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

Abstract

The invention belongs to the technical field of polarization optics, and particularly relates to a metasurface and a polarization aberration compensation method based on refraction-metasurface hybrid design, and the method comprises the steps: S1, obtaining a to-be-compensated optical system; s2, performing parameter scanning on the metasurface; s3, obtaining a target phase of the metasurface; s4, obtaining two-direction attenuation and phase delay distribution of the polarization aberration at the exit pupil of the optical system to be compensated; s5, enabling the polarization aberration compensation function to carry out bidirectional attenuation compensation and phase delay compensation on the optical system to be compensated; s6, judging whether the bidirectional attenuation compensation result and the phase delay compensation result meet respective preset values or not; s7, analyzing wavefront phase distribution introduced by the anisotropic unit structure; and S8, enabling the sum of the phase of the isotropic unit structure and the phase of the anisotropic unit structure to be equal to the target phase of the metasurface. The invention provides an optical system polarization aberration compensation method with high applicability and high degree of freedom.

Description

Technical Field

[0001] The present invention belongs to the technical field of polarization optics, and in particular relates to a metasurface and a polarization aberration compensation method based on a refraction-metasurface hybrid design. Background Art

[0002] In modern optical applications, the propagation characteristics of polarized light play a critical role in the performance of optical systems. When polarized light propagates through an optical system, the transmission coefficients of the optical medium surface for S- and P-light differ. This difference varies with each incident light passage through the medium, depending on the angle of incidence and the dielectric material. In fields such as ultra-high-precision lithography, lidar, target polarization property measurement, and laser communications, high polarization-maintaining optical systems are essential, and polarization aberrations must be strictly controlled or compensated. Some researchers have proposed using the s-polarization of the first mirror to orient the p-polarization of the second mirror to compensate for the polarization aberration of the folding mirror. Others have proposed combining reflective and refractive elements to compensate for polarization aberrations. However, these approaches have several drawbacks: while effective in their respective cases, they are not applicable to other optical systems; the compensation effect is uncontrollable, and the emphasis cannot be flexibly adjusted to suit specific application scenarios. 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 of the Invention

[0003] In view of this, the present invention aims to provide a metasurface and a polarization aberration compensation method based on a refractive-metasurface hybrid design to solve the problem that the existing technology lacks universality in polarization aberration compensation of optical systems. The present invention can be used to analyze and compensate for polarization aberration of various types of optical systems. Regardless of whether the optical system is transmissive or reflective, coaxial or off-axis, centrosymmetric or non-centrosymmetric, the corresponding polarization aberration compensation can be achieved through metasurface design.

[0004] To achieve the above object, the technical solution created by the present invention is implemented as follows: A metasurface comprises: a substrate and an isotropic unit structure and an anisotropic unit structure respectively arranged on both sides of the substrate. The substrate and the isotropic unit structure constitute an isotropic phase surface for correcting the wavefront phase; the substrate and the anisotropic unit structure constitute an anisotropic phase surface for compensating for polarization aberration.

[0005] Furthermore, the anisotropic unit structure is an array composed of multiple anisotropic units, and the isotropic unit structure is an array composed of multiple isotropic units.

