Metasurface and metasurface preparation method

Abstract

The invention provides a metasurface and a metasurface preparation method, and relates to the field of optical devices. The metasurface comprises a silicon substrate, a silicon catenary structure with a plurality of silicon cambered surfaces and a phase change material, a silicon catenary structure formed by periodically arranging a plurality of silicon cambered surfaces in a first direction and a second direction is etched on the first surface of the silicon substrate; wherein each silicon cambered surface is symmetrical by taking the axis of the vertex in the second direction as a symmetry axis; the phase change material is deposited on the end face of the silicon cambered surface in the third direction; when light is transmitted to the silicon catenary structure deposited with the phase change material, the light is modulated to be transmitted in a one-way mode. Wherein the third direction intersects with a plane determined by the first direction and the second direction. According to the metasurface provided by the embodiment of the invention, the continuous catenary structure is combined with the volatile phase change material, so that relatively high efficiency and nonreciprocity can be achieved in a wide-band and wide-angle range.

Description

Technical Field

[0001] The present application relates to the field of optical devices, and in particular, to a metasurface and a method for preparing the metasurface. Background Art

[0002] Non-reciprocal optical devices are a type of optical device that can achieve unidirectional transmission or regulation of light. The core feature of non-reciprocal optical devices is that the transmission characteristics of light show asymmetry in the positive and negative directions, that is, the behavior of light when passing through the device from one direction is different from when passing through it from the opposite direction. In the field of high-power laser protection, broadband non-reciprocal optical devices are often required.

[0003] In the design of non-reciprocal optical devices, the dielectric constant or permeability tensor of the non-reciprocal optical device material needs to break at least one of the symmetry, time invariance and linearity to achieve non-reciprocity.

[0004] Currently, there are commercial non-reciprocal devices that rely on an external magnetic field to achieve asymmetry in the permeability tensor, but they still face great challenges in integration and application. There are also some new non-reciprocal devices that do not require an external magnetic field, but the existing devices have deficiencies in processing and use. Summary of the invention

[0005] The purpose of the embodiments of the present application is to provide a metasurface and a method for preparing a metasurface, which achieves high efficiency and non-reciprocity in a wide bandwidth and wide angle range by combining a continuous catenary structure with a volatile phase change material.

[0006] In a first aspect, an embodiment of the present application provides a metasurface, comprising: a silicon substrate, a silicon catenary structure having a plurality of silicon arc surfaces, and a phase change material; a silicon catenary structure composed of a plurality of silicon arc surfaces periodically arranged in a first direction and a second direction is etched on the first surface of the silicon substrate; wherein each silicon arc surface is symmetrical with the axis at which the vertex is located in the second direction as the axis of symmetry; a phase change material is deposited on the end face of the silicon arc surface in a third direction; wherein, when light is transmitted to the silicon catenary structure on which the phase change material is deposited, it is modulated into unidirectional propagation; wherein the third direction intersects with the plane determined by the first direction and the second direction.

[0007] In the above implementation process, the metasurface provided in the embodiment of the present application realizes efficient non-reciprocal optical regulation by combining the silicon catenary structure with the phase change material. The metasurface adopts a continuous catenary structure to achieve high efficiency and non-reciprocity in a wide bandwidth and wide angle range; wavefront modulation is achieved through a continuous catenary structure, and it has a multifunctional laser protection effect; and the metasurface is a weak resonance structure, which improves the high-power tolerance and tunability of the metasurface; overcomes the wavelength dependence problem of the strong resonance structure and broadens the working range. The metasurface structure provided in the embodiment of the present application combines the geometric phase characteristics and the advantages of special materials. It not only has the characteristics of high efficiency and wide bandwidth, but also can realize laser protection in a wide power range through the phase change characteristics of phase change materials, and is suitable for the protection of high-power lasers.

[0008] Optionally, in an embodiment of the present application, the thickness of the catenary structure in the third direction, the period of the catenary structure in the first direction and the period of the catenary structure in the second direction are related to the central wavelength of the light.

[0009] In the above implementation process, the period in the first direction, the period in the second direction, and the thickness in the third direction (etched thickness of the silicon substrate) of the catenary structure of the metasurface provided by the embodiment of the present application are all related to the central wavelength of the incident light. By precisely controlling the geometric parameters, the metasurface provided by the embodiment of the present application can achieve multifunctional optical response in a broadband and wide angle range, such as beam deflection, laser protection, etc., while having high power tolerance and tunability.

[0010] Optionally, in the embodiment of the present application, the period range of the catenary structure in the first direction is (λ 0 / 3, 2λ 0 ), the period range of the catenary structure in the second direction is (λ 0 / 6,λ 0 ), the thickness range of the catenary structure in the third direction is (λ 0 / 10,λ 0 ), where λ 0 is the central wavelength of light.

