Metasurface and polarization aberration compensation method based on refractive-metasurface hybrid design

Abstract

The present application belongs to the technical field of polarized optics, and particularly relates to a metasurface and a polarized aberration compensation method based on a refractive-metasurface hybrid design, comprising: S1: obtaining an optical system to be compensated; S2: performing parameter scanning on the metasurface; S3: obtaining a target phase of the metasurface; S4: obtaining a two-way attenuation and phase delay distribution of the polarized aberration at an exit pupil of the optical system to be compensated; S5: making a polarized aberration compensation function compensate the optical system to be compensated in terms of two-way attenuation and phase delay; S6: judging whether the two-way attenuation compensation result and the phase delay compensation result both satisfy respective preset values; S7: analyzing a wavefront phase distribution introduced by an anisotropic unit structure; and S8: making a sum of a phase of an isotropic unit structure and a phase of the anisotropic unit structure equal to the target phase of the metasurface. The present application proposes a polarized aberration compensation method for an optical system with high applicability and high degree of freedom.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of polarized optics, and particularly relates to a metasurface and a polarized aberration compensation method based on a refractive-metasurface hybrid design. BACKGROUND

[0002] In the field of modern optical applications, the propagation characteristics of polarized light play a key role in the performance of optical systems. When polarized light propagates in an optical system, the transmission coefficients of S light and P light at the medium surface of the optical system are different, and this difference will change to a certain extent each time the incident light passes through the medium due to the difference in incident angle and medium material. In the fields of ultra-high precision lithography, laser radar, target polarization characteristic measurement and laser communication, it is necessary to ensure the high polarization maintaining property of the optical system, and the polarization aberration of the optical system must be strictly controlled or compensated. Some scholars propose that the s polarization of the first mirror can be used to direct the p polarization of the second mirror to compensate for the polarization aberration of the folding mirror; some scholars also propose to combine reflective elements and refractive elements to compensate for polarization aberration. However, their methods have some shortcomings: they can compensate in their respective cases, but cannot be applied to other types of optical systems; the compensation effect is uncontrollable, and the focus of compensation cannot be flexibly adjusted according to the specific application scenario. However, there is currently a lack of a polarization aberration compensation method that can be widely applied to various optical systems, especially polarization-sensitive optical systems, which greatly limits the further development and application of related fields. Therefore, a universal polarization aberration compensation method is of great significance for various optical systems, especially polarization-sensitive optical systems. SUMMARY

[0003] Therefore, the present application aims to provide a metasurface and a polarization aberration compensation method based on a refractive-metasurface hybrid design to solve the problem of lack of universality of the polarization aberration compensation of the prior art for optical systems. The present application can be used to analyze and compensate for the polarization aberration of various types of optical systems. Whether the optical system is transmissive or reflective, coaxial or off-axis, centrally symmetric or non-centrally symmetric, the corresponding polarization aberration compensation can be achieved through metasurface design.

[0004] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0005] A metasurface, comprising: a substrate and isotropic unit structures and anisotropic unit structures arranged on both sides of the substrate, respectively; the substrate and the isotropic unit structures form an isotropic phase surface for correcting wavefront phase; and the substrate and the anisotropic unit structures form an anisotropic phase surface for compensating polarization aberration.

[0006] Further, the anisotropic unit structure is an array of a plurality of anisotropic units, and the isotropic unit structure is an array of a plurality of isotropic units.

[0007] A polarization aberration compensation method based on a refraction-hybrid metasurface design, realized by a metasurface, specifically comprising the following steps:

[0008] S1: obtaining an initial optical system, optimizing the wave aberration of the initial optical system based on optical software, and obtaining a to-be-compensated optical system;

[0009] S2: determining the shape of the anisotropic unit structure, performing parameter scanning on the anisotropic unit structure to obtain the P light phase, S light phase, and transmittance of the anisotropic unit structure and the structure parameter value, and performing parameter scanning on the isotropic unit structure to obtain the transmittance, structure parameter value, and phase value of the isotropic unit structure;

[0010] S3: placing the metasurface obtained in step S2 as a phase surface at the exit pupil of the to-be-compensated optical system for optimization to obtain a target phase of the metasurface;

[0011] S4: combining the imaging principle of the to-be-compensated optical system, performing full-aperture polarization ray tracing on the to-be-compensated optical system to obtain the distribution of the polarization aberration in the exit pupil of the to-be-compensated optical system;

