Spectral polarization detection method based on quasi-continuous domain bound state metasurface

Abstract

The invention discloses a spectrum polarization detection method based on a quasi-continuous domain bound state metasurface, and belongs to the application field of micro-nano optics and spectrum polarization detection. The implementation method comprises the following steps: adopting a symmetrical broken elliptical amorphous silicon nano-column arrangement mode to obtain a metasurface structure unit with a narrow-band formant, a high-quality factor and linear polarization dependence; the method comprises the following steps: analyzing a change rule of resonance wavelength along with geometric parameters of a structural unit and a change rule of resonance intensity along with a polarization state of incident light through numerical simulation to obtain a series of metasurface structures with different resonance wavelengths and different polarization responses, reasonably arranging the metasurface structures, processing a metasurface sample, and testing a reflection spectrum of the metasurface sample, and the spectrum and polarization response characteristics are calibrated. A spectrum polarization detection system composed of a detection target, a metasurface and a CMOS detector is built, and the spectrum and polarization information of the target is detected based on the spatial position arrangement of the metasurface structure and the Stokes relation by using gray information shot by the CMOS detector.

Description

TECHNICAL FIELD

[0001] The present application relates to a spectral polarization detection method, in particular to a method for simultaneously regulating the resonance wavelength and polarization response based on quasi-continuous domain bound state super surface, and belongs to the technical field of micro-nano optics, multi-dimensional light field regulation, spectral polarization detection. BACKGROUND

[0002] Spectrum and polarization are two important optical information, which can be used to distinguish and identify different substances, and help to complete various visual tasks. Spectral information is mainly used for analysis and identification of material composition, while polarization information can provide information about object surface texture, internal stress and material birefringence characteristics. Both of them have wide applications in remote sensing detection, chemical composition analysis, machine vision and other industrial and scientific scenarios. However, the common spectral polarization detection equipment at present is usually composed of a large number of heavy optical dispersion elements and polarization regulation elements, such as tunable optical filter, beam splitter, grating, polarizer and wave plate, which together with the image detector constitute the spectral polarization detection system to realize the acquisition of spectral and polarization information. Traditional spectral polarization detection methods mainly include dispersion type, interference type, filter type and channel spectral polarization technology.

[0003] The dispersion-based spectral polarization detection is based on a dispersion spectrometer inserted into a polarization detection model to realize spectral polarization detection. The technology has the advantages of high spectral resolution and simultaneous acquisition of spectral and polarization information, but the dispersion spectrometer usually contains dispersion prisms, gratings and other light splitting elements, and a long beam propagation distance is usually required to obtain high spectral resolution, so the volume of the system is relatively large. The spectral polarization detection based on the interference type is to separate the wavelength of the incident light by using an interferometer, and then detect the polarization state of each wavelength component. The technology has high sensitivity and is particularly suitable for polarization detection tasks with high accuracy requirements. However, the interference optical path is usually sensitive to external disturbances, so the system has high requirements for environmental stability. The filter type spectral polarization detection selects specific wavelengths of light by using a series of filters, and then measures the polarization state of the selected wavelength light by using a polarization element. This scheme is the simplest and most direct, and is also more practical. However, a series of spectral and polarization elements are usually required to separate the wavelength and polarization channels, which increases the complexity of the actual operation, and the switching of the light splitting elements may reduce the time resolution of the detection, affecting its application in real-time detection scenarios. The channel spectral polarization detection technology uses a high-order phase delay component and a polarizer to combine a polarization modulation module. After the module, the full Stokes parameters of the light wave are modulated into different frequency carriers. The power spectrum of the module output is a linear superposition of each modulation signal. The spectral polarization information after modulation is received by a spectrometer, and each modulation signal is demodulated by using the "frequency division multiplexing" technology, so as to realize the simultaneous demodulation of spectral polarization information. The system is also composed of multiple optical elements, and the volume of the system is relatively large.

[0004] As a two-dimensional artificial super material, the metasurface is usually composed of a single layer of metal or dielectric nano antenna array, and can flexibly control the amplitude, phase, polarization state, wavelength and other degrees of freedom of light wave with subwavelength resolution. In addition, compared with traditional optical elements, the metasurface also has the advantages of light weight, portability and easy integration. The above advantages make the metasurface expected to develop into the next generation of optical elements. In recent years, researchers have applied metasurfaces to many application fields, including holographic imaging and display, beam shaping, super lens imaging, optical communication and optical detection. SUMMARY

[0005] The main purpose of the present application is to provide a spectral polarization detection method based on quasi-continuous domain bound state metasurface, which realizes accurate control of the resonant wavelength and polarization response of the metasurface structure by adjusting the geometric parameters and structural orientation of the quasi-continuous domain bound state metasurface. The present application is applied to spectral polarization imaging, multi-dimensional detection and multi-functional optical system to realize a miniaturized, multi-functional spectral polarization multi-dimensional detection system, and to improve the efficiency and accuracy of spectral polarization detection.