[0006] A polarization aberration compensation method based on a refraction-metasurface hybrid design is implemented using a metasurface and specifically includes the following steps: S1: Obtain an initial optical system, optimize the wavefront aberration of the initial optical system based on optical software, and obtain the optical system to be compensated; S2: Determine the shape of the anisotropic unit structure, perform parameter scanning on the anisotropic unit structure, obtain the P-light phase, S-light phase, transmittance and structural parameter values ​​of the anisotropic unit structure, and perform parameter scanning on the isotropic unit structure to obtain the transmittance, structural parameter values ​​and phase values ​​of the isotropic unit structure; S3: The metasurface obtained in step S2 is placed as a phase surface at the exit pupil of the optical system to be compensated for optimization to obtain the target phase of the metasurface; S4: Based on the imaging principle of the optical system to be compensated, full-aperture polarization ray tracing is performed on the optical system to be compensated to obtain the bidirectional attenuation and phase delay distribution of the polarization aberration at the exit pupil of the optical system to be compensated; S5: Designing a polarization aberration compensation function of the metasurface, and adjusting the weight of the polarization aberration compensation function based on the distribution structure of the bidirectional attenuation and phase delay of the optical system to be compensated, so that the polarization aberration compensation function can perform bidirectional attenuation compensation and phase delay compensation on the optical system to be compensated; S6: Determine whether the two-way attenuation compensation result and the phase delay compensation result both meet their respective preset values. If so, execute step S7; otherwise, execute step S2 to adjust the shape, material, and parameter scanning range of the anisotropic unit structure. S7: Analysis of the wavefront phase distribution introduced by the anisotropic unit structure; S8: Use the isotropic unit structure of the metasurface to compensate for 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, thereby realizing polarization aberration compensation for the optical system to be compensated.

[0007] Furthermore, in step S4, based on the imaging principle of the optical system to be compensated, the optical system to be compensated is divided into a transmissive optical system and a reflective optical system. For the transmissive optical system, an anisotropic unit structure in which the transmission coefficient of s-polarized light is greater than the transmission coefficient of p-polarized light is selected to compensate for the biaxial attenuation of the transmissive optical system; for the reflective optical system, an anisotropic unit structure in which the reflection coefficient of s-polarized light is less than the reflection coefficient of p-polarized light is selected to compensate for the biaxial attenuation of the reflective optical system, and the anisotropic unit structure 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.

[0008] Furthermore, in step S4, the polarization aberration compensation function The expression is: ; in, is the weight factor, is the bidirectional attenuation compensation value of the metasurface, D is the bidirectional attenuation value at the pupil coordinate of the optical system to be compensated, is the phase delay compensation value of the metasurface, and R is the phase delay value at the pupil coordinate of the optical system to be compensated.

[0009] Furthermore, in step S8, the formula used to compensate the wavefront phase introduced by the anisotropic unit structure using the isotropic unit structure is: ; in, represents the phase introduced by the anisotropic unit structure, represents the phase introduced by the isotropic unit structure, are the normalized coordinates of the exit pupil.

[0010] Furthermore, in step S8, before using the isotropic unit structure to compensate for the wavefront phase introduced by the anisotropic 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 of the exit pupil position are normalized to obtain the normalized coordinates of the exit pupil. The range of the normalized coordinates of the exit pupil is a circular area with (0, 0) as the center and a radius of 1.

[0011] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) The metasurface and polarization aberration compensation method based on a refractive-metasurface hybrid design created by the present invention can be widely used in various types of optical systems such as transmission or reflection, on-axis or off-axis, centrosymmetric or non-centrosymmetric. The present invention uses an anisotropic unit structure to form a high-freedom metasurface for compensating the polarization aberration of the optical system, and integrates the metasurface into the optical system, thereby completing the design of the polarization aberration compensation metasurface.

[0012] (2) The present invention creates the metasurface and the polarization aberration compensation method based on the refractive-metasurface hybrid design. The polarization aberration of the off-axis optical system is obtained by full-aperture polarization ray tracing, and the polarization aberration is compensated using an anisotropic unit structure. It is verified that the anisotropic unit structure has good polarization response characteristics and achieves a very good compensation effect. The present invention defines the polarization aberration compensation function F and the weight factor By reasonably setting the weight of the polarization aberration compensation function, the average value of the two-way attenuation was reduced by 91.8%, and the average value of the phase delay was reduced by 95.0%, ultimately achieving a very good compensation effect for the two-way attenuation and phase delay.

