Metasurface based on spin decoupling and preparation method thereof

Abstract

The invention provides a metasurface based on spin decoupling and a preparation method thereof. The metasurface comprises a substrate layer and a plurality of rectangular nano columns located on the substrate layer. Wherein the lengths, the widths and the rotation angles of the rectangular nano-columns are different, and the rectangular nano-columns have high transmittance and [0, 2pi] all-phase coverage and meet the conditions of a half-wave plate; the plurality of rectangular nanorods regulate and control the left-handed circularly polarized light and the right-handed circularly polarized light through a preset phase, so that a preset function is realized; the preset phase comprises a propagation phase and a geometric phase. According to the metasurface provided by the invention, the substrate layer and the rectangular nanorod array with various sizes and different rotation angles are fused, so that accurate and independent phase regulation and control on the circular polarization state of incident light are realized, and the constraint of mutual interference of spinning states in a traditional optical element is thoroughly eliminated; different circularly polarized light signals can be distinguished and independently processed under a single wavelength, and the optical regulation degree of freedom is shown.

Description

Technical Field

[0001] This application relates to the field of micro-nano photonics, and particularly to a metasurface based on spin decoupling and a preparation method thereof. Background Art

[0002] With the rapid development of information technology, the functional diversity and intelligent level of optical components have become key factors driving the development of science and technology. Although traditional optical systems play an important role in the fields of imaging and image processing, they highly rely on complex lens combinations and optical filter designs, which not only increase the construction difficulty and cost burden of the system, but also severely restrict their further expansion in application scenarios that pursue high-speed response and high integration. Therefore, exploring new optical materials and structures to achieve more functional and more compact optical systems has become one of the hotspots in current optical research.

[0003] In this context, metasurface technology stands out with its unique advantages. As an artificial "optical antenna" array formed by carefully arranging sub-wavelength-scale microstructural units on a two-dimensional plane, a metasurface can manipulate key properties of electromagnetic waves such as polarization, phase, amplitude, and even frequency with unprecedented precision and flexibility. This physical mechanism endows metasurfaces with great application potential in the fields of optical computing, imaging processing, etc., and opens up a new path for the integration, miniaturization, and even functional customization of optical components.

[0004] In particular, the metasurface design based on spin decoupling makes it possible to diversify and dynamically switch optical functions. The spin decoupling technology allows independent and flexible control of the response of the metasurface to different light fields by regulating the spin state of the incident light (such as left-handed and right-handed circularly polarized light), thereby realizing instant switching of various optical functions such as focusing imaging and edge detection. This feature not only greatly broadens the application scenarios of metasurfaces, but also lays a solid foundation for the intelligent and dynamic regulation of optical systems. In addition, spin-decoupled metasurfaces also serve as an ideal platform to support the construction of complex and efficient optical diffraction neural networks, which show excellent performance in advanced computing tasks such as image classification and target recognition, indicating infinite possibilities in the fields of optical information processing, optical computing, and even the intersection of artificial intelligence and photonics.

[0005] However, the current development of spin-decoupled metasurface technology still faces challenges. A single phase modulation method is insufficient in breaking the inherent constraints of the spin state response in traditional optical elements. Although the combined phase method offers the possibility of realizing spin-decoupled metasurfaces, it often encounters technical bottlenecks such as low efficiency in practical applications, which limits the wide application of metasurface technology in more complex scenarios with high-performance requirements. Therefore, further optimizing the spin-decoupling mechanism and improving the conversion efficiency and performance stability of metasurfaces have become important research directions and the key to promoting the continuous innovation and in-depth application of optical technology.

[0006] The content in the background art section is only the technology known to the inventor and does not necessarily represent the prior art in this field. Summary of the Invention

[0007] The present invention aims to propose an efficient spin-decoupled based metasurface and its preparation method, which can intelligently distinguish and respond to left-handed circularly polarized light and right-handed circularly polarized light at a single wavelength, respectively realizing different functions. It can not only greatly simplify the structure of the optical system, reduce the number and volume of optical elements, but also completely break the fixed mode and mirror constraint of the spin state response in traditional optical elements, significantly improving the efficiency and flexibility of image processing.

