A snapshot broadband full Stokes vector measuring instrument and measuring method

Abstract

The present invention discloses a snapshot wideband full Stokes vector measuring instrument and a measuring method, belonging to the field of micro-nano optics, which includes a wave plate array, a linear polarizer, a light intensity detector and a data processing module; the linear polarizer is installed on the light intensity detector, the wave plate array is installed on the linear polarizer, and the size of the wave plate array is not larger than that of the linear polarizer; the light intensity detector and the data processing module are electrically connected. The wave plate array is completely arranged on the linear polarizer, reducing the alignment accuracy during use. In addition, through the wave plate array, each small area of the photosensitive area can correspondingly capture the light intensity values under different polarization modulations, enabling the calculation and inversion of the polarization state in a single measurement and ensuring the real-time nature of the measurement results. At the same time, combined with the broadband characteristics of the sub-wavelength dielectric wire grid, the defect of limited working bandwidth in the existing full Stokes vector measurement technology is overcome.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano optics and relates to a measuring instrument, specifically a snapshot wideband full Stokes vector measuring instrument and a measuring method. Background Art

[0002] A polarization measuring instrument is an optical instrument used for optical property analysis and characterization. During the processes of reflection, transmission, or scattering of light in a medium, polarization state changes that are significantly correlated with its structural properties, material type, surface roughness, and texture characteristics will occur. By precisely measuring the polarization state change information generated after the signal light is modulated by the medium and according to the quantitative model of the interaction between light and matter, non-contact property analysis and characterization of the medium can be achieved, and it has a wide range of application scenarios in the fields of optical sensing, laser communication, and semiconductor industry.

[0003] At present, the technical solutions for measuring the polarization state of incident light are mainly divided into time-sharing type, amplitude-division type, Fourier type and sub-focal plane type. Patent No. CN201820907945.5 provides a time-sharing type polarization state measuring device. This method combines a phase retarder and a linear polarizer, and by collecting the light intensity values received by the detector at different azimuth angles of the phase retarder, uses these light intensity values to reconstruct the Stokes vector of the incident light; Patent No. CN202310966473.6 provides an amplitude-division type polarization measurement system and method for all Stokes parameters. This method is based on a Michelson interferometer device, divides the incident light into four beams of light by amplitude and sequentially passes through a polarizer and an imaging module, and obtains the full Stokes vector of the entire beam to be measured in a wide wavelength band by analyzing the polarization interference pattern on the detector; Patent No. CN202010446907.6 provides a device and method for detecting the polarization state of light waves based on Fourier analysis. This method converts the incident light with an unknown polarization state into a specific vector polarization light field through a zero-order vortex half-wave plate, and after being modulated by a polarizer, forms an intensity pattern with a bright and dark wedge-shaped distribution on the detector. Its intensity distribution satisfies the scalar diffraction theorem with the initial polarization state. By performing Fourier analysis on the intensity image collected by the detector after preprocessing, the initial polarization state of the incident light can be calculated; Patent No. CN201810111548.1 proposes a compact polarization state measuring instrument based on a dielectric metasurface. This method uses nanoantennas to form a polarization-specific lens array, places the detector array at the focal length of the lens array, and calculates the Stokes vector of the incident light by extracting the focusing intensity of different nanoantenna array regions. These existing technologies can measure the Stokes parameters of incident light, but there are the following deficiencies: (1) The core of the time-sharing type polarization detection technology is to modulate the intensity of incident light by controlling the rotation of the phase retarder device, and it is impossible to achieve real-time measurement of the polarization state in principle; (2) Due to the need to use a polarization beam splitter to separate the light beams of two orthogonal polarization states and then obtain and process the polarization information through multiple detectors or an interference structure in the amplitude-division type, the entire system structure is very large and the calibration difficulty is relatively high; (3) The Fourier type polarization detection technology first loads the incident light into a specific complex amplitude distribution to form an incident light field, so that its polarization state presents a corresponding relationship with the light intensity distribution of far-field diffraction. Therefore, this system requires a sufficient optical path or a lens combination, and the entire structure is difficult to integrate, and the effect of this method is not good in a wide wavelength band; (4) Although the sub-focal plane type polarization detection technology based on a nanoantenna array can achieve snapshot polarization detection, the nanoantenna structure usually has a low extinction ratio, which means that the efficiency of separating and detecting light signals of different polarization states is not high, thus affecting the detection accuracy and the sensitivity to weak signals. At the same time, due to the resonant characteristics of the nanoantenna, its operating wavelength range is restricted to narrow-band incident light in principle, making it difficult to operate effectively in a wide spectral range.These limiting factors greatly narrow the practical applicability of this technology in multi-band and wide-band applications, restricting its wide application in various complex optical environments. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a snapshot wideband full Stokes vector measuring instrument and a measuring method to solve the technical problem that the existing technology cannot simultaneously achieve wide-band and high extinction ratio full Stokes vector measurement.