[0013] (3) The present invention creates the aforementioned metasurface and polarization aberration compensation method based on a refractive-metasurface hybrid design. Taking into account the influence of the phase introduced by the metasurface on the wavefront phase, the present invention combines a polarization-sensitive cubic prism structure with a polarization-insensitive cylindrical structure to form a new metasurface. While compensating for the polarization aberration of an optical system, it does not affect the wavefront phase of the optical system. In summary, the polarization aberration compensation metasurface of the present invention has the advantages of wide applicability, high degree of freedom, and good compensation effect. It significantly reduces the influence of polarization aberration on polarization detection and provides an innovative solution to the polarization aberration compensation problem of various optical systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 A schematic flow chart of a polarization aberration compensation method based on a refractive-metasurface hybrid design according to an embodiment of the present invention; FIG2( a ) is a point diagram of an optimized optical system to be compensated according to an embodiment of the present invention; FIG2( b ) is an MTF diagram of the optimized optical system to be compensated according to an embodiment of the present invention; Figure 3 A schematic diagram of the optical path structure of the optical system to be compensated and the metasurface according to an embodiment of the present invention; Figure 4 A schematic diagram of the anisotropic unit structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the isotropic unit structure described in an embodiment of the present invention; Figure 6 Result diagram of parameter scanning of the isotropic unit structure described in the embodiment of the present invention; FIG7( a ) is a two-dimensional attenuation distribution diagram before compensation according to an embodiment of the present invention; FIG7( b ) is a diagram of the two-way attenuation distribution after compensation according to an embodiment of the present invention; FIG7 (c) is a diagram showing the two-way attenuation average compensation result according to an embodiment of the present invention; FIG7( d ) is a phase delay distribution diagram before compensation according to an embodiment of the present invention; FIG7( e ) is a phase delay distribution diagram after compensation according to an embodiment of the present invention; FIG7( f ) is a diagram showing the phase delay average value compensation result according to an embodiment of the present invention; Figure 8 A diagram of a metasurface structure generated by combining anisotropic units and isotropic units as described in an embodiment of the present invention; Figure 9 The results obtained by parameter scanning of anisotropic structures according to the embodiments of the present invention; Figure 10 A schematic diagram of the structure of the laser communication system according to an embodiment of the present invention; Figure 11 This is a result diagram obtained by analyzing the field of view as described in an embodiment of the present invention.

[0015] Description of reference numerals: 1. Optical system to be compensated; 2. Metasurface; 3. Receiving system; 4. Laser; 5. Detector; 21. Substrate; 22. Isotropic unit structure; 23. Anisotropic unit structure. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0017] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0018] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0019] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0020] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0021] The present invention proposes a metasurface 2, comprising: a substrate 21 and an isotropic unit structure 22 and an anisotropic unit structure 23 respectively arranged on both sides of the substrate 21. The substrate 21 and the isotropic unit structure 22 constitute an isotropic phase surface for correcting the wavefront phase; the substrate 21 and the anisotropic unit structure 23 constitute an anisotropic phase surface for compensating for polarization aberration.

[0022] In some embodiments, the anisotropic unit structure 23 is an array composed of a plurality of anisotropic units, and the isotropic unit structure 22 is an array composed of a plurality of isotropic units.

[0023] It should be noted that the substrate 21 is made of a high-transmittance material corresponding to the optical system's wavelength band, typically silicon, silicon dioxide, or the like. The anisotropic unit structure 23 is an array composed of multiple anisotropic units. These units are rectangular or elliptical columnar structures, and are polarization-sensitive. The isotropic unit structure 22 is an array composed of multiple isotropic structures. These are circular columnar structures, and are polarization-insensitive. The number of anisotropic unit structures 23 and isotropic unit structures 22 depends on the aperture of the optical system 1 to be compensated. The unit structures (anisotropic unit structures 23 and isotropic unit structures 22) are nanometer-scale. The larger the exit pupil of the optical system 1 to be compensated, the greater the number of unit structures.