[0011] In the above implementation process, the catenary linear metasurface provided in the embodiment of the present application realizes efficient polarization conversion and beam deflection functions by optimizing the first direction period (λ / 3, 2λ), the second direction period (λ / 6, λ) and the third direction thickness (λ / 10, λ). The metasurface can be regarded as a half-wave plate, which can convert left circularly polarized light into right circularly polarized light and deflect an angle at the same time, demonstrating multifunctional optical regulation capabilities. By reasonably designing the characteristic length of the subwavelength structure, the metasurface structure provided by the implementation of the present application takes into account manufacturing feasibility while meeting optical performance.

[0012] Optionally, in the embodiment of the present application, a portion of the cross section of the silicon arc surface on the plane formed by the first direction and the second direction is y(x)=P x / π·ln|sec(πx / P x )|; where P x is the period of the catenary structure in the first direction.

[0013] Optionally, in an embodiment of the present application, the sizes of the silicon arc surface in the second direction are the same, or the sizes of the silicon arc surface in the second direction decrease uniformly from the vertex toward both sides.

[0014] In the above implementation process, the metasurface structure provided by the embodiment of the present application achieves near-perfect wavefront modulation due to its continuous catenary structure; at the same time, scattering and unnecessary diffraction are minimized, further ensuring efficient transmission. On the other hand, the metasurface structure provided by the embodiment of the present application is a weak resonance structure, which overcomes the wavelength dependence problem of the strong resonance structure and broadens the working range. In addition, the metasurface structure provided by the embodiment of the present application has a relatively large lithographic size and does not require a high refractive index resonance layer, which simplifies the manufacturing process.

[0015] Optionally, in the embodiment of the present application, the thickness range of the phase change material along the third direction is (100 nm, 300 nm).

[0016] In the above implementation process, the embodiment of the present application optimizes the deposition thickness range (100nm to 300nm) of the phase change material in the third direction, thereby ensuring the high efficiency performance of the device while taking into account the feasibility of the preparation process.

[0017] Optionally, in an embodiment of the present application, the phase change material includes a volatile phase change material.

[0018] In the above implementation process, the phase change material deposited on the silicon substrate of the metasurface provided by the embodiment of the present application is a volatile phase change material (such as VO, VO, VO), which gives the metasurface device dynamic optical regulation capability. Since the transmittance of the volatile phase change material changes with temperature and light intensity, it can switch between high transmittance and low transmittance states, thereby achieving precise control of whether light passes through or not.

[0019] In a second aspect, an embodiment of the present application provides a method for preparing a supersurface, which includes: etching a plurality of silicon arc surfaces periodically arranged in a first direction and a second direction on a first surface of a silicon substrate to form a silicon catenary structure; wherein each silicon arc surface is symmetrical with the axis at the vertex in the second direction as the axis of symmetry; depositing a phase change material on the end face of the silicon arc surface in a third direction; and depositing an anti-reflective coating on the second surface of the silicon substrate to complete the preparation of the supersurface.

[0020] Optionally, in the embodiment of the present application, the period range of the catenary structure in the first direction is (λ 0 / 3, 2λ 0 ), the period range of the catenary structure in the second direction is (λ 0 / 6,λ 0 ), the thickness range of the catenary structure in the third direction is (λ 0 / 10,λ 0 ), where λ 0 is the central wavelength of light.

[0021] Optionally, in an embodiment of the present application, the phase change material includes a volatile phase change material, and a thickness range of the phase change material along the third direction is (100 nm, 300 nm).

[0022] In summary, the metasurface structure provided in the embodiments of the present application combines geometric phase design with the characteristics of phase change materials, which not only realizes efficient, broadband, and wide-angle optical regulation, but also provides new solutions for laser protection, optical isolators, and dynamic optical devices, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of the structure of a metasurface provided in an embodiment of the present application;

[0025] Figure 2 A schematic diagram of the layout structure of the metasurface provided in an embodiment of the present application;

[0026] Figure 3 The wide-band transmittance of the metasurface provided in the embodiment of the present application at different temperatures;

[0027] Figure 4 The average transmittance of the metasurface provided by the embodiment of the present application in a wide range of incident angles;

[0028] Figure 5 A critical phase change power density diagram of the forward and reverse lasers at different wavelengths of the metasurface provided in the embodiment of the present application;

[0029] Figure 6 Non-reciprocal transmission performance diagram of forward and reverse lasers at different temperatures on the metasurface provided in the embodiment of the present application;