[0012] S5: designing a polarization aberration compensation function of the metasurface, and adjusting the weight of the polarization aberration compensation function based on the distribution of the to-be-compensated optical system to make the polarization aberration compensation function compensate the to-be-compensated optical system for the diattenuation and phase delay;

[0013] S6: judging whether the diattenuation compensation result and the phase delay compensation result meet the respective preset values, if yes, executing step S7, otherwise executing step S2 to adjust the shape, material, and parameter scanning range of the anisotropic unit structure;

[0014] S7: analyzing the wavefront phase distribution introduced by the anisotropic unit structure;

[0015] S8: using the isotropic unit structure of the metasurface to compensate the wavefront phase introduced by the anisotropic unit structure, so that the sum of the phase of the isotropic unit structure and the phase of the anisotropic unit structure is equal to the target phase of the metasurface, and the polarization aberration compensation of the to-be-compensated optical system is realized.

[0016] Further, in step S4, based on the imaging principle of the optical system to be compensated, the optical system to be compensated is distinguished into a transmissive optical system and a reflective optical system, for the transmissive optical system, an anisotropic unit structure with a transmission coefficient of s-polarized light greater than a transmission coefficient of p-polarized light is selected to compensate for the two-way attenuation of the transmissive optical system; for the reflective optical system, an anisotropic unit structure with a reflection coefficient of s-polarized light less than a reflection coefficient of p-polarized light is selected to compensate for the two-way attenuation of the reflective optical system, and the anisotropic unit structure satisfies that a phase of s light is less than a phase of p light to compensate for the phase delay of the reflective optical system.

[0017] Further, in step S4, the polarization aberration compensation function is expressed as:

[0018] ;

[0019] wherein, is a weight factor, is a two-way attenuation compensation value of the metasurface, D is a two-way attenuation value at a pupil coordinate of the optical system to be compensated, is a phase delay compensation value of the metasurface, R is a phase delay value at a pupil coordinate of the optical system to be compensated.

[0020] Further, in step S8, the formula used for compensating the wavefront phase introduced by the anisotropic unit structure by using the isotropic unit structure is:

[0021] ;

[0022] wherein, represents the phase introduced by the anisotropic unit structure, represents the phase introduced by the isotropic unit structure, is an exit pupil normalized coordinate.

[0023] Further, in step S8, before compensating the wavefront phase introduced by the anisotropic unit structure by using the isotropic unit structure, the metasurface obtained in step S6 is placed at an exit pupil position of the optical system to be compensated, and a coordinate at the exit pupil position is normalized to obtain an exit pupil normalized coordinate, and the exit pupil normalized coordinate ranges in a circular area with (0, 0) as the center and a radius of 1.

[0024] Compared with the prior art, the present application can achieve the following beneficial effects:

[0025] (1) The super surface and the polarization aberration compensation method based on the refractive-super surface hybrid design can be widely applied to various optical systems such as transmission or reflection, coaxial or off-axis, central symmetry or non-central symmetry, etc. The super surface is formed by anisotropic unit structures, which is used for compensating polarization aberration of the optical system, and the super surface is integrated into the optical system to complete the design of the polarization aberration compensation super surface.

[0026] (2) The super surface and the polarization aberration compensation method based on the refractive-super surface hybrid design obtain the polarization aberration of the off-axis optical system through full-aperture polarization light tracing, and the polarization aberration is compensated by using anisotropic unit structures. It is verified that the anisotropic unit structure has good polarization response characteristics, and very good compensation effect is achieved. The polarization aberration compensation function F and the weight factor are defined in the application. By reasonably setting the weight of the polarization aberration compensation function, the average value of the diattenuation is reduced by 91.8%, and the average value of the phase retardation is reduced by 95.0%, so that the diattenuation and the phase retardation are finally compensated very well.