[0008] According to one aspect of the present application, a preparation method of a spin-decoupled based metasurface is proposed, which is characterized by comprising:

[0009] S1: Construct a structural unit library applicable to linearly polarized incident light in the x and y directions of the three-dimensional coordinate system xyz; each structural unit in the structural unit library includes a substrate and rectangular nanocolumns with different lengths and widths, the rectangular nanocolumns have high transmittance, full phase coverage of [0, 2π], and meet the half-wave plate condition, and the materials of the substrate and the rectangular nanocolumns are determined according to the preset function of the metasurface;

[0010] S2: Determine the target phase distribution of the target rectangular nanocolumns according to the preset function; the target phase distribution includes the length and width distribution of propagation phase regulation and the angle distribution of geometric phase regulation;

[0011] S3: According to the structural unit library and the target phase distribution, construct the mapping relationship between the target position of the target rectangular nanocolumns and their lengths, widths, and rotation angles, so as to obtain a metasurface model; and

[0012] S4: Based on the metasurface model, prepare the target rectangular nanocolumns on the target substrate to obtain the metasurface.

[0013] According to some embodiments, in step S1, the structural unit is simulated and optimized by the finite-difference time-domain method based on Maxwell's equations. Each structural unit in the structural unit library maintains the same parameters in the z direction of the three-dimensional coordinate system xyz, and the periods of each substrate in the structural unit library are the same.

[0014] According to some embodiments, step S1 includes:

[0015] Constructing a corresponding model and setting the parameter variation range in the finite-difference time-domain method, and respectively scanning the phase values and transmittance corresponding to the structural units with different size parameters under the incidence of linearly polarized light incident in the x and y directions; and

[0016] Taking high transmittance, full-phase coverage of [0, 2π], and meeting the half-wave plate condition as the evaluation criteria, and using the length and width of the rectangular nanorods as the set structural parameters, select the most suitable parameter combination from the scanning results to construct the structural unit library.

[0017] According to some embodiments, the preset function includes one or more of aggregation imaging, edge detection, image classification, and target recognition.

[0018] According to some embodiments, step S2 includes:

[0019] Obtaining the preset target phase of the left-handed circularly polarized light according to the preset function and the preset target phase of the right-handed circularly polarized light

[0020] According to the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light Calculate the phase distribution required for the target position; and

[0021] According to the phase distribution required for the target position, combined with the principles of propagation phase and geometric phase modulation, respectively obtain the length and width distributions of the propagation phase modulation and the angle distribution of the geometric phase modulation.

[0022] According to some embodiments, the preset target phase The preset target phase where λ 1 is the wavelength of the left-handed circularly polarized light, λ 2 is the wavelength of the right-handed circularly polarized light, r is the radius of the metasurface, f is the focal length of the metasurface, is the spiral phase of the metasurface.

[0023] According to some embodiments, step S3 includes:

[0024] According to the length and width distributions of the propagation phase modulation, by comparing the matching degrees of the structural units in the structural unit library with the required length and width at the target position, the structural unit with the smallest absolute value of the phase difference is selected, thereby constructing the mapping relationship between the target position and the length and width of the target rectangular nanocolumn; and

[0025] According to the angular distribution of the geometric phase modulation, calculate the rotation angle of the target rectangular nanocolumn at the target position, thereby constructing the mapping relationship between the target position and the rotation angle of the target rectangular nanocolumn to obtain the metasurface model.

[0026] According to some embodiments, in step S2, the target phase distribution further includes the length and width distributions of the resonance phase modulation;

[0027] Step S2 includes:

[0028] Obtain the preset target phase of the left-handed circularly polarized light according to the preset function and the preset target phase of the right-handed circularly polarized light

[0029] According to the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light Calculate the phase distribution required for the target position of the target rectangular nanocolumn; and

[0030] According to the phase distribution required for the target position, in combination with the modulation principles of the propagation phase, geometric phase, and resonance phase, respectively obtain the length and width distributions of the propagation phase modulation, the angular distribution of the geometric phase modulation, and the length and width distributions of the resonance phase modulation.