[0030] Figure 7 A schematic diagram of the function of the metasurface provided in an embodiment of the present application;

[0031] Figure 8 A schematic diagram of a supersurface structure provided in an embodiment of the present application passing direct current;

[0032] Fig. 9 A schematic diagram of the preparation of the super surface structure provided in the embodiment of the present application;

[0033] Fig.10 A flow chart for preparing the super surface structure provided in the embodiment of the present application;

[0034] Icons: metasurface-100; silicon substrate-110; first surface of silicon substrate-S1; second surface of silicon substrate-S2; silicon catenary structure-120; silicon arc surface-121; phase change material-130; first direction-X; second direction-Y; third direction-Z. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings in the embodiments of the present application. For example, the flowcharts and block diagrams in the accompanying drawings show the possible architectures, functions and operations of the systems, methods and computer program products according to multiple embodiments of the present invention. In this regard, each box in the flowchart or block diagram may represent a module, a program segment or a part of a code, and the module, a program segment or a part of a code contains one or more executable instructions for implementing the specified logical functions. It should also be noted that in some alternative implementations, the functions marked in the box may also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they may sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or the flowchart, and the combination of boxes in the block diagram and / or the flowchart, can be implemented by a dedicated hardware-based system that performs a specified function or action, or can be implemented by a combination of dedicated hardware and computer instructions. In addition, the functional modules in the various embodiments of the present invention can be integrated together to form an independent part, or each module can exist separately, or two or more modules can be integrated to form an independent part.

[0036] Non-reciprocal optical devices are a type of optical device that can achieve unidirectional transmission or regulation of light. Its core feature is that the transmission characteristics of light show asymmetry in the positive and negative directions, that is, the behavior of light when passing through the device from one direction is different from when passing through the device from the opposite direction. In the design of non-reciprocal optical devices, the dielectric constant or permeability tensor of the non-reciprocal optical device material needs to break at least one of the symmetry, time invariance and linearity to achieve non-reciprocity. Common non-reciprocity is usually achieved through magneto-optical effects, nonlinear effects or time modulation. Non-reciprocal optical devices have important applications in optical isolators, circulators, unidirectional waveguides and other fields. They can effectively prevent reflected light in the optical path from interfering with the stability of the light source and improve the performance and reliability of the optical system.

[0037] Currently, most commercial non-reciprocal devices rely on the magneto-optical effect, using an external magnetic field to achieve the asymmetry of the magnetic permeability tensor. However, such devices are large in size and difficult to integrate; the magnetic field has an adverse effect on surrounding sensitive electronic components. In addition, magneto-optical materials have a high absorption rate in the infrared band, which makes the integration and application of efficient non-reciprocal devices challenging.

[0038] There are also two new types of non-reciprocal devices that do not require an external magnetic field. One is a non-reciprocal design based on the principle of spatiotemporal modulation to break the time-invariance of the dielectric constant, and the other is a non-reciprocal device based on nonlinear effects. The first requires external high-frequency light or high-frequency electrical modulation, which increases the complexity of device processing and power consumption. The second requires extremely high light intensity or a resonant structure with an extremely high Q value because the optical nonlinear coefficient of common nonlinear materials is low. These requirements are difficult to meet in actual use conditions, especially in the use environment of free-space light.

[0039] Based on this, the present application proposes a metasurface and a method for preparing the metasurface. The metasurface structure adopts a continuous catenary structure, achieves high efficiency and non-reciprocity in a wide bandwidth and wide angle range, and has broad application prospects.

[0040] Please see Figure 1 , Figure 1 A schematic diagram of the structure of a metasurface provided in an embodiment of the present application; the present application provides a metasurface 100, which includes: a silicon substrate 110, a silicon catenary structure 120 having a plurality of silicon arc surfaces 121, and a phase change material 130. In the embodiment of the present application, the first direction, the second direction, and the third direction are the X direction, the Y direction, and the Z direction, and the third direction Z intersects with the plane defined by the first direction X and the second direction Y.

[0041] A silicon catenary structure 120 formed by periodically arranging a plurality of silicon arc surfaces 121 in a first direction X and a second direction Y is etched on the first surface S1 of the silicon substrate. Figure 1As shown, each silicon arc surface 121 is symmetrical with the axis where the vertex in the second direction Y is located as the symmetry axis.

[0042] It should be noted that the catenary structure refers to a common curved shape in physics, which is specifically manifested as a chain with uniform thickness and mass distribution, soft and inextensible, fixed at both ends, forming a downward curved shape (such as hanging wires, suspension bridges, etc.) under the action of uniform gravitational force (usually gravity).

