3 is Sb2Se3, Sb2S3 or AgInSbTe.

[0051] As a preferred scheme, the extinction coefficient k of the Sb2Se3 in the amorphous state is less than 0.05 at the wavelength of 1550 nm, and the refractive index change Δn between the crystalline state and the amorphous state is greater than or equal to 0.77.

[0052] As a preferred scheme, the thickness of the phase change functional layer 3 is 155±5 nm. ​

[0053] As a preferred scheme, the material of the full dielectric nanocolumn of the super surface layer 1 is germanium, and the period of the full dielectric nanocolumn is 0.873±0.02 μm, the diameter is 400±20 nm, and the height is 170±10 nm.

[0054] As a preferred scheme, the material of the upper isolation layer 2 and the lower isolation layer 4 is both silicon dioxide, and the thickness of the upper isolation layer and the lower isolation layer is both 470±20 nm.

[0055] As a preferred scheme, the reflective layer 5 is a metal silver film with a thickness not less than 0.2 μm or a distributed Bragg reflector.

[0056] The application proposes a brand-new working mechanism of a dynamic optical switch, utilizes the reversible transition between the amorphous state and the crystalline state of a phase change material (including Sb2Se3, Sb2S3 or AgInSbTe), dynamically controls the super surface resonance mode, and enables the super surface resonance mode to switch between a completely uncoupled Fabry-Perot continuous domain bound state (FW-BIC state, corresponding to a switch-off state of the switch with γ r ≈ 0) and a critically coupled quasi-continuous domain bound state (QBIC state, corresponding to a switch-on state of the switch with γ r =γ n The application further discloses specific structural design and key parameters for realizing the dynamic optical switch. The dynamic optical switch provided by the application adopts a single-port reflection system architecture, and includes, from top to bottom, a specially designed germanium-based super surface layer (with a nanocolumn diameter of 400±20 nm and a height of about 170±10 nm), an isolation layer (a double-layer structure with a single-layer thickness of about 470 nm or an equivalent optical thickness design), a chalcogenide phase change functional layer (for example, Sb2Se3, with a thickness of 155±5 nm), and a bottom reflective layer (which can be a metal mirror or a distributed Bragg reflector), and by setting the lattice constant P to 0.873±0.02 μm, the working wavelength can be accurately tuned.

[0057] The dynamic optical switch based on the phase change super surface BIC state of the application limits the optical performance requirements that the phase change material needs to meet. In the 1550 nm communication waveband, the phase change material required by the application should have an extremely low extinction coefficient (k<0.05) in the amorphous state, so as to ensure the low radiation loss characteristic in the BIC state; the phase change material needs to have a significant refractive index change (Δn ≥ 0.77) in the crystalline state, so as to effectively destroy the structural symmetry and realize the critical coupling condition, and the application discloses a method for realizing a high-performance switch function. By accurately controlling the thickness of the upper and lower isolation layers, the radiation loss rate (γ r ) and the non-radiation loss rate (γ n ) of the system reach a match (that is, γr = γ n ). The non-radiative loss γ n is mainly contributed by the absorption loss of materials such as Sb2Se3, and is well matched with the radiative loss.

[0058] The design principle of the application is as follows:

[0059] 1. Time-domain coupled mode theory analysis of single-port reflection system

[0060] When the loss of the metasurface material is ignored, the guided mode resonance (GMR) and the Fabry-Pérot cavity mode can be made to interfere destructively by adjusting the lattice constant and the resonant cavity spacing, thereby forming a Fabry-Pérot continuous domain bound state (FW-BIC). This state is a non-radiative loss intrinsic state, which is derived from the interference cancellation of two coupled modes in a non-Hermite system. In a system that actually considers material loss, the absorption characteristics can be described by the time-domain coupled mode theory as follows:

[0061] .

[0062] Wherein: γ r represents the radiative decay rate (the rate of energy leakage to the far field), γ n represents the non-radiative decay rate (mainly determined by the material absorption loss), and ω0 is the resonant frequency;

[0063] When the system satisfies the critical coupling condition γ r = γ n , perfect absorption (A = 1) can be achieved at the resonant frequency ω0. This theory provides an important guide for designing high-performance narrow-band absorbers: by precisely regulating the metasurface structure parameters (controlling γ r ) and the state of the phase change material (adjusting γ n ), the critical coupling condition can be dynamically adjusted.

