CN116358705A - A full Stokes polarimeter based on dielectric metasurface - Google Patents

Abstract

The invention discloses a full stop polarization measuring instrument based on a medium super surface, and belongs to the technical field of optical devices. Comprises a layer of medium super surface and a detector array, wherein the detector array is positioned at the focal plane of the medium super surface. According to the full-stokes polarization measuring instrument based on the medium super surface, the attached design framework can randomly select the interested target polarization states and the focusing points of the interested target polarization states, and target polarization state detection of regular tetrahedron distribution which cannot be realized by the traditional design thought can be easily realized. The design of six polarization state detection for regular polyhedron distribution has smaller volume than the existing design, and the design of four polarization state detection for non-regular polyhedron distribution has smaller noise interference than the existing design.

Description

A full Stokes polarimeter based on dielectric metasurface

technical field

The invention relates to the technical field of optical devices, in particular to a full Stokes polarization measuring instrument based on a dielectric metasurface.

Background technique

Polarization detection is a technology used to detect the polarization information of light waves. It has been widely used in communication, biomedical imaging, remote sensing, image fog removal and other fields. The Stokes parameters of the target can be reconstructed by measuring the different polarization components of the target outgoing light for a limited number of times (at least 4 times). The traditional detection method mainly realizes the collection of multiple polarization information of the target by time-sharing, amplitude-sharing, aperture-dividing or focal-plane-dividing. Among them, the time-division polarization detection is a class, through different combinations of phase retarders and linear polarizers, and record the corresponding output light intensity, and use these light intensities to reconstruct the Stokes vector of the incident light. Although this method has a simple structure, it cannot obtain the instantaneous value of the light wave polarization due to the need for multiple measurements, and the time resolution is low. Sub-amplitude, sub-aperture, and sub-focal plane can be classified into another category. They split the incident beam in different ways, and then record the light intensity information of different polarization components of the beam at the same time, so that the polarization information can be reconstructed in a single measurement. . However, the measurement system using this method often has a large and complex structure and high cost, which is not conducive to the miniaturization of the device.

A metasurface is an artificially designed single-layer structure with subwavelength thickness, which can flexibly control the amplitude, phase and polarization properties of light. Among them, the dielectric metasurface has lower loss than other metasurfaces, and is a very potential medium for polarization detection. In 2018, Yang et al. designed a metalens array by using the polarization-sensitive properties of shape-birefringent medium metasurfaces. Each metalens can only focus on one polarized light, so the focused spots at different positions on the focal plane are It reflects the intensity of different polarization components of the incident light, so that the full Stokes vector of the incident light can be reconstructed. However, the selection of the target focusing polarization state of the metalens by its design is limited to linear polarization and circular polarization. In order to minimize the influence of noise in the actual polarization detection process, it is necessary to form a regular polyhedron on the Poincaré sphere. For this reason, the design The method of focusing on 6 polarization states is adopted, while the full stokes reconstruction only needs to focus on 4 polarization states at least, so this design is not conducive to the further miniaturization of the device; the utilization efficiency of incident light is low, and each metalens only needs to focus on 4 polarization states. The light intensity of the polarization state to be focused in the incident light is utilized, while the energy of the polarization state orthogonal to it is discarded. In the same year, Arbabi et al. used the phase-independent control capability of a set of orthogonal polarization states by means of shape-birefringent metasurfaces to achieve separate focusing on a set of orthogonal polarization states, and then realized multiple sets of orthogonal polarization states through spatial multiplexing. Separate focusing of the cross-polarization states enables full Stokes vector reconstruction of the incident light. The choice of the target focusing polarization state in this design is also limited, because the selected focusing objects must be pairs of orthogonal polarization states, so the design of focusing on 6 polarization states is also used, which is not conducive to the miniaturization of the device. In 2019, Rubin et al. proposed a design framework called "Matrix Fourier Optics", and based on this design, realized a metasurface grating, which can present a polarization response similar to that of a polarizer at different diffraction orders, and There is no restriction on the target polarization state, thus realizing beam splitting for multiple polarization states, combined with the imaging system, full Stokes polarization imaging can be realized. However, using the "matrix Fourier optics" proposed in this work cannot complete the metasurface design that can focus the beam, so an additional lens is needed for auxiliary focusing, which is not conducive to the miniaturization of the device; the polarization imaging system based on this grating The structure is complex and the degree of integration is poor.

Contents of the invention

Aiming at the defects of the prior art, the object of the present invention is to provide a full Stokes polarimeter based on a dielectric metasurface, aiming at realizing the functions of integrating beam splitting and focusing of multiple arbitrary polarization states on the same metasurface, and improving the device integration.

In order to achieve the above object, the present invention proposes a metasurface design framework, and is used to realize a full Stokes polarimeter based on a dielectric metasurface, which includes a layer of dielectric metasurface and a detector array, and the detector array is located in the dielectric metasurface. at the focal plane of the surface;

Among them, the dielectric metasurface is composed of the same basic modules arranged periodically, and the transverse dimension of each basic module is a square.