[0043] In the above implementation process, the metasurface 100 structure provided in the embodiment of the present application is composed of periodically arranged silicon arc surfaces 121, and the structure of these silicon arc surfaces 121 is a catenary structure. It should be noted that the catenary structure in the embodiment of the present application is used to refer to the shape of the periodically arranged silicon surface, and in some cases, the structure of the silicon arc surface 121 provided in the embodiment of the present application partially or completely satisfies the catenary equation.

[0044] The phase change material 130 is deposited on the end surface of the silicon arc surface 121 in the third direction Z. When light is transmitted to the silicon catenary structure 120 on which the phase change material 130 is deposited, it is modulated to propagate in one direction.

[0045] Phase change material 130 is a type of material that can undergo reversible phase change under external stimuli (such as temperature, light, electric field, etc.). Common phase change materials 130 include VO. Due to the adjustable optical properties of the phase change material 130, it is applied to the metasurface 100 structure provided in the embodiment of the present application to realize the construction of dynamically tunable optical devices. In the embodiment of the present application, after the phase change material 130 is deposited on the end face of the silicon arc surface 121 in the third direction Z, the propagation characteristics of light will be modulated to achieve unidirectional propagation.

[0046] In the embodiment of the present application, the substrate material is single crystal silicon, that is, silicon substrate 110. Single crystal silicon achieves a lower absorptivity in the mid- and far-infrared bands due to its crystal structure. The all-silicon structure metasurface 100 in the embodiment of the present application has a large and stable out-of-plane refractive index contrast, so that the phase change material 130 layer can exhibit significant asymmetric photothermal coupling in a wide band and a large incident angle range, thereby achieving non-reciprocal transmission.

[0047] pass Figure 1It can be seen that the metasurface 100 provided in the embodiment of the present application realizes efficient non-reciprocal optical regulation by combining the silicon catenary structure 120 with the phase change material 130. The metasurface 100 adopts a continuous catenary structure to achieve high efficiency and non-reciprocity in a wide bandwidth and wide angle range; wavefront modulation is achieved through a continuous catenary structure, and it has a multifunctional laser protection effect; and the metasurface 100 is a weak resonance structure, which improves the high power tolerance and tunability of the metasurface 100; overcomes the wavelength dependence problem of the strong resonance structure and broadens the working range. The metasurface 100 structure provided in the embodiment of the present application combines the geometric phase characteristics and the advantages of special materials. It not only has the characteristics of high efficiency and wide bandwidth, but also can realize laser protection in a wide power range through the phase change characteristics of the phase change material 130, which is suitable for the protection of high-power lasers.

[0048] In an optional embodiment, the thickness of the catenary structure in the third direction Z, the period of the catenary structure in the first direction X, and the period of the catenary structure in the second direction Y are related to the central wavelength of the light.

[0049] Please continue to see Figure 1 , the key parameters of the catenary structure of the metasurface 100 provided in the embodiment of the present application include the thickness in the third direction Z, the period in the first direction X, and the period in the second direction Y. Among them, the thickness in the third direction Z, that is, the thickness of the catenary structure in the direction perpendicular to the substrate (Z direction), directly affects the phase modulation ability and transmission / reflection characteristics of light. The period in the first direction X, that is, the arrangement period of the catenary structure in the X direction, determines the diffraction effect and wavefront control ability of light. The period in the second direction Y, that is, the arrangement period of the catenary structure in the Y direction, works together with the period in the first direction X to affect the polarization and propagation characteristics of light.

[0050] In the embodiment of the present application, the period of the catenary structure in the first direction X, the period in the second direction Y, and the thickness in the third direction Z are all related to the central wavelength of the incident light; by adjusting the above-mentioned key parameters, the propagation behavior of light in the metasurface 100 can be precisely controlled, thereby improving the performance of the metasurface 100, such as improving efficiency, expanding working bandwidth, etc.

[0051] It can be seen that the period of the catenary structure of the metasurface 100 provided in the embodiment of the present application in the first direction X, the period in the second direction Y, and the thickness in the third direction Z (the etching thickness of the silicon substrate 110) are all related to the central wavelength of the incident light. By precisely controlling the geometric parameters, the metasurface 100 provided in the embodiment of the present application can achieve multifunctional optical response in a broadband and wide angle range, such as beam deflection, laser protection, etc., while having high power tolerance and tunability.

[0052] In an optional embodiment, the period range of the catenary structure in the first direction X is (λ 0 / 3, 2λ 0 ), the period range of the catenary structure in the second direction Y is (λ 0 / 6,λ 0 ), the thickness range of the catenary structure in the third direction Z is (λ 0 / 10,λ 0 ), where λ 0 is the central wavelength of light.