[0064] 2. Dynamic absorption regulation mechanism

[0065] The application proposes a dynamic absorption regulation scheme based on a metasurface structure, which constructs a periodic microstructure by a symmetric all-dielectric metasurface, and combines a phase change material to realize controllable switching of BIC mode and QBIC mode, thereby obtaining excellent absorption performance in the communication waveband (1550 nm).

[0066] Specifically, the dynamic optical switch based on the phase transition super surface BIC state of the application can convert the BIC mode into the QBIC mode by introducing a periodic symmetric structure in the full medium super surface and reasonably adjusting the lattice constant and the structure thickness. In this process, the system can realize the resonant characteristics with a high quality factor (Q>10 4 ) at the 1550 nm waveband. Further, by optimizing the lattice constant, unit geometric size and other key parameters, a precise balance between radiation loss and non-radiation loss can be obtained, thereby ensuring high absorption efficiency (>95%) and narrow linewidth (<0.1 nm).

[0067] In the device optimization process, the application systematically studies the influence of the thickness of the silicon dioxide isolation layer on the optical characteristics, and finds that the change of the thickness of the medium layer can significantly change the resonant characteristics of the Fabry-Pérot cavity. Specifically, as the thickness of the SiO2 layer increases, the BIC resonant peak is obviously red-shifted, and the application further verifies through experiments that the switching between the BIC state and the critical coupling state can be realized by accurately controlling the thickness of the SiO2 layer. However, this kind of regulation based on a fixed medium layer belongs to static adjustment, and it is difficult to meet the demand for dynamic reconfigurable function in actual application.

[0068] Specifically as Figure 3 shown, the application first studies the influence law of the thickness S of the silicon dioxide isolation layer on the resonant cavity quality factor (Q value) and absorption characteristics: the silicon dioxide layer as the core medium of the Fabry-Pérot (FP) cavity, its optical thickness directly determines the phase matching condition of the multi-beam interference in the cavity. As Figure 3 the simulation results show that when S is about 0.4 μm and 1.0 μm, the system is in the BIC mode, and the Q value can be as high as 10 5 –10 6 , corresponding to extremely low radiation loss (γ r ≈0); and when S deviates from this thickness interval, the BIC is converted into the QBIC mode, the Q value drops to 10 2 –10 3 , and limited absorption occurs, Figure 3 The test and results show that although the pure dependence on the thickness adjustment of the silicon dioxide can realize the switching of the Q value, it belongs to the static geometric regulation mode, and once the thickness is fixed, it is irreversible, and the intrinsic loss of the medium cannot be adjusted, so it is difficult to meet the actual demand for dynamic reconfigurable optical switch.

[0069] In order to overcome the above limitations, the application innovatively proposes to replace the traditional passive medium layer with a phase change material, which has reversible refractive index modulation characteristics, can introduce an in-situ controllable dielectric constant mutation in the resonant cavity, and thus realize dynamic switching between BIC state and critical coupling state. Figure 4 As shown in Figure 2, Sb2Se3 has a significant refractive index mutation (Δn ≈ 0.77) between amorphous state and crystalline state, which can effectively change the equivalent optical thickness of the FP cavity and drive the system to dynamically switch between BIC and QBIC modes. Figure 4 (a) shows that the absorption spectra of amorphous state and crystalline state are significantly different under different lattice constants, wherein P = 0.873 μm is the design point optimized in the application, Figure 4 (b) shows the comparison of the two states under the above conditions, and the results show that the crystalline state absorption is close to 100%, and the amorphous state is less than 8%, achieving an extinction ratio of 91.9%, while the Q value of the crystalline state remains above 2000, thereby realizing high-contrast dynamic switching while ensuring narrow-band high-Q characteristics.

[0070] The working mechanism of the dynamic optical switch based on phase change metasurface BIC state of the application is as follows:

[0071] Off state (amorphous state): when the phase change material (such as Sb2Se3) is in an amorphous state, the system is maintained in a Fabry-Perot BIC (FW-BIC) protection mode, the radiation channel is closed (γ r ≈ 0), and the coupling with the outside world is very weak, at this time the device absorption is less than 8%, and most of the light is reflected efficiently (> 92%), showing a low insertion loss "off" state.