[0006] The purpose of the application is achieved by the following technical solutions:

[0007] The application discloses a spectrum polarization detection method based on a quasi-continuous domain bound state super surface, and the super surface for realizing spectrum polarization multi-dimensional light field detection is composed of medium nanometer column arrays with different geometric parameters and structural orientations. The quasi-continuous domain bound state principle is introduced into the design process of the super surface structural unit, the rotation angle symmetry of the super surface structural unit is broken, narrow-band, high-quality factor and polarization-sensitive optical resonance modes are realized, and then the separation and detection of the spectrum and polarization channels are realized. The application discloses a spectrum polarization detection method based on a quasi-continuous domain bound state super surface, and the super surface for realizing spectrum polarization multi-dimensional light field detection is composed of medium nanometer column arrays with different geometric parameters and structural orientations.

[0008] The application discloses a spectrum polarization detection method based on a quasi-continuous domain bound state super surface, and the super surface for realizing spectrum polarization multi-dimensional light field detection is composed of medium nanometer column arrays with different geometric parameters and structural orientations.

[0009] Step one, the quasi-continuous domain bound state super surface for realizing spectrum polarization multi-dimensional light field detection is composed of medium nanometer column arrays with different geometric parameters and structural orientations. The geometric parameters include the long axis r a , the short axis r b , the x-direction period P x , the y-direction period P y , the height h and the rotation angle δ.

[0010] The super surface structural unit for realizing the breaking of the rotation angle symmetry is composed of two medium nanometer columns rotating at the clockwise and counterclockwise rotation angles δ respectively. According to the reflection spectrum and the electromagnetic field distribution of the structural unit, the resonance wavelength and the polarization response are analyzed. The polarization response of the structural unit is calculated by a Jones matrix shown in formula (1).

[0011] (1)

[0012] where t ij (i, j=x or y) is the reflection coefficient, j and i represent the polarization direction of the incident light and the reflected light, respectively. The relationship between the metasurface structure unit and the polarization response of the reflected light is described according to equation (1).

[0013] The simulation software described in step one is completed based on the finite-difference time-domain method (FDTD).

[0014] Step two, constructing quasi-continuous domain bound state metasurfaces for realizing spectral polarization multi-dimensional light field detection. In order to realize spectral polarization multi-dimensional detection, the metasurface is used to realize specific modulation of the spectral and polarization information of the incident light. The spectral response of the metasurface structure unit with different geometric parameters under different linear polarization states is calculated by scanning using the finite-difference time-domain method, and the metasurface arrangement mode, i.e. the metasurface structure, is determined in combination with the target waveband range and the number of spectral channels. According to the determined metasurface structure, the corresponding metasurface structure processing file is generated.

[0015] The modulation process of the metasurface on the incident light is represented by equation (2):

[0016] (2)

[0017] where k represents the serial number of the metasurface structure unit, and its value ranges from 1 to m. The structure units corresponding to different k values have different geometric parameters. p represents the orthogonal polarization component required to recover the polarization state, and the orthogonal polarization basis is selected as 0° and 90°, 45° and 135°, or left-handed circular polarization and right-handed circular polarization. k (p) represents the light intensity corresponding to the p polarization component in the kth metasurface structure unit, represents the reflection coefficient of the kth metasurface structure unit under the wavelength λ and the p component, η(λ) is the quantum efficiency of the CMOS detector, n k is the error in the measurement process. For simplicity of expression, define According to equation (2), the information obtained by the CMOS detector is the light intensity information obtained through the integration process, and cannot reflect the spectral and polarization characteristics of the incident light.

[0018] In order to separate the spectral and polarization information, equation (2) is discretized to obtain its matrix expression form:

[0019] (3)

[0020] According to equation (3), the wavelength dimension is modulated while keeping the p polarization basis uniform, so as to realize the decoupling of the wavelength and polarization dimensions. The polarization information is calculated by the Stokes relationship shown in equations (4)-(6):

[0021] (4)

[0022] (5)

[0023] (6)

[0024] where DoLP and AoLP are the degree of linear polarization and the angle of linear polarization, S0, S1, S2 are the Stokes components, and I(0°), I(45°), I(90°), I(135°) represent the light intensity corresponding to different polarization bases.

[0025] As preferred, the super surface designed in step one is used as a basic structural unit, and its geometric parameters are changed to adjust the resonance wavelength, so as to realize the wavelength modulation in formula (3). The geometric parameters of the super surface structural unit are multiplied by a scaling factor γ to adjust the resonance wavelength, so as to realize the filtering of light in different wavelength channels. After obtaining the preferred super surface structural units with different geometric parameters, each kind of super surface structural unit is arranged periodically at 0°, 45°, 90°, and 135°, respectively, which is called a spectral polarization detection pixel, so as to realize the polarization separation process in formula (3). The spectral polarization detection pixels are regularly arranged in a 2x2 form in space, and the above arrangement is called a spectral polarization detection unit. The super surfaces with different geometric parameters are arranged in space in the above manner to obtain a series of spectral polarization detection pixels, and the series of spectral polarization detection pixels are combined to form a complete spectral polarization multi-dimensional detection super surface. The above super surface design method is combined with the decoupling process shown in formula (3), and a single-chip super surface is used to realize the detection of spectral polarization multi-dimensional light field information in an integrated and miniaturized system, avoiding the shortcomings of complex system and large volume in the traditional spectral polarization detection method. The geometric parameters include the major axis r a , the minor axis r b , the x-direction period P x , and the y-direction period P y of the elliptical section.

[0026] In order to ensure the generation of quasi-continuous domain bound states, as preferred, the area of each spectral polarization detection pixel is set to 50 μm x 50 μm.