[0027] (3) The super surface and the polarization aberration compensation method based on the refractive-super surface hybrid design consider the influence of the phase introduced by the super surface on the wavefront phase. The application combines the polarization-sensitive cubic column structure and the polarization-insensitive cylindrical structure to form a new super surface, which compensates the polarization aberration of the optical system without affecting the wavefront phase of the optical system. In summary, the polarization aberration compensation super surface has the advantages of wide applicability, high degree of freedom and good compensation effect, greatly reduces the influence of polarization aberration on polarization detection, and provides an innovative solution for polarization aberration compensation problems of various optical systems. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the application and their description are used to explain the application without forming an improper limitation to the application. In the drawings:

[0029] Figure 1 The flowchart of the polarization aberration compensation method based on the refractive-super surface hybrid design described in the embodiments of the application is shown in the figure;

[0030] Figure 2 (a) is a point diagram of the optimized optical system to be compensated described in the embodiments of the application;

[0031] Figure 2 (b) is an MTF diagram of the optimized optical system to be compensated described in the embodiments of the application;

[0032] Figure 3A schematic diagram of an optical path structure of the metasurface to be compensated for according to an embodiment of the present application;

[0033] Figure 4 A schematic diagram of an anisotropic unit structure according to an embodiment of the present application;

[0034] Figure 5 A schematic diagram of an isotropic unit structure according to an embodiment of the present application;

[0035] Figure 6 A result diagram of a parameter scan of the isotropic unit structure according to an embodiment of the present application;

[0036] FIG. 7(a) is a bivariate attenuation distribution diagram before compensation according to an embodiment of the present application;

[0037] FIG. 7(b) is a bivariate attenuation distribution diagram after compensation according to an embodiment of the present application;

[0038] FIG. 7(c) is a bivariate attenuation average value compensation result diagram according to an embodiment of the present application;

[0039] FIG. 7(d) is a phase delay distribution diagram before compensation according to an embodiment of the present application;

[0040] FIG. 7(e) is a phase delay distribution diagram after compensation according to an embodiment of the present application;

[0041] FIG. 7(f) is a phase delay average value compensation result diagram according to an embodiment of the present application;

[0042] Figure 8 A metasurface structure diagram generated by combining an anisotropic unit and an isotropic unit according to an embodiment of the present application;

[0043] Figure 9 A result obtained by parameter scanning of the anisotropic structure according to an embodiment of the present application;

[0044] Figure 10 A schematic diagram of a laser communication system according to an embodiment of the present application;

[0045] Figure 11 A result diagram obtained by analyzing a field of view according to an embodiment of the present application.

[0046] Explanation of reference signs:

[0047] 1, optical system to be compensated for; 2, metasurface; 3, receiving system; 4, laser; 5, detector; 21, substrate; 22, isotropic unit structure; 23, anisotropic unit structure. DETAILED DESCRIPTION

[0048] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not constitute a limitation on the present application.

[0049] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0050] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0051] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0052] The present application will be described in detail below with reference to the drawings and embodiments.

[0053] The present application proposes a metasurface 2, comprising: a substrate 21 and isotropic unit structures 22 and anisotropic unit structures 23 arranged on both sides of the substrate 21 respectively, the substrate 21 and the isotropic unit structures 22 constitute an isotropic phase surface for correcting wavefront phase; the substrate 21 and the anisotropic unit structures 23 constitute an anisotropic phase surface for compensating polarization aberration.

[0054] In some embodiments, the anisotropic unit structures 23 are an array of a plurality of anisotropic units, and the isotropic unit structures 22 are an array of a plurality of isotropic units.

[0055] It should be noted that the substrate 21 is made of a high-transmittance material corresponding to the wavelength band of the optical system, and the material is generally silicon, silicon dioxide, etc. The anisotropic unit structure 23 is an array composed of a plurality of anisotropic units, and the anisotropic unit is a columnar structure in the shape of a rectangle or an ellipse, etc. This type of structure is sensitive to polarization. The isotropic unit structure 22 is an array composed of a plurality of isotropic structures, and the isotropic structure is a columnar structure in the shape of a circle. This type of structure is not sensitive to polarization. The number of the anisotropic unit structure 23 and the isotropic unit structure 22 is determined according to the aperture size of the optical system 1 to be compensated. The unit structure (the anisotropic unit structure 23 and the isotropic unit structure 22) is in the nanometer level. The larger the exit pupil of the optical system 1 to be compensated is, the more the number of the unit structure will be.