[0072] On state (crystalline state): after laser or electric pulse induced crystallization, the refractive index of the phase change material (such as Sb2Se3) increases (Δn ≈ 0.77), breaking the original symmetry, and the FW-BIC is converted into a QBIC mode, and through reasonable design (including optimization of the thickness of the upper and lower isolation layers 2 and 4 of SiO2 and the thickness of the phase change functional layer 3), the radiation loss γ r of the crystalline state can be accurately matched with the non-radiation loss γ n (γ r = γ n ), reaching the critical coupling condition. At this time, the device absorption is more than 99%, the quality factor Q is greater than 2000, forming a high-efficiency narrow-band absorption "on" state, and the theoretical reflectivity is close to 0.

[0073] The dynamic optical switch based on the phase change metasurface BIC state of the application is based on the dynamic switching mechanism of the phase change material, which not only solves the problem of the traditional static structure being not reconfigurable, but also realizes the non-volatility (the state does not need to be maintained by additional power consumption), nanosecond-level switching speed and low-energy driving of the optical switch while maintaining the super-high Q value characteristics (crystalline state Q>2000), thereby having significant application value.

[0074] The application further provides a driving method of the dynamic optical switch, which comprises the following steps: by applying an energy pulse to the phase change functional layer, driving the phase change functional layer to reversibly transform between the amorphous state and the crystalline state, so that the optical switch reversibly converts between the high-reflection off state and the high-absorption on state.

[0075] As a preferred scheme, the energy pulse is a laser pulse or an electric pulse.

[0076] The application further provides an application of the dynamic optical switch, which comprises applying the dynamic optical switch to an optical device, and the optical device is an optical modulator, a wavelength selection switch or an optical path switch.

[0077] The following provides specific examples combined with actual data to further illustrate the application:

[0078] Example 1

[0079] The embodiment provides a dynamic optical switch based on the phase change metasurface BIC state, and the overall structure is a multilayer stack from top to bottom, which comprises a metasurface layer 1, an upper isolation layer 2, a phase change functional layer 3, a lower isolation layer 4 and a reflection layer 5.

[0080] The metasurface layer 1 is composed of periodically arranged all-dielectric nanocolumns, the nanocolumns are made of germanium (Ge) material, the period P is 0.873 μm, the diameter is 400 nm, the height is 170 nm, and the complex refractive index of the germanium material is 4.25+0.005i at a wavelength of 1550 nm, which is the core structure of the metasurface unit of the embodiment as a resonant control.

[0081] The upper isolation layer 2 is arranged below the metasurface layer 1 and is a layer of silicon dioxide (SiO2) with a thickness of 470 nm and a refractive index of 1.45, which functions to adjust the optical path and control the Fabry-Pérot cavity interference condition.

[0082] The phase change functional layer 3 is located below the upper isolation layer 2 and is made of a chalcogenide compound Sb2Se3 with a thickness of 155 nm. In an amorphous state, the complex refractive index is about 3.28+0i, and the extinction coefficient is close to zero (k≈0); in a crystalline state, the refractive index increases to 4.05, and the extinction coefficient is only 0.0002, corresponding to a refractive index change Δn≈0.77, thereby providing significant optical contrast for the switching of BIC and QBIC.

[0083] The lower isolation layer 4 is arranged below the phase change functional layer 3 and is also a silicon dioxide film layer with a thickness of 470 nm. In this embodiment, the upper and lower isolation layers are designed to be equal in thickness, which can not only relieve stress but also enhance the localization of light fields through interference effects;

[0084] The reflective layer 5 is arranged below the lower isolation layer 4 and is made of a silver film with a thickness of 0.2 μm. The complex refractive index of the silver film at a wavelength of 1550 nm is 0.39+10.1i. The reflective layer blocks the transmission of light, thereby forming a single-port resonant cavity for the system.

[0085] The embodiment also provides a driving method for the above-mentioned dynamic optical switch based on the BIC state of the phase change metasurface, which includes the following steps:

[0086] By applying an external energy pulse (an electric pulse), the Sb2Se3 phase change functional layer 3 is reversibly converted between an amorphous state and a crystalline state, thereby realizing the switching of the dynamic optical switch based on the BIC state of the phase change metasurface between an off state and an on state:

[0087] In the amorphous state: the device maintains the BIC mode, the radiation loss γ r ≈0, the absorption rate is less than 8%, and the reflectivity is greater than 92%, which represents the off state with low insertion loss;

[0088] In the crystalline state: the system enters the QBIC critical coupling state, γ r matches γ n (γ r =γ n ), the absorption rate is more than 99%, the quality factor Q value is greater than 2000, and there is almost no reflected output, thereby realizing the on state with narrowband and high-efficiency absorption.