Divide the square area matching each basic module on the focal plane into four congruent sub-square areas. When the incident light illuminates the basic module vertically, the four different polarization state components in the light field received by the basic module The center of the sub-square area in the lower left corner, the center of the sub-square area in the upper left corner, the center of the sub-square area in the lower right corner, and the center of the sub-square area in the upper right corner will be respectively focused. The Stokes vectors corresponding to these polarization states form four vertices of a regular tetrahedron on the Poincaré sphere, thereby satisfying the condition of minimizing the influence of noise.

Preferably, the incident light passes through the basic module to form four focused light spots on the detector located on the focal plane, and the intensity of these light spots can be used to reconstruct the polarization information of the incident light. The basic module is spliced by a large number of basic units, and each basic unit is composed of a dielectric column with shape birefringence and a dielectric substrate.

Preferably, the dielectric column with shape birefringence can be an elliptical column or a rectangular column, and the selected material can be titanium dioxide, silicon, germanium or zinc sulfide.

表示。其中参数

θ为介质柱绕经过截面中心并垂直于基本模块表面的转轴旋转的角度；

表示基本单元在旋转角θ为0时对横向线偏振入射光的相位变化能力，/>

表示基本单元在旋转角θ为0时对纵向线偏振入射光的相位变化能力。/>

与基本单元的结构存在一一对应的映射关系F：Polarization tuning capability of a single basic unit using a Jones matrix

express. where parameters

θ is the rotation angle of the medium column around the axis passing through the center of the section and perpendicular to the surface of the basic module;

Indicates the phase change capability of the basic unit for transverse linearly polarized incident light when the rotation angle θ is 0, />

Indicates the phase change capability of the basic unit for longitudinal linearly polarized incident light when the rotation angle θ is 0. />

There is a one-to-one mapping relationship F with the structure of the basic unit:

表示，以下简写为/>

其中/>

表示基本模块上每个基本单元的坐标。Among them, D _x is the transverse length of the cross-section of the dielectric column, the length of the major axis for the ellipse, and the length of the transverse side for the rectangle; D _y is the longitudinal length of the cross-section of the medium column. The basic module can use a Jones matrix distribution function

means, hereinafter abbreviated as />

where />

Indicates the coordinates of each basic unit on the basic module.

The polarimeter described above is implemented based on the design framework described below.

在通过基本模块后偏振态在该基本模块后表面上的分布变为/>

电磁学理论中的等效原理指出，当全空间由一个平面所分割，对于半空间内的电磁场分布，可等效为分布在平面上的磁流源的贡献。此处该磁流源分布可表示为：When the incident polarized light is uniformly distributed on the surface of the same basic module, that is, the polarization state received at any position on the surface is

The distribution of the polarization state on the rear surface of the basic module after passing through the basic module becomes />

The equivalence principle in the theory of electromagnetism points out that when the whole space is divided by a plane, the electromagnetic field distribution in the half space can be equivalent to the contribution of the magnetic current source distributed on the plane. Here the magnetic current source distribution can be expressed as:

为垂直于基本模块并指向探测器平面的单位向量，并且上式省略了一项常数因子。in

is a unit vector perpendicular to the basic module and pointing to the detector plane, and a constant factor is omitted from the above formula.

其在空间上任意一点/>

处的电场贡献可由下式给出：According to the relevant electromagnetic theory, for the known magnetic current source distribution

its arbitrary point in space />

The electric field contribution at can be given by:

为并矢格林函数，描述了/>

处的单位磁流源在/>

处的复振幅贡献，S所描述的区域为该基本模块的整个后表面，上式也省略了一项常数因子。in

is the dyadic Green's function, describing the />

The unit magnetic current source at />

The complex amplitude contribution at , the area described by S is the entire rear surface of the basic module, and a constant factor is also omitted in the above formula.

的表达式带入至上述公式，可整理为如下形式：magnetic current source

The expression of is brought into the above formula, which can be organized into the following form:

上的复振幅取值可以表示为：Therefore, for any form of polarized light uniformly incident on the surface of a single basic module, at any spatial point in the space behind the basic module

The complex amplitude value on can be expressed as:

in

和/>

有关。/>

表示一个基本模块上所有基本单元的/>

的集合，它唯一决定了/>

的取值。/>

反映了该基本模块在空间点/>

处的偏振响应能力，并且可以通过/>

直接对其进行优化。is a matrix independent of the polarization state of the incident light, which is only related to the selected spatial point

and />

related. />

Indicates the /> of all basic units on a basic module

The set of , which uniquely determines the />

value of . />

Reflects the basic module at point /> in space

Polarization responsiveness at and can be passed by />

directly optimize it.