[0056] The isotropic unit structure 22 which is not sensitive to polarization is used to compensate for the wavefront phase introduced by the anisotropic unit structure 23. The purpose is to eliminate the influence of the metasurface 2 on the wavefront phase of the optical system 1 to be compensated. The size and distribution of the phase introduced by the isotropic unit structure 22 which is not sensitive to polarization are determined according to the specific optical system 1 to be compensated. In general, the phase of the metasurface 2 is equal to the target phase.

[0057] Further, the anisotropic unit structure 23 can be composed of a rectangular columnar structure, and the isotropic unit structure 22 can be composed of a circular columnar structure. The present application not only includes the structure of the rectangular columnar structure + the circular columnar structure, but also includes any structure which can compensate for the polarization aberration of various optical systems by combining the anisotropic structure (such as the rectangular columnar structure, the elliptical columnar structure, etc.) with the isotropic structure (such as the circular columnar structure, etc.). In addition, in order to reduce the volume and achieve high integration, the present application arranges the two unit structures on the two sides of the substrate 21. As long as the metasurface 2 composed of the anisotropic unit structure 23 (such as a rectangle, an ellipse, etc.) and the isotropic unit structure 22 (such as a circle, etc.) can compensate for the polarization aberration of the optical system, it is within the protection scope of the present application.

[0058] As shown in Figure 1 The present application proposes a polarization aberration compensation method based on a refractive-metasurface 2 hybrid design, which is realized by using the metasurface 2 and specifically includes the following steps:

[0059] S1: Obtain an initial optical system, and optimize the wave aberration of the initial optical system based on optical software. The optimization result is shown in FIG. 2 (a), FIG. 2 (b) and Figure 3 FIG. 3 (a) and FIG. 3 (b), to obtain the optical system 1 to be compensated.

[0060] S2: determine the shape of the anisotropic unit structure 23, perform parameter scanning on the anisotropic unit structure 23 to obtain the P light phase, the S light phase, the transmittance and the structure parameter value of the anisotropic unit structure 23, and perform parameter scanning on the isotropic unit structure 22 to obtain the transmittance, the structure parameter value and the phase value of the isotropic unit structure 22;

[0061] The anisotropic unit structure 23 exhibits in Figure 4 The isotropic unit structure 22 exhibits in Figure 5 The result of the parameter scanning of the isotropic unit structure 22 is shown in Figure 6 .

[0062] S3: place the metasurface 2 obtained in step S2 as a phase plane at the exit pupil of the optical system to be compensated 1 for optimization to obtain the target phase of the metasurface 2;

[0063] S4: combine the imaging principle of the optical system to be compensated, perform full-aperture polarized light ray tracing on the optical system to be compensated 1 to obtain the distribution of the polarization aberration birefringence and phase delay at the exit pupil of the optical system to be compensated 1;

[0064] S5: design a polarization aberration compensation function of the metasurface 2, and adjust the weight of the polarization aberration compensation function based on the distribution of the birefringence and phase delay of the optical system to be compensated 1, so that the polarization aberration compensation function compensates the birefringence and phase delay of the optical system to be compensated 1, and the analysis of the compensation result is shown in Figs. 7(a)-7(f);

[0065] S6: determine whether the birefringence compensation result and the phase delay compensation result meet the respective preset values (set according to actual needs), if yes, execute step S7, otherwise execute step S2 to adjust the shape, material and parameter scanning range of the anisotropic unit structure 23;

[0066] S7: analyze the wavefront phase distribution introduced by the anisotropic unit structure 23;

[0067] S8: use the isotropic unit structure 22 of the metasurface 2 to compensate the wavefront phase introduced by the anisotropic unit structure 23, so that the sum of the phase of the isotropic unit structure 22 and the phase of the anisotropic unit structure 23 is equal to the target phase of the metasurface 2, realizing the polarization aberration compensation of the optical system to be compensated 1, and the structure of the metasurface 2 composed of the two is shown in Figure 8 .

[0068] It should be noted that the substrate 21 is used to construct the metasurface 2, the arrayed anisotropic units are used to compensate the polarization aberration of the optical system, and the arrayed isotropic units are used to correct the wavefront destroyed by the phase introduced by the anisotropic units. The present application proposes a refractive-metasurface 2 hybrid design for compensating the polarization aberration, which combines the anisotropic unit structure 23 and the isotropic unit structure 22, improves the compensation effect of the polarization aberration of the optical system, and provides a new solution for the polarization aberration compensation of various optical systems.