[0024] The polarization-insensitive isotropic unit structure 22 is used to compensate for the wavefront phase introduced by the anisotropic unit structure 23, with the aim of eliminating 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 polarization-insensitive isotropic unit structure 22 are determined according to the specific optical system 1 to be compensated. The overall goal is to make the phase of the metasurface 2 equal to the target phase.

[0025] Furthermore, an anisotropic unit structure 23 can be formed from a rectangular columnar structure, and an isotropic unit structure 22 can be formed from a circular columnar structure. The present invention not only encompasses the rectangular columnar structure + circular columnar structure structure. Any combination of anisotropic structures (such as rectangular columnar structures, elliptical columnar structures, etc.) and isotropic structures (such as circular columnar structures, etc.) to compensate for polarization aberrations of various optical systems falls within the scope of protection of the present invention. In addition, to reduce volume and achieve high integration, the present invention arranges two unit structures on either side of the substrate 21. As long as the metasurface 2 is composed of anisotropic unit structures 23 (such as rectangular, elliptical, etc.) and isotropic unit structures 22 (such as circular, etc.), it can achieve the function of compensating for polarization aberrations of optical systems and falls within the scope of protection of the present invention.

[0026] like Figure 1 As shown, the present invention proposes a polarization aberration compensation method based on a refraction-metasurface 2 hybrid design, which is implemented using the metasurface 2 and specifically includes the following steps: S1: Obtain the initial optical system and optimize the wavefront aberration of the initial optical system based on optical software. The optimization results are shown in Figures 2(a), 2(b) and Figure 3 As shown, an optical system 1 to be compensated is obtained.

[0027] S2: Determine the shape of the anisotropic unit structure 23, perform parameter scanning on the anisotropic unit structure 23, obtain the P light phase, S light phase, transmittance and structural parameter values ​​of the anisotropic unit structure 23, and perform parameter scanning on the isotropic unit structure 22 to obtain the transmittance, structural parameter values ​​and phase values ​​of the isotropic unit structure 22; The anisotropic unit cell structure 23 is shown in Figure 4 In the example, the isotropic unit cell structure 22 is shown in Figure 5 The results of parameter scanning of the isotropic unit structure 22 are as follows Figure 6 shown.

[0028] S3: The metasurface 2 obtained in step S2 is placed as a phase surface at the exit pupil of the optical system 1 to be compensated for optimization to obtain the target phase of the metasurface 2; S4: Based on the imaging principle of the optical system to be compensated, full-aperture polarization ray tracing is performed on the optical system to be compensated 1 to obtain the bidirectional attenuation and phase delay distribution of the polarization aberration at the exit pupil of the optical system to be compensated 1; S5: Design a polarization aberration compensation function for the metasurface 2, and adjust the weight of the polarization aberration compensation function based on the distribution structure of the biaxial attenuation and phase delay of the optical system 1 to be compensated, so that the polarization aberration compensation function can perform biaxial attenuation compensation and phase delay compensation on the optical system 1 to be compensated. The analysis of the compensation results is shown in Figures 7(a) to 7(f); S6: Determine whether the two-way attenuation compensation result and the phase delay compensation result both meet their respective preset values ​​(set according to actual needs). If so, execute step S7; otherwise, execute step S2 to adjust the shape, material, and parameter scanning range of the anisotropic unit structure 23; S7: analyzing the wavefront phase distribution introduced by the anisotropic unit structure 23; 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, thereby achieving polarization aberration compensation for the optical system 1 to be compensated. The structure of the metasurface 2 composed of the two is shown in FIG. Figure 8 middle.

[0029] It should be noted that the metasurface 2 is constructed using a substrate 21; an array of anisotropic units is used to compensate for the polarization aberration of the optical system; and an array of isotropic units is used to correct the wavefront destroyed when the anisotropic units introduce phase. The present invention addresses the problem of polarization aberration compensation in optical systems and proposes a hybrid refractive-metasurface 2 design for compensating for polarization aberration. By combining anisotropic unit structures 23 with isotropic unit structures 22, the polarization aberration compensation effect of the optical system is improved, providing a new innovative solution for polarization aberration compensation in various optical systems.