表示在庞加莱球上所选取的位于一个正四面体上的四个偏振态，/>

为焦平面上希望/>

聚焦的位置坐标，即四个子正方形的中心区域，/>

表示与/>

正交的Jones矢量。则入射光为/>

时在

处的光强即可表示为/>

与之正交的偏振光/>

入射时在/>

处的光强即可表示为/>

优化目标希望{I_l}最大化，同时/>

最小化。Based on the framework mentioned above, the design of the full Stokes polarimeter is completed. set up

Indicates the four polarization states on a regular tetrahedron selected on the Poincaré sphere, />

For the focal plane desired />

Focused position coordinates, i.e. the central area of the four sub-squares, />

express with />

Orthogonal Jones vectors. Then the incident light is />

when

The light intensity at can be expressed as />

Orthogonal polarization />

Incidence at />

The light intensity at can be expressed as />

The optimization objective hopes to maximize {I _l }, while />

minimize.

为如下优化问题的解：Specifically, in the present invention,

is the solution to the following optimization problem:

约束为接近于0的值，以保证聚焦效果的偏振敏感性。Among them, std() means to take the standard deviation, and D is a hyperparameter, which is a positive number close to 0. The optimization goal is to maximize the sum of {I _l }, while constraining the standard deviation of {I _l } to a value close to 0, so that the four focused spots have relatively low intensity differences while having high light intensities. In addition will

Constrained to a value close to 0 to guarantee the polarization sensitivity of the focusing effect.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

(1) The full stokes polarimeter based on the dielectric metasurface provided by the present invention can arbitrarily select the target polarization states of interest and their respective focal points in the design framework attached to it, and can easily realize the unachievable problems of traditional design ideas Polarization state detection of targets with regular tetrahedral distribution. Compared with the existing design for detection of six polarization states distributed by regular polyhedrons, it has a smaller volume, and compared with the existing design for detection of four polarization states distributed by non-regular polyhedrons, it has smaller noise interference.

(2) The full stokes polarimeter based on the dielectric metasurface provided by the present invention can integrate all functions on the same metasurface because it is optimized and realized based on the metasurface design framework also constructed in the present invention, compared to the Designing the focusing lens separately for each polarization state and adopting the design method of spatial multiplexing has higher absolute efficiency.

(3) The full Stokes polarimeter based on the dielectric metasurface provided by the present invention can be directly integrated on the detector array of the camera, which has a higher integration level than the existing polarization imaging system based on the metasurface grating.

(4) The full stokes polarimeter based on the dielectric metasurface provided by the present invention, its basic unit structure substrate is alumina, quartz or silicon, and the material of the cylinder is a medium (such as: silicon, germanium, titanium dioxide, zinc sulfide), using The dielectric material modulates the incident light. Titanium dioxide and zinc sulfide have very little loss in the visible light band, and silicon and germanium have almost no loss in the near-infrared to infrared band, which greatly reduces the light loss and improves the detection sensitivity.

Description of drawings

1 is a schematic diagram of the overall structure of a full Stokes polarimeter based on a dielectric metasurface provided by an embodiment of the present invention;

Fig. 2 is the structural representation of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided by the embodiment;

Fig. 3 is the structural representation of the basic unit of the full Stokes polarimeter based on the dielectric metasurface provided by the embodiment;

Fig. 4 is the top view of the basic unit of the full Stokes polarimeter based on the dielectric metasurface provided by the embodiment;

Fig. 5 is the structural plan view of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided in embodiment 1;

Fig. 6 is the light intensity distribution on the focal plane after different polarized lights pass through the basic module in embodiment 1;

Fig. 7 is the structural top view of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided in embodiment 2;

Fig. 8 is the light intensity distribution on the focal plane after different polarized lights pass through the basic module in embodiment 2;

Fig. 9 is the structural plan view of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided in embodiment 3;

Fig. 10 is the light intensity distribution on the focal plane after different polarized lights pass through the basic module in embodiment 3;

Fig. 11 is the structural top view of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided by embodiment 4;

Fig. 12 is the distribution of light intensity on the focal plane after different polarized lights pass through the basic module in embodiment 4.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute conflicts with each other.

Figure 1 is a schematic diagram of the overall structure of the full Stokes polarimeter based on the dielectric metasurface provided by the embodiment, and the CCD array 2 is integrated at the focal plane behind the dielectric metasurface 1; the dielectric metasurface is periodically arranged by a plurality of basic modules Composition, each basic module works independently to obtain the polarization information of the incident light incident on the surface of the basic module; each small square divided by the solid line in the dielectric metasurface 1 in Fig. is the incident light, and the dotted inclined cone between the dielectric metasurface and the CCD array indicates the converging light of different polarization states by the dielectric metasurface.

Fig. 2 is a schematic structural diagram of a basic module of a full-stokes polarimeter based on a dielectric metasurface provided in an embodiment.

The above-mentioned basic modules converge the four polarization components that can form regular tetrahedrons in the Poincaré sphere in the incident light to the CCD array; the above four polarization components form four focusing spots in the centers of the four sub-square regions on the CCD array ; Among Fig. 2, the short dotted lines on the CCD array have shown four sub-square regions; Among Fig. 2, the long dotted lines have shown that the incident light that arrives on this basic module is focused on different regions on the CCD array by different polarization components after passing through the basic module process.