[0069] The operation flow of the present application is divided into two parts: polarization aberration compensation and wavefront phase compensation.

[0070] Polarization aberration compensation: first, the initial optical system is optimized to achieve the optimal wave aberration, and the result of the optical system to be compensated 1 is obtained and fixed; then the difference in polarization response of the anisotropic unit to S light and P light is obtained by scanning, and the two-way attenuation compensation effect and the phase delay compensation effect corresponding to the anisotropic unit structure 23 of different sizes are obtained. Next, the polarization light tracing of the optical system to be compensated 1 is performed to obtain the two-way attenuation and phase delay distribution of the polarization aberration at the exit pupil of the optical system to be compensated 1; then the weight factor of the polarization aberration compensation function is adjusted to obtain the wavefront phase distribution of the anisotropic unit structure 23 for compensating the two-way attenuation and the phase delay, and it is judged whether the compensation effect meets the requirements.

[0071] Wavefront phase compensation: first, analyze the phase distribution introduced by the anisotropic unit structure 23, and the ideal phase distribution of the metasurface 2 in the optical system to be compensated 1; then obtain the corresponding relationship between the structure parameters of the isotropic unit structure 22 and the wavefront phase introduced by the anisotropic unit structure 23 by scanning; use the isotropic unit structure 22 to compensate the wavefront phase introduced by the anisotropic unit structure 23 to the target phase distribution; then optimize and analyze the whole optical system to be compensated 1 to complete all the processes.

[0072] In addition, in step S1, the optical software can use Zemax or CodeV; in step S2, the parameter scanning can use Comsol or FDTD software, and the structure parameters include height and radius parameters; in step S3, the software used for optimization is Zemax or CodeV; in step S7, the analysis of the wavefront phase distribution introduced by the anisotropic unit structure 23 belongs to the prior art, and will not be described hereinafter.

[0073] In some embodiments, in step S4, based on the imaging principle of the optical system 1 to be compensated, the optical system 1 to be compensated is distinguished into a transmissive optical system and a reflective optical system, for the transmissive optical system, the anisotropic unit structure 23 with the transmittance of s-polarized light being greater than the transmittance of p-polarized light is selected to compensate for the diattenuation of the transmissive optical system; for the reflective optical system, the anisotropic unit structure 23 with the reflectance of s-polarized light being less than the reflectance of p-polarized light is selected to compensate for the diattenuation of the reflective optical system, and the anisotropic unit structure 23 satisfies that the phase of s-light is less than the phase of p-light to compensate for the phase delay of the reflective optical system.

[0074] Further, the optical system 1 to be compensated also includes a catadioptric optical system, for the catadioptric optical system, the diattenuation and phase delay directions of the refractive part and the reflective part are analyzed respectively, since the diattenuation directions of the two are opposite, it is judged which component is larger, and the final direction of the diattenuation and the phase delay is the same as the direction of the larger component.

[0075] It should be noted that the polarization state of light is defined using Stokes vector, and the change of polarization characteristics of light passing through an optical system is described using Mueller matrix. The expression of Stokes vector is as follows: , represents the sum of horizontal polarization component and vertical polarization component, represents the difference between horizontal polarization component and vertical polarization component, represents the difference between 45° and 135° polarization components, represents the difference between right circular polarization and left circular polarization components.

[0076] The Mueller matrix of an optical system can be expressed as follows:

[0077] ;

[0078] The Stokes vectors before and after passing through the optical system satisfy the following relationship: , wherein represents the Stokes vector of incident light, represents the Stokes vector of outgoing light.

[0079] The Mueller matrix of an ideal optical system should be a unit matrix, so as to ensure that the polarization state of incident light is the same as that of outgoing light, i.e. the polarization state of incident light does not change, however, almost all optical systems contain polarization aberration, which cannot be completely eliminated in the design stage, and therefore needs to be compensated.

[0080] According to the Fresnel law, the reflectance and refractive index of s-polarized light and p-polarized light can be expressed as:

[0081] ;

[0082] wherein, Rsis the reflectivity of s-polarized light; Rpis the reflectivity of p-polarized light; Tsis the transmissivity of s-polarized light; Tpis the transmissivity of p-polarized light; is the incident angle; is the refracted angle. The difference of the reflection and transmission coefficients of s and p light changes the polarization state of the incident light.