[0030] The overall operation process of the present invention is divided into two parts: polarization aberration compensation and wavefront phase compensation.

[0031] Polarization aberration compensation: First, the initial optical system is optimized to achieve the optimal wavefront aberration, obtaining the optical system 1 to be compensated, and the results of the optical system 1 to be compensated are fixed. Next, the difference in the polarization response of the anisotropic unit to S-light and P-light is obtained through scanning, and the corresponding bidirectional attenuation compensation effect and phase delay compensation effect of the anisotropic unit structure 23 of different sizes are obtained. Next, full-aperture polarization ray tracing is performed on the optical system 1 to be compensated to obtain the bidirectional attenuation and phase delay distribution of the polarization aberration at the exit pupil of the optical system 1 to be compensated. Next, the weight factor of the polarization aberration compensation function is adjusted to obtain the wavefront phase distribution of the anisotropic unit structure 23 used to compensate for the bidirectional attenuation and phase delay, and a judgment is made as to whether the compensation effect meets the requirements.

[0032] Wavefront phase compensation: First, analyze the phase distribution introduced by the anisotropic unit structure 23, and what kind of phase distribution of the metasurface 2 in the optical system 1 to be compensated should be ideal; then, obtain the correspondence between the structural parameters of the isotropic unit structure 22 and the wavefront phase introduced by the anisotropic unit structure 23 through 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 entire optical system 1 to be compensated to complete all processes.

[0033] In addition, in step S1, the optical software can be Zemax or CodeV; in step S2, Comsol or FDTD software can be used to perform parameter scanning, and the structural parameters include parameters such as height and radius; 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 existing technology and will not be repeated below.

[0034] 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 divided into a transmissive optical system and a reflective optical system. For the transmissive optical system, an anisotropic unit structure 23 whose transmission coefficient of s-polarized light is greater than that of p-polarized light is selected to compensate for the biaxial attenuation of the transmissive optical system; for the reflective optical system, an anisotropic unit structure 23 whose reflection coefficient of s-polarized light is less than that of p-polarized light is selected to compensate for the biaxial attenuation of the reflective optical system, and the anisotropic unit structure 23 satisfies that the phase of s-light is less than that of p-light to compensate for the phase delay of the reflective optical system.

[0035] Furthermore, the optical system 1 to be compensated also includes a catadioptric optical system. For the catadioptric optical system, the two-way attenuation and phase delay directions of the refractive part and the reflective part are analyzed respectively. Since the two-way attenuation directions are opposite, it is determined which of the two components is larger. The final direction of the two-way attenuation and phase delay is the same as the direction of the parameter with the larger component.

[0036] It should be noted that the Stokes vector is used to define the polarization state of light, and the Mueller matrix is ​​used to describe the change in polarization characteristics when light passes through an optical system. The Stokes vector expression is as follows: , represents the sum of the horizontal polarization component and the vertical polarization component, represents the difference between the horizontal polarization component and the vertical polarization component, represents the difference between the 45° and 135° polarization components, Represents the difference between right-handed and left-handed circularly polarized components.

[0037] The Mueller matrix of an optical system can be expressed as follows: ; The Stokes vector before and after the optical system satisfies the relationship: ,in represents the Stokes vector of the incident light, represents the Stokes vector of the outgoing light.

[0038] The Mueller matrix of an ideal optical system should be a unit matrix, which ensures that the polarization state of the incident light and the outgoing light is the same, that is, the polarization state of the incident light does not change. However, almost all optical systems contain polarization aberration, which cannot be completely eliminated during the design stage and therefore needs to be compensated.

