A circularly polarized decoupled metasurface based on a two-layer C4 structure and its design method

Abstract

This invention discloses a circularly polarized decoupled metasurface based on a two-layer C4 structure and its design method. The metasurface consists of a substrate, a bottom subwavelength structural unit, an intermediate dielectric layer, and a top structural unit, with both the top and bottom layers using high-refractive-index materials. Based on the principle of symmetry breaking, this invention constructs a two-layer physical system with rotational symmetry while simultaneously breaking mirror symmetry, inducing the system's circularly polarized eigenresponse, thus overcoming the physical limitations of traditional single-layer structures on spin-state manipulation. During the design process, this invention combines optical simulation tools and multi-objective optimization algorithms to collaboratively optimize the spatial distribution and geometric parameters of the two-layer structure, achieving precise control over the transmission amplitude and phase of the circularly polarized component. This metasurface can achieve continuous linear polarization angle rotation of incident linearly polarized light over a wide angle range, while maintaining efficient transmission and extremely low exit ellipticity within the target wavelength band.

Description

Technical Field

[0001] This invention belongs to the field of optical technology, specifically relating to a circularly polarized decoupled metasurface based on a double-layer C4 structure and its design method. Background Technology

[0002] Metamaterials are composite materials composed of subwavelength artificial microstructures arranged in a specific pattern. They have attracted widespread attention due to their extraordinary physical properties not found in naturally occurring materials, such as negative refractive index and perfect transmission. Metasurfaces, as a two-dimensional planar realization of metamaterials, have become a research hotspot in the field of micro-nano optics due to their thinness, low loss, and powerful ability to control the amplitude, phase, and polarization state of electromagnetic waves.

[0003] In the field of micro-nano optics, spin decoupling using metasurfaces is the mainstream technique for controlling the independent responses of left- and right-hand circularly polarized light. Existing technologies mostly employ a linear combination of geometric phase and propagation phase design. However, conventional single-layer structures or unit topologies with high symmetry are physically constrained by intrinsic symmetry, making it difficult to completely break spatial inversion symmetry at subwavelength scales. This symmetry constraint leads to devices exhibiting strong spin conservation characteristics when processing circularly polarized light, failing to induce high intrinsic circular polarization contrast. In practical applications, this manifests as the inability to achieve intrinsic decoupling at the same frequency, limiting the development of chiral analysis, high-security optical information processing, and high-performance circularly polarized detectors.

[0004] To overcome the aforementioned physical bottlenecks, introducing multilayer structures has become a necessary approach to improve chiral response. However, while the increased number of structural layers significantly enhances design freedom, it also leads to a geometrical increase in the geometric dimensions of parameters to be optimized, such as multilayer nanopillars, posing significant challenges to structural design. Traditional parameter scanning methods primarily rely on manual experience to search in local space, resulting in extremely high computational costs in high-dimensional parameter spaces. With the evolution of optimization algorithms, introducing optimization algorithms with global search capabilities has become an inevitable trend. By employing heuristic intelligent algorithms such as genetic algorithms, the optimal solution set can be efficiently identified and obtained in high-dimensional parameter spaces. This algorithm-driven reverse design method can accurately balance multiple functional indicators, thus providing an effective technical path for developing spin-decoupled devices with extreme intrinsic contrast. Summary of the Invention

[0005] The purpose of this invention is to propose a circularly polarized decoupled metasurface based on a double-layer C4 structure and its design method. This metasurface can overcome the limitations of traditional designs that are difficult to achieve circularly polarized intrinsic response due to the constraints of mirror symmetry. While achieving high-performance spin-selective control, it also has extremely high circularly polarized intrinsic contrast, meeting the diverse needs of highly integrated optical systems for complex optical rotation control.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a design method for a circularly polarized decoupled metasurface based on a double-layer C4 structure, comprising the following steps:

[0007] The initial form of the Jones matrix is ​​established based on rotational symmetry constraints;

[0008] By breaking the mirror symmetry through a double-layer asymmetric arrangement, the circular polarization eigenresponse of the system is induced.

[0009] The geometric parameters of the metasurface and the arrangement of the QR code-like structure are used as optimization variables to construct a multi-objective fitness function, which includes an average transmission efficiency term and a left-right rotation component amplitude difference balance term.

