Multispectral full-polarization imaging device based on rotating wave plate and error correction method

Abstract

The invention belongs to the field of optical imaging, particularly relates to a multispectral full-polarization imaging device based on a rotating wave plate and an error correction method, and aims to realize high-precision multispectral full-polarization imaging. The device comprises a front imaging lens, a symmetric relay optical module, a polarization modulation module, a light splitting module, an image sensor, a rotation driving mechanism and a data processing and control module which are sequentially arranged along a light path. The symmetric relay optical module comprises a front lens group and a rear lens group which are in mirror symmetry about the aperture diaphragm, and the polarization modulation module and the light splitting module are located in a parallel light beam area formed between the front lens group and the rear lens group; the polarization modulation module comprises a quarter-wave plate capable of rotating around an optical axis and a fixedly arranged linear polarizer; the image sensor is located on an image space focal plane of the rear lens group, the rotation driving mechanism is connected with the quarter-wave plate, and the data processing and control module is in communication connection with the image sensor and the rotation driving mechanism.

Description

Technical Field

[0001] This invention relates to the field of optical imaging, and more particularly to a multispectral full polarization imaging device and error correction method based on a rotating waveplate. Background Technology

[0002] Polarization is one of the fundamental physical properties of light waves, forming a complete dimension of optical information along with light intensity and spectrum. Multispectral Stokes polarization imaging technology can simultaneously acquire the spatial, spectral, and complete polarization information of a target, significantly improving the ability to detect and identify the material, morphology, and surface characteristics of targets against complex backgrounds. This technology has broad application prospects in fields such as geological exploration, biomedical diagnostics, industrial non-destructive testing, and military target identification.

[0003] To achieve full Stokes polarization imaging, existing technologies mainly include focal plane modulation, spatial modulation, and time-division modulation. Focal plane modulation, by integrating a micro-polarizer array into the image sensor's image plane, enables rapid measurement of linear polarization components and boasts a compact system structure. However, it struggles to directly acquire circular polarization components, and its performance is limited by specific lens and sensor combinations, resulting in poor compatibility and flexibility. Spatial modulation techniques, such as those based on birefringent wedges or Savart plates, acquire interferometric images through a single exposure. After spectral demodulation, full Stokes parameters can be reconstructed, offering snapshot advantages. However, its effective bandwidth is typically limited by the carrier frequency characteristics of the interference fringes, making it difficult to meet the demands of multispectral imaging. Furthermore, it places stringent requirements on the image plane stability and resolution of the imaging system. When used with zoom lenses, image plane drift can easily lead to fringe mismatch, increasing demodulation errors.

[0004] In time-division modulation schemes, the rotating waveplate method is widely used due to its relatively simple structure and clear modulation principle. This method uses a rotating waveplate in conjunction with a fixed analyzer to acquire a series of intensity images, and then calculates the complete Stokes vector. However, in practical systems, when polarization modulation elements such as waveplates are placed in the converging beam of the imaging optical path, changes in the image plane position caused by zooming or focusing of commercial lenses can alter the actual incident angle of the waveplate, introducing dynamically changing wavefront aberrations and image drift, affecting image quality and polarization measurement accuracy. Furthermore, existing systems generally do not effectively correct for phase delay deviations caused by the non-perpendicular incident waveplate of the edge beam due to changes in the field of view, limiting the accuracy of polarization measurements across the entire field of view. Summary of the Invention

[0005] The purpose of this invention is to provide a multispectral polarization imaging device and error correction method based on a rotating waveplate, aiming to provide a high-precision multispectral polarization imaging solution that is compatible with various lenses, adapts to focusing and zooming operations, and can systematically correct the incident angle error across the entire field of view.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a multispectral full polarization imaging device based on a rotating waveplate, comprising a front imaging lens, a symmetrical relay optical module, a polarization modulation module, a beam splitting module, an image sensor, a rotation drive mechanism, and a data processing and control module arranged sequentially along the optical path. The front imaging lens is used to perform the initial imaging of the target under test, forming a first intermediate image plane. The symmetrical relay optical module includes a front lens group and a rear lens group that are mirror-symmetrical about the aperture stop, forming a telecentric optical path with a secondary imaging magnification of 1. The first intermediate image plane is located at the object-side focal plane of the front lens group, and the symmetrical relay optical module is used to perform secondary imaging of the first intermediate image plane. The polarization modulation module and the beam splitting module are located at... Within the parallel beam region formed between the front and rear lens groups; the polarization modulation module includes a quarter-wave plate rotatable around the optical axis and a fixed linear polarizer; the beam splitting module is used to select a beam from multiple predetermined spectral bands; the image sensor is located at the image-side focal plane of the rear lens group and is used to acquire the target light intensity image after secondary imaging; the rotation drive mechanism is connected to the quarter-wave plate and is used to drive the quarter-wave plate to rotate to multiple preset angles; the data processing and control module is communicatively connected to the image sensor and the rotation drive mechanism respectively, and is used to control the rotation drive mechanism, acquire image data from the image sensor, and perform polarization information inversion and error correction.