[0027] Step three, using the processing file of the medium super surface obtained in step two, a spectral polarization multi-dimensional light field detection super surface is prepared. The different geometric parameters and structural orientations of the super surface are used to realize the regulation of the resonance response center wavelength and the polarization response, and then the specific selection of different spectral and polarization channels is realized.

[0028] In order to ensure that the size of the nanometer column in each unit of the processed super surface is consistent with the preset, as preferred, the medium super surface is prepared by an electron beam etching micro-nano processing method.

[0029] Step four, for the medium metasurface obtained by step three, the nanometer column is tested and characterized by a scanning electron microscope SEM. Due to the inevitable factors such as machining error and material refractive index error in the actual machining process, the size of the nanometer column of the machined metasurface may have errors compared with the design, and thus the resonance center wavelength of the actual metasurface may be inconsistent with the resonance center wavelength calculated in step two. Therefore, a spectral polarization multi-dimensional detection metasurface optical response test calibration system is built to test the resonance center wavelength and polarization extinction ratio of each metasurface pixel, so as to obtain the resonance center wavelength and polarization extinction ratio of each metasurface pixel.

[0030] Step five, a spectral polarization multi-dimensional light field detection system based on the quasi-continuous domain bound state metasurface is built and spectral polarization detection application is carried out. The spectral polarization multi-dimensional light field detection system is composed of a detection target, a quasi-continuous domain bound state metasurface, a CMOS detector and optical elements, wherein different pixels on the quasi-continuous domain bound state metasurface filter different spectral and polarization components on the detection target, the filtered spectral and polarization information is recorded as a gray scale image by the CMOS detector, and the spectral and polarization information of the target object is calculated by the spatial position relationship between different metasurface pixels in step two and the Stokes relationship, that is, the spectral polarization detection is realized based on the quasi-continuous domain bound state metasurface.

[0031] Advantages:

[0032] 1. Compared with the dispersion type, interference type, filter type and channel spectral polarization technology, the spectral polarization detection method based on the quasi-continuous domain bound state metasurface disclosed in the application adopts a single metasurface to replace the dispersion elements (prism, grating, narrow-band filter) and polarization elements (polarizer, wave plate) in the traditional system, realizes the modulation of the spectral polarization information of the detection target, and realizes the spectral polarization detection with smaller system volume and lighter system.

[0033] 2. The spectral polarization detection method based on the quasi-continuous domain bound state metasurface disclosed in the application adopts two elliptical nanometer columns breaking the rotational symmetry to form a basic metasurface structure unit, which can produce a narrow-band resonance peak, and the polarization response at the resonance center wavelength is similar to that of a traditional polarizer, so that the spectral and polarization can be simultaneously regulated, the integration of the spectral polarization detection device is improved, and the system volume is greatly reduced.

[0034] 3. The spectral polarization detection method based on quasi-continuous domain bound state metasurface disclosed in the application arranges multiple spectral polarization characteristic pixels with different geometric parameters and structural orientations together through spatial multiplexing, records the light intensity information of the metasurface reflection direction through a CMOS, and calculates the spectral and polarization information of the incident light in combination with the Stokes relationship, thus having the advantages of intuitiveness and high precision.

[0035] 4. The spectral polarization detection method based on quasi-continuous domain bound state metasurface disclosed in the application, on the basis of realizing the above-mentioned three beneficial effects, constructs a spectral polarization multi-dimensional detection system, realizes effective modulation of the spectral and polarization information of a detection target based on a single metasurface, and calculates the spectral polarization information according to the basic Stokes relationship, thus, compared with a traditional spectral polarization detection system, a large number of traditional optical elements such as gratings, dispersive prisms, polarizing plates and wave plates are omitted, and the volume of the optical system is significantly reduced. In addition, the spectral polarization information of a target object is calculated through the spatial position relationship between different metasurface pixels and the Stokes relationship, the spectral polarization information can be calculated more simply and directly, and the complexity of calculating the spectral polarization information is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a spectral polarization detection method implementation flowchart based on quasi-continuous domain bound state metasurface.

[0037] Figure 2 It is a designed metasurface structure unit and FDTD simulation result. Wherein (a) is a metasurface structure unit schematic diagram, wherein r a , r b are the long axis and the short axis of the elliptical section respectively, P x , P y are the periods of the metasurface structure unit in the x direction and the y direction respectively, h is the height of the nanometer column, and δ is the rotation angle of the nanometer column along the z axis, (b) is the electric field and magnetic field intensity distribution of the structure unit under x polarization light and y polarization light incidence, (c) is the reflection spectrum curve of the structure unit under four kinds of incident linear polarization states (0°, 45°, 90°, 135°), (d) is the spectral curve of each coefficient in the Jones matrix of the structure unit, and (e) is the reflection intensity distribution of the structure unit in the process of rotating θ angle.

[0038] Figure 3 It is a designed metasurface reflection spectrum, schematic diagram and spectral polarization detection principle schematic diagram. Wherein (a) is the reflection spectrum simulation result of the metasurface unit with different geometric parameters, (b) is a spectral polarization detection metasurface schematic diagram obtained by spatially arranging the metasurface units with different geometric parameters and structural orientations, and (c) is a spectral polarization detection principle schematic diagram based on the designed metasurface.