[0005] To solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0006] A snapshot wideband full Stokes vector measuring instrument includes a waveplate array, a linear polarizer, a light intensity detector, and a data processing module;

[0007] The linear polarizer is installed on the light intensity detector, the waveplate array is installed on the linear polarizer, and the size of the waveplate array is not larger than the size of the linear polarizer;

[0008] The light intensity detector is electrically connected to the data processing module.

[0009] The present invention also includes the following technical features:

[0010] The waveplate array includes basic units, each basic unit includes a dielectric substrate and a sub-wavelength dielectric wire grid disposed on the dielectric substrate; the phase delay amount of each sub-wavelength dielectric wire grid is constant, and the azimuth angle of each sub-wavelength dielectric wire grid relative to the transmission direction of the linear polarizer is different, where , is a set of positive integers.

[0011] The distance between the photosensitive area of the light intensity detector and the linear polarizer satisfies the following formula:

[0012]

[0013] Where:

[0014] is the side length of the basic unit of the waveplate array (1), μm;

[0015] is the working wavelength of the light intensity detector, nm.

[0016] The period of the sub-wavelength dielectric wire grid of the waveplate array is less than the working wavelength λ; the extinction ratio of each basic unit and the linear polarizer is greater than 1000:1.

[0017] The material of the sub-wavelength dielectric wire grid of the wave plate array is silicon nitride, silicon carbide or titanium dioxide; the material of the dielectric substrate is quartz, sapphire or N-BK7.

[0018] A photoresist layer is provided at the edge of the surface of the wave plate array close to the linear polarizer;

[0019] The vibration direction of the linear polarizer is unique.

[0020] The material of the photoresist layer is SU8.

[0021] A snapshot broadband full Stokes vector measurement method, based on the snapshot broadband full Stokes vector measuring instrument, specifically includes the following steps:

[0022] Step 1, the light to be measured is incident on the wave plate array of the snapshot broadband full Stokes vector measuring instrument;

[0023] Step 2, the light intensity detector transmits the collected light intensity value to the data processing module, and the data processing module calculates the Stokes vector of the light to be measured using the following formula ;

[0024]

[0025] Where:

[0026] is the light intensity value detected by the photosensitive area of the light intensity detector corresponding to the

[0027] th basic unit, W / m²; is the azimuth angle of the sub-wavelength dielectric wire grid of the

[0028] th basic unit, rad;

[0029] In step 2, the solution methods for the azimuth angle and the phase delay are as follows:

[0030] S1, the double-layer sub-wavelength gratings of different basic units decompose the light to be measured into a set of elliptical polarization states ;

[0031] The elliptical polarization state is non-coplanar on the Poincaré sphere;

[0032] S2, according to the coordinate values of the elliptical polarization state on the Poincaré sphere, calculate the azimuth angle and phase delay of the elliptical polarization state by the Davidson formula or the cross product method Volume of the formed polyhedron ;

[0033]

[0034]

[0035]

[0036] S3, the particle swarm optimization algorithm is used to perform global traversal and optimization in the parameter space to obtain the maximum volume discriminant function ;

[0037] The azimuth angle of the parameter space is and the phase delay is ;

[0038] S4, through multiple iterations and global search of and the optimal satisfying the maximum volume discriminant function and the optimal .

[0039] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0040] (Ⅰ) In the present invention, the waveplate array is completely arranged on the linear polarizer, reducing the alignment accuracy during use. In addition, through the waveplate array, each small area of the photosensitive area can correspondingly capture the light intensity values under different polarization modulations, enabling the calculation and inversion of the polarization state in a single measurement and ensuring the real-time nature of the measurement results. At the same time, combined with the broadband characteristics of the sub-wavelength dielectric wire grid, the defect of limited working bandwidth in the existing full Stokes vector measurement technology is overcome.