Fig. 3 is the schematic structural view of the basic unit of the full Stokes polarimeter based on the dielectric metasurface provided by the embodiment, and Fig. 4 is a corresponding top view; in the present embodiment, the basic unit includes a cube-shaped substrate 3 and a A dielectric column with an ellipse 4 or a cuboid 5 cross-section, wherein the substrate material includes quartz, silicon, and germanium, and the dielectric column material includes titanium dioxide, silicon, and germanium. The dielectric column is formed by depositing on the substrate; multiple basic units are spliced to form a basic module.

The substrate period P of the basic unit is selected between 0.5λ～λ to achieve the scale of Mie resonance and reduce the diffraction effect, where λ is the working wavelength of the incident light in the substrate material; the height H of the dielectric column of the basic unit needs to satisfy H> λ ₀ /(n-1) to ensure that the phase modulation range of 2π can be covered, where λ ₀ is the wavelength of the incident light in vacuum, and n is the refractive index of the dielectric column; as shown in Figure 4, D _x and D _y Respectively refer to the major and minor axis diameters of the elliptical cylinder cross-section or the length and width of the rectangular cylinder cross-section, and the value range of D _x and D _y is between 0.1 times H and 0.9 times H; as shown in Figure 4, θ Angle refers to the angle of rotation of the dielectric column, with the axis of rotation passing through the center of the section and perpendicular to the substrate. The mapping relationship F can be determined by scanning the phase modulation capabilities of the basic unit under different (D _x , D _y ) combinations through a finite difference time domain (FDTD) algorithm.

With the help of the time domain finite difference algorithm, the light intensity distribution on the focal plane when different polarized light is incident can be simulated, and then the light intensity of the spot in the four sub-square areas can be determined; the Stokes vector of the incident light has a relationship with the four light intensities The following linear relationship:

为斯托克斯矢量，/>

为四个不同偏振分量各自的聚焦光斑的光强所构成的向量，A_4×4为描述/>

与/>

之间线性关系的4×4的矩阵，其具体取值可以通过实验标定；当矩阵标定完成后，对于任意未知偏振的光入射的情况下，利用CCD阵列获取相应的四个光斑的光强，就可通过/>

恢复入射光的stokes矢量，从而唯一确定入射光的偏振信息。in,

is a Stokes vector, />

is the vector composed of the light intensities of the focused spots of the four different polarization components, A _4×4 is the description />

with />

The 4×4 matrix of the linear relationship between, its specific value can be calibrated through experiments; when the matrix calibration is completed, for any incident light of unknown polarization, use the CCD array to obtain the corresponding light intensity of the four spots, you can pass />

Recover the Stokes vector of the incident light, so as to uniquely determine the polarization information of the incident light.

The full Stokes polarimeter based on the dielectric metasurface provided by the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following description will be made by taking the visible light wavelength of 532 nm, the short-wave infrared wavelength of 1550 nm, the mid-wave infrared wavelength of 3 μm, and the long-wave infrared wavelength of 10.6 μm as examples.

Example 1:

Fig. 5 is the top view of the structure of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided in Embodiment 1; for the detection of the polarization state, the FDTD algorithm is used to simulate the linearly polarized light in the x and y directions when it is incident perpendicular to the basic module. The complex amplitude distribution on the plane, and then use the Jones vector of the expected polarization state of the incident light to weight and sum the two sets of complex amplitude distributions to obtain the focal plane light field distribution under any incident light. The Stokes vectors corresponding to the four target polarization states that can form a regular tetrahedron on the Poincaré sphere selected in Embodiment 1 are respectively: [1001] ^T , [10.940-0.33] ^T , [1-0.470 .82-0.33] ^T , [1-0.47-0.82-0.33] ^T . The vacuum wavelength of the incident light is 532 nm.

In Example 1, the base material of the basic unit is quartz, the width P of the transverse section is 420 nanometers, the material of the rectangular dielectric column is titanium dioxide, the height H is 600 nanometers, the length D _x of the rectangular section ranges from 50 to 300 nanometers, and the width D of the rectangular section is The range of _y is 50-300 nanometers, the rotation angle θ of the dielectric column is 0-180 degrees, and the CCD array is 4 microns away from the basic module, which is also the focal length of the basic module.

In order to obtain the influence of the length and width of the cross-section of the rectangular dielectric cylinder on the amplitude and phase of the transmitted light of the horizontal (x direction) polarization incident light with a wavelength of 532nm, the FDTD algorithm is used for simulation; the incident light wavelength is set to 532nm, and the x direction line Polarization, normal incidence from the bottom of the substrate, the boundary conditions around the basic unit are periodic boundary conditions (Periodic), the boundary conditions of the two longitudinal boundaries are perfect absorption boundary conditions (PML), and a point detector is placed directly above the basic unit Record the complex amplitude, and place another surface detector with the same coverage area as the substrate at the same height to record the transmittance. Change the length and width of the transverse section of the rectangular column to conduct multiple simulations, and collect the complex amplitude and transmittance detected above the basic unit under different (D _x , D _y ) combinations, where the phase information is obtained through the complex amplitude, so as to The mapping relationship F is obtained; the simulation results show that the phase modulation capability of this part of the basic unit with high transmittance within the above selected size structure range is sufficient to cover the 2π range.