[0031] According to some embodiments, the preparation method further includes:

[0032] S5: Simulate the metasurface model to verify whether the metasurface model meets the preset function;

[0033] If not, adjust the mapping relationship so that the metasurface model meets the preset function.

[0034] According to another aspect of the present application, a metasurface based on spin decoupling is proposed, which is characterized by including:

[0035] A base layer; and

[0036] A plurality of rectangular nanocolumns located on the base layer;

[0037] Among them, the lengths, widths, and rotation angles of each of the multiple rectangular nanocolumns are different, and each has a high transmittance, full-phase coverage in [0, 2π], and satisfies the half-wave plate condition;

[0038] The multiple rectangular nanocolumns regulate left-handed circularly polarized light and right-handed circularly polarized light through a preset phase, thereby realizing a preset function; the preset phase includes a propagation phase and a geometric phase.

[0039] According to some embodiments, the heights of each of the multiple rectangular nanocolumns are the same, and the spacing between any two adjacent rectangular nanocolumns is equal.

[0040] According to some embodiments, the preset phase further includes a resonance phase.

[0041] According to some embodiments, the metasurface is a multi-layer structure.

[0042] According to some embodiments, the base layer is made of a high-transmittance material, and the multiple rectangular nanocolumns are made of a semiconductor material and / or a metal material.

[0043] The metasurface based on spin decoupling proposed by the present invention innovatively integrates a base layer and a rectangular nanocolumn array with diverse sizes and different rotation angles. It realizes precise and independent phase regulation of the circular polarization state of incident light, completely getting rid of the bondage of mutual interference of spin states in traditional optical elements. The metasurface provided by the present invention can distinguish and independently process different circularly polarized light signals at a single wavelength, demonstrating the degree of freedom of optical regulation. Moreover, the rectangular nanocolumn array satisfies the half-wave plate condition, ensuring high conversion efficiency and effectively overcoming the problem of low efficiency of traditional combined-phase metasurfaces, bringing great performance improvement to fields such as optical information processing, optical communication, optical computing, and optical neural networks.

[0044] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without exceeding the scope required to be protected by the present application.

[0046] Figure 1 Shows a process flow chart of the preparation of the metasurface based on spin decoupling provided by an embodiment of the present invention.

[0047] Figure 2 andFigure 3 The front view and top view of the structural unit provided by an embodiment of the present invention are shown.

[0048] Figure 4 It is a schematic diagram of the transmittance and phase scanning of the structural unit suitable for the incidence of linearly polarized light in the x direction provided by an embodiment of the present invention.

[0049] Figure 5 It is a schematic diagram of the transmittance and phase scanning of the structural unit suitable for the incidence of linearly polarized light in the y direction provided by an embodiment of the present invention.

[0050] Figure 6 It is the phase distribution required at the target position of the target rectangular nanorod under left-handed and right-handed circularly polarized light provided by an embodiment of the present invention.

[0051] Figure 7 It is the target phase distribution of propagation phase modulation and the angular distribution of geometric phase modulation provided by an embodiment of the present invention.

[0052] Figure 8 It is a partially enlarged view of the metasurface model provided by an embodiment of the present invention.

[0053] Figure 9 The process flow chart of the preparation of the metasurface based on spin decoupling provided by an embodiment of the present invention is shown.

[0054] Figure 10 The schematic diagram of the near-field phase distribution of the metasurface under left-handed and right-handed circularly polarized light provided by an embodiment of the present invention is shown.

[0055] Figure 11 The intensity distribution diagrams of the metasurface in the x-z plane and the x-y plane under left-handed circularly polarized light provided by an embodiment of the present invention are shown.

[0056] Figure 12 The intensity distribution diagrams of the metasurface in the x-z plane and the x-y plane under right-handed circularly polarized light provided by an embodiment of the present invention are shown. Detailed implementation manners

[0057] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present application.