[0041] (Ⅱ) In the structure of the present invention, by optimizing the basic parameters such as the phase delay and azimuth angle of the sub-wavelength dielectric wire grid, the optimal distribution of the ellipsometric state modulation basis vectors in each area thereof is realized on the surface of the Poincaré sphere, greatly reducing the influence of factors such as light intensity jitter and noise error on the polarization state recovery in the polarization measurement system, improving the measurement accuracy and anti-noise ability of the system. And compared with the metasurface structure, the sub-wavelength dielectric wire grid has a higher polarization extinction ratio, more accurate polarization conversion, minimizing the calibration pressure of the system as much as possible, and solving the technical problem that it is impossible to simultaneously achieve full Stokes vector measurement with a wide band and a high extinction ratio in the prior art.

[0042] (III) The present invention has high integration and independence. It realizes multi-functional integration through multiple sub-wavelength dielectric wire grids, such as polarization state detection and real-time computational inversion, avoiding the dependence on external devices such as wave plates and beam splitters in traditional systems, thus simplifying the system architecture and enhancing the operation convenience. At the same time, the system does not require high-energy-consuming devices, has the advantage of low power consumption, and is suitable for energy-constrained scenarios such as unmanned aerial vehicle remote sensing and portable medical imaging. In addition, as a miniaturized and integrated independent component, the present invention can provide a modular and lightweight solution for polarization state analysis systems, meeting the application requirements with strict limitations on space and energy consumption. Description of the Drawings

[0043] Figure 1 is a schematic structural diagram of the snapshot-type broadband full Stokes vector measuring instrument of the present invention;

[0044] Figure 2 is a schematic diagram of the distribution of polarization basis vectors on the Poincaré sphere under different detection times;

[0045] Figure 3 is the curve of the figure of merit function of the measuring instrument under different detection times;

[0046] Figure 4(a) is a schematic diagram of the working crosstalk of the snapshot-type broadband full Stokes vector measuring instrument;

[0047] Figure 4(b) is a side view structural diagram of the snapshot-type broadband full Stokes vector measuring instrument;

[0048] Figure 5(a) is a schematic structural diagram of the sub-wavelength dielectric wire grid;

[0049] Figure 5(b) is a schematic diagram of the azimuth angle of the sub-wavelength dielectric wire grid;

[0050] Figure 6 is the phase delay curve of the polarization modulation basic unit;

[0051] Figure 7 is the broadband full Stokes vector detection result;

[0052] Figure 8 is the anti-noise curve of the full Stokes vector recovery.

[0053] The following further elaborates on the specific content of the present invention in conjunction with embodiments. Specific Embodiments

[0054] It should be noted that all components in the present invention, without special instructions, are components known in the art.

[0055] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of this application fall within the protection scope of the present invention.

[0056] The present invention provides a snapshot broadband full Stokes vector measuring instrument, which includes a waveplate array 1, a linear polarizer 2, a light intensity detector 3, and a data processing module 4;

[0057] The linear polarizer 2 is installed on the light intensity detector 3, the waveplate array 1 is installed on the linear polarizer 2, and the size of the waveplate array 1 is not greater than that of the linear polarizer 2;

[0058] The light intensity detector 3 and the data processing module 4 are electrically connected.

[0059] In the above technical solution, the waveplate array 1 is used to provide a specific phase delay amount, realize the modulation of the arbitrary polarization state of the incident light, and convert it into a corresponding elliptical polarization state, laying a foundation for subsequent measurements; the linear polarizer 2 is used to convert the elliptical polarized light modulated by the waveplate array 1 into unified linearly polarized light, and present the polarization information in the form of intensity change by selectively transmitting light in a specific direction for the light intensity detector to receive; the light intensity detector 3 is used to receive the light intensity after passing through the above two structures (waveplate array 1, linear polarizer 2); the data processing module 4 is used to analyze and process the received light intensity data, and use the full Stokes vector recovery method mentioned in the present invention to complete the calculation and inversion of the full Stokes vector of the incident light.