[0010] The optimization variables are iteratively optimized using a non-dominated sorting genetic algorithm to obtain the optimal combination of structural parameters under the target phase difference.

[0011] Furthermore, the metasurface is composed of a top silicon nanopillar, an intermediate silicon nitride dielectric layer, and a bottom pixelated silicon structure in the height direction; the bottom pixelated silicon structure adopts a QR code-like C4 symmetrical distribution, and the top layer adopts a nanopillar array with C4 symmetry characteristics, and the mirror symmetry is completely broken by rotating the first quadrant structure.

[0012] Furthermore, the transformation of the Jones matrix under the circularly polarized basis satisfies and The phase difference between left-handed and right-handed circularly polarized light is controlled by adjusting structural parameters, thereby achieving a rotation angle of the outgoing polarized light. Regulation; among which The complex coefficients that remain in the left-handed state in the outgoing light when the incident light is left-handed circularly polarized (LCP) represent the structure's ability to modulate the intrinsic phase and amplitude of the LCP light. The complex coefficients that remain in the right-handed state in the outgoing light when the incident light is right-handed circularly polarized (RCP) represent the structure's ability to modulate the intrinsic phase and amplitude of the LCP light. It represents the complex transmission coefficient maintained in the x-direction of the outgoing light when the incident light is linearly polarized in the x-direction; It represents the complex transmission coefficient that remains in the y-direction in the outgoing light when the incident light is linearly polarized in the y-direction.

[0013] Furthermore, the linear polarization rotation achieved by the method follows a mapping relationship. ,in The deflection angle of the emitted light polarization, The phase difference between the left and right circularly polarized components When the incident light is linearly polarized, the metasurface can maintain the outgoing light in a linearly polarized state while achieving continuous polarization direction rotation within the range of 0° to 180° through phase compensation of the double-layer structure.

[0014] Furthermore, through a hierarchical optimization strategy, individuals with transmission efficiency reaching a preset threshold are first screened, and their polarization evolution trajectory is then optimized to ensure that the final device has high transmittance and high polarization purity at the operating wavelength. The high transmittance threshold is that the transmittance is not less than 0.7 at any designed polarization rotation angle; the high polarization purity means that the ratio of the minor axis to the major axis of the polarization ellipse of the emitted light is not greater than 0.004 at any designed polarization rotation angle.

[0015] A circularly polarized decoupled metasurface based on a dual-layer C4 structure is designed using the method described above. The metasurface consists of a top silicon nanopillar, an intermediate silicon nitride dielectric layer, and a bottom pixelated silicon structure in the height direction. The bottom pixelated silicon structure adopts a C4 symmetrical distribution similar to a QR code, and the top layer adopts a nanopillar array with C4 symmetry characteristics. The mirror symmetry is completely broken by rotating the structure in the first quadrant.

[0016] Compared with existing technologies, this invention has the following significant advantages: Unlike traditional spin decoupling devices that rely on a linear combination of geometric phase and propagation phase and are constrained by physical symmetry, resulting in insufficient circular polarization contrast, this invention achieves a true circular polarization eigenresponse through a two-layer topology structure composed of silicon and silicon nitride, enabling completely independent control of left-hand and right-hand components for decoupling. Furthermore, the multi-objective intelligent optimization design method introduced in this invention solves the technical challenge of synergistically balancing multiple performance indicators, significantly improving the development efficiency of complex multilayer structures. This design features a compact structure, mature material system, and high functional integration, making it of significant practical value in fields such as chiral optical detection, high-security optical information processing, vector beam generation, and polarization-sensitive imaging.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1 (a) is a three-dimensional overall view of the double-layer metasurface, (b) is an exploded view, and (c) is a top view.

[0019] Figure 2 This is the optimization flowchart for the NSGA-II algorithm.

[0020] Figure 3 The results of the analysis of the polarization state of the transmitted light are shown in the far-field polarization ellipse diagram.