[0039] Figure 4are the test results of the processed super surface. Wherein (a) is the oblique view of the super surface taken by SEM, (b) is the plan view of the super surface taken by SEM, (c) is the light path diagram for testing the optical response of the super surface, wherein P is a polarizer, HWQ is a half wave plate, BS is a beam splitter prism, L1 and L2 are lenses, (d) is the reflection spectrum of the super surface structure unit with different structure orientations under the condition of x-polarized light incidence, (e) is a graph of the reflection spectrum of the super surface structure unit with 20 different geometric parameters under the condition of x-polarized light incidence.

[0040] Figure 5 are the spectral polarization detection results. Wherein (a) is a schematic diagram of the light path for testing the absorption spectrum of the solution, (b) is the true value of the absorption spectrum of the water and anhydrous ethanol mixed solution, (c) is the test value of the water and anhydrous ethanol mixed solution tested by the designed super surface, (d) is the polarization state test result.

[0041] Figure 6 are the spectral polarization image test results.

[0042] Figure 7 are the polarization image test results. DETAILED DESCRIPTION

[0043] The present application will be described in detail below with reference to the accompanying drawings and examples. At the same time, the technical problems solved by the technical solutions of the present application and the beneficial effects are described. It should be pointed out that the described examples are only intended to facilitate the understanding of the present application and do not limit the present application in any way.

[0044] As shown in Figure 1 , the spectral polarization detection method based on quasi-continuous domain bound state super surface disclosed in the present example is implemented as follows:

[0045] Step one, the quasi-continuous domain bound state super surface for realizing spectral polarization multi-dimensional light field detection is composed of different geometric parameters and different structure orientations of dielectric nanocolumn arrays with elliptical cross section. By breaking the rotational angular symmetry of the super surface structure unit, quasi-continuous domain bound state is introduced into the design process of the super surface, and the quantitative regulation of the outgoing light in different wavelength channels and different polarization channels is realized through super pixel structure, thereby realizing spectral polarization multi-dimensional detection. The geometric parameters include the long axis r a , the short axis r b of the elliptical cross section, the x-direction period P x , the y-direction period P y of the super surface structure unit, the height h and the rotation angle δ. The above parameters are shown in Figure 2 (a).

[0046] The super surface structure unit for realizing the breaking of rotational angle symmetry is composed of two dielectric nanometer pillars rotating by an angle δ clockwise and counterclockwise, respectively, and as preferred, we set the initial values of the aforementioned geometric parameters as r a = 280 nm, r b = 100 nm, P x = 500 nm, P y = 400 nm, h = 150 nm, δ = 17.5°. In the FDTD simulation software, the structure model is established according to the above parameters, the nanometer pillar material is set as amorphous silicon, the substrate material is set as silicon dioxide, the wavelength range of the incident light is 800-1100 nm, and the polarization state is fixed as a specific linear polarization, a surface monitor is set at a certain distance in the reflection direction to monitor the reflection spectrum of the structure unit, and a surface monitor is set in the height range of the nanometer pillar to monitor the field distribution inside the structure unit, and the field distribution of the super surface structure unit under the resonant wavelength is obtained as shown in Figure 2 (b), the white ellipse is the position of the nanometer pillar, the first row is the field distribution of the structure unit under the x-polarized light incidence, and the second row is the field distribution of the structure unit under the y-polarized light incidence, it can be seen that the field distribution of the structure unit under the x-polarized light is obviously stronger than that under the y-polarized light, indicating that the structure can be used as a spectral polarization response device; Figure 2 (c) is the reflection spectrum of the super surface structure unit under different linear polarization incidences, it can be seen that the structure has obvious specific polarization response, that is, the polarization response at the resonant wavelength has significant difference, in addition, it can also be seen that the structure can produce a sharp narrowband resonance peak at a polarization angle of 0°, and can realize the component of the spectral channel; in order to further quantitatively characterize the polarization response of the super surface structure unit, it is necessary to analyze the components of the Jones matrix, the specific method is as follows: the x component and the y component of the reflected electric field of the structure unit under the x-polarized plate and the polarized light incidence are extracted, respectively, and the results are shown in Figure 2 (d), the values of t xx , t xy , t xy, , and t yy are 0.99, 0, 0, and 0.16, respectively, while the ratio of |t xx | 2 and |t yy | 2 is as high as 38:1, indicating that the designed structure unit at the resonant wavelength can be regarded as a polarizer for polarization state detection. For a traditional polarizer, the filtering effect on the incident polarized light can be described by Malus law I=I0cos 2(θ) is described, where I is the light intensity transmitted through the polarizer, I0 is the incident light intensity, and θ is the angle between the polarization direction of the incident polarized light and the detection direction of the polarizer. According to Malus quantification, the reflected light intensity under different angles θ is simulated in FDTD, and compared with the theoretical value of Malus quantification. The comparison results are shown in Figure 2 (e) is in good agreement.

[0047] The foregoing process is a modeling and verification process for aligning the quasi-continuous domain bound state metasurface structure unit, indicating that the quasi-continuous domain bound state metasurface structure has good spectral polarization modulation and rotation characteristics, and can be used as a basic structure of an optimal spectral polarization detection device.