[0053] Please Figure 1 See on the basis of Figure 2 , Figure 2 Schematic diagram of the layout structure of the metasurface provided in the embodiment of the present application; the catenary metasurface 100 provided in the embodiment of the present application can be regarded as a half-wave plate, which can convert left circularly polarized light (LCP) into right circularly polarized light (RCP) and deflect it at an angle. The optical axis direction of each point on the metasurface 100 is along Figure 2 Its function is to convert left circularly polarized light into right circularly polarized light and deflect it by an angle.

[0054] Since the catenary structure provided in the embodiment of the present application is a sub-wavelength structure, the characteristic length of the structure needs to be as small as possible from the central wavelength λ of the incident light working band. 0 , to meet the sub-wavelength condition, thereby avoiding high-order diffraction and achieving efficient optical control. However, if the characteristic length is too small, it will increase the difficulty of processing; therefore, the metasurface 100 structure provided in the embodiment of the present application balances the performance and the feasibility of manufacturing, and sets the period range of the catenary structure in the first direction X to (λ 0 / 3, 2λ 0 ), the period range of the catenary structure in the second direction Y is (λ 0 / 6,λ 0 ), the thickness range of the catenary structure in the third direction Z is (λ 0 / 10,λ 0 ).

[0055] pass Figure 1 and Figure 2It can be seen that the catenary metasurface 100 provided in the embodiment of the present application achieves efficient polarization conversion and beam deflection functions by optimizing the first direction X period (λ / 3, 2λ), the second direction Y period (λ / 6, λ) and the third direction Z thickness (λ / 10, λ). The metasurface 100 can be regarded as a half-wave plate, which can convert left circularly polarized light into right circularly polarized light and deflect an angle at the same time, demonstrating multifunctional optical regulation capabilities. By reasonably designing the characteristic length of the subwavelength structure, the metasurface 100 structure provided by the implementation of the present application takes into account manufacturing feasibility while meeting optical performance.

[0056] In an optional embodiment, a portion of a cross section of the silicon arc surface 121 on a plane formed by the first direction X and the second direction Y is y(x)=P x / π·ln|sec(πx / P x )|; where P x is the period of the catenary structure in the first direction X.

[0057] In the above implementation process, the period range of the catenary structure provided in the embodiment of the present application in the first direction X is (λ 0 / 3, 2λ 0 ), the period range in the second direction Y is (λ 0 / 6,λ 0 ), the thickness range in the third direction Z is (λ 0 / 10,λ 0 ). Since it satisfies the catenary equation, y(x) = P x / π·ln|sec(πx / P x )|, so that specific parameters can be selected.

[0058] In order to deflect the propagation direction of light, the metasurface 100 structure provided in the embodiment of the present application can generate a uniform and continuous phase gradient. By calculating based on the geometric phase principle of circularly polarized light, the center line of the arc structure is the catenary y(x)=P x / ·ln|sec( / x )|; among them, P x The periodically arranged arc structure can produce the above-mentioned geometric phase gradient and the circular polarization conversion effect, where H and P y Can affect the diffraction efficiency.

[0059] In an optional embodiment, the sizes of the silicon arc surface 121 in the second direction Y are the same, or the size of the silicon arc surface 121 in the second direction Y decreases uniformly from the vertex to both sides.

[0060] Optionally, the multiple silicon arc surfaces 121 of the metasurface 100 provided in the embodiment of the present application can be set to have the same width everywhere in the second direction Y.

[0061] Optionally, the dimensions of the multiple silicon arc surfaces 121 of the metasurface 100 provided in the embodiment of the present application in the second direction Y decrease uniformly from the vertex to both sides, that is, a structure that is thick in the middle and thin at both ends.

[0062] In the above implementation process, no matter which setting mode is selected for the silicon arc surface 121 provided in the embodiment of the present application, each arc structure is symmetrical about the central axis, and the size distribution of the silicon arc surface 121 in the second direction Y can affect the continuity of the light wavefront.

[0063] In practical applications, the various dimensional parameters of the unit structure (such as the period in the first direction X, the period in the second direction Y, the thickness in the third direction Z, and the thickness of the silicon arc surface 121 in the second direction Y) can be further optimized through numerical simulation. According to the central wavelength of the working band, appropriate parameters are selected to make the +1 order diffraction efficiency of the metasurface 100 the highest.