[0083] The polarization aberration of an optical system can be divided into two categories, namely, diattenuation and phase retardation.

[0084] Diattenuation The difference of the transmission of s and p light can be measured as:

[0085] ;

[0086] wherein, Rsis the reflection or transmission coefficient of s light, Rpis the reflection or transmission coefficient of p light.

[0087] Phase retardation can be expressed as:

[0088] ;

[0089] wherein, is the phase of s light, is the phase of p light.

[0090] The anisotropic unit needs to meet the following conditions according to the compensation requirements: the metasurface 2 should provide the opposite polarization aberration to the optical system 1 to be compensated, specifically, the following conditions are met: 1) for a transmissive system: the metasurface 2 with is selected to compensate the diattenuation;

[0091] 2) for a reflective system: the metasurface 2 with is selected to compensate the diattenuation, and the metasurface 2 with is selected to compensate the phase retardation;

[0092] 3) for catadioptric systems and other types of complex optical systems: according to the polarization ray tracing results, the directions of diattenuation and phase retardation are determined, and then the metasurface 2 is selected.

[0093] In some embodiments, in step S4, the polarization aberration compensation function has the expression:

[0094] ;

[0095] wherein, is a weight factor, is a retardation compensation value of the metasurface 2, D is a retardation value at a pupil coordinate of the optical system 1 to be compensated, is a phase delay compensation value of the metasurface 2, R is a phase delay value at a pupil coordinate of the optical system 1 to be compensated.

[0096] In some embodiments, in step S8, the formula used to compensate the wavefront phase introduced by the anisotropic unit of the metasurface 2 is:

[0097] ;

[0098] wherein, represents the phase introduced by the anisotropic unit, represents the phase introduced by the isotropic unit, is an exit pupil normalized coordinate, and is centered at (0, 0) with a radius of 1.

[0099] In some embodiments, in step S8, before compensating the wavefront phase introduced by the anisotropic unit structure 23 using the isotropic unit structure 22, the metasurface 2 obtained in step S6 is placed at the exit pupil position of the optical system 1 to be compensated, and the coordinate at the exit pupil position is normalized to obtain an exit pupil normalized coordinate, the range of the exit pupil normalized coordinate is a circular area centered at (0, 0) with a radius of 1.

[0100] The polarization response of the metasurface 2 where the anisotropic structure is also different for S light and P light, as shown in Figure 9 W, L, H, P are parameters of the anisotropic structure, corresponding to width, length, height, and period respectively, represents the transmittance of s light, represents the transmittance of p light, represents the phase of s light, represents the phase of p light, length represents length, and width represents width. By screening the optimal metasurface 2, the compensation of the birefringence and the phase delay of the optical system is realized. However, while compensating the birefringence and the phase delay of the optical system, the anisotropic structure unit introduces a phase, which changes the wavefront phase distribution at the exit pupil and affects the imaging quality of the optical system. Therefore, the phase introduced by the anisotropic phase plane (composed of the substrate 21 and the anisotropic structure unit) must be compensated to the ideal state (a plane wave in this example), so there are the following two requirements for the isotropic phase plane (composed of the isotropic structure and the substrate 21):

[0101] 1) Isotropic phase surfaces require the introduction of wavefront compensation phase, but bidirectional attenuation and phase delay cannot be introduced. 2) After introducing wavefront compensation phase, the wavefront phase is corrected to the target phase (plane wave in this example).

[0102] The isotropic unit cell structure 22 exhibits identical polarization responses to both S- and P-beams, meaning that introducing phase does not introduce bidirectional attenuation or phase delay. Therefore, we use isotropic unit cells to construct the isotropic phase surface. To ensure that the incident and outgoing wavefronts remain plane waves, the following formula must be satisfied:

[0103] ;

[0104] In the formula, This represents the phase introduced by the anisotropic unit structure 23. This indicates the phase introduced by the isotropic element structure 22, in the upper right corner. The exit pupil normalized coordinates are defined as a circular region centered at (0, 0) with a radius of 1. This formula means that at all positions along the entire pupil, the sum of the phases introduced by the two structures is the same, ensuring that the emitted light remains a plane wave and does not disrupt the wavefront phase.

[0105] To make the metasurface 2 more miniaturized and integrated, the two phase surfaces share the same substrate 21 and are distributed on both sides of this substrate 21 respectively.