[0048] Step two, quasi-continuous domain bound state metasurface design for realizing spectral polarization multi-dimensional light field detection. When the geometric parameters of the structure unit change, the resonance wavelength will change. By multiplying the geometric parameters (the long axis r a , the short axis r b , the x-direction period P x , and the y-direction period P y ) of the metasurface structure unit by a scaling factor γ, the wavelength channel can be adjusted, thereby realizing the filtering effect of light in different wavelength channels. As an optimization, in the present method, the value of the scaling factor γ is limited to between 1.08 and 1.479, and the step size of the value change is set to 0.021, so there are 20 different γ values. According to the initial values of the scaling factor γ and the geometric parameters, the corresponding metasurface structure unit geometric parameters are calculated, and numerical simulation is performed in the FDTD software to calculate the resonance wavelength of the structure unit under different geometric parameters. Figure 3 (a) shows the reflection spectra of the 20 structure units under x-polarized light incidence. It can be seen that each structure unit can form a narrow-band resonance peak, and the specific resonance wavelength is different, so it can be used as a spectral sampling structure to realize the selection and detection of different spectral channels.

[0049] After obtaining the preferred metasurface structure units with different geometric parameters, each metasurface structure unit is arranged periodically at an orientation of 0°, 45°, 90°, and 135°, which is called a spectral polarization detection pixel. The spectral polarization detection pixels are regularly arranged in a 2x2 form in space, and the above arrangement is called a spectral polarization detection unit. The metasurfaces with different geometric parameters are all arranged in the above manner to obtain a series of spectral polarization detection pixels, which are combined to form a complete spectral polarization multi-dimensional detection metasurface. Figure 3(b) shows the structure of the above spectral polarization multidimensional detection metasurface, each dashed box is a spectral polarization detection unit, and the metasurface unit in the dashed box is divided into four blocks, which are directed to 0°, 45°, 90° and 135°, and each block corresponds to a spectral polarization detection pixel. The structure shown in the figure can be divided into 4 rows and 5 columns according to the spectral polarization detection unit, and the resonance wavelength drifts to the long wave direction in the order of left to right and bottom to top, so as to realize sampling of different wavelength channels. In each unit, four pixels constitute four different direction linear polarizers, which correspond to two groups of orthogonal polarization bases to realize polarization state detection. According to the design scheme shown in (b), the metasurface processing file is generated. Figure 3 (b) shows the design scheme, and the metasurface processing file is generated.

[0050] Figure 3 (c) shows the process of spectral polarization detection by using the designed spectral polarization multidimensional detection metasurface.

[0051] Step three, using the metasurface processing file obtained in step two, a spectral polarization multidimensional light field detection metasurface is prepared. By adjusting the geometric parameters and structure orientation of the metasurface, the resonance response center wavelength and polarization response are controlled, and then the specific selection of different spectral and polarization channels is realized.

[0052] In order to ensure that the size of the nanometer column in each unit of the processed metasurface is consistent with the preset, a micro-nano processing method of electron beam lithography is used to prepare the metasurface.

[0053] The micro-nano processing method of electron beam lithography includes the following steps:

[0054] Step 3.1: using the method of plasma enhanced chemical vapor deposition, a layer of 150nm thick amorphous silicon film is plated on the silicon dioxide substrate;

[0055] Step 3.2: clean the surface of the amorphous silicon film and spin coat a layer of resist on it;

[0056] Step 3.3: process the metasurface pattern by electron beam lithography;

[0057] Step 3.4: plate a layer of 30nm thick chromium film on the processed metasurface pattern;

[0058] Step 3.5: perform stripping in hot acetone, and transfer the required structure from chromium to silicon by inductively coupled plasma reactive ion etching.

[0059] Step four, for the medium metasurface obtained in step three, the nanorods are tested and characterized by SEM. Adjust the key parameters and settings of SEM such as magnification, astigmatism, voltage, etc. until the clear metasurface structure unit morphology is observed, and then take pictures from the side view and top view Figure 4 (a) and Figure 4 (b) SEM images, it can be seen that the cross section of the metasurface is elliptical, and the elliptical column in the structure unit shows the characteristic of symmetry breaking, which reflects that the processing of the metasurface is good.

[0060] However, due to the inevitable factors such as processing error and material refractive index error in the actual processing process, there may be errors between the size of the processed metasurface nanorods and the design, which may further cause the resonance center wavelength of the actual metasurface to be inconsistent with the simulation calculation in step two, so the Figure 4 (c) spectral polarization multi-dimensional detection metasurface optical response test calibration system is built to test the resonance center wavelength and polarization extinction ratio of each metasurface pixel. Figure 4 In the light path system shown in (c), the metasurface is clearly imaged to the CMOS detector target surface through lenses L1 and L2. Using a tunable NKT laser to output monochromatic light, a gray scale image of the metasurface structure unit is taken under each monochromatic light channel, and the light power of each NKT monochromatic light channel is tested using a light power meter. Read the gray value corresponding to each metasurface structure unit on the gray scale image taken under each wavelength channel, and divide it by the light power value of the wavelength channel to obtain the reflectance of all metasurface structure units under the wavelength channel. Connect the transmittance under different wavelength channels to obtain the reflectance spectrum of the metasurface structure unit.