[0064] It can be seen that the metasurface 100 structure provided in the embodiment of the present application achieves near-perfect wavefront modulation due to its continuous catenary structure; at the same time, scattering and unnecessary diffraction are minimized, further ensuring efficient transmission. On the other hand, the metasurface 100 structure provided in the embodiment of the present application belongs to a weak resonance structure, which overcomes the wavelength dependence problem of the strong resonance structure and broadens the working range. In addition, the metasurface 100 structure provided in the embodiment of the present application has a relatively large lithographic size and does not require a high refractive index resonance layer, which simplifies the manufacturing process.

[0065] Please see Figure 3 and Figure 4 , Figure 3 The wide-band transmittance of the metasurface 100 provided in the embodiment of the present application at different temperatures; Figure 4 The average transmittance of the metasurface 100 provided in the embodiment of the present application in a wide range of incident angles.

[0066] Figure 3 The broadband transmittance at 30°C and 80°C is shown. Figure 4 The broadband average transmittance at different incident angles at 30°C and 80°C is shown. Figure 3 and Figure 4 It can be seen that the metasurface 100 provided in the embodiment of the present application adopts an all-dielectric catenary structure, which can achieve high efficiency and non-reciprocal transmission in a wide band and wide angle range.

[0067] In an alternative embodiment, the phase change material 130 includes a volatile phase change material.

[0068] For example, the volatile phase change material deposited in the embodiment of the present application may be VO 2 、V 2 O 3 、V 2 O 5 It should be noted that the transmittance of the volatile phase change material changes with temperature and light intensity, so that two states of high transmittance and low transmittance can be achieved to control whether light passes through.

[0069] The embodiments of the present application do not impose any particular restrictions on the specific types of volatile phase change materials. In practical applications, the material can be selected according to different temperature range requirements to select a material with a suitable phase change temperature.

[0070] It can be seen that the phase change material 130 deposited on the silicon substrate 110 of the metasurface 100 provided in the embodiment of the present application is a volatile phase change material (such as VO, VO, VO), which gives the metasurface 100 device dynamic optical control capability. Since the transmittance of the volatile phase change material changes with temperature and light intensity, it can switch between high transmittance and low transmittance states, thereby achieving precise control of whether light passes through or not.

[0071] In an optional embodiment, please continue to see Figure 1 , the thickness range of the phase change material 130 along the third direction Z is (100 nm, 300 nm).

[0072] The volatile phase change material deposited on the surface of the silicon substrate 110 is VO 2 For example, in the low temperature medium state, the absorption loss of light is low, so VO 2 The deposition thickness has little effect on the device efficiency; in the high-temperature metal state, the absorption rate of the material is large, so VO 2 The deposition thickness can significantly affect the light-off effect.

[0073] In theory, VO 2 The thicker the deposition thickness, the higher the switching ratio of the device and the better the effect. However, in the preparation process, VO 2 After high temperature annealing, if VO 2 If the deposition thickness is too thick, cracking problems may occur.

[0074] Therefore, the metasurface 100 provided in the embodiment of the present application is based on a laser pulse deposition method, and the optimal deposition thickness is between 100 nm and 300 nm.

[0075] It can be seen that the embodiment of the present application optimizes the deposition thickness range (100 nm to 300 nm) of the phase change material 130 in the third direction Z, thereby ensuring the high efficiency performance of the device while taking into account the feasibility of the preparation process.

[0076] Please refer to Figure 5 and Figure 6 , Figure 5 A critical phase change power density diagram of the forward and reverse lasers at different wavelengths for the metasurface 100 provided in an embodiment of the present application; Figure 6 This is a diagram of the non-reciprocal transmission performance of forward and reverse lasers at different temperatures of the metasurface 100 provided in an embodiment of the present application.

[0077] like Figure 5 As shown, the critical phase change power density of the forward and reverse lasers at different wavelengths is simulated, showing the non-reciprocal transmission performance of the metasurface 100 broadband provided by the embodiment of the present application. Figure 5 Temperature control was also performed, and the critical phase change power density of lasers with different wavelengths in the forward and reverse directions was measured at 30°C and 60°C. Figure 5 It can be seen from the curve shown that the non-reciprocal power application range of the metasurface 100 structure provided in the embodiment of the present application can be extended to 3 orders of magnitude, showing extremely strong environmental adaptability and regulation flexibility.

[0078] like Figure 6 As shown, the non-reciprocal transmission performance of the forward and reverse lasers at 60°C and 65°C was measured respectively. Figure 6 It can be seen that the power range of the metasurface 100 provided in the embodiment of the present application is adjustable.

[0079] pass Figure 5 and Figure 6 It can be seen that the metasurface 100 structure provided in the embodiment of the present application combines the electrical and thermal control characteristics of the VO phase change material 130, and utilizes its photothermally induced strong nonlinear effect and wide-band refractive index change characteristics to achieve non-reciprocal transmission performance in a wide band and wide power range.