[0106] like Figure 10 As shown, taking a low-polarization-aberration laser communication system as an example, the complete design flow is illustrated. The laser communication system includes a laser (4), an optical system to be compensated (1), a metasurface (2), a receiving system (3), and a detector (5). For other types of optical systems, the process may differ depending on the specific type of optical system. For example, the field-of-view factors to be considered when using it for imaging systems will be discussed later.

[0107] A polarization aberration compensation metasurface 2 is integrated at the exit pupil of the transmitter, and a transmission structure is used at the receiver to receive the laser.

[0108] Furthermore, as shown in Figure 7, by reasonably setting the weights of the polarization aberration compensation function of metasurface 2, the average bidirectional attenuation of the laser communication system was reduced by 91.8%, and the average phase delay was reduced by 95.0%. Moreover, after joint design with the receiving system 3, the final bidirectional attenuation value was further reduced, achieving a very good compensation effect for both bidirectional attenuation and phase delay.

[0109] In the establishment of laser communication link, the field of view of the optical system is kept in the order of micro-radians, and the polarization aberration difference of the optical system is very small, so only the 0° field of view can be considered. However, in some other applications of optical systems with field of view, different fields of view lead to different polarization aberrations. Compared with the central field of view, the influence of other fields of view on the effect of polarization aberration compensation is mainly determined by the following two factors:

[0110] Factor 1: The incidence angle leads to the error of the two-way attenuation and phase delay derived by the polarization ray tracing.

[0111] Factor 2: The exit angle will be obliquely incident into the metasurface 2 at a certain angle, and the oblique incidence of the beam will cause changes in transmittance and phase, i.e. the exit angle will cause the transmittance and phase error of the incident metasurface 2.

[0112] The influence of these two factors needs to be analyzed according to the specific type of optical system, and the analysis method is as follows. For the off-axis laser optical system 1 to be compensated, the magnification of the off-axis laser optical system 1 to be compensated is 5X, the incident field of view angle is 1.5°, and the exit field of view angle is 0.3°. The incidence angle range of the metasurface 2 is very small, and the light source is incident into the metasurface 2 at a certain angle (0.3° here), and the simulation results show that its transmittance and phase data are basically consistent with the case where the light source is incident into the metasurface 2 at 0°. Therefore, the main influencing factor is factor 1, and the polarization ray tracing is performed for the five fields of view of the laser optical system 1 to be compensated to obtain the polarization aberration distribution results. Then, according to the polarization ray tracing, the polarization aberration distribution of the five fields of view is obtained, and it is found that with the increase of the field of view angle, the values of the two-way attenuation and phase delay of the off-axis laser optical system 1 to be compensated increase, and the two-way attenuation RMS values of the last four fields of view increase by 8.15428%, 13.66313%, 18.95242%, and 26.83650%, respectively, and the phase delay RMS values increase by 8.30751%, 13.77378%, 19.15122%, and 27.21705%, respectively. This means that with the increase of the field of view angle, the value of the polarization aberration continuously increases, while the polarization aberration compensation value provided by the metasurface 2 basically remains unchanged, indicating that the compensation effect for the polarization aberration of the edge field of view will decrease to a certain extent, but still maintains a good compensation effect. The analysis results of the fields of view are shown in Figure 11 Figure 11 The first row in Figure 11 represents the two-way attenuation change graph of 0°, 0.45°, 0.75°, 1.05°, and 1.5°, respectively.

[0113] ​The metasurface 2 for compensating for polarization aberration of an optical system provided by the present application can compensate for various types of polarization aberration of optical systems, and has higher applicability. Meanwhile, the present application can flexibly control the focus of polarization aberration compensation by adjusting the weight factor, and can achieve ideal compensation effect in different application scenarios.

[0114] It should be understood that the various forms of flow shown above can be used to reorder, add or delete steps. For example, the steps described in the present disclosure can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solutions of the present disclosure can be achieved, which is not limited herein.

[0115] The above specific embodiments do not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent replacement and improvement within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A metasurface, characterized in that: The application relates to a super surface, which comprises a substrate and isotropic unit structures and anisotropic unit structures arranged on two sides of the substrate respectively, the substrate and the isotropic unit structures constitute an isotropic phase surface for correcting a wavefront phase, and the substrate and the anisotropic unit structures constitute an anisotropic phase surface for compensating for a polarization aberration. The anisotropic unit structures are an array of a plurality of anisotropic unit structures, and the isotropic unit structures are an array of a plurality of isotropic unit structures.