[0058] In addition, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of the embodiments of the present application. However, those skilled in the art will realize that the technical solutions of the present application can be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, well-known methods, devices, implementations, or operations are not shown or described in detail to avoid obscuring aspects of the present application.

[0059] The block diagrams shown in the drawings are only functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0060] The flowcharts shown in the drawings are only illustrative and do not necessarily include all the contents and operations / steps, nor are they necessarily executed in the described order. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to the actual situation.

[0061] It should be understood that although terms such as first, second, and third may be used herein to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another. Therefore, the first component discussed below can be referred to as the second component without departing from the teachings of the concept of the present application. As used herein, the term "and / or" includes any one of the associated listed items and all combinations of one or more of them.

[0062] Specific implementation manners can refer to the following embodiments.

[0063] Figure 1 A preparation method of a metasurface based on spin decoupling provided by an embodiment of the present invention is shown. As Figure 1 shown, the preparation method includes steps S1 to S4.

[0064] S1: Construct a structural unit library suitable for linearly polarized incident light in the x and y directions of a three-dimensional coordinate system xyz.

[0065] Among them, each structural unit in the structural unit library includes a substrate and rectangular nanocolumns with different lengths and widths, and has high transmittance, full phase coverage of [0, 2π], and meets the half-wave plate condition.

[0066] Figure 2 and Figure 3The structural unit provided by an embodiment of the present invention is shown, and the structural unit includes a substrate and rectangular nanocolumns located on the substrate.

[0067] The materials of the substrate of the structural unit and the materials of the rectangular nanocolumns need to be determined according to the preset function of the metasurface. In Figure 2 and Figure 3 the shown embodiment, the preset function is switchable aggregation imaging and edge detection, the selected substrate is Al 2 O 3 substrate, and the rectangular nanocolumns are rectangular GaN nanocolumns. In the present invention, the preset function may include one or more of aggregation imaging, edge detection, image classification, and target recognition, and can be applied to fields such as optical information processing, optical communication, optical computing, and optical neural networks. In the present invention, the substrate can be made of other high transmittance materials (such as SiO 2 ), the rectangular nanocolumns can be made of other semiconductor materials (such as TiO 2 , Si, SiN), the rectangular nanocolumns can also be made of metal materials (such as Cu), and of course, a composite of multiple materials can also be used. The materials selected for the rectangular nanocolumns need to achieve full phase coverage of [0, 2π], and preferably have a very high transmission efficiency in the entire visible light band.

[0068] In the present invention, the lengths and widths of the rectangular nanocolumns in each structural unit are not the same. The finite-difference time-domain method (FDTD) based on Maxwell's equations can be used for simulation and optimization to construct a structural unit library.

[0069] Optionally, step S1 includes:

[0070] Construct a corresponding model in FDTD and set the parameter variation range, and scan the phase values and transmittances corresponding to the structural units with different size parameters under the incidence of linearly polarized light incident in the x and y directions respectively; and

[0071] Taking high transmittance, full phase coverage of [0, 2π], and meeting the half-wave plate condition as the evaluation criteria, and taking the lengths and widths of the rectangular nanocolumns as the set structural parameters, select the most suitable parameter combination from the scanning results to construct a structural unit library.

[0072] Specifically, according to the determined substrate and the material of the rectangular nanorods, a corresponding model can be constructed in FDTD and the parameter variation range can be set. The phase values and transmittance corresponding to the unit structures with different size parameters are scanned respectively under the incidence of linearly polarized light in the x and y directions (hereinafter simply referred to as x-polarized light and y-polarized light). Here, the parameter variation range is the length l and width w of the rectangular nanorods. Optionally, in the present invention, each structural unit in the structural unit library maintains the same parameters in the z direction of the three-dimensional coordinate system xyz, and the periods of each substrate in the structural unit library are the same, that is, the period P x 、P y and the height as well as the height h of the rectangular nanorods are all fixed values.

[0073] According to the principle of photon spin separation, in order to make the additional phases generated by the left-handed circularly polarized light (LCP) and the right-handed circularly polarized light (RCP) through the metasurface conjugate with each other, each structural unit of the metasurface needs to satisfy the half-wave plate condition, that is, δ x -δ y =π. Wherein, δ x and δ y are the phase responses of the structural unit to the polarization in the x and y directions respectively.