[0060] The waveplate array 1 is completely set on the linear polarizer 2, reducing the alignment accuracy during use. In addition, through the waveplate array, each small area of the photosensitive area can correspondingly capture the light intensity values under different polarization modulations, enabling the calculation and inversion of the polarization state in a single measurement, ensuring the real-time nature of the measurement results. At the same time, combined with the broadband characteristics of the sub-wavelength dielectric wire grid, the defect of limited working bandwidth in the existing full Stokes vector measurement technology is overcome.

[0061] The waveplate array 1 includes basic units, each basic unit includes a dielectric substrate and a sub-wavelength dielectric wire grid arranged on the dielectric substrate; the phase delay amount of each sub-wavelength dielectric wire grid is constant, and the azimuth angle of each sub-wavelength dielectric wire grid relative to the transmission axis direction of the linear polarizer 2 is different, where , is the set of positive integers.

[0062] In the above technical solution, using the waveplate array 1 to divide the photosensitive surface into N units can realize snapshot measurement of the full polarization state; the phase delay amount is only related to the parameters of the sub-wavelength dielectric wire grid, and controlling this value to be constant is to unify the process parameters and reduce the manufacturing difficulty of the waveplate array.

[0063] Among them, all basic units are squares with equal side lengths.

[0064] The distance between the photosensitive area of the light intensity detector 3 and the linear polarizer 2 Satisfies the following formula:

[0065]

[0066] Wherein:

[0067] Is the side length of the basic unit of the wave plate array (1), μm;

[0068] Is the working wavelength of the light intensity detector 3, nm.

[0069] The period of the sub-wavelength dielectric wire grid of the wave plate array 1 is less than the working wavelength λ; the extinction ratio of each basic unit and the linear polarizer 2 is greater than 1000:1.

[0070] In the above technical solution, the distance between the photosensitive area and the linear polarizer is restricted to reduce the intensity crosstalk caused by the diffraction effect; the extinction ratio is controlled to ensure its polarization modulation performance.

[0071] The material of the sub-wavelength dielectric wire grid of the wave plate array 1 is silicon nitride, silicon carbide or titanium dioxide; the material of the dielectric substrate is quartz, sapphire or N-BK7.

[0072] In the above technical solution, the low-loss characteristics of the material of the sub-wavelength dielectric wire grid and the slow change of the refractive index are suitable for micro-nano processing technology; the selection of the material of the dielectric substrate is mainly the commonly used materials of existing optical window glasses.

[0073] A photoresist layer is provided at the edge of the side of the wave plate array 1 close to the linear polarizer 2.

[0074] In the above technical solution, since the sub-wavelength dielectric wire grid is a micro-nano structure and is very fragile and cannot be in direct contact with other objects (linear polarizer), a photoresist layer with a height higher than the sub-wavelength dielectric wire grid is provided around its micro-nano structure as a fence.

[0075] The vibration direction of the linear polarizer 2 is unique.

[0076] In the above technical solution, it is defined that the polarizer is a whole and not an array structure like the sub-wavelength dielectric wire grid.

[0077] The material of the photoresist layer is SU8.

[0078] In the above technical solution, the commonly used photoresist material, as a fence for the sub-wavelength dielectric wire grid, plays a role in protection and support.

[0079] The present invention also provides a snapshot broadband full Stokes vector measurement method, which is based on a snapshot broadband full Stokes vector measuring instrument and specifically includes the following steps:

[0080] Step 1: The light to be measured is incident on the wave plate array 1 of the snapshot broadband full Stokes vector measuring instrument;

[0081] Step 2: The light intensity detector 3 transmits the collected light intensity value to the data processing module, and the data processing module calculates the Stokes vector of the light to be measured using the following formula ;

[0082]

[0083] where:

[0084] is the light intensity value detected in the photosensitive area of the light intensity detector 3 corresponding to the th basic unit, W / m²;

[0085] is the azimuth angle of the subwavelength dielectric wire grid of the th basic unit, rad;

[0086] is the phase delay of each subwavelength dielectric wire grid, rad.

[0087] In the above technical solution, by optimizing the basic parameters such as the phase delay and azimuth angle of the subwavelength dielectric wire grid, the optimal distribution of the ellipsometric state modulation basis vectors in each region on the surface of the Poincaré sphere is realized, greatly reducing the influence of factors such as light intensity jitter and noise error on the polarization state recovery in the polarization measurement system, and improving the measurement accuracy and anti-noise ability of the system. And compared with the metasurface structure, the subwavelength dielectric wire grid has a higher polarization extinction ratio, more accurate polarization conversion, and reduces the calibration pressure of the system as much as possible.