[0089] Performance effect:

[0090] The simulation results show that the dynamic optical switch of this embodiment realizes a high switching contrast with an extinction ratio greater than 91%; in the crystalline state, the quality factor Q value is maintained to be greater than 2000, and the highest value can reach 2800; at the same time, the device has non-volatility, nanosecond-level switching speed, and micro-joule-level driving energy, and is suitable for optical systems such as optical modulators, wavelength selection switches, and optical path switches.

[0091] Example 2

[0092] This example 2 is similar to example 1, the difference is that the material of phase change functional layer 3 uses Sb2S3, the thickness of upper isolation layer 2, lower isolation layer 4 and phase change functional layer 3 is different from example 1.

[0093] Specifically including:

[0094] The thickness of upper isolation layer 2 is 450 nm; the thickness of phase change functional layer 3 is 150 nm; the thickness of lower isolation layer 4 is 450 nm.

[0095] Under this parameter condition, the device can still realize the off and on of optical switch through the reversible transition between amorphous state and crystalline state of Sb2S3; simulation shows that this structure can maintain high extinction ratio and high Q value in communication band, and has good dynamic regulation performance.

[0096] Example 3

[0097] This example 3 is similar to example 1, the difference is that the material of phase change functional layer 3 uses AgInSbTe, the thickness of upper and lower isolation layers and phase change functional layer is different from example 1.

[0098] Specifically including:

[0099] The thickness of upper isolation layer 2 is 490 nm; the thickness of phase change functional layer 3 is 160 nm; the thickness of lower isolation layer 4 is 490 nm.

[0100] Under this parameter condition, the device can still realize the reversible switching between amorphous state and crystalline state through the phase change characteristics of AgInSbTe, forming high reflection off state and high absorption on state.

[0101] Performance simulation results show that this structure can still realize high switching contrast and stable Q value at 1550 nm band, meeting the application requirements of dynamic optical switch in optical communication system.

[0102] The following also provides comparative examples of different isolation layers and phase change functional layer thicknesses to further demonstrate the technical solutions of the present application, and the specific test results are shown in Table 1. Figure 5 Figure 5 It is verified that the design parameters of example 1 (the thickness of upper and lower isolation layers S1=470 nm, the thickness of phase change functional layer S2=155 nm) ensure low absorption and high reflection in amorphous state, nearly full absorption in crystalline state, and realize high contrast switching, and comparative examples 1-4 are as follows:

[0103] Comparative example 1: ​

[0104] Comparative Example 1 is similar to Example 1, except that the thickness of the upper spacer layer 2 (S1) and the lower spacer layer 4 (S1) is 670 nm.

[0105] The performance results of the test thereof are shown in Figure 5 (a). In the amorphous state (Am), the device has almost no absorption, maintaining a high reflection state; in the crystalline state (Cr), although an absorption peak appears, the peak value is significantly lower than that of Example 1, approaching a full absorption state, and the spectral line width is widened, indicating that the system fails to meet the critical coupling condition (γ r ≠ γ n ). Therefore, the extinction ratio under the condition of a larger thickness (470 ± 20 nm, which exceeds the limited range of the present application) is significantly reduced, making it difficult to achieve a high-contrast switch.

[0106] Comparative Example 2

[0107] Comparative Example 2 is similar to Example 1, except that the thickness of the upper spacer layer 2 (S1) and the lower spacer layer 4 (S1) is 270 nm.

[0108] The performance results of the test thereof are shown in Figure 5 (a). In the amorphous state, the device maintains a high reflection; in the crystalline state, although absorption occurs, the peak value is much lower than that of Example 1, and the resonant wavelength is significantly blue-shifted. This result shows that when the thickness of the upper spacer layer 2 and the lower spacer layer 4 is thin, the FP cavity phase condition is destroyed, and it is impossible to form a state close to full absorption in the crystalline state, resulting in insufficient contrast of the switch.

[0109] Comparative Example 3

[0110] Comparative Example 3 is similar to Example 1, except that the thickness of the phase change functional layer 3 (S2) is 175 nm.

[0111] The performance results of the test thereof are shown in Figure 5 (b). In the amorphous state, the device has almost no absorption; while in the crystalline state, although an absorption peak appears, the peak value is significantly lower than that of Example 1 with a thickness of 155 nm, indicating that the excessively thick phase change functional layer 3 leads to a too large non-radiative loss γ n , which destroys the matching relationship between γ r and γ n , so that perfect absorption cannot be achieved, and the switching performance is reduced.