[0061] After the above test process, the spectral polarization response of all structure units on the spectral polarization detection metasurface can be obtained, wherein Figure 4 (d) draws the reflectance spectrum of four different direction pixels in a spectral polarization detection unit, which is in good agreement with the result shown in Figure 2 (c) in the spectral curve shape. 4 (e) shows the reflectance spectrum of 20 structure units under x-polarized incidence. It can be seen that the 20 structure units have narrow-band resonance peaks, and the resonance wavelength moves to the long-wave direction with the increase of the proportional factor. It should be noted that Figure 4 The center wavelength of the resonance peak in (e) is shifted compared to Figure 3 (a), which is caused by processing error, but overall Figure 4 The test results in (e) are consistent with the simulation results shown in Figure 3 (a) in the resonance peak shape and the drift direction of the resonance wavelength.

[0062] Step five, build a spectral polarization multi-dimensional light field detection system based on quasi-continuous domain bound state metasurface and carry out spectral polarization detection application. The system is composed of a detection target, a quasi-continuous domain bound state metasurface, a CMOS detector and optical elements, wherein different pixels on the quasi-continuous domain bound state metasurface filter different spectral and polarization components on the detection target, the filtered spectral and polarization information is recorded as a gray scale image by the CMOS detector, and the spectral and polarization information of the target object can be calculated by the spatial position relationship between different metasurface pixels in step two and by using the Stokes relationship.

[0063] Step five includes the following steps:

[0064] Step 5.1: Build a spectral polarization multi-dimensional light field detection system based on quasi-continuous domain bound state metasurface, which is mainly composed of a detection target, a quasi-continuous domain bound state metasurface and a CMOS detector. The detection target is imaged onto the metasurface, and the detection target on the metasurface and the metasurface are imaged onto the CMOS detector at the same time. The actual optical path is as shown in Figure 5 (a);

[0065] A tunable NKT laser is used as a light source, and the polarization state of the light source is modulated by a polarizer P and passes through an object. In this step, a mixture of water and anhydrous ethanol is used as a detection target. After the laser passes through the detection target, the reflected beam is incident on the metasurface, and the light beam incident on the metasurface is reflected through the beam splitter and the lens, and finally incident on the target surface of the CMOS detector. Therefore, the clear imaging of the metasurface can be observed on the target surface of the CMOS detector.

[0066] In the above optical path, the light intensity transmitted through the solution will change due to the absorption of the solution. As a preferred embodiment, water and anhydrous ethanol are mixed in a ratio of 1:0, 3:1, 1:1, 1:3 and 0:1 respectively, and the absorption spectra of different solutions are tested. In the experiment, 20 kinds of resonant wavelengths of the metasurface output by the NKT are used to record the reflected light intensity of the metasurface with and without the solution in the optical path, and the transmittance of the solution at the wavelength can be obtained by calculating the ratio of the two. The transmittance at each wavelength is connected together to obtain the transmission spectrum of the solution, and the transmission spectrum obtained by the above metasurface intensity is taken as the test value. The true value of the transmission spectrum of the solution is obtained by placing a spectrometer directly behind the solution and repeating the above process. The true value and the test value of the transmission spectrum of the solution are shown in Figure 5 (b) and (c), respectively. It can be seen that the two values are well matched in trend. In addition, the average correlation coefficient between the test values and the true values of the five solutions is 77.69%, which also indicates the accuracy of the spectral detection.

[0067] In addition to spectral measurements, the results of polarization state detection were also investigated in this example. Figure 5 In the optical path shown in (a), removing the solution and adjusting the direction of polarizer P changes the polarization state of the incident light. In actual testing, the polarization states of the incident light were adjusted to 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, and 157.5°, respectively. The reflection intensity values ​​of the metasurface when these linearly polarized states were incident on the metasurface were recorded using CMOS, and the polarization angle was calculated based on the Stokes relation. The results are shown below. Figure 5 As shown in (d), the black arrow represents the true value of the polarization angle, and the green arrow represents the measured value of the polarization angle. The two values ​​match well, verifying the accuracy of the polarization detection.

[0068] Step 5.2: [The sentence is incomplete and requires more context to be translated accurately.] Figure 5 In (a), the solution is replaced with a spectral polarization image containing two-dimensional spatial information, and the metasurface is fixed on a mechanical scanning platform to detect targets in the spectral polarization image. A schematic diagram of the experiment is shown below. Figure 6 As shown in (a), NKT and polarizer combinations are used to output lasers with different wavelengths and polarization states. After passing through a mask, a target image is obtained, which is then imaged onto a metasurface through an optical lens. Mechanical scanning allows the metasurface to traverse and probe every spatial point on the target. CMOS is used to record the light intensity information of each spatial point after being modulated by the metasurface. Spectral polarization information is calculated based on the illuminated positions of the metasurface pixels, the intensity between different pixels, and the Stokes relation.

[0069] In this example, four letters—M, E, T, and A—were used as detection targets. NKT lasers outputting 910nm, 928nm, 940nm, and 954nm wavelengths were passed through masks representing these four letters. When the NKT output these four wavelength channels, the polarization angles of the polarizers were set to 30°, 75°, 120°, and 165°, respectively. Since each different detection pixel on the metasurface corresponds to one of the four polarization states (0°, 45°, 90°, and 135°) of the orthogonal linear polarization base, therefore... Figure 6 (c) shows the intensities I0, I10, and I20 of the four polarization bases at wavelengths of 910 nm, 928 nm, 940 nm, and 954 nm, respectively. 45 I 90 I 135 The intensity distribution is shown, where different colors represent different wavelengths, and different hues of the same color represent the intensity of light. The polarization state of each letter is calculated based on the Stokes relation and plotted together with the wavelength image reconstruction results. Figure 6 (d) The above process verifies the spectral polarization imaging detection performance of the system.