[0088] In step 2, the solution methods for the azimuth angle and the phase delay are as follows:

[0089] S1: The double-layer subwavelength gratings of different basic units decompose the light to be measured into a group of elliptical polarization states ;

[0090] The elliptical polarization states are non-coplanar on the Poincaré sphere;

[0091] S2: According to the coordinate values of the elliptical polarization states on the Poincaré sphere, calculate the volume of the polyhedron formed by the elliptical polarization states through the Davidson formula or the cross product method , that is, by using to calculate the volume of the polyhedron formed by the elliptical polarization state ; ;

[0092]

[0093]

[0094]

[0095] S3. The particle swarm algorithm is used to perform global traversal and optimization in the parameter space to obtain the maximum volume discriminant function ;

[0096] The azimuth angle of the parameter space is and the phase delay is ;

[0097] S4. Through multiple iterations and global search of and , the optimal that satisfies the maximum volume discriminant function and the optimal are obtained.

[0098] Among them, is a function mapping, representing a function about and . When the number of basic units is different, the expression of is different;

[0099] In the above technical solution, the selection of the phase delay and azimuth angle of the wave plate array is crucial for the robustness of the full Stokes vector recovery. The full Stokes vector detection, as a typical linear system, can be written as . Among them, represents the intensity vector detected by the modulation of the Stokes parameters of the incident light to be measured through the analysis matrix . Obviously, the full Stokes vector of the incident light to be measured can be expressed as the left multiplication of the inverse of the analysis matrix by the intensity vector, that is . If a noise factor is introduced in the process of obtaining the intensity vector, then recovery will surely introduce deviation, that is , therefore, a reasonable research and design of the analysis matrix can, on the one hand, reduce the error brought to the Stokes vector restoration due to intensity perturbation or noise, and on the other hand, make the designed polarization detection basis vectors cover the entire surface of the Poincaré sphere as much as possible. In this embodiment, the equally weighted variance (EWV) merit function is used as the judgment criterion, that is:

[0100]

[0101] where, represents the eigenvalue of the analysis matrix . According to the details shown in the invention content, the above formula can be equivalent to the position coordinates of the pixel points of a single polarization state detection on the Poincaré sphere. Therefore, the method for solving the above discriminant merit function is transformed into finding the minimum volume of the polyhedron formed by several points corresponding to the analysis matrix on the Poincaré sphere, that is, satisfying:

[0102]

[0103] where, represents the volume of the polyhedron composed of the polarization state set , and this polyhedron is inscribed in a Poincaré sphere with a radius R = 1, that is .

[0104] Figure 2 shows the distribution of the polarization detection basis vectors on the Poincaré sphere for the cases of detection times N being 4, 6, 7, and 8 according to the EWV merit function. According to geometric theory, among the polyhedrons inscribed in a unit sphere, the one with the largest volume is the inscribed regular polyhedron. Obviously, the distribution of the polarization detection basis vectors calculated according to the EWV merit function is consistent with the geometric theory.

[0105] Figure 3 shows the change curves of the merit function of the system for different detection times N. In the figure, the conventional structure is that the wave plate phase delay used in the detection system is λ / 4, and the azimuth angles for different detection times are 2π / N, that is, evenly divided on the unit circle according to the detection times. Obviously, compared with the test structure and measurement principle of the conventional polarimeter, the structure of the present invention has more advantages in terms of stability and robustness to noise.

[0106] In addition, since the sizes of the components involved in this solution are in the micron range, special attention needs to be paid to the diffraction effects of the components. As shown in Fig. 4(a), the incident light first passes through the polarization modulation array (i.e., the waveplate array 1 and the linear polarizer 2), propagates a certain distance, and is received by the photosensitive area of the light intensity detector 3. Due to the existence of diffraction effects, there will be a certain degree of crosstalk among the individual basic units in the photosensitive area. Fig. 4(b) is a side view structural diagram of Fig. 4(a), and the shaded part is the spatial position of the light to be measured after propagating a certain distance and the photosensitive surface of the light intensity detector 3. Preferably , the influence of the diffraction effect is reduced as much as possible.