Fig. 6 is a schematic diagram of light intensity distribution on the focal plane of different polarized lights passing through the basic module in embodiment 1; the dotted line in Fig. 6 divides the focal plane into four sub-square regions. Among them, (a) in Fig. 6 corresponds to the light intensity distribution of the focal plane when the Stokes vector of the incident light is [1001] ^T , and the specific feature is four focused spots, including the focused spot with the polarization component of [1001] ^T 1.1 , the focused spot with the polarization component of [10.940-0.33] ^T is 1.2, the focused spot with the polarized component of [1-0.470.82-0.33] ^T is 1.3, the focused spot with the polarized component of [1-0.47-0.82-0.33] ^T is 1.4 ; It can be seen from the figure that the focused spot with the polarization component of [1001] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(b) in Figure 6 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [10.940-0.33] ^T , and the specific feature is four focused spots, including the focused spot 1.5 with a polarization component of [1001] ^T , the focused spot with the polarization component of [10.940-0.33] ^T is 1.6, the focused spot with the polarized component of [1-0.470.82-0.33] ^T is 1.7, the focused spot with the polarized component of [1-0.47-0.82-0.33] ^T is 1.8 ; It can be seen from the figure that the focused spot with the polarization component of [10.940-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(c) in Figure 6 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1-0.470.82-0.33] ^T , and the specific feature is four focused spots, including the polarization component of [1001] ^T The focused spot of 1.9, the polarization component is [10.940-0.33] ^T The focused spot of 1.10, the polarization component is [1-0.470.82-0.33] ^T The focused spot of 1.11, the polarization component is [1-0.47-0.82-0.33] ^T The focused spot of 1.12; It can be seen from the figure that the focused spot with the polarization component of [1-0.470.82-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(d) in Figure 6 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1-0.47-0.82-0.33] ^T , and the specific feature is four focused spots, including the polarization component of [1001] ^T The focused spot of 1.13, the polarization component is [10.940-0.33] ^T The focused spot of 1.14, the polarization component is [1-0.470.82-0.33] ^T The focused spot of 1.15, the polarization component is [1-0.47-0.82-0.33] ^T The focused spot of 1.16; It can be seen from the figure that the focused spot with the polarization component of [1-0.47-0.82-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

The Stokes vector of the incident light can be recovered by using the light intensity information of the light spots obtained on the four sub-square areas, combined with the linear relationship between the Stokes vector of the incident light obtained in advance and the light intensity of the four positions, In this way, the polarization information of the incident light is uniquely determined.

Example 2:

Fig. 7 is the top view of the structure of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided in embodiment 2; for the detection of the polarization state, the FDTD algorithm is used to simulate the linearly polarized light in the x and y directions when it is incident perpendicular to the basic module. The complex amplitude distribution on the plane, and then use the Jones vector of the expected polarization state of the incident light to weight and sum the two sets of complex amplitude distributions to obtain the focal plane light field distribution under any incident light. The Stokes vectors corresponding to the four target polarization states that can form a regular tetrahedron on the Poincaré sphere selected in embodiment 2 are respectively: [1001] ^T , [10.940-0.33] ^T , [1-0.470 .82-0.33] ^T , [1-0.47-0.82-0.33] ^T . The vacuum wavelength of the incident light is 1550 nm.

In Embodiment 2, the base material of the basic unit is quartz, the width P of the transverse section is 1 micron, the material of the rectangular dielectric column is silicon, the height H is 1.2 microns, the length D _x of the rectangular section is in the range of 100 to 700 nanometers, and the width P of the rectangular section is D The range of _y is 100-700 nanometers, the rotation angle θ of the dielectric column is 0-180 degrees, and the distance between the CCD array and the basic module is 12 microns, which is also the focal length of the basic module.

In order to obtain the influence of the length and width of the cross-section of the rectangular dielectric cylinder on the amplitude and phase of the transmitted light of the horizontal (x direction) polarized incident light with a wavelength of 1550nm, the FDTD algorithm is used for simulation; the incident light wavelength is set to 1550nm, and the x direction line Polarization, normal incidence from the bottom of the substrate, the boundary conditions around the basic unit are periodic boundary conditions (Periodic), the boundary conditions of the two longitudinal boundaries are perfect absorption boundary conditions (PML), and a point detector is placed directly above the basic unit Record the complex amplitude, and place another surface detector with the same coverage area as the substrate at the same height to record the transmittance. Change the length and width of the transverse section of the rectangular column to conduct multiple simulations, and collect the complex amplitude and transmittance detected above the basic unit under different (D _x , D _y ) combinations, where the phase information is obtained through the complex amplitude, so as to The mapping relationship F is obtained; the simulation results show that the phase modulation capability of this part of the basic unit with high transmittance within the above selected size structure range is sufficient to cover the 2π range.