[0070] Step 5.3: Verify the polarization image detection capability of the designed system, and the results are shown in Figure 7

[0071] In this example, a vector structured light and a vector hologram are selected as the detection targets, respectively. The characteristics of the detection targets are that the images have two-dimensional polarization information distribution, but the intensity is uniformly distributed, so it is difficult to obtain the polarization distribution information through traditional imaging detection. However, through the scanning of the detection targets by the detection system designed in this example, the polarization distribution images of the targets can be obtained. Figure 7 The first column from left to right is the true value of the light intensity of the vector structured light (subgraph (a)), the true value of the polarization angle distribution (subgraph (b)), the test value of the light intensity (subgraph (c)), and the test value of the polarization angle distribution (subgraph (d)). The second column from left to right is the true value of the light intensity of the vector hologram (subgraph (e)), the true value of the polarization angle distribution (subgraph (f)), the test value of the light intensity (subgraph (g)), and the test value of the polarization angle distribution (subgraph (h)). As can be seen from the comparison between the test value and the true value, the system has good polarization image detection capability, and it can be seen that the light intensity distribution of the target object is uniform, while the polarization angle distribution presents rich image information, which can reveal the inherent polarization characteristics of the target object.

[0072] In summary, the spectral polarization multi-dimensional detection system of the quasi-continuous domain bound state super surface provided in this embodiment is composed of a detection target, a super surface, and a detector. In order to separate different wavelengths and polarization channels, a super surface structure unit with simultaneous spectral and polarization control function needs to be designed. After the detection target is modulated by the super surface, it is recorded in the form of a gray scale image on the detector, and then the spectral and polarization information of the object is calculated from the recorded gray scale image using the Stokes relationship.

[0073] In a remote sensing detection system, the spectral polarization multi-dimensional detection system based on the quasi-continuous domain bound state super surface can realize the synchronous detection of the spectral and polarization information of the target scene, greatly reducing the volume of the detection system and thus the payload. In a chemical composition analysis system, the designed system can realize accurate analysis of the composition of the material and miniaturization of the detection instrument. In the field of machine vision, the system can realize integration and miniaturization, and help the industrial sorting and detection machine to accurately identify various information of the external world, and improve the accuracy of judging the characteristics of the material type, composition, texture, and anisotropy.

[0074] The above specific description further details the purpose, technical solutions, and advantages of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.​

Claims

1. A spectral polarization detection method based on a quasi-continuous bound metasurface, characterized in that: This method designs a metasurface with an elliptical cross section and selects its geometric parameters and structural unit orientation to excite the quasi-continuous domain bound state mode of the metasurface structure, thereby achieving specific modulation of the incident light spectrum and polarization information. Numerical simulation methods are used to scan and calculate the spectral response of the designed structural units under different linear polarization incident conditions. The metasurface arrangement is determined in combination with the usage requirements, and a file for processing metasurface samples is generated. The designed metasurface sample was prepared, and the processing quality of the sample was characterized by scanning electron microscopy (SEM). An optical response testing and calibration system was built to test the actual spectral and polarization responses of the metasurface, and the results were compared and verified with simulation results. A multidimensional light field detection system was built and applied to spectral polarization detection. By measuring the intensity of different metasurface structural units on a CMOS detector, information on different spectral and polarization channels of the target was directly obtained, thereby realizing spectral polarization detection. The geometric parameters include the major and minor axes of the elliptical nanopillars, and the period, height, and rotation angle of the metasurface structural units.

2. The method as described in claim 1, characterized in that: Includes the following steps, Step 1: A quasi-continuous domain bound state metasurface for realizing multidimensional spectral polarization light field detection is constructed from an array of dielectric nanopillars with different geometric parameters and structural orientations, each having an elliptical cross-section. By breaking the rotational angular symmetry of the metasurface structural units, the quasi-continuous domain bound state is introduced into the metasurface design process. Quantitative control of different wavelength and polarization channels of the emitted light is achieved through a superpixel structure, thereby realizing multidimensional spectral polarization detection. The geometric parameters include the major axis r of the elliptical cross-section. a minor axis r b The metasurface structure unit has a periodicity P in the x-direction. x Period P in the y-direction y Height h and rotation angle δ; Step 2: Construct a quasi-continuous bound-state metasurface for realizing multidimensional spectral polarization detection. To achieve multidimensional spectral polarization detection, the metasurface is used to specifically modulate the spectral and polarization information of the incident light. The spectral response of the metasurface structural units with different geometric parameters under different linear polarization states is calculated using the finite-difference time-domain method. The metasurface arrangement, i.e., the metasurface structure, is determined by combining the target wavelength range and the number of spectral channels. Based on the determined metasurface structure, the corresponding metasurface structure fabrication file is generated. Step 3: Using the fabrication file of the dielectric metasurface obtained in Step 2, prepare a spectral polarization multidimensional optical field detection metasurface; by controlling the center wavelength of the resonance response and the polarization response through different geometric parameters and structural orientations of the metasurface, thereby achieving specific selection of different spectral and polarization channels; Step 4: For the metasurface obtained in Step 3, the nanopillars are tested and characterized using scanning electron microscopy (SEM); a spectral polarization multidimensional detection metasurface optical response testing and calibration system is built to test the resonance center wavelength and polarization extinction ratio of each metasurface pixel, and obtain the resonance center wavelength and polarization extinction ratio of each metasurface pixel. Step 5: Construct a spectral polarization multidimensional optical field detection system based on a quasi-continuous domain bound metasurface and apply it to spectral polarization detection. The spectral polarization multidimensional optical field detection system consists of a detection target, a quasi-continuous domain bound metasurface, a CMOS detector, and optical elements. Different pixels on the quasi-continuous domain bound metasurface filter different spectral and polarization components on the detection target. The filtered spectral polarization information is recorded as a grayscale image by the CMOS detector. By using the spatial positional relationship between different metasurface pixels in Step 2 and the Stokes relation, the spectral polarization information of the target object is calculated, thus realizing spectral polarization detection based on a quasi-continuous domain bound metasurface.