[0080] Please see Figure 7 , Figure 7 Schematic diagram of the function of the metasurface 100 provided in the embodiment of the present application; The non-reciprocal principle of the structure of the metasurface 100 provided in the embodiment of the present application is that the volatile phase change material (such as VO2) deposited on the surface of the silicon substrate 110 2 )There is a large difference in refractive index between the air and the silicon structure on the upper and lower surfaces, resulting in different electric field strengths inside the volatile phase change material under the two directions of incidence.

[0081] like Figure 7 As shown, the incident light is incident from one side of the volatile phase change material deposited on the surface of the silicon substrate 110, that is, Figure 7 and incident from the bottom side of the silicon substrate 110 which has not been etched, that is, Figure 7 The incident direction of the opponent's laser.

[0082] According to the electromagnetic field numerical simulation of the metasurface 100 structure provided in the embodiment of the present application, the incident light beams are incident on the metasurface 100 in two directions (such as Figure 7 The electric field intensity of the laser incident direction of the second party and the laser incident direction of the other party is integrated to obtain the photothermal intensity distribution. The results show that the photothermal intensity generated by the incident direction of the silicon substrate 110 is about twice that of the incident direction of the air end. Therefore, under the appropriate light intensity, the laser of one side can pass through the device of the metasurface 100 structure provided by the embodiment of the present application, while the laser of the other direction will induce a photothermal phase change, and the transmittance is greatly reduced. Figure 7 As shown, the circularly polarized light emitted by the laser itself can pass smoothly through the metasurface 100 provided in the embodiment of the present application, while the external laser with the same energy incident from the opposite direction cannot pass through.

[0083] pass Figure 7 It can be seen that the metasurface 100 device achieves a multifunctional laser protection effect through wavefront modulation and phase change material 130 (VO), overcoming the problems of limited protection power range and reflected light interference of traditional phase change schemes. Specifically, under low power conditions, the device filters external lasers, especially near-infrared pulsed lasers, through wavelength and polarization selection mechanisms; within the phase change power range (0.1-45kW / cm 2 ), the device can effectively block the reverse laser and prevent the reflected light from interfering with the stability of the own laser; when the reverse laser intensity is too high, the metasurface 100 structure is damaged, and the light beam is directly transmitted along the original direction, thereby protecting the own laser. In addition, by manipulating light deflection through wavefront modulation, the device can also hide the position of the own laser, further enhancing the protection effect.

[0084] In an optional embodiment, please refer to Figure 8 , Figure 8 Schematic diagram of the metasurface 100 structure provided in an embodiment of the present application passing direct current.

[0085] Due to the volatile phase change materials (such as VO 2 ) is sensitive to temperature, and the substrate temperature can be controlled by external heat sources, such as Figure 8 As shown, a number of wires can be arranged at regular intervals on the metasurface 100 provided in the embodiment of the present application and a direct current can be passed through, so that the absorption rate of the volatile phase change material can be flexibly controlled, and its nonlinear response can be adjusted to adapt to different laser powers and realize the regulation of the non-reciprocal power range.

[0086] It can be seen that the metasurface 100 structure provided in the embodiment of the present application is a weak resonance structure design, so that the metasurface 100 device can operate at a higher power level, and the existing tunable non-reciprocal range is extended by an order of magnitude through thermal control. The high power tolerance and tunability of the metasurface 100 are improved; the wavelength dependence problem of the strong resonance structure is overcome, and the working range is widened.

[0087] Please see Fig. 9 and Fig.10 , Fig. 9 A schematic diagram of the preparation of the super surface structure provided in the embodiment of the present application; Fig.10 A preparation flow chart of a supersurface structure provided in an embodiment of the present application; the present application provides a method for preparing a supersurface, and the method for preparing a supersurface comprises the following steps:

[0088] Step S100: etching a plurality of silicon arc surfaces periodically arranged in a first direction and a second direction on a first surface of a silicon substrate to form a silicon catenary structure.

[0089] Each silicon arc surface is symmetrical with the axis where the vertex in the second direction is located as the symmetry axis.

[0090] Step S200: depositing a phase change material on an end surface of the silicon arc surface in a third direction.

[0091] Step S300: depositing an anti-reflective coating on the second surface of the silicon substrate to complete the preparation of the metasurface.

[0092] For example, first, a catenary periodic structure is prepared on a smooth silicon substrate by combining laser direct writing with inductively coupled plasma reactive ion etching (ICP-RIE); then, a 100 nm thick VO film is deposited on the silicon nanostructure by pulsed laser deposition (PLD); finally, an anti-reflective coating is deposited on the back of the substrate by sputtering to optimize the optical performance.