[0039] According to Fresnel's law, the reflection coefficient and refraction coefficient of s-polarized light and p-polarized light can be expressed as: ; Where, is the reflectivity of s-polarized light; is the reflectivity of p-polarized light; is the transmittance of s-polarized light; is the transmittance of p-polarized light; is the angle of incidence; is the refraction angle. The difference in reflection and transmission coefficients between S and P light changes the polarization state of the incident light.

[0040] Polarization aberrations in optical systems can be divided into two categories, namely bidirectional attenuation and phase retardation.

[0041] Two-way attenuation Used to measure the difference in light transmittance between S and P: ; Where, is the reflection coefficient or refraction coefficient of S light, is the reflection coefficient or refraction coefficient of p light.

[0042] Phase Delay It can be expressed as: ; Where, is the phase of s light, is the phase of the p light.

[0043] The anisotropic unit must meet the following conditions according to the compensation requirements: the metasurface 2 should provide a polarization aberration opposite to that of the optical system 1 to be compensated. Specifically, it must meet the following conditions: 1) For a transmissive system: select The metasurface 2 is used to compensate for the two-way attenuation; 2) For reflective systems: Select The metasurface 2 is used to compensate for the two-way attenuation, and the Metasurface 2 to compensate for phase delay; 3) For catadioptric systems and other types of complex optical systems: Determine the direction of bidirectional attenuation and phase delay based on the polarization ray tracing results, and then decide which metasurface to use.

[0044] In some embodiments, in step S4, the polarization aberration compensation function The expression is: ; in, is the weight factor, is the bidirectional attenuation compensation value of the metasurface 2, D is the bidirectional attenuation value at the pupil coordinate of the optical system 1 to be compensated, is the phase delay compensation value of the metasurface 2, and R is the phase delay value at the pupil coordinate of the optical system 1 to be compensated.

[0045] In some embodiments, in step S8, the formula used to compensate the wavefront phase introduced by the anisotropic unit using the isotropic unit of the metasurface 2 is: ; in, represents the phase introduced by the anisotropic element, represents the phase introduced by the isotropic element, is the normalized coordinate of the exit pupil, centered at (0, 0) and with a radius of 1.

[0046] In some embodiments, in step S8, before using the isotropic unit structure 22 to compensate for the wavefront phase introduced by the anisotropic unit structure 23, the metasurface 2 obtained in step S6 is placed at the exit pupil position of the optical system 1 to be compensated, and the coordinates of the exit pupil position are normalized to obtain the normalized coordinates of the exit pupil. The range of the normalized coordinates of the exit pupil is a circular area with (0, 0) as the center and a radius of 1.

[0047] The polarization response of the metasurface 2 where the anisotropic structure is located to S light and P light is also different, such as Figure 9 As shown, W, L, H, and P are the 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 the p-light, length represents the length, and width represents the width. By screening the optimal metasurface 2, compensation for the bidirectional attenuation and phase delay of the optical system is achieved. However, while compensating for the bidirectional attenuation and phase delay of the optical system, the anisotropic structural 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 surface (composed of the substrate 21 and the anisotropic structural unit) must be compensated to the ideal state (plane wave in this example). Therefore, there are two requirements for the isotropic phase surface (composed of the isotropic structure and the substrate 21): 1) The isotropic phase plane requires the introduction of a wavefront compensation phase, but bidirectional attenuation and phase delay cannot be introduced. 2) After the wavefront compensation phase is introduced, the wavefront phase is corrected to the target phase (a plane wave in this example).

[0048] The isotropic unit structure 22 has the same polarization response for S light and P light, that is, while introducing phase, it does not introduce bidirectional attenuation and phase delay. Therefore, we use isotropic structural units to construct an isotropic phase surface. In order to ensure that the incident and outgoing wavefronts remain in the state of plane waves, the formula must be satisfied: ; Where, represents the phase introduced by the anisotropic unit structure 23, Indicates the phase introduced by the isotropic unit structure 22, the upper right corner is the normalized coordinate of the exit pupil, which is a circular area centered at (0, 0) with a radius of 1. This formula means that the sum of the phases introduced by the two structures is the same at all positions across the pupil, so the exiting light remains a plane wave and does not destroy the phase of the wavefront.