[0112] Comparative Example 4

[0113] Comparative Example 4 is similar to Example 1, except that the thickness of the phase change functional layer 3 (S2) is 125 nm.

[0114] The performance results of its test are as follows Figure 5 (b) As shown, in amorphous state, the device maintains high reflection; in crystalline state, the absorption peak appears but the intensity is insufficient to reach the level of nearly full absorption. This result shows that when the thickness of the phase change functional layer 3 is too thin, the non-radiation loss γ n is too small to match the radiation loss γ r , the critical coupling condition cannot be established, resulting in the decrease of the extinction ratio.

[0115] Through the comparison of the above-mentioned Examples 1-3 and Comparative Examples 1-4, the necessity and superiority of the design parameters of the present application are further proved: Example 1 selects the combination of the SiO2 isolation layer thickness of 470 nm and the Sb2Se3 phase change functional layer 3 thickness of 155 nm, which exactly makes the system meet the critical coupling condition (γ r = γ n ) in the crystalline state, thereby realizing nearly perfect absorption (>99%), high Q value (>2000) and extinction ratio of more than 91%, showing excellent dynamic optical switching performance. Through Examples 2 and 3, it is also proved that when the material is replaced by Sb2Se3 or AgInSbTe, high extinction ratio and stable Q value can also be maintained, showing the scalability of material selection, and the thickness of the isolation layer and the phase change functional layer in the present application can also fluctuate within a range, also having good performance.

[0116] When the SiO2 isolation layer thickness is changed to 670 nm or 270 nm in Comparative Example 1 and Comparative Example 2, although the system still appears an absorption peak in the crystalline state, the peak value is obviously insufficient, and is accompanied by red shift or blue shift, indicating that the FP cavity phase condition is destroyed and the critical coupling cannot be maintained; when the thickness of the phase change functional layer 3 is changed to 175 nm or 125 nm in Comparative Example 3 and Comparative Example 4, the non-radiation loss γ n is unbalanced with the radiation loss γ r , resulting in the significant decrease of the absorption efficiency and the extinction ratio.

[0117] As can be seen, the dynamic optical switch based on the phase change metasurface BIC state of the present application does not depend on the thickness design of a single layer, but through the synergistic effect of the metasurface layer 1 parameters, the thickness of the upper isolation layer 2, the thickness of the lower isolation layer 4 and the thickness of the phase change functional layer 3, the accurate matching of γ r and γ n in the crystalline state is ensured. Under this condition, perfect absorption, high contrast switch and narrowband high Q characteristics can be realized; when the thickness of any layer deviates from the optimized value (the case of Comparative Examples 1-4), the synergistic relationship is destroyed, resulting in performance degradation, which fully proves the rationality and technical effect of the structure design of the present application.

[0118] In summary, the beneficial effects of the present application are: by introducing a phase change material in the full dielectric metasurface structure, combined with the BIC principle, the dynamic controllable switching between the off state (FW-BIC) and the on state (QBIC critical coupling) of the optical switch is realized. In the present application, the device maintains the FW-BIC protection mode in the amorphous state, the radiation channel is closed (γ r ≈ 0), the absorption is less than 8%, the reflectivity is greater than 92%, which shows the off state with low insertion loss; in the crystalline state, the refractive index of the phase change functional layer (for example, Sb2Se3) increases (Δn ≈ 0.77), which destroys the symmetry and induces the system to enter the QBIC mode, and through reasonable design (including the thickness of the isolation layer, the thickness optimization of the phase change functional layer), the precise matching (γ r ≈ γ n ) is realized (γ r =γ n ), so as to achieve the critical coupling condition, the absorption is more than 99%, and the Q value remains above 2000, realizing the on state of narrowband and high-efficiency absorption. Compared with the existing static regulation mode based on fixed dielectric layer, the present application not only realizes the dynamic reconfiguration of the optical switch, but also has the following significant advantages in performance:

[0119] (1) High switching performance: the dynamic optical switch based on the phase change metasurface BIC state of the present application can realize super high extinction ratio (>91%), and the absorption rate switches between more than 99% and less than 8%, which is suitable for high-speed optical signal modulation;