Fig. 8 is a schematic diagram of light intensity distribution on the focal plane of different polarized lights passing through the basic module in embodiment 2; the dotted line in Fig. 8 divides the focal plane into four sub-square regions. Among them, (a) in Figure 8 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1001] ^T , and the specific feature is four focused spots, including the focused spot 1.1 with the polarization component of [1001] ^T , the focused spot with the polarization component of [10.940-0.33] ^T is 1.2, the focused spot with the polarized component of [1-0.470.82-0.33] ^T is 1.3, the focused spot with the polarized component of [1-0.47-0.82-0.33] ^T is 1.4 ; It can be seen from the figure that the focused spot with the polarization component of [1001] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(b) in Figure 8 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [10.940-0.33] ^T , and the specific feature is four focused spots, including the focused spot 1.5 with a polarization component of [1001] ^T , the focused spot with the polarization component of [10.940-0.33] ^T is 1.6, the focused spot with the polarized component of [1-0.470.82-0.33] ^T is 1.7, the focused spot with the polarized component of [1-0.47-0.82-0.33] ^T is 1.8 ; It can be seen from the figure that the focused spot with the polarization component of [10.940-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(c) in Figure 8 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1-0.470.82-0.33] ^T , and the specific feature is four focused spots, including the polarization component of [1001] ^T The focused spot of 1.9, the polarization component is [10.940-0.33] ^T The focused spot of 1.10, the polarization component is [1-0.470.82-0.33] ^T The focused spot of 1.11, the polarization component is [1-0.47-0.82-0.33] ^T The focused spot of 1.12; It can be seen from the figure that the focused spot with the polarization component of [1-0.470.82-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(d) in Figure 8 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1-0.47-0.82-0.33] ^T , and the specific feature is four focused spots, including the polarization component of [1001] ^T The focused spot of 1.13, the polarization component is [10.940-0.33] ^T The focused spot of 1.14, the polarization component is [1-0.470.82-0.33] ^T The focused spot of 1.15, the polarization component is [1-0.47-0.82-0.33] ^T The focused spot of 1.16; It can be seen from the figure that the focused spot with the polarization component of [1-0.47-0.82-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

The Stokes vector of the incident light can be recovered by using the light intensity information of the light spots obtained on the four sub-square areas, combined with the linear relationship between the Stokes vector of the incident light obtained in advance and the light intensity of the four positions, In this way, the polarization information of the incident light is uniquely determined.

Example 3:

Fig. 9 is the top view of the structure of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided in embodiment 3; for the detection of the polarization state, the FDTD algorithm is used to simulate the linearly polarized light in the x and y directions when it is incident perpendicular to the basic module. The complex amplitude distribution on the plane, and then use the Jones vector of the expected polarization state of the incident light to weight and sum the two sets of complex amplitude distributions to obtain the focal plane light field distribution under any incident light. The Stokes vectors corresponding to the four target polarization states that can form a regular tetrahedron on the Poincare sphere selected in Embodiment 3 are respectively: [1001] ^T , [10.940-0.33] ^T , [1-0.470 .82-0.33] ^T , [1-0.47-0.82-0.33] ^T . The vacuum wavelength of the incident light is 3 μm.

In Embodiment 3, the base material of the basic unit is silicon, the width P of the transverse section is 1.2 microns, the material of the rectangular dielectric column is silicon, the height H is 4 microns, the length D _x of the rectangular section ranges from 300 to 900 nanometers, and the width D of the rectangular section is The range of _y is 300-900 nanometers, the rotation angle θ of the dielectric column is 0-180 degrees, and the distance between the CCD array and the basic module is 23 microns, which is also the focal length of the basic module.

In order to obtain the influence of the length and width of the cross-section of the rectangular dielectric cylinder on the amplitude and phase of the transmitted light with a wavelength of 3 μm in the horizontal (x direction) polarization state, the FDTD algorithm is used for simulation; the incident light wavelength is set to 3 μm, and the x direction line Polarization, normal incidence from the bottom of the substrate, the boundary conditions around the basic unit are periodic boundary conditions (Periodic), the boundary conditions of the two longitudinal boundaries are perfect absorption boundary conditions (PML), and a point detector is placed directly above the basic unit Record the complex amplitude, and place another surface detector with the same coverage area as the substrate at the same height to record the transmittance. Change the length and width of the transverse section of the rectangular column to conduct multiple simulations, and collect the complex amplitude and transmittance detected above the basic unit under different (D _x , D _y ) combinations, where the phase information is obtained through the complex amplitude, so as to The mapping relationship F is obtained; the simulation results show that the phase modulation capability of this part of the basic unit with high transmittance within the above selected size structure range is sufficient to cover the 2π range.