[0074] Optionally, in the specific operation, first, at a predetermined wavelength, the rectangular nanorods within a certain length and width range under the incidence of x-polarized light and y-polarized light are finely scanned to obtain their phase and transmittance distributions. Figure 4 and Figure 5 respectively show the changes in the phase and transmittance corresponding to the unit columns with different lengths and widths under x-polarized light and y-polarized light. Subsequently, according to the scanning results, taking high transmittance (>90%), full phase coverage ([0, 2π]) and satisfying the half-wave plate condition (the absolute value of the phase difference between x-polarized light and y-polarized light is π) as the evaluation criteria, the appropriate parameter combination is determined, so as to obtain the required structural unit library.

[0075] S2: Determine the target phase distribution of the target rectangular nanorods according to the preset function.

[0076] The present invention realizes the independent regulation of the phases of LCP and RCP on the metasurface through the spin decoupling technology, and constructs the positive and negative point spread function (PSF) components respectively.

[0077] If the length and width of the structural unit remain unchanged, the additional phases conjugated by the left and right spin components of the outgoing light cannot be independently regulated. The present invention realizes spin decoupling by combining the rotation-related geometric phase and the size-related propagation phase, and the target phase distribution includes the length and width distributions of the propagation phase regulation and the angle distribution of the geometric phase regulation.

[0078] Optionally, step S2 includes:

[0079] Obtain the preset target phase of the left-handed circularly polarized light according to the preset function and the preset target phase of the right-handed circularly polarized light

[0080] According to the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light Calculate the phase distribution required for the target position of the target rectangular nanorod; and

[0081] According to the phase distribution required for the target position, combined with the propagation phase and geometric phase modulation principles, obtain the length and width distributions of the propagation phase modulation and the angle distribution of the geometric phase modulation respectively.

[0082] Optionally, for LCP, the preset target phase As shown in formula (1), is consistent with the phase of the metalens; for RCP, the preset target phase As shown in formula (2), in addition to the metalens phase, a helical phase is added

[0083]

[0084] where, λ 1 is the wavelength of the left-handed circularly polarized light, λ 2 is the wavelength of the right-handed circularly polarized light, r is the radius of the metasurface, f is the focal length of the metasurface, is the helical phase of the right-handed circularly polarized light. The helical phase can be obtained according to the preset function of the metasurface.

[0085] The present invention adds a unique helical phase distribution to the RCP incidence, and this phase characteristic is associated with the generation of vortex light, enabling the metasurface to have a unique light field modulation ability.

[0086] Specifically, the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light can be obtained first according to the preset function through the above formulas (1) and (2) and the preset target phase of the right-handed circularly polarized light Then, according to the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light Calculate the phase distribution required for each target position (as Figure 6 shown, Figure 6 the left side corresponds to LCP, and the right side corresponds to RCP). Subsequently, combined with the propagation phase and geometric phase modulation principles, calculate the target phase distribution (length and width distributions) of the propagation phase modulation and the angle distribution of the geometric phase modulation respectively, as Figure 7 shown(Figure 7 The left side corresponds to LCP, and the right side corresponds to RCP).

[0087] Optionally, in the present invention, the target phase distribution further includes the length and width distributions of the resonant phase regulation. At this time, step S2 may include:

[0088] Obtaining the preset target phase of the left-handed circularly polarized light according to the preset function and the preset target phase of the right-handed circularly polarized light

[0089] According to the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light Calculating the phase distribution required for the target position of the target rectangular nanorod; and

[0090] According to the phase distribution required for the target position, combining the regulation principles of the propagation phase, geometric phase, and resonant phase, respectively obtaining the length and width distributions of the propagation phase regulation, the angular distribution of the geometric phase regulation, and the length and width distributions of the resonant phase regulation.

[0091] The present invention can be combined only with the geometric phase and propagation phase modulation as needed, or combined with the geometric phase, propagation phase, and resonant phase for joint modulation.