[0120] (2) Dynamic high Q value retention: the dynamic optical switch based on the phase change metasurface BIC state of the present application relies on the extremely low loss of Sb2Se3 in the crystalline state (k ≈ 0.0002), and the QBIC mode quality factor is still greater than 2000, effectively avoiding the Q value degradation problem of traditional devices, and being compatible with high-precision wavelength selection;

[0121] (3) Non-volatility and fast switching: the phase change process of the dynamic optical switch based on the phase change metasurface BIC state of the present application has a response time of nanoseconds, the switching energy is in the microjoule level, and the switching state does not need additional power consumption to maintain, which is better than the liquid crystal or thermal optical switch scheme;

[0122] (4) High integration potential: the dynamic optical switch based on the phase change metasurface BIC state of the present application adopts a full dielectric structure, which has good compatibility with CMOS process and 1550 nm optical communication platform, can be widely applied to reconfigurable photonic integrated circuits, and has significant application prospect and industrialization value.

[0123] It should be noted that, in the description of the embodiments of the present application, the terms of direction or position relationship indicated in the description of the present application are based on the direction or position relationship shown in the drawings, which is merely for the convenience of description, and does not indicate or imply that the device or member must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0124] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "in this embodiment", "specific examples", or "some examples" and the like means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the skilled person in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0125] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A dynamic optical switch based on phase-change metasurface BIC state, characterized in that, The application relates to a dynamic optical switch based on a phase-change super surface BIC state, which comprises the following layers arranged from top to bottom: a super surface layer (1) composed of periodically arranged all-dielectric nano columns; an upper isolation layer (2) arranged below the super surface layer (1); a phase-change functional layer (3) arranged below the upper isolation layer (2), which is made of a thin film material capable of reversible conversion between amorphous and crystalline states, wherein the phase-change functional layer (3) satisfies the extinction coefficient k < 0.1 in the amorphous state and the refractive index change Delta n >= 0.5 between the crystalline and amorphous states in the 1550 nm wavelength band; a lower isolation layer (4) arranged below the phase-change functional layer (3); a reflective layer (5) arranged below the lower isolation layer (4) for blocking transmitted light and constituting a single-port optical cavity.

2. The dynamic optical switch based on phase-change metasurface BIC state according to claim 1, characterized in that, The material of the phase-change functional layer (3) is Sb2Se3, Sb2S3 or AgInSbTe.

3. The dynamic optical switch based on phase-change metasurface BIC state according to claim 2, characterized in that, The Sb2Se3 has an extinction coefficient k < 0.05 in the amorphous state at a wavelength of 1550 nm, and the refractive index change Delta n >= 0.77 between the crystalline and amorphous states.

4. The dynamic optical switch based on phase-change metasurface BIC state according to claim 1, characterized in that, The thickness of the phase-change functional layer (3) is 155+ / -5 nm.

5. The dynamic optical switch based on phase-change metasurface BIC state according to claim 1, characterized in that, The material of the all-dielectric nano column of the super surface layer (1) is germanium, the period of the all-dielectric nano column is 0.873+ / -0.02 mu m, the diameter is 400+ / -20 nm, and the height is 170+ / -10 nm.

6. The dynamic optical switch based on phase-change metasurface BIC state according to claim 1, characterized in that, The materials of the upper isolation layer (2) and the lower isolation layer (4) are both silicon dioxide, and the thicknesses of the upper isolation layer (2) and the lower isolation layer (4) are both 470+ / -20 nm.

7. The dynamic optical switch based on phase-change metasurface BIC state according to claim 1, characterized in that, The reflective layer (5) is a metal silver film with a thickness not less than 0.2 mu m or a distributed Bragg reflector.

8. A driving method of the dynamic optical switch based on the phase-change metasurface BIC state according to any one of claims 1-7, characterized in that, The application further relates to a method for using the dynamic optical switch based on the phase-change super surface BIC state, which comprises the following steps: applying an energy pulse to the phase-change functional layer (3) to drive the phase-change functional layer (3) to reversibly convert between the amorphous and crystalline states, so that the dynamic optical switch based on the phase-change super surface BIC state reversibly converts between the high-reflection off state and the high-absorption on state.

9. The driving method according to claim 8, wherein The energy pulse is a laser pulse or an electric pulse.

10. Use of a dynamic optical switch based on phase change metasurface BIC state according to any one of claims 1-7, characterized in that, The application of the dynamic optical switch based on the phase-change super surface BIC state includes applying the dynamic optical switch to an optical device, and the optical device is an optical modulator, a wavelength selection switch or an optical path switch.

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