[0021] Figure 4 This represents the transmission electric field intensity distribution at a typical rotation angle. Detailed Implementation

[0022] This invention provides a bilayer rotationally symmetric metasurface that breaks the mirror symmetry constraint. The metasurface consists of a substrate, a bottom dielectric nanopillar, an intermediate dielectric layer, and a top dielectric nanopillar in the height direction. On one hand, by constructing an asymmetric bilayer topology, the mirror symmetry of the unit structure is completely broken in the spatial dimension by utilizing the geometrical difference and specific relative deflection angle between the top and bottom rectangular nanopillars. This symmetry breaking induces a strong intrinsic chiral optical response, enabling asymmetric control of left-handed and right-handed circularly polarized light at the subwavelength scale. This invention selects silicon (Si) as the material for the top and bottom rectangular nanopillars, fully utilizing its high refractive index advantage in the high-frequency range; simultaneously, silicon nitride (Si3N4) is selected as the intermediate dielectric layer, utilizing its low refractive index and low loss characteristics to achieve precise decoupling and compensation of the interlayer phase. On the other hand, the height, width, and arrangement of the silicon nanopillars are used as optimization variables. A non-dominated sorting genetic algorithm (NSGA-II) is employed for global multi-objective optimization. By constructing a fitness function centered on the phase difference of the target spin component, and combining it with full-wave electromagnetic simulation tools, the optimal solution set is searched within a vast parameter space. This design method can precisely lock the combination of structural parameters that achieves extreme intrinsic contrast while maintaining high absorption rate, ensuring the robustness of device performance.

[0023] This invention designs a spin-decoupled asymmetric absorbing metasurface based on a double-layer symmetry-broken structure, the schematic diagram of which is shown below. Figure 1 As shown, the metasurface consists of a silicon dioxide (SiO2) substrate, a bottom silicon (Si) nanopillars, an intermediate silicon nitride (Si3N4) layer, and a top silicon (Si) nanopillars. Its structural parameters include the unit cell period W1, the width and height W2 of the top nanopillars, the height d1 of the top nanopillars, the thickness d2 of the intermediate dielectric layer, and the width W3 and height d3 of the bottom nanopillars.

[0024] To achieve high-performance circularly polarized eigenresponse, this invention breaks the inherent mirror symmetry constraint of traditional single-layer structures through an asymmetric design of a two-layer structure. In this embodiment, the electromagnetic response characteristics of the metasurface are expressed using the Jones matrix. Describe the following relationship in a Cartesian coordinate system:

[0025] (1)

[0026] in, This represents the complex transmission coefficient maintained in the x-direction of the outgoing light when the incident light is linearly polarized in the x-direction. This represents the complex transmission coefficient in the outgoing light that remains in the y-direction when the incident light is linearly polarized in the y-direction. This represents the complex coefficient of the outgoing light converted to the y-direction when the incident light is linearly polarized in the x-direction. This represents the complex coefficient of the outgoing light when the incident light is linearly polarized in the y direction and then converted to the x direction.

[0027] For traditional mirror-symmetric structures, the transfer matrix is ​​diagonalized, and the eigenstates are linearly polarized. For example, when there is x-axis mirror symmetry with (y, z) as the mirror plane, the symmetry matrix can be written as:

[0028] (2)

[0029] At this point, the linear polarization basis Jones matrix of the metasurface structure with x-axis mirror symmetry can be written as:

[0030] (3)

[0031] Similarly, when a metasurface structure has y-axis mirror symmetry with the (x,z) plane as its mirror plane, its symmetry matrix... It can be written as:

[0032] (4)

[0033] Then, the linear polarization basis Jones matrix of a metasurface structure that is mirror-symmetric along the y-axis can be written as:

[0034] (5)

[0035] Comparing both sides of the equation, we can obtain (3) and (5). and ,Right now:

[0036] (6)

[0037] For a longitudinally mirror-symmetric structure (with the (x,y) plane as the mirror plane), the directions of the electric field components in the (x,y) plane remain unchanged, and the corresponding Jones vector transformation matrix is: Incorporating the constraint of time reversal symmetry (TRS), i.e., in a reciprocal system the reverse transfer matrix equals the transpose of the forward matrix, the constraint equation for the metasurface is:

[0038] (7)

[0039] You will get:

[0040] (8)

[0041] If the structure is rotated by an angle θ, the Jones matrix of the structure can be written as Its R is the rotation matrix:

[0042] (9)

[0043] When the superunit possesses C4 rotational symmetry, its transfer matrix In a Cartesian coordinate system, rotational invariance constraints must be satisfied, i.e. The matrix after rotation is:

[0044] (10)

[0045] Considering the rotational symmetry of C4, the structure after rotation is identical to the original structure, that is:

[0046] (11)

[0047] By comparing the matrix elements, we can obtain:

[0048] (12)

[0049] To further illustrate how this invention achieves independent control of light with different spin states, the matrix in the Cartesian coordinate system is... Jones matrix transformed to a circularly polarized basis .