[0092] S3: According to the structural unit library and the target phase distribution, constructing the mapping relationship between the target position of the target rectangular nanorod and its length, width, and rotation angle, so as to obtain the metasurface model.

[0093] Optionally, step S3 includes:

[0094] According to the length and width distributions of the propagation phase regulation, by comparing the matching degree between the structural units in the structural unit library and the required length and width of the target position, screening out the structural unit with the smallest absolute value of the phase difference, so as to construct the mapping relationship between the target position of the target rectangular nanorod and its length and width; and

[0095] According to the angular distribution of the geometric phase regulation, calculating the rotation angle of the target rectangular nanorod at the target position, so as to construct the mapping relationship between the target position of the target rectangular nanorod and its rotation angle to obtain the metasurface model.

[0096] In specific operations, first, according to the target phase distribution required for propagation phase modulation, advanced algorithms can be used to accurately screen structural units in the structural unit library, aiming to minimize the error between the actual phase and the target phase, and accordingly determine the length and width dimensions of the target positions of each rectangular nanocolumn; then, according to the angular requirements of geometric phase modulation, clarify the rotation angle of the rectangular nanocolumn at each target position; finally, comprehensively consider the length and width dimensions and rotation angles of each target position, determine the overall layout of the metasurface, and draw it into a layout, so as to obtain a metasurface model, and its partial enlarged view is as shown in Figure 8 shown. In this process, manufacturing tolerances and process limitations are fully considered, and necessary fine-tuning is performed on the metasurface model to ensure accuracy and consistency during the manufacturing process.

[0097] S4: Based on the metasurface model, prepare the target rectangular nanocolumns on the target substrate to obtain the metasurface.

[0098] Here, the materials of the target substrate and the target rectangular nanocolumns are the same as those of the substrate and the rectangular nanocolumns in the previous step S1. This step can use various techniques such as metalorganic chemical vapor deposition technology, hard mask deposition method, etching, inductively coupled plasma reactive etching technology, etc. to prepare the metasurface, which will not be elaborated here.

[0099] Optionally, as shown in Figure 9 shown, before step S4, the present invention can also include step S5:

[0100] Simulate the metasurface model to verify whether the metasurface model meets the preset function;

[0101] If not, adjust the mapping relationship to make the metasurface model meet the preset function.

[0102] In one embodiment, a metasurface model capable of realizing edge detection function is designed, which consists of a left-handed / right-handed circularly polarized light source, an Al 2 O 3 substrate, a GaN metasurface, a point monitor, and a simulation model of a surface monitor. The FDTD is used to calculate the near-field distribution and far-field distribution characteristics of the metasurface under the action of left-handed circularly polarized light and right-handed circularly polarized light respectively. From the analysis of the near-field distribution, a significant phase modulation effect is observed (as shown in Figure 10 shown, Figure 10 the left side corresponds to LCP, and the right side corresponds to RCP): when LCP is incident, the metasurface exhibits a uniform phase distribution similar to that of a superlens, which is beneficial to the convergence of light; on the contrary, the RCP incidence induces a unique helical phase distribution, and this phase characteristic is associated with the generation of vortex light, indicating the unique light field modulation ability of the metasurface. Further analyze the far-field distribution, as shown in Figure 11As shown, under the incidence of LCP, the metasurface successfully achieved the focusing of light at the preset focal length, which verified its function as an efficient lens. Under the illumination of RCP, instead of forming a traditional focal point, the metasurface showed an edge enhancement phenomenon at the focal length (as shown in Figure 12 ), that is, the detection of the edge information of the incident light field was realized, and this characteristic has potential application value in the fields of optical imaging, information processing, etc.

[0103] The preparation method of the metasurface based on spin decoupling proposed by the present invention can not only achieve the functions of focusing imaging and edge detection for different circularly polarized lights respectively, but also be applied in the design of other metasurfaces, providing new design ideas and technical paths for the fields of optical information processing (optical computing encryption and information hiding, etc.), optical communication, optical computing, and optical neural networks.