[0007] The secondary imaging magnification of the symmetrical relay optical module is 1. The front imaging lens and image sensor are independently replaceable modules, and the beam splitting module is a switchable bandpass filter wheel. Multiple predetermined spectral bands include at least three center wavelengths located in the visible light band.

[0008] Both the front and rear lens groups contain multiple lenses and are distributed in a mirror-symmetric manner with respect to the aperture stop; the aperture stop is located between the front and rear lens groups.

[0009] The front lens group includes a first single lens, a first cemented lens group, a second single lens, a third single lens, and a fourth single lens arranged sequentially along the incident direction of light; the rear lens group includes a fifth single lens, a sixth single lens, a seventh single lens, a second cemented lens group, and an eighth single lens arranged sequentially along the exit direction of light; the first cemented lens group and the second cemented lens group have a symmetrical structure about the aperture stop.

[0010] The quarter-wave plate is an achromatic quarter-wave plate, and the rotary drive mechanism consists of a stepper motor and a controller with a high-precision angle encoder. The controller is connected to the stepper motor, and the quarter-wave plate is connected to the stepper motor.

[0011] This invention also provides a method for correcting errors in multispectral polarization imaging based on a rotating waveplate, applicable to the aforementioned multispectral polarization imaging device based on a rotating waveplate. The method includes: S1, a system calibration step: calibrating the system using a beam with known Stokes parameters to obtain the calibration error parameters of the quarter-wave plate; S2, an image acquisition step: controlling a rotating drive mechanism to rotate the quarter-wave plate to N different angular positions, and at each angular position, controlling an image sensor to acquire the target light intensity image under the current spectral channel, obtaining N original light intensity images; where N is an integer greater than 4; S3, an error correction and parameter calculation step: for each pixel, based on its light intensity value sequence in the N original light intensity images, the calibration error parameters, and the incident angle information of the principal ray corresponding to the pixel, performing polarization measurement error correction, and calculating the corrected Stokes parameters; S4, an image generation step: generating a full Stokes polarization image for the corresponding spectral channel based on the Stokes parameters calculated for all pixels.

[0012] In step S1, the calibration error parameters include at least the fast axis angle installation error of the quarter-wave plate and the deviation between the actual phase delay and the nominal value.

[0013] In step S3, the polarization measurement error correction specifically includes: calculating the additional phase delay error caused by the beam incident at a non-perpendicular angle on the quarter-wave plate based on the incident angle information of the principal ray corresponding to the pixel, and superimposing the additional error with the calibration error parameter to construct the corrected polarization modulation model.

[0014] In step S3, the corrected Stokes parameters are obtained by Fourier analysis. Specifically, the Fourier series expansion of the light intensity value sequence is performed, the Fourier coefficients are extracted, and the Stokes parameters are calculated using the relationship between the Fourier coefficients and the Stokes parameters established based on the corrected polarization modulation model.

[0015] The method also includes a spectral switching and fusion step: repeating steps S2 to S4 to sequentially obtain the full Stokes polarization image of each band in multiple predetermined spectral bands, and fusing the image data of different bands to generate a multispectral full polarization data cube.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This application provides a multispectral polarization imaging device and error correction method based on a rotating waveplate. It employs a modular design where the front imaging lens and image sensor are independently replaceable. Combined with the 1x magnification of the symmetrical relay optical module, the front imaging lens and image sensor do not rely on specific combinations and can be flexibly replaced according to actual field-of-view and resolution requirements without reconstructing the core optical system. This significantly reduces system adaptation costs, is compatible with various commercial lenses and image sensors, and broadens the application scenarios of the device. Simultaneously, the switchable bandpass filter wheel design enables rapid switching between multiple predetermined spectral bands without disassembly or adjustment of the optical path. This solves the problem of limited effective working bandwidth and inability to meet multi-wavelength requirements in existing spatial modulation technologies, making it suitable for multispectral detection scenarios.