[0050] First, use the linear polarization basis vectors. and Combine to obtain the circular polarization basis vectors, that is:

[0051] (13)

[0052] The basis transformation matrix can be written as:

[0053] (14)

[0054] Jones matrix of circularly polarized basis vectors The calculation yields:

[0055] (15)

[0056] The Jones matrix of the circularly polarized basis vectors can be obtained. :

[0057] (16)

[0058] In the traditional C4 structure that breaks mirror symmetry, the transformed matrix for:

[0059] (17)

[0060] At this point, the system exhibits a significant circularly polarized eigenresponse, thus physically achieving spin decoupling.

[0061] In this embodiment, when linearly polarized light is incident, the present invention utilizes the phase difference between the left-hand and right-hand components to achieve continuous polarization rotation. The complex transmission coefficients of the left-hand and right-hand components are respectively... and The total range of shots can be further derived as follows:

[0062] (18)

[0063] in: The complex coefficients that remain in the left-handed state in the outgoing light when the incident light is left-handed circularly polarized (LCP) represent the structure's ability to modulate the intrinsic phase and amplitude of the LCP light. The complex coefficients that maintain a right-handed circularly polarized (RCP) state in the outgoing light represent the structure's ability to modulate the intrinsic phase and amplitude of the LCP light when the incident light is right-handed circularly polarized (RCP). and These represent the transmittance of the left-handed and right-handed components, respectively. and These represent the phase delays of the left-hand and right-hand components, respectively.

[0064] Incident X-ray polarized light Under the linear polarization basis vectors, it can be written as:

[0065] (19)

[0066] From (13), we can obtain the unit vector in the x-direction. = Therefore, the circular polarization basis vectors can be written as:

[0067] (20)

[0068] The corresponding ejection field after passing through the metasurface can be written as:

[0069] (twenty one)

[0070] During the structural design optimization process, we made ,Right now

[0071] At this time, it is ordered that:

[0072] (twenty two)

[0073] The emitted light in the form of circularly polarized basis vectors The word can be written as:

[0074] (twenty three)

[0075] The circular polarization basis vector of (13) and Substitute and expand to synthesize:

[0076] (twenty four)

[0077] (25)

[0078] According to the Cartesian decomposition, the electric field is divided into x and y components:

[0079] (26)

[0080] At this point, it can be obtained and Sharing the same complex exponential factor and amplitude Therefore, the phase difference between the two is 0, and the emitted light is purely linearly polarized. The deflection angle of the emitted light is the same as the deflection angle of the linearly polarized light. Depend on and The amplitude ratio determines:

[0081] (27)

[0082] Therefore, the angle between the outgoing x-polarized light and the incident x-polarized light is:

[0083] (28)

[0084] This invention allows for precise control of the rotation angle of incident ray-polarized light by adjusting the geometric parameters of silicon nanopillars.

[0085] Since the above physical derivation involves interference compensation at multiple levels, this embodiment uses a non-dominated sorting genetic algorithm for inverse parameter search. For example... Figure 2 As shown, the algorithm uses the length and width of the upper silicon nanopillars and the arrangement of the lower nanopillars as optimization parameters. The fitness function is set as the phase difference of the circular polarization component of the target polarization angle, and a transmittance threshold is also set. ,in and The transmittance of the left-hand and right-hand circularly polarized components of the individual structure are given. After multiple iterations, the algorithm finally converges and outputs the optimal solution set, providing accurate structural parameter support for realizing spin-decoupled devices with extreme contrast. By combining the optimization algorithm and optical simulation software, the finite-difference time-domain (FDTD) method is used to calculate the phases of the left-hand and right-hand circularly polarized components of the bilayer metasurface structure. The fitness function is used to evaluate the performance of the generated structure, assigning weights to each parameter according to the design goal to optimize its ability to control the circularly polarized components. In multiple iterations, the accuracy of the target phase is gradually improved. Finally, as the algorithm gradually converges, the optimal structural parameters that meet the design requirements are obtained, achieving the expected results.