[0104] The metasurface based on spin decoupling provided by the present invention includes:

[0105] A substrate layer; and

[0106] A plurality of rectangular nanocolumns located on the substrate layer.

[0107] Among them, the length, width, and rotation angle of each rectangular nanocolumn in the plurality of rectangular nanocolumns are different, and each has a high transmittance, full phase coverage of [0, 2π], and meets the half-wave plate condition; the plurality of rectangular nanocolumns regulate the left-handed circularly polarized light and the right-handed circularly polarized light through a preset phase, so as to achieve a preset function; the preset phase includes a propagation phase and a geometric phase.

[0108] The metasurface based on spin decoupling proposed by the present invention innovatively integrates a substrate layer with a rectangular nanocolumn array with various sizes and different rotation angles. It realizes precise and independent phase regulation of the circular polarization state of incident light, and completely gets rid of the bondage of mutual interference of spin states in traditional optical elements. The metasurface provided by the present invention can distinguish and independently process different circularly polarized light signals at a single wavelength, demonstrating the optical regulation freedom. Moreover, the rectangular nanocolumn array meets the half-wave plate condition, ensuring high conversion efficiency and effectively overcoming the problem of low efficiency of traditional combined phase metasurfaces, bringing great performance improvement to the fields of optical information processing, optical communication, and optical computing.

[0109] Optionally, the height of each rectangular nanocolumn in the plurality of rectangular nanocolumns is the same, and the distance between any two adjacent rectangular nanocolumns is equal.

[0110] Optionally, the preset phase further includes a resonance phase. With the addition of resonance phase regulation, the functions that the metasurface can achieve can be increased.

[0111] Optionally, the metasurface is a multi-layer structure. The structural unit can be designed as a multi-layer structure, with each layer containing nanostructures of different shapes, sizes or materials, so as to achieve more functions.

[0112] Optionally, the base layer is made of a material with high transmittance, and the plurality of rectangular nanocolumns are made of a semiconductor material and / or a metal material. The material selected for the rectangular nanocolumns needs to achieve full phase coverage in the range of [0, 2π], and preferably has a high transmission efficiency in the entire visible light band. The material with high transmittance can be, for example, Al 2 O 3 , SiO 2 etc., the semiconductor material can be, for example, GaN, TiO 2 , Si, SiN, etc., the metal material can be, for example, Cu, etc. Of course, other materials or composites of multiple materials can also be used, and they can be selected according to needs.

[0113] The metasurface provided by the present invention can be applied to fields such as optical information processing, optical communication, optical computing, and optical neural networks.

[0114] The above has introduced the embodiments of the present application in detail. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application. At the same time, changes or deformations made by those skilled in the art based on the idea of the present application, in terms of the specific implementation manner and application scope of the present application, all fall within the protection scope of the present application. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A method for preparing a metasurface based on spin decoupling, characterized in that: include: S1: Construct a library of structural units suitable for incident light with linear polarization in the x and y directions in the three-dimensional coordinate system xyz; Each structural unit in the structural unit library includes a substrate and rectangular nanocolumns with different lengths and widths, wherein the rectangular nanocolumns have high transmittance, [0,2π] full phase coverage, and meet half-wave plate conditions, and the materials of the substrate and the rectangular nanocolumns are determined according to the preset functions of the metasurface; S2: determining a target phase distribution of a target rectangular nanocolumn according to the preset function; the target phase distribution includes a length and width distribution of a propagation phase regulation and an angle distribution of a geometric phase regulation; S3: constructing a mapping relationship between the target position and the length, width, and rotation angle of the target rectangular nanocolumn according to the structural unit library and the target phase distribution, thereby obtaining a supersurface model; and S4: Based on the supersurface model, the target rectangular nanocolumns are prepared on a target substrate to obtain the supersurface.

2. The preparation method according to claim 1, characterized in that: In step S1, the structural unit is simulated and optimized using a time-domain finite difference method based on Maxwell's equations, each structural unit in the structural unit library maintains the same parameters in the z direction of the three-dimensional coordinate system xyz, and the period of each substrate in the structural unit library is the same.