[0017] 2. The symmetrical relay optical module adopts a mirror-symmetric structure of the front lens group, aperture stop, and rear lens group. This symmetrical design ensures that the principal rays of the entrance and exit pupils are parallel to the optical axis. On the one hand, it pushes the system's entrance pupil to object infinity, ensuring consistent magnification across the depth of field. On the other hand, the coma, distortion, and chromatic aberration generated by the front and rear lens groups cancel each other out, significantly reducing imaging distortion and improving image uniformity. Furthermore, both the polarization modulation module and the beam splitter module are placed in the parallel beam region between the front and rear lens groups, ensuring a consistent beam angle incident on the quarter-wave plate. This avoids the problem in existing technologies where the polarization modulation element is placed in the converging optical path, causing the incident angle to change with focusing. This reduces beam distortion and image plane drift, ensuring imaging stability. The use of an achromatic quarter-wave plate effectively overcomes the wavelength sensitivity of ordinary wave plates, making it suitable for polarization state conversion requirements in multiple visible light bands. Combined with a fixed high-performance linear polarizer, it forms a stable polarization modulation unit. The rotation drive mechanism uses a stepper motor with a high-precision angle encoder, which can accurately control the rotation angle of the quarter-wave plate, ensuring the consistency and accuracy of multi-angle acquisition and solving the problem of image drift caused by dynamic wavefront aberration in the existing rotating wave plate method. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a multispectral polarization imaging device based on a rotating waveplate provided in an embodiment of this application; Figure 2 This is a schematic diagram of a front lens group and a rear lens group provided in an embodiment of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] This application provides a multispectral full polarization imaging device based on a rotating waveplate, exemplarily, such as... Figure 1 As shown. The multispectral polarization imaging device based on rotating waveplate includes a front imaging lens 1, a symmetrical relay optical module 2, a polarization modulation module 3, a beam splitting module 4, an image sensor 5, a rotation drive mechanism 6, and a data processing and control module 7 arranged sequentially along the optical path.

[0021] The front imaging lens 1 is used to perform the initial imaging of the target under test, forming a first intermediate image plane; the symmetrical relay optical module 2 includes a front lens group 21 and a rear lens group 23 that are mirror-symmetrical about the aperture stop 22, forming a telecentric optical path with a secondary imaging magnification of 1. The first intermediate image plane is located at the object-side focal plane of the front lens group 21, and the symmetrical relay optical module 2 is used to perform secondary imaging of the first intermediate image plane; the polarization modulation module 3 and the beam splitting module 4 are located in the parallel beam region formed between the front lens group 21 and the rear lens group 23; the polarization modulation module 3 includes a quarter-wave plate that can rotate around the optical axis. The system includes a fixed linear polarizer 31 and a beam splitter 32; a beam splitter module 4 for selecting a beam from multiple predetermined spectral bands; an image sensor 5 located on the image-side focal plane of the rear lens group 23 for acquiring the target light intensity image after secondary imaging; a rotation drive mechanism 6 connected to the quarter-wave plate 31 for driving the quarter-wave plate 31 to rotate to multiple preset angles; and a data processing and control module 7 communicatively connected to the image sensor 5 and the rotation drive mechanism 6 for controlling the rotation drive mechanism 6, acquiring image data from the image sensor 5, and performing polarization information inversion and error correction.

[0022] For example, the secondary imaging magnification of the symmetrical relay optical module 2 is 1, the front imaging lens 1 and the image sensor 5 are independently replaceable modules, and the beam splitting module 4 is a switchable bandpass filter wheel, which includes filters of at least three different wavelengths, and the multiple predetermined spectral bands include at least three center wavelengths located in the visible light band.

[0023] As one possible implementation, the bandpass filter wheel uses high-performance bandpass filters with center wavelengths of 495nm and 600±2nm and FWHM of 11.5nm and 10±2nm, respectively, and laser line filters with center wavelengths of 532±0.6nm and FWHM of 3±0.6nm.