3. The spectral polarization detection method based on a quasi-continuous domain bound metasurface as described in claim 2, characterized in that: The metasurface structural unit used to achieve rotational angular symmetry breaking consists of two dielectric nanopillars rotated clockwise and counterclockwise by angle δ, respectively. Based on the reflection spectrum and electromagnetic field distribution of the structural unit, its resonant wavelength and polarization response are analyzed. The polarization response of the structural unit is calculated using the Jones matrix shown in formula (1). (1) Where t ij (i, j=x or y) are the reflection coefficients, and j and i represent the polarization directions of the incident light and the reflected light, respectively; the relationship between the metasurface structural unit and the polarization response of the reflected light is described according to equation (1).

4. The spectral polarization detection method based on a quasi-continuous domain bound metasurface as described in claim 2, characterized in that: The modulation process of incident light by the metasurface is represented by equation (2): (2) Where k represents the index of the metasurface structural unit, ranging from 1 to m, and different k values ​​correspond to structural units with different geometric parameters; p represents the orthogonal polarization components required to restore the polarization state; I k (p) represents the light intensity corresponding to the p-polarization component in the k-th metasurface structural unit. Let η(λ) represent the reflection coefficient of the k-th metasurface structural unit at wavelength λ and p component, and let η(λ) be the quantum efficiency of the CMOS detector. k Errors during the measurement process; for simplicity, defined as... According to equation (2), the information finally obtained by the CMOS detector is the light intensity information obtained through the integration process, which cannot reflect the spectrum and polarization characteristics of the incident light. Discretizing equation (2) yields its matrix representation: (3) Equation (3) modulates the wavelength dimension while maintaining the uniformity of the p-polarization basis, thereby achieving decoupling between the wavelength and polarization dimensions; the polarization information is calculated using the Stokes relations shown in equations (4)-(6): (4) (5) (6) Where DoLP and AoLP are the degree of linear polarization and the angle of linear polarization, respectively; S0, S1, and S2 are the Stokes components; and I(0°), I(45°), I(90°), and I(135°) represent the light intensity corresponding to different polarization bases.

5. The spectral polarization detection method based on a quasi-continuous domain bound metasurface as described in claim 2, characterized in that: In step two, the metasurface designed in step one is used as the basic structural unit. Its geometric parameters are changed to adjust the resonant wavelength, thereby realizing wavelength modulation in equation (3). The geometric parameters of the metasurface structural unit are multiplied by the scaling factor γ to adjust the resonant wavelength, thereby filtering light from different wavelength channels. After obtaining the preferred metasurface structural units with different geometric parameters, each metasurface structural unit is periodically arranged with orientations of 0°, 45°, 90°, and 135°, respectively, which are called spectral polarization detection pixels, to realize the polarization separation process in equation (3). The spectral polarization detection pixels are arranged regularly in space in a 2×2 form, and the arrangement result is called a spectral polarization detection unit. The metasurfaces with different geometric parameters are arranged in space in the above manner to obtain a series of spectral polarization detection pixels. The series of spectral polarization detection pixels are combined to form a complete spectral polarization multidimensional detection metasurface. The above metasurface design method is combined with the decoupling process shown in equation (3). A single metasurface is used to realize the detection of spectral polarization multidimensional light field information in an integrated and miniaturized system. The geometric parameters include the major axis r of the elliptical cross section. a minor axis r b The metasurface structure unit has a periodicity P in the x-direction. x Period P in the y-direction y .

6. The spectral polarization detection method based on a quasi-continuous domain bound metasurface as described in claims 1, 2, 3, or 4, characterized in that: The simulation software described in step one is implemented using FDTD based on the finite-difference time-domain method.

7. The spectral polarization detection method based on a quasi-continuous domain bound metasurface as described in claim 2, 3, or 4, characterized in that: Orthogonal polarization bases are selected as 0° and 90°, 45° and 135°, or left-handed circular polarization and right-handed circular polarization.

8. The spectral polarization detection method based on a quasi-continuous domain bound metasurface as described in claim 2, 3, or 4, characterized in that: The area of ​​each spectral polarization detection pixel is set to 50 μm × 50 μm.

9. The spectral polarization detection method based on a quasi-continuous domain bound metasurface as described in claim 3 or 4, characterized in that: Dielectric metasurfaces are fabricated using electron beam etching micro / nano fabrication methods.

Images