[0049] In order to make the metasurface 2 more miniaturized and integrated, the two phase planes share the same substrate 21 and are respectively distributed on both sides of the substrate 21 .

[0050] like Figure 10 The figure shows the entire design process, taking a low-polarization-aberration laser communication system as an example. 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 design may vary depending on the specific optical system type. For example, the field of view factor that needs to be considered when used in an imaging system will be discussed later.

[0051] A polarization aberration compensation metasurface 2 is integrated at the exit pupil of the transmitting end, and a transmissive structure is used at the receiving end to receive the laser.

[0052] Furthermore, as shown in Figure 7, by properly 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%. Furthermore, after combining this with the design of receiving system 3, the final bidirectional attenuation value was further reduced, achieving excellent compensation for both bidirectional attenuation and phase delay.

[0053] When establishing a laser communication link, the field of view of the optical system is kept at the micro-radian level, and the polarization aberration difference of the optical system is very small. Therefore, only the 0° field of view can be considered. However, in some other applications of optical systems with a field of view, different fields of view lead to different polarization aberrations. Compared with the central field of view, the impact of other fields of view on the polarization aberration compensation effect is mainly determined by the following two factors: Factor 1: The angle of incidence causes bidirectional attenuation and phase delay errors in polarization ray tracing.

[0054] Factor 2: The incident light will enter the metasurface 2 at a certain angle, and the oblique incidence of the light beam will cause changes in transmittance and phase, that is, the incident light angle will cause errors in the transmittance and phase of the incident metasurface 2.

[0055] 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 angle is 1.5°, and the exit field angle is 0.3°. The incident angle range of the metasurface 2 is very small. The light source is incident on the metasurface 2 at a certain angle (here 0.3°). The simulation results show that its transmittance and phase data are basically consistent with the case where the light source is incident on the metasurface 2 at 0°. Therefore, the main influencing factor is factor 1. Polarization ray tracing is performed on the five fields of view of the laser optical system 1 to obtain the distribution results of polarization aberration. Then, based on the polarization ray tracing, the polarization aberration distribution of the five fields of view was obtained. It was found that as the field of view angle increases, the bidirectional attenuation and phase delay values ​​of the off-axis laser optical system 1 to be compensated increase. The RMS values ​​of the bidirectional attenuation of the last four fields of view increased by 8.15428%, 13.66313%, 18.95242%, and 26.83650%, respectively, and the RMS values ​​of the phase delay increased by 8.30751%, 13.77378%, 19.15122%, and 27.21705%, respectively. This means that as the field of view angle increases, the value of the polarization aberration continues to increase, while the polarization aberration compensation value provided by the metasurface 2 remains basically unchanged, indicating that the compensation effect of the polarization aberration of the edge field of view will decline to a certain extent, but still maintain a good compensation effect. The analysis results of the field of view are shown in Figure 11 middle, Figure 11 The first row represents the two-way attenuation change diagram of 0°, 0.45°, 0.75°, 1.05°, and 1.5° respectively. Figure 11 The first row represents the phase delay variation diagrams of 0°, 0.45°, 0.75°, 1.05°, and 1.5° respectively.

[0056] The metasurface 2 for compensating polarization aberration in optical systems proposed in this invention can compensate for polarization aberration in various optical systems, demonstrating greater applicability. Furthermore, the invention can flexibly adjust the emphasis of polarization aberration compensation by adjusting weighting factors, achieving ideal compensation effects in various application scenarios.

[0057] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0058] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A metasurface, characterized in that: include: A substrate and an isotropic unit structure and an anisotropic unit structure respectively arranged on both sides of the substrate, wherein the substrate and the isotropic unit structure constitute an isotropic phase surface for correcting the wavefront phase; the substrate and the anisotropic unit structure constitute an anisotropic phase surface for compensating for polarization aberration.