[0086] This invention, based on the principle of symmetry breaking, constructs a two-layer physical system with rotational symmetry while simultaneously breaking mirror symmetry, inducing the circularly polarized eigenresponse of the system, thus overcoming the physical limitations of traditional single-layer structures on spin-state manipulation. During the design process, this invention combines optical simulation tools and multi-objective optimization algorithms to collaboratively optimize the spatial distribution and geometric parameters of the two-layer structure, achieving precise control over the transmission amplitude and phase of the circularly polarized component. This metasurface enables continuous linear polarization angle rotation of incident linearly polarized light over a wide angle range, while maintaining efficient transmission and extremely low exit ellipticity within the target wavelength band. This invention offers advantages such as high design freedom, compact structure, and stable performance, and has broad application prospects in optical communication, polarization detection, and spin optics system integration.

[0087] To better understand the above technical solutions, the following detailed description will be provided in conjunction with the accompanying drawings and specific embodiments. However, the scope of protection of this invention is not limited to the following embodiments.

[0088] Example

[0089] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0090] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0091] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0092] This embodiment provides a design method for a spin-decoupled asymmetric absorption metasurface based on a bilayer symmetry-broken structure. The center wavelength of the incident light is 1550 nm. The metasurface unit consists of a silicon dioxide (SiO2) substrate, a bottom silicon (Si) rectangular nanopillar, an intermediate silicon nitride (Si3N4) dielectric layer, and a top silicon (Si) rectangular nanopillar. To balance fabrication accuracy and subwavelength tuning requirements, the unit structure period is set to 900 nm, the height of the upper nanopillar is set to 600 nm, and the height of the lower silicon nanopillar is set to 800 nm.

[0093] First, a Jones matrix model under symmetry constraints is established according to the formulas described in the instruction manual. By introducing mirror symmetry breaking, the mirror symmetry of the unit structure is broken, thereby transforming the circularly polarized basis Jones matrix into a diagonal matrix. Calculations show that, under specific geometric dimensions, this structure can produce a significant difference in the eigenresponse between left-handed and right-handed circularly polarized light, laying the physical foundation for achieving spin-decoupled absorption.

[0094] Secondly, the structural parameters of the metasurface are defined as the optimization parameters of the non-dominated sorting genetic algorithm (NSGA-II). The components of left-handed and right-handed light on the metasurface in each iteration are calculated using the simulation software FDTD Solutions. and Its fitness function is set as follows:

[0095] (29)

[0096] in For the set target phase difference, The phase difference of the circular polarization components of the current individual. and is the amplitude of the circular polarization component of the current individual. This function aims to minimize the deviation between the actual phase difference and the target phase difference, and at the same time strengthen the control of the amplitude balance of the left and right circular components through the weight coefficient 1.5, so as to ensure that the outgoing light has extremely high linear polarization purity.

[0097] Finally, this embodiment realizes a metasurface device that can arbitrarily rotate the incident linearly polarized light at a wavelength of 1550 nm. The experimental simulation results show that this structure can achieve continuous polarization angle regulation from 0 to , the average transmission efficiency reaches 0.82, and the maximum rotation angle deviation is only 2.09°.

[0098] Figure 1 Shows the schematic diagram of the principle of the symmetric metasurface unit structure adopted in the present invention. Among them, Figure (a) is the three-dimensional overall view, Figure (b) is the exploded view, and Figure (c) is the top view. The structure consists of a substrate, a bottom Si-like QR code structure, an intermediate layer, and a top Si "卍"-shaped structure. The rotational symmetry of the structure is ensured through rotational operations, and at the same time, the mirror symmetry is completely broken through the double-layer spatial arrangement.

[0099] Figure 2 Is the optimization flowchart of the NSGA-II algorithm involved in the present invention. This process reflects the complete reverse design process from parameter input, electromagnetic simulation feedback, hierarchical screening to multi-objective convergence.