[0024] As one possible implementation, both the front lens group 21 and the rear lens group 23 contain multiple lenses and are distributed in a mirror-symmetric manner with respect to the aperture stop 22. The aperture stop 22 is located between the front lens group 21 and the rear lens group 23. This symmetrical structural design makes the principal rays of the entrance pupil and exit pupil parallel to the optical axis and forms a parallel light collimation region at the aperture stop 22.

[0025] For example, the aperture stop 22 has a diameter of 14mm. The angle of light passing through the aperture stop 22 remains unchanged. The polarization modulation module 3 and the beam splitter 4 are placed between the front lens group 21 and the rear lens group 23 to form a parallel light collimation region, which facilitates polarization correction and improves polarization measurement accuracy. At the same time, the entrance pupil of the system is pushed to infinity on the object side, and as a geometric symmetry plane, the reverse coma, distortion, and magnification chromatic aberration generated by the front lens group 21 and the rear lens group 23 cancel each other out, so that the magnification is independent of the object distance and the image quality is independent of the field of view.

[0026] For example, the quarter-wave plate 31 is an achromatic quarter-wave plate with an optical path difference of λ / 4 and an ideal phase delay of π / 2. It can be used for polarization state conversion of light of any wavelength within a certain band, converting linearly polarized light into circularly polarized light. It has wide spectral applicability, large incident angle and low environmental sensitivity. Its phase delay varies with the wavelength and angle of the incident beam.

[0027] For example, the linear polarizer 32 is a nanoparticle thin film linear polarizer with an extinction ratio of up to 100,000:1. It has a high damage threshold and a wide operating temperature range, and maintains good performance within a ±20° incident angle range. Together with the quarter-wave plate 31, it forms the polarization modulation module 3 of the system to polarize the beam.

[0028] The rotary drive mechanism 6 includes a stepper motor 61 with a high-precision angle encoder and a controller 62. The controller 62 is connected to the stepper motor 61, and the quarter-wave plate 31 is also connected to the stepper motor 61. For example, the stepper motor 61 is an OSMS-60YAW, consisting of a high-resolution rotary motor and a high-precision angle encoder, used to rotate the rotor and its load with high angular accuracy. The quarter-wave plate 31 is integrated into the stepper motor 61. After fast-axis calibration, the stepper motor 61 provides the initial fast-axis position of the quarter-wave plate 31. The controller 62 is a GSC-01, used to control the stepper motor 61 to precisely adjust the angular position of the quarter-wave plate 31.

[0029] After the first imaging by the front imaging lens 1, the imaging beam enters the device and passes through the front lens group 21 before entering the polarization modulation module 3, which consists of a quarter-wave plate 31 and a linear polarizer 32. The polarization modulation module 3 performs full Stokes polarization measurement on the beam, in which the polarizer 5 is fixed, and the quarter-wave plate 31 is mounted on the stepper motor 61 connected to the controller 62. The beam splitting module 4 performs spectral selection on the beam modulated by the polarization modulation module 3, allowing single-wavelength beams to pass through. The rear lens group 23 performs a second imaging and converges the beam after full Stokes polarization measurement and filtering onto the image sensor 5, and uses the image sensor 5 to complete the light intensity detection. The data processing and control module 7 obtains high-precision full Stokes polarization images of the target under different spectra by image acquisition, storage, and data inversion.

[0030] As one possible implementation, the image sensor 5 uses a Basler CMOS camera with a GigE data transmission interface, an effective pixel count of 1920*1200, a frame rate of 50fps, and a pixel size of 5.86μm*5.86μm, and is used to detect the intensity of the emitted light after each polarization modulation.

[0031] As one possible implementation, the front imaging lens 1 can be a fixed-focus or zoom lens, C-mount or F-mount, and the image can be made clear by focusing and zooming. The first image of the entire device is located behind the front imaging lens 1, and its image plane is the object plane of the symmetrical relay optical module 2.

[0032] For example, refer to Figure 1 and Figure 2 The front lens group 21 includes a first single lens 211, a first cemented lens group 212, a second single lens 213, a third single lens 214, and a fourth single lens 215 arranged sequentially along the incident direction of light. The rear lens group 23 includes a fifth single lens 231, a sixth single lens 232, a seventh single lens 233, a second cemented lens group 234, and an eighth single lens 235 arranged sequentially along the exit direction of light. The first cemented lens group 212 further includes a first lens 2121, a second lens 2122, and a third lens 2123; the second cemented lens group 234 further includes a fourth lens 2341, a fifth lens 2342, and a sixth lens 2343.