[0107] Example:

[0108] In this example, a four-detection structure is adopted, that is, N = 4. Then, the polarization modulation transmission matrix model under this condition can be expressed as:

[0109]

[0110] According to the above formula, the last three elements in each row of the polarization modulation transmission matrix model are used as the normalized coordinates on the Poincaré sphere , and axes, and are substituted into the equal-weight variance coefficient (EWV) merit function. The particle swarm optimization algorithm is used to find the and corresponding to the minimum value of the tetrahedron formed by these four points.

[0111] After optimization, in this example, the fixed phase delay , that is, the range is controlled between [0.6π, 0.9π], and there is also a certain corresponding relationship between the major axis azimuth angles of the four groups of waveplates. That is, the polyhedron of each polarization basis vector on the Poincaré sphere is a regular tetrahedron, that is, the azimuth angles , , and are in the ranges of [0.2π, 0.3π], [0.4π, 0.5π], [0.6π, 0.7π], and [0.8π, 0.9π], respectively.

[0112] The above-mentioned polarization basis vectors refer to the structure composed of the phase delays and corresponding azimuth angles of four waveplates included in each superpixel in the example. This structure is completely transparent to a certain polarization state, and the modulation efficiency is 100%. Therefore, it is called a basis vector here.

[0113] To achieve the device effects demonstrated by the above anti-noise theory, we adopt the FDTD (Finite-Difference Time-Domain) method to perform modeling and simulation on the wave plate based on the subwavelength grating theory. Figure 5(a) shows the schematic structure diagram of the subwavelength dielectric wire grid, where p is the period of the subwavelength dielectric wire grid, is the width of the subwavelength dielectric wire grid, and h is the thickness of the subwavelength dielectric wire grid. Taking the case of a beam incident perpendicularly as an example, during FDTD simulation, the phase delay amounts of the incident light of a pair of orthogonal polarization states (TE light and TM light) passing through the grating model are obtained respectively. In the wide wavelength range of 450 - 650 nm, achromatic design is carried out for five wavelengths to achieve a specific uniform phase delay in the entire visible light spectrum range. After sampling and selection, it is finally determined that the subwavelength dielectric wire grid and the substrate material are fused quartz, the period p is 400 nm, the thickness h of the subwavelength dielectric wire grid is 2.5 μm, and the width of the subwavelength dielectric wire grid is 240 nm. Figure 5(b) is the schematic diagram of the azimuth angle of the subwavelength dielectric wire grid. Figure 6 Figure 6 is the phase delay curve of the subwavelength dielectric wire grid under this structure. It can be seen from this figure that under the incidence of TE light and TM light, the phase delay in the visible light range is controlled near 0.73π, indicating that in this embodiment, the phase delay of the subwavelength dielectric wire grid has certain broadband characteristics in the visible light range of 450 nm - 650 nm.

[0114] The broadband full Stokes vector detection results in this embodiment are as Figure 7 shown, where (a), (b), and (c) are the detection results under the incident light with wavelengths of 450 nm, 550 nm, and 650 nm respectively. To describe the polarization response of the broadband full Stokes vector detection chip, four polarization basis vectors (Ⅰ, Ⅱ, Ⅲ, and Ⅳ) are used to illuminate it in this embodiment, and its Stokes parameters are respectively , , and . For the incident light of each polarization state, the light intensities of the four pixels obtained after modulation are different.

[0115] In addition, four sets of ellipsometric states (Ⅴ, Ⅵ, Ⅶ, and Ⅷ) orthogonal to the polarization basis vectors of the basic unit are also used to irradiate the measuring instrument to verify the function, which are respectively , , and , as Figure 7As shown, where (d), (e), and (f) are the detection results under incident light with wavelengths of 450 nm, 550 nm, and 650 nm respectively. It can be seen that there is an obvious extinction phenomenon under the designed polarization basis vectors. In this embodiment, after normalizing the intensity information recorded by each pixel, the intensity distributions of the four polarization components can be quantified, substituted into the polarization transfer matrix model given above, and based on this, the full polarization information of the incident light can be reconstructed. Table 1 shows the full Stokes vector results measured in this embodiment under the illumination of the above-mentioned polarization state of the light to be measured, indicating that the broadband full Stokes vector measuring instrument based on this embodiment has high precision without additional polarization calibration.