[0100] Figure 3 Shows the analysis results of the polarization state of the transmitted light in the present invention. Figure (a) is the polarization ellipse of the incident linearly polarized light; Figures (b)-(h) correspond to the polarization ellipses of the outgoing light when the designed rotation angles are 9 degrees, 30 degrees, 150 degrees, 45 degrees, 135 degrees, 60 degrees, and 120 degrees respectively. The insets in each subfigure show the corresponding optimized structures. The results show that the outgoing light always maintains a very low ellipticity (close to linear polarization), and the azimuth angle is highly consistent with the design target, verifying the ability of the present invention to achieve precise polarization control while maintaining high transmission efficiency.

[0101] Figure 4 Shows the transmitted electric field distributions at five typical rotation angles (90°, 45°, 135°, 120°, 60°). The figure clearly describes the amplitude and phase relationships of the polarization components and the polarization components. For example, in the 90° rotation case (a), the component is completely suppressed; in the 45° rotation case (b), the components have the same amplitude and phase; while in the 135° rotation case (c), the two have the same amplitude but a phase difference of. These details of the electric field evolution not only verify the effectiveness of the circular polarization eigenresponse at the physical level but also prove the reliability of the design scheme of the present invention.

[0102] This article uses specific examples to illustrate the principles and implementation methods of the present invention, but it should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the protection scope of the present invention.

[0103] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for a circularly polarized decoupled metasurface based on a two-layer C4 structure, characterized in that, Includes the following steps: The initial form of the Jones matrix is ​​established based on rotational symmetry constraints; By breaking the mirror symmetry through a double-layer asymmetric arrangement, the circular polarization eigenresponse of the system is induced. The geometric parameters of the metasurface and the arrangement of the QR code-like structure are used as optimization variables to construct a multi-objective fitness function, which includes an average transmission efficiency term and a left-right rotation component amplitude difference balance term. The optimization variables are iteratively optimized using a non-dominated sorting genetic algorithm to obtain the optimal combination of structural parameters under the target phase difference.

2. The method according to claim 1, characterized in that: The metasurface consists of a top silicon nanopillar, an intermediate silicon nitride dielectric layer, and a bottom pixelated silicon structure in the height direction. The bottom pixelated silicon structure adopts a QR code-like C4 symmetric distribution, and the top layer adopts a nanopillar array with C4 symmetry characteristics. The mirror symmetry is completely broken by rotating the structure in the first quadrant.

3. The method according to claim 1, characterized in that: The transformation of the Jones matrix under a circularly polarized basis satisfies and By adjusting structural parameters to controllably change the phase difference between left-handed and right-handed circularly polarized light, the rotation angle of the outgoing polarized light can be achieved. Regulation; among which This represents the complex coefficients in the outgoing light that remain in a left-handed state when the incident light is left-handed circularly polarized; This represents the complex coefficients in the outgoing light that remain in a right-handed circular polarization when the incident light is right-handed circularly polarized. It represents the complex transmission coefficient maintained in the x-direction of the outgoing light when the incident light is linearly polarized in the x-direction; It represents the complex transmission coefficient that remains in the y-direction in the outgoing light when the incident light is linearly polarized in the y-direction.

4. The method according to claim 1, characterized in that: The linear polarization rotation achieved by the method follows a mapping relationship. ,in The deflection angle of the emitted light polarization, The phase difference is between the left and right circularly polarized components. When the incident light is linearly polarized, the metasurface can maintain the outgoing light in a linearly polarized state while achieving continuous polarization direction rotation within the range of 0° to 180° through phase compensation of the double-layer structure.

5. The method according to claim 1, characterized in that: Through a hierarchical optimization strategy, individuals with transmission efficiency reaching a preset threshold are first screened, and their polarization evolution trajectory is then optimized to ensure that the final device has high transmittance and high polarization purity at the operating wavelength. The high transmittance means that the transmittance is not less than 0.7 at any designed polarization rotation angle. The high polarization purity means that the ratio of the minor axis to the major axis of the polarization ellipse of the emitted light is not greater than 0.004 at any designed polarization rotation angle.

6. A circularly polarized decoupling metasurface based on a double-layer C4 structure, designed according to the method described in any one of claims 1 to 5, characterized in that: The metasurface consists of a top silicon nanopillar, an intermediate silicon nitride dielectric layer, and a bottom pixelated silicon structure in the height direction. The bottom pixelated silicon structure adopts a QR code-like C4 symmetric distribution, and the top layer adopts a nanopillar array with C4 symmetry characteristics. The mirror symmetry is completely broken by rotating the structure in the first quadrant.

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