[0033] For example, the front mirror surface of the first lens 2121 has a radius of curvature of 750.956 mm and a thickness of 3.007 mm; The front mirror surface of the second lens 2122 has a radius of curvature of 33.850 mm and a thickness of 14.458 mm; The front mirror surface curvature radius of the third lens 2123 is -25.000mm, and the thickness is 3.000mm; The rear mirror surface curvature radius of the third lens 2123 is -88.707mm; The fourth lens 2341 has a front mirror surface curvature radius of 88.707 mm and a thickness of 3.000 mm. The fifth lens 2342 has a front mirror surface curvature radius of 25.000 mm and a thickness of 14.458 mm. The sixth lens 2343 has a front mirror surface curvature radius of -33.850mm and a thickness of 3.007mm; The rear mirror surface curvature radius of the sixth lens 2343 is -750.956mm; The first single lens 211 has a front mirror curvature radius of -18.880 mm and a rear mirror curvature radius of -25.184 mm, and a thickness of 12.491 mm. The second single lens 213 has a front mirror curvature radius of 97.000 mm and a rear mirror curvature radius of -52.350 mm, and a thickness of 14.757 mm. The third single lens 214 has a front mirror curvature radius of 51.200 mm and a rear mirror curvature radius of Infinity, with a thickness of 8.387 mm. The fourth single lens 215 has a front mirror curvature radius of 31.800 mm and a rear mirror curvature radius of 19.468 mm, and a thickness of 19.588 mm. The fifth single lens 231 has a front mirror curvature radius of -19.468mm and a rear mirror curvature radius of -31.800mm, and a thickness of 19.588mm. The sixth single lens 232 has a front mirror curvature radius of Infinity and a rear mirror curvature radius of -51.200mm, and a thickness of 8.387mm. The seventh single lens 233 has a front mirror curvature radius of 52.350 mm and a rear mirror curvature radius of -97.000 mm, and a thickness of 14.757 mm. The eighth single lens 235 has a front mirror curvature radius of 25.184 mm, a rear mirror curvature radius of 18.880 mm, and a thickness of 12.491 mm. The distance from the rear mirror surface of the fourth single lens 215 to the aperture stop is 33.543 mm, and the distance from the aperture stop 22 to the front mirror surface of the fifth single lens 231 is 33.543 mm. The distance from the rear mirror of the front imaging lens 1 to the front mirror of the first single lens 211 is 22.137mm. The distance from the rear mirror surface to the imaging plane of the eighth single lens 235 is 22.129 mm.

[0034] This application also provides a method for correcting errors in multispectral full polarization imaging based on a rotating waveplate, applied to the aforementioned multispectral full polarization imaging device based on a rotating waveplate. The method includes: S1. System calibration steps: Use a beam with known Stokes parameters to calibrate the system and obtain the calibration error parameters of the quarter-wave plate.

[0035] In step S1, the calibration error parameters include at least the fast axis angle installation error of the quarter-wave plate. And the deviation between the actual phase delay and the nominal value .

[0036] S2. Image acquisition steps: Control the rotation drive mechanism to drive the quarter-wave plate to N different angular positions, and at each angular position, control the image sensor to acquire the target light intensity image under the current spectral channel to obtain N original light intensity images; where N is an integer greater than 4.

[0037] S3. Error Correction and Parameter Calculation Steps: For each pixel, based on its light intensity value sequence in N original light intensity images, calibration error parameters, and the incident angle information of the principal ray corresponding to the pixel, polarization measurement error correction is performed, and the corrected Stokes parameter is calculated.

[0038] In step S3, the polarization measurement error correction specifically includes: calculating the additional phase delay error caused by the beam incident at a non-perpendicular angle on the quarter-wave plate based on the incident angle information of the principal ray corresponding to the pixel, and superimposing the additional error with the calibration error parameter to construct the corrected polarization modulation model.