2. The metasurface according to claim 1, wherein: The anisotropic unit structure is an array composed of multiple anisotropic units, and the isotropic unit structure is an array composed of multiple isotropic units.

3. A polarization aberration compensation method based on a refractive-metasurface hybrid design, implemented using the metasurface according to claim 1 or claim 2, characterized in that: The specific steps include: S1: Obtain an initial optical system, optimize the wavefront aberration of the initial optical system based on optical software, and obtain the optical system to be compensated; 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, transmittance and structural parameter values ​​of the anisotropic unit structure, and performing parameter scanning on the isotropic unit structure to obtain the transmittance, structural parameter values ​​and phase values ​​of the isotropic unit structure; S3: The metasurface obtained in step S2 is placed as a phase surface at the exit pupil of the optical system to be compensated for optimization to obtain the target phase of the metasurface; S4: Based on the imaging principle of the optical system to be compensated, full-aperture polarization ray tracing is performed on the optical system to be compensated to obtain the bidirectional attenuation and phase delay distribution of the polarization aberration at the exit pupil of the optical system to be compensated; S5: Designing a polarization aberration compensation function of the metasurface, and adjusting the weight of the polarization aberration compensation function based on the distribution structure of the bidirectional attenuation and phase delay of the optical system to be compensated, so that the polarization aberration compensation function can perform bidirectional attenuation compensation and phase delay compensation on the optical system to be compensated; S6: Determine whether the two-way attenuation compensation result and the phase delay compensation result both meet their respective preset values. If so, execute step S7; otherwise, execute step S2 to adjust the shape, material, and parameter scanning range of the anisotropic unit structure. S7: analyzing the wavefront phase distribution introduced by the anisotropic unit structure; S8: Use the isotropic unit structure of the metasurface to compensate for 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, thereby realizing polarization aberration compensation for the optical system to be compensated.

4. The polarization aberration compensation method based on a refraction-metasurface hybrid design according to claim 3, wherein: In step S4, based on the imaging principle of the optical system to be compensated, the optical system to be compensated is divided into a transmissive optical system and a reflective optical system. For the transmissive optical system, an anisotropic unit structure in which the transmission coefficient of s-polarized light is greater than the transmission coefficient of p-polarized light is selected to compensate for the biaxial attenuation of the transmissive optical system; for the reflective optical system, an anisotropic unit structure in which the reflection coefficient of s-polarized light is less than the reflection coefficient of p-polarized light is selected to compensate for the biaxial attenuation of the reflective optical system, and the anisotropic unit structure 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.

5. The polarization aberration compensation method based on a refraction-metasurface hybrid design according to claim 3, wherein: In step S4, the polarization aberration compensation function The expression is: ； in, is the weight factor, is the bidirectional attenuation compensation value of the metasurface, D is the bidirectional attenuation value at the pupil coordinate of the optical system to be compensated, is the phase delay compensation value of the metasurface, and R is the phase delay value at the pupil coordinate of the optical system to be compensated.

6. The polarization aberration compensation method based on a refraction-metasurface hybrid design according to claim 3, wherein: In step S8, the formula used to compensate the wavefront phase introduced by the anisotropic unit structure using the isotropic unit structure is: ； in, represents the phase introduced by the anisotropic unit structure, represents the phase introduced by the isotropic unit structure, are the normalized coordinates of the exit pupil.

7. The polarization aberration compensation method based on a refraction-metasurface hybrid design according to claim 6, wherein: In step S8, before using the isotropic unit structure to compensate for the wavefront phase introduced by the anisotropic 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 of the exit pupil position are normalized to obtain the normalized coordinates of the exit pupil. The range of the normalized coordinates of the exit pupil is a circular area with (0, 0) as the center and a radius of 1.

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