3. The preparation method according to claim 2, characterized in that: Step S1 includes: Constructing a corresponding model and setting a parameter variation range in the finite difference time domain method, and scanning the phase values ​​and transmittances corresponding to the structural units with different size parameters under the incident light of linear polarization in the x and y directions respectively; and The structural unit library is constructed by using high transmittance, [0,2π] full phase coverage and meeting half-wave plate conditions as evaluation criteria, and the length and width of the rectangular nanorods as set structural parameters, selecting the most suitable parameter combination from the scanning results.

4. The preparation method according to claim 1, characterized in that: The preset functions include one or more of cluster imaging, edge detection, image classification and target recognition.

5. The preparation method according to claim 1, characterized in that: Step S2 includes: Obtaining a preset target phase of left-handed circularly polarized light according to the preset function and the preset target phase of right-handed circularly polarized light According to the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light calculating a phase distribution required for the target position; and According to the phase distribution required by the target position, combined with the propagation phase and geometric phase control principles, the length and width distribution of the propagation phase control and the angle distribution of the geometric phase control are obtained respectively.

6. The preparation method according to claim 5, characterized in that: The preset target phase The preset target phase Wherein, λ1 is the wavelength of the left-handed circularly polarized light, λ2 is the wavelength of the right-handed circularly polarized light, r is the radius of the metasurface, and f is the focal length of the metasurface. is the spiral phase of the right-handed circularly polarized light.

7. The preparation method according to claim 1, characterized in that: Step S3 includes: According to the length and width distribution of the propagation phase regulation, by comparing the matching degree between the structural units in the structural unit library and the length and width required by the target position, the structural unit with the smallest absolute value of the phase difference is screened out, thereby constructing a mapping relationship between the target position and the length and width of the target rectangular nanocolumn; and According to the angular distribution of the geometric phase regulation, the rotation angle of the target rectangular nanocolumn at the target position is calculated, so as to construct a mapping relationship between the target position and the rotation angle of the target rectangular nanocolumn to obtain the supersurface model.

8. The preparation method according to claim 1, characterized in that: In step S2, the target phase distribution also includes the length and width distribution of the resonance phase regulation; Step S2 includes: Obtaining a preset target phase of left-handed circularly polarized light according to the preset function and the preset target phase of right-handed circularly polarized light According to the preset target phase of the left-handed circularly polarized light and the preset target phase of the right-handed circularly polarized light Calculating a phase distribution required for a target position of the target rectangular nanorod; and According to the phase distribution required by the target position, combined with the control principles of propagation phase, geometric phase and resonance phase, the length and width distribution of the propagation phase control, the angle distribution of the geometric phase control, and the length and width distribution of the resonance phase control are obtained respectively.

9. The preparation method according to claim 1, characterized in that: Also includes: S5: simulating the hypersurface model to verify whether the hypersurface model satisfies the preset function; If not, the mapping relationship is adjusted so that the hypersurface model satisfies the preset function.

10. A metasurface based on spin decoupling, characterized in that: include: Basal layer; and A plurality of rectangular nanorods are located on the base layer; Wherein, each of the plurality of rectangular nanocolumns has different lengths, widths and rotation angles, and all have high transmittance, [0,2π] full phase coverage and meet half-wave plate conditions; The plurality of rectangular nanorods regulate left-handed circularly polarized light and right-handed circularly polarized light through a preset phase, thereby achieving a preset function; the preset phase includes a propagation phase and a geometric phase.

11. The supersurface according to claim 10, characterized in that The height of each rectangular nanocolumn in the plurality of rectangular nanocolumns is the same, and the spacing between any two adjacent rectangular nanocolumns is equal.

12. The supersurface according to claim 10, characterized in that The preset phase also includes a resonance phase.

13. The supersurface according to claim 10, characterized in that The super surface is a multi-layer structure.

14. The metasurface according to claim 10, characterized in that The base layer is made of a high-transmittance material, and the plurality of rectangular nanorods are made of a semiconductor material and / or a metal material.

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