[0116] Table 1 Full Stokes vector recovery results

[0117]

[0118] Verification example:

[0119] To verify the robustness of the recovery of the full Stokes parameters of the measuring instrument when the detection intensity in this embodiment is interfered or the detector noise cannot be suppressed, we randomly select a point on the Poincaré sphere. Taking as an example, Gaussian noises with different weights are respectively introduced into the detection intensity distribution results. The relative error of the Stokes parameters before and after recovery is defined as the evaluation criterion, which can be written as . For this Stokes parameter, the optimized polarization detection structure and the traditional structure in this embodiment are used for recovery. As Figure 8 shown, it can be seen that when random noise is introduced into the optimized structure, as the noise weight increases, the recovery error of the Stokes parameter is approximately linear, and with the increase of the noise weight, the change in robustness represented by its slope is significantly improved compared with the traditional structure.

Claims

1. A snapshot wideband full Stokes vector measurement method, characterized in that Based on the snapshot broadband full Stokes vector measuring instrument, the following steps are specifically included: Step 1: The light to be measured is incident on the waveplate array (1) of the snapshot broadband full Stokes vector measuring instrument; Step 2: The light intensity detector (3) transmits the collected light intensity value to the data processing module, and the data processing module calculates the Stokes vector of the light to be measured using the following formula ; Wherein: is the detected light intensity value of the photosensitive area of the light intensity detector (3) corresponding to the th basic unit, in W / m²; is the azimuth angle of the sub-wavelength dielectric wire grid of the th basic unit, in rad; is the phase delay of each sub-wavelength dielectric wire grid, in rad; The azimuth angle and the phase delay amount are solved as follows: S1, the double-layer sub-wavelength gratings of different basic units decompose the light to be measured into a set of elliptical polarization states ; The elliptical polarization state is non-coplanar on the Poincaré sphere; S2, according to the elliptical polarization state The coordinate values on the Poincaré sphere , calculate the volume of the polyhedron formed by the elliptical polarization state through the Davidson formula or the cross product method ; S3. Use the particle swarm optimization algorithm to perform global traversal and optimization in the parameter space to obtain the maximum volume discrimination function ; The azimuth angle of the parameter space is and the phase delay amount is ; S4, through multiple iterations and global search on and , the optimal and the optimal that satisfy the maximized volume discriminant function are obtained; The snapshot broadband full Stokes vector measuring instrument includes a waveplate array (1), a linear polarizer (2), a light intensity detector (3), and a data processing module (4); The linear polarizer (2) is installed on the light intensity detector (3), the waveplate array (1) is installed on the linear polarizer (2), and the size of the waveplate array (1) is not larger than the size of the linear polarizer (2); the vibration direction of the linear polarizer (2) is unique; the light intensity detector (3) and the data processing module (4) are electrically connected; The wave plate array (1) includes basic units, each of the basic units including a dielectric substrate and a sub-wavelength dielectric wire grid disposed on the dielectric substrate; the phase delay amount of each sub-wavelength dielectric wire grid is constant, and the azimuth angle of each sub-wavelength dielectric wire grid with respect to the polarization direction of the linear polarizer (2) is different, where , is a set of positive integers; The distance between the photosensitive area of the light intensity detector (3) and the linear polarizer (2) satisfies the following formula: Wherein: is the side length of the basic unit of the wave plate array (1), in μm; is the operating wavelength of the optical intensity detector (3), in nm.

2. The snapshot wideband full Stokes vector measurement method according to claim 1, wherein The period of the sub-wavelength dielectric wire grid of the waveplate array (1) is less than the working wavelength λ; the extinction ratio of each basic unit and the linear polarizer (2) is greater than 1000:

1.

3. The snapshot wideband full Stokes vector measurement method according to claim 1, characterized in that The material of the sub-wavelength dielectric wire grid of the waveplate array (1) is silicon nitride, silicon carbide or titanium dioxide; the material of the dielectric substrate is quartz, sapphire or N-BK7.

4. The snapshot wideband full Stokes vector measurement method according to claim 1, characterized in that A photoresist layer is provided at the edge of the side of the waveplate array (1) close to the linear polarizer (2).

5. The snapshot wideband full Stokes vector measurement method according to claim 4, characterized in that The material of the photoresist layer is SU8.

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