[0039] In step S3, the corrected Stokes parameters are obtained by Fourier analysis. Specifically, the Fourier series expansion of the light intensity value sequence is performed, the Fourier coefficients are extracted, and the Stokes parameters are calculated using the relationship between the Fourier coefficients and the Stokes parameters established based on the corrected polarization modulation model.

[0040] S4. Image generation steps: Generate a full Stokes polarization image for the corresponding spectral channels based on the Stokes parameters obtained from solving all pixels.

[0041] The method also includes a spectral switching and fusion step: repeating steps S2 to S4 to sequentially obtain the full Stokes polarization image of each band in multiple predetermined spectral bands, and fusing the image data of different bands to generate a multispectral full polarization data cube.

[0042] The more detailed operation process is as follows: A quarter-wave plate is installed in a stepper motor, which is then connected to the controller. After the device is powered on, the initial position of the fast axis of the quarter-wave plate is calibrated, and the stepper motor's angular position is set to zero. The quarter-wave plate, linear polarizer, and bandpass filter wheel are sequentially installed in the parallel light collimation area between the front and rear lens groups. The data processing and control module is connected to the image sensor and the controller, respectively. The front imaging lens is installed at the front of the device. Different filters are used, and the data processing and control module adjusts the exposure time and gain coefficient of the image sensor. The lens is focused and zoomed to achieve a clear image of the target. Once the image is clear, the data processing and control module sends a command to the controller, which drives the stepper motor to rotate the quarter-wave plate 18 times continuously from the zero position, each time in 10° increments. The linear polarizer remains fixed throughout the process. The image sensor synchronously acquires images at each angle, for a total of 18 images. After each measurement, the controller controls the stepper motor to return to the zero position. The data processing and control module acquires, stores, and inverts data from 18 images captured by the image sensor to obtain high-precision full Stokes polarization images of the target under different spectra.

[0043] Based on the steps described above, the optical system is analyzed using Stokes parameters and the Mueller matrix: The device provided in this application embodiment adopts a symmetrical object-side telecentric optical system design. The polarization modulation module is located in the parallel light collimation region between the front lens group and the rear lens group. Therefore, the light beam passing through the quarter-wave plate is parallel light, and beams of the same wavelength are incident on the quarter-wave plate at the same angle. Since the phase delay is when the quarter-wave plate is perpendicularly incident, the phase delay is... However, the phase delay does not remain constant when the incident light is not perpendicular. This affects the accuracy of polarization imaging measurements. Therefore, it is assumed that the incident light is perpendicular. The azimuth angle of the incident beam on the quarter-wave plate is α, the elevation angle is β, the initial direction of the fast axis is in the yoz plane, and the angle with the z-axis is α. ,when When =0°, the expression for the fast axis vector is: (1) when For other different angles, the expression for the fast axis vector is: (2) Let the rotation matrix (a two-dimensional angle coupled with azimuth and pitch) be R. z If we consider the incident angle of the beam as equivalent to the rotation angle of the waveplate, then the direction of the fast axis of the rotated quarter-wave plate is: Then the angle γ between the incident light vector and the fast axis of the quarter-wave plate is: (3) Then the angle γ can be expressed as: (4) The relationship between the phase retardation of the quarter-wave plate and the incident wavelength, incident angle, and fast axis direction can be expressed as equation (5): n of the quarter-wave plate o =1.544, n e =1.553, d=14.78μm. The phase delay of the quarter-wave plate for different incident polarization measurement systems can be calculated according to equation (5).

[0044] Because the front imaging lens is rotationally symmetrical, all light beams entering the device are symmetrical about the optical axis. There is a fixed linear relationship between the image height of the image sensor and the principal ray angle at the aperture stop. As the image height increases, the principal ray angle at the aperture stop increases sequentially. The image height at the optical axis is defined as 0 mm, and the principal ray angle at the aperture stop is defined as 0°.

[0045] Once the relationship between the image height and the incident angle of the image sensor, and the relationship between the incident angle, wavelength, and phase delay of the quarter-wave plate are known, error correction can be performed on the device.