[0093] In an optional embodiment, the period range of the catenary structure in the first direction is (λ 0 / 3, 2λ 0 ), the period range of the catenary structure in the second direction is (λ 0 / 6,λ 0 ), the thickness range of the catenary structure in the third direction is (λ 0 / 10,λ 0 ), where λ 0 is the central wavelength of light.

[0094] In an optional embodiment, the phase change material includes a volatile phase change material, and the thickness of the phase change material along the third direction ranges from (100 nm to 300 nm).

[0095] The metasurface device provided in the embodiment of the present application achieves efficient multifunctional optical regulation and laser protection effects by combining the silicon catenary periodic structure with phase change materials (such as VO). The metasurface preparation method provided in the embodiment of the present application ensures the high precision, high performance and structural stability of the device.

[0096] Functionally, the metasurface provided in the embodiment of the present application exhibits non-reciprocal transmission performance in a wide band and wide power range. The applicable range of non-reciprocal power is extended to 3 orders of magnitude through temperature control, while achieving efficient polarization conversion and beam deflection. In addition, the metasurface overcomes the limited protection power range and reflected light interference problems of traditional phase change schemes. It can filter external lasers through wavelength and polarization selection mechanisms at low power, effectively block reverse lasers within the phase change power range, and protect its own lasers through structural damage at high power. Based on weak resonant structures and thermal control, the device further improves high-power tolerance and environmental adaptability.

[0097] In summary, the metasurface device provided in the embodiments of the present application combines geometric phase design with the characteristics of phase change materials, which not only realizes efficient, broadband, and wide-angle optical regulation, but also provides new solutions for laser protection, optical isolators, and dynamic optical devices, and has broad application prospects.

[0098] In this article, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0099] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A metasurface, characterized in that: The super surface comprises: a silicon substrate, a silicon catenary structure having a plurality of silicon arc surfaces, and a phase change material; The silicon catenary structure formed by periodically arranging a plurality of silicon arc surfaces in a first direction and a second direction is etched on the first surface of the silicon substrate; wherein each of the silicon arc surfaces is symmetrical with the axis where the vertex in the second direction is located as the symmetry axis; The phase change material is deposited on the end surface of the silicon arc surface in the third direction; wherein, when light is transmitted to the silicon catenary structure on which the phase change material is deposited, it is modulated to propagate in one direction; The third direction intersects with a plane defined by the first direction and the second direction.

2. The supersurface according to claim 1, characterized in that The thickness of the catenary structure in the third direction, the period of the catenary structure in the first direction, and the period of the catenary structure in the second direction are related to the central wavelength of the light.

3. The supersurface according to claim 2, characterized in that The period range of the catenary structure in the first direction is (λ0 / 3, 2λ0), the period range of the catenary structure in the second direction is (λ0 / 6, λ0), and the thickness range of the catenary structure in the third direction is (λ0 / 10, λ0); wherein λ0 is the central wavelength of the light.

4. The supersurface according to claim 1, characterized in that A portion of the cross section of the silicon arc surface on the plane formed by the first direction and the second direction is y(x)=P x / π·ln|sec(πx / P x )|; where P x is the period of the catenary structure in the first direction.

5. The supersurface according to claim 1, characterized in that The sizes of the silicon arc surface in the second direction are the same, or the sizes of the silicon arc surface in the second direction decrease uniformly from the vertex to both sides.

6. The supersurface according to claim 1, characterized in that The thickness of the phase change material along the third direction ranges from (100 nm to 300 nm).

7. The supersurface according to claim 1, characterized in that The phase change material includes a volatile phase change material.

8. A method for preparing a super surface, characterized in that: The super surface preparation method comprises: Etching a plurality of silicon arc surfaces periodically arranged in a first direction and a second direction on a first surface of a silicon substrate to form a silicon catenary structure; wherein each of the silicon arc surfaces is symmetrical with the axis where the vertex in the second direction is located as the symmetry axis; Depositing a phase change material on the end surface of the silicon arc surface in the third direction; An anti-reflective coating is deposited on the second surface of the silicon substrate to complete the preparation of the metasurface.

9. The metasurface according to claim 8, characterized in that The period range of the catenary structure in the first direction is (λ0 / 3, 2λ0), the period range of the catenary structure in the second direction is (λ0 / 6, λ0), and the thickness range of the catenary structure in the third direction is (λ0 / 10, λ0); wherein λ0 is the central wavelength of the light.

10. The supersurface according to claim 8, characterized in that The phase change material includes a volatile phase change material, and a thickness of the phase change material along the third direction ranges from (100 nm to 300 nm).

Images