Fig. 10 is a schematic diagram of light intensity distribution on the focal plane of different polarized lights passing through the basic module in embodiment 3; the dotted line in Fig. 10 divides the focal plane into four sub-square regions. Among them, (a) in Figure 10 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1001] ^T , and the specific feature is four focused spots, including the focused spot 1.1 with the polarization component of [1001] ^T , the focused spot with the polarization component of [10.940-0.33] ^T is 1.2, the focused spot with the polarized component of [1-0.470.82-0.33] ^T is 1.3, the focused spot with the polarized component of [1-0.47-0.82-0.33] ^T is 1.4 ; It can be seen from the figure that the focused spot with the polarization component of [1001] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(b) in Figure 10 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [10.940-0.33] ^T , and the specific feature is four focused spots, including the focused spot 1.5 with the polarization component of [1001] ^T , the focused spot with the polarization component of [10.940-0.33] ^T is 1.6, the focused spot with the polarized component of [1-0.470.82-0.33] ^T is 1.7, the focused spot with the polarized component of [1-0.47-0.82-0.33] ^T is 1.8 ; It can be seen from the figure that the focused spot with the polarization component of [10.940-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(c) in Figure 10 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1-0.470.82-0.33] ^T , and the specific feature is four focused spots, including the polarization component of [1001] ^T The focused spot of 1.9, the polarization component is [10.940-0.33] ^T The focused spot of 1.10, the polarization component is [1-0.470.82-0.33] ^T The focused spot of 1.11, the polarization component is [1-0.47-0.82-0.33] ^T The focused spot of 1.12; It can be seen from the figure that the focused spot with the polarization component of [1-0.470.82-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(d) in Figure 10 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1-0.47-0.82-0.33] ^T , and the specific feature is four focused spots, including the polarization component of [1001] ^T The focused spot of 1.13, the polarization component is [10.940-0.33] ^T The focused spot of 1.14, the polarization component is [1-0.470.82-0.33] ^T The focused spot of 1.15, the polarization component is [1-0.47-0.82-0.33] ^T The focused spot of 1.16; It can be seen from the figure that the focused spot with the polarization component of [1-0.47-0.82-0.33] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

The Stokes vector of the incident light can be recovered by using the light intensity information of the light spots obtained on the four sub-square areas, combined with the linear relationship between the Stokes vector of the incident light obtained in advance and the light intensity of the four positions, In this way, the polarization information of the incident light is uniquely determined.

Example 4:

Fig. 11 is the top view of the structure of the basic module of the full Stokes polarimeter based on the dielectric metasurface provided in embodiment 4; for the detection of the polarization state, the FDTD algorithm is used to simulate the linearly polarized light in the x and y directions when it is incident perpendicular to the basic module. The complex amplitude distribution on the plane, and then use the Jones vector of the expected polarization state of the incident light to weight and sum the two sets of complex amplitude distributions to obtain the focal plane light field distribution under any incident light. The Stokes vectors corresponding to the four target polarization states that can form a regular tetrahedron on the Poincaré sphere selected in Embodiment 4 are respectively: [1-0.8200.58] ^T , [10.8200.58] ^T , [100.82-0.58] ^T , [10-0.82-0.58] ^T . The vacuum wavelength of the incident light is 10.6 μm.

In embodiment 4, the base material of the basic unit is germanium, the lateral cross-sectional width P is 2.5 microns, the material of the elliptical dielectric column is germanium, the height H is 12 microns, and the major axis D _x of the elliptical cross-section ranges from 600 to 2000 nanometers. The section width D _y ranges from 600 to 2000 nanometers, the dielectric column rotation angle θ is 0 to 180 degrees, and the CCD array is 55 microns away from the basic module, which is also the focal length of the basic module.

In order to obtain the influence of the length and width of the cross-section of the rectangular dielectric cylinder on the amplitude and phase of the transmitted light of the horizontal (x direction) polarized incident light with a wavelength of 10.6 μm, the FDTD algorithm is used for simulation; the incident light wavelength is set to 10.6 μm, x The direction is linearly polarized, normal incidence from the bottom of the substrate, the boundary conditions around the basic unit are periodic boundary conditions (Periodic), the boundary conditions of the two vertical boundaries are perfect absorption boundary conditions (PML), and a point is placed directly above the basic unit The detector records the complex amplitude, and at the same height, another surface detector with the same coverage area as the substrate is placed to record the transmittance. Change the length and width of the transverse section of the rectangular column to conduct multiple simulations, and collect the complex amplitude and transmittance detected above the basic unit under different (D _x , D _y ) combinations, where the phase information is obtained through the complex amplitude, so as to The mapping relationship F is obtained; the simulation results show that the phase modulation capability of this part of the basic unit with high transmittance within the above selected size structure range is sufficient to cover the 2π range.