2. The metasurface of claim 1, wherein: The application further discloses a method for designing the super surface, which comprises the following steps:

3. A polarization aberration compensation method based on a hybrid design of refraction-hyper-surface, implemented by the hyper-surface of claim 1 or claim 2, characterized in that: S1: obtaining an optical initial system, optimizing wave aberration of the optical initial system based on optical software, and obtaining an optical system to be compensated for; S2: determining a shape of the anisotropic unit structures, performing parameter scanning on the anisotropic unit structures, obtaining P light phase, S light phase, transmittance and structure parameter values of the anisotropic unit structures, and performing parameter scanning on the isotropic unit structures, obtaining transmittance, structure parameter values and phase values of the isotropic unit structures; S3: placing the super surface obtained in step S2 as a phase surface at an exit pupil of the optical system to be compensated for to perform optimization, and obtaining target phase of the super surface; S4: combining an imaging principle of the optical system to be compensated for, performing full-aperture polarization light tracing on the optical system to be compensated for, and obtaining distribution of a polarization aberration, a retardation and a phase delay of the optical system to be compensated for at the exit pupil; S5: designing a polarization aberration compensation function of the super surface, and adjusting weights of the polarization aberration compensation function based on the distribution of the retardation and the phase delay of the optical system to be compensated for, so that the polarization aberration compensation function compensates for the retardation and the phase delay of the optical system to be compensated for; S6: judging whether the retardation compensation result and the phase delay compensation result meet preset values respectively, if yes, executing step S7, and if not, executing step S2 to adjust the shape, material and parameter scanning range of the anisotropic unit structures; S7: analyzing wavefront phase distribution introduced by the anisotropic unit structures; S8: compensating for the wavefront phase introduced by the anisotropic unit structures by using the isotropic unit structures of the super surface, so that the sum of the phase of the isotropic unit structures and the phase of the anisotropic unit structures is equal to the target phase of the super surface, and the polarization aberration compensation of the optical system to be compensated for is realized. In step S4, based on the imaging principle of the optical system to be compensated for, the optical system to be compensated for is divided into a transmission type optical system and a reflection type optical system, for the transmission type optical system, anisotropic unit structures with a transmission coefficient of s polarized light greater than that of p polarized light are selected to compensate for the retardation of the transmission type optical system, for the reflection type optical system, anisotropic unit structures with a reflection coefficient of s polarized light less than that of p polarized light are selected to compensate for the retardation of the reflection type optical system, and the anisotropic unit structures satisfy that the phase of s light is less than that of p light to compensate for the phase delay of the reflection type optical system.

4. The polarization aberration compensation method based on a hybrid design of refraction-hyper-surface according to claim 3, characterized in that: In step S8, the formula used for compensating for the wavefront phase introduced by the anisotropic unit structures by using the isotropic unit structures is as follows:

5. The polarization aberration compensation method based on a hybrid design of refraction-hyper-surface according to claim 3, characterized in that: In step S4, the polarization aberration compensation function is expressed as: ； wherein, is a weight factor, is a two-dimensional attenuation compensation value of the super surface, and D is a two-dimensional attenuation value at a pupil coordinate of an optical system to be compensated, is a phase delay compensation value of the super surface, and R is a phase delay value at a pupil coordinate of an optical system to be compensated.

6. The polarization aberration compensation method based on a hybrid design of refraction-hyper-surface according to claim 3, characterized in that: ​ ； wherein, denotes the phase introduced by the anisotropic cell structure, denotes the phase introduced by the isotropic cell structure, is the exit pupil normalized coordinate.

7. The polarization aberration compensation method based on a hybrid design of refractive-hyper-surface according to claim 6, characterized in that: In step S8, before compensating the wavefront phase introduced by the anisotropic unit structure using the isotropic unit structure, the metasurface obtained in step S6 is placed at the exit pupil position of the optical system to be compensated, and the coordinates where the exit pupil position is located are normalized to obtain exit pupil normalized coordinates, the range of the exit pupil normalized coordinates being a circular region with (0, 0) as the center and a radius of 1.

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