Fig. 12 is a schematic diagram of light intensity distribution on the focal plane of different polarized light passing through the basic module in embodiment 1; the dotted line in Fig. 6 divides the focal plane into four sub-square regions. Among them, (a) in Figure 12 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [1-0.8200.58] ^T , and the specific feature is four focused spots, including polarization components of [1-0.8200 .58] ^T focus spot 1.1, polarization component is [10.8200.58] ^T focus spot 1.2, polarization component is [100.82-0.58] ^T focus spot 1.3, polarization component is [10-0.82-0.58] ^T focus Spot 1.4; It can be seen from the figure that the focused spot with a polarization component of [1-0.8200.58] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

(b) in Figure 12 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [10.8200.58] ^T , and the specific feature is four focused spots, including the polarization component of [1-0.8200.58] ^T Focusing spot of 1.5, polarization component of [10.8200.58] ^T of focusing spot of 1.6, polarization component of [100.82-0.58] ^T of focusing spot of 1.7, polarization component of [10-0.82-0.58] ^T of focusing spot of 1.8; by It can be seen from the figure that the focused spot with the polarization component of [10.8200.58] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensities among the three are basically the same.

(c) in Figure 12 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [100.82-0.58] ^T , and the specific feature is four focused spots, including the polarization component of [1-0.8200.58] ^T Focusing spot of 1.9, polarization component of [10.8200.58] ^T of focusing spot of 1.10, polarization component of [100.82-0.58] ^T of focusing spot of 1.11, polarization component of [10-0.82-0.58] ^T of focusing spot of 1.12; by It can be seen from the figure that the focused spot with the polarization component of [100.82-0.58] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensities among the three are basically the same.

(d) in Figure 12 corresponds to the light intensity distribution at the focal plane when the Stokes vector of the incident light is [10-0.82-0.58] ^T , and the specific feature is four focused spots, including the polarization component of [1-0.8200.58 ] The focus spot of ^T is 1.13, the polarization component is [10.8200.58] The focus spot of ^T is 1.14, the polarization component is [100.82-0.58] The focus spot of ^T is 1.15, the polarization component is [10-0.82-0.58] The focus spot of ^T is 1.16 ; It can be seen from the figure that the focused spot with the polarization component of [10-0.82-0.58] ^T has the largest light intensity, and the other three spots have smaller light intensities, and the intensity among the three is basically the same.

The Stokes vector of the incident light can be recovered by using the light intensity information of the light spots obtained on the four sub-square areas, combined with the linear relationship between the Stokes vector of the incident light obtained in advance and the light intensity of the four positions, In this way, the polarization information of the incident light is uniquely determined.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (7)

1. The full stokes polarization measuring instrument based on the medium super surface is characterized by comprising the medium super surface and a detector array, wherein the detector array is positioned at a focal plane of the medium super surface; the medium super surface is formed by periodically arranging the same basic modules, and the cross section of each basic module is square;

when the incident light vertically irradiates the basic module, the basic module carries out polarization regulation and control on the incident light by optimizing parameters of the basic module, a square area matched with each basic module on a focal plane is divided into four congruent sub-square areas, four different polarization state components are respectively focused at the center of the sub-square area at the left upper corner of the center of the sub-square area at the left lower corner, the center of the sub-square area at the right lower corner and the center of the sub-square area at the right upper corner, and Stokes vectors corresponding to the polarization states form four vertexes of a regular tetrahedron on a Poincar sphere.

2. The full stokes polarization measurement instrument based on dielectric supersurface of claim 1, wherein the base module comprises a plurality of base units, each base unit comprising a dielectric pillar having shape birefringence properties and a dielectric substrate.

3. The medium super surface based full stop polarization measurement instrument according to claim 1, wherein for incident light uniformly distributed on the same basic module surface

The complex amplitude distribution is +.>

The complex amplitude values above are expressed as:

wherein,,

is a matrix irrelevant to incident light, reflecting field point +.>

Polarization response capability at ∈>

Representing +.about.all basic units on a basic module>

Is a set of (3).

4. The medium super surface based full stop polarization measuring instrument according to claim 3, wherein,

solution to the following optimization problem:

wherein,,

representing the four selected polarization states on a regular tetrahedron on the poincare sphere,

is hoped to be->

Focusing position coordinates>

Representation and->

Orthogonalization of Jones vectors, std, represents taking standard deviation, D is a super parameter greater than 0.

5. The medium super surface based full stokes polarization measurement instrument according to claim 4, wherein the polarization control capability of a single basic unit is represented by jones matrix

Representation, wherein the parameter->

θ is the angle by which the dielectric pillar rotates about a rotation axis passing through the center of the cross section and perpendicular to the surface of the base module, +.>

Indicating the phase-change capability of the basic cell for transversely linearly polarized incident light at a rotation angle θ of 0, is>

Indicating the phase change capability of the basic unit for longitudinally linearly polarized incident light at a rotation angle θ of 0; />

There is a one-to-one mapping relation F to the structure of the base unit:

wherein D is _x Is the transverse length of the cross section of the medium column, D _y For longitudinal length of cross section of dielectric column, the basic module uses a Jones matrix distribution function

Representation of->

Representing the coordinates of each elementary cell on the elementary module.

6. The medium super surface based full stokes polarization measurement instrument of claim 1, wherein the medium column is an elliptic column or a rectangular column.

7. The medium super surface based full stokes polarization measurement instrument of claim 6, wherein the material of the medium column is titanium dioxide, silicon, germanium or zinc sulfide.

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