[0046] Depending on the method of acquiring polarization images, the main methods of full Stokes vector polarization imaging include time-division method, real-time method, aperture division method, and focal plane array method. Among them, the time-division method is mainly suitable for static target measurement. The polarization measurement system of the time-division method consists of a rotatable waveplate and a fixed linear polarizer. The specific mathematical expression is as follows: (6) Among them, S in Stokes parameters for the incident light: (7) Among them, M p The Mueller matrix of a linear polarizer with a polarization angle of θ is: (8) Among them, M R It is the Mueller matrix of a quarter-wave plate, assuming its fast axis angle is... The phase delay is In reality, ideal polarization devices do not exist. Therefore, the parameter errors of the polarization device must be considered. The magnitude of each parameter error is determined through error calibration, and then error compensation is achieved. Let the fast axis angle error be... The phase delay error is Then the actual , Then the Mueller matrix of the quarter-wave plate is as follows (9): Substituting equations (7), (8), and (9) into equation (6) for matrix operations, the Stokes parameter S of the emitted beam can be obtained. out Since the image sensor can only detect the light intensity signal I, i.e. the Stokes parameter S of the emitted beam, out The first component S out0 The expression for light intensity is as follows (10): The light intensity signal I detected by the image sensor can also be expressed by the following Fourier series (11): in, Comparing equation (11) with equation (12) above, we can obtain equation (13), that is, obtain the Stokes parameter S of the incident beam. in and the Fourier coefficients related to the errors of the two parameters of the quarter-wave plate: The fast axis angle error of the quarter-wave plate can be obtained by comparing the Fourier coefficients in equation (13). Phase delay error The calculation formula is: (14) (15) This yields the relationship between the Stokes parameters of the incident beam and the fast axis angle error and phase delay error of the quarter-wave plate. It should be noted that to obtain the error... and To perform measurement calibration, you need to input an incident light with known Stokes parameters before you can substitute it into the following formula to solve for the polarization state of other incident light with unknown Stokes parameters.

[0047] Based on the Fourier coefficients obtained above, the Stokes parameter (16) of the incident beam can be obtained as follows: but The Stokes parameters S0, S1, S2, and S3 after error correction can be obtained. Then, by substituting the obtained Stokes parameters into the polarization state calculation formula, all polarization information of the target under test can be obtained.

[0048] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0049] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multispectral full polarization imaging device based on a rotating waveplate, characterized in that, The system includes a front imaging lens, a symmetrical relay optical module, a polarization modulation module, a beam splitting module, an image sensor, a rotation drive mechanism, and a data processing and control module, arranged sequentially along the optical path. The front imaging lens is used to perform the initial imaging of the target, forming a first intermediate image plane. The symmetrical relay optical module includes a front lens group and a rear lens group that are mirror-symmetrical about the aperture stop, forming a telecentric optical path with a secondary imaging magnification of 1. The first intermediate image plane is located at the object-side focal plane of the front lens group, and the symmetrical relay optical module is used to perform secondary imaging of the first intermediate image plane. The polarization modulation module and the beam splitting module are located between the front lens group and the rear lens group. Within the parallel beam region; the polarization modulation module includes a quarter-wave plate rotatable about the optical axis and a fixedly set linear polarizer; the beam splitting module is used to select a beam of a certain band from multiple predetermined spectral bands; the image sensor is located at the image-side focal plane of the rear lens group and is used to acquire the target light intensity image after secondary imaging; the rotation drive mechanism is connected to the quarter-wave plate and is used to drive the quarter-wave plate to rotate to multiple preset angles; the data processing and control module is communicatively connected to the image sensor and the rotation drive mechanism respectively, and is used to control the rotation drive mechanism, acquire image data from the image sensor, and perform polarization information inversion and error correction.

2. The multispectral full polarization imaging device based on a rotating waveplate according to claim 1, characterized in that, The secondary imaging magnification of the symmetrical relay optical module is 1. The front imaging lens and the image sensor are independently replaceable modules. The beam splitting module is a switchable bandpass filter wheel. The plurality of predetermined spectral bands include at least three center wavelengths located in the visible light band.

3. The multispectral full polarization imaging device based on a rotating waveplate according to claim 1, characterized in that, Both the front lens group and the rear lens group contain multiple lenses and are distributed in a mirror-symmetric manner with respect to the aperture stop; the aperture stop is located between the front lens group and the rear lens group.

4. The multispectral full polarization imaging device based on a rotating waveplate according to claim 1, characterized in that, The front lens group includes a first single lens, a first cemented lens group, a second single lens, a third single lens, and a fourth single lens arranged sequentially along the incident direction of light; the rear lens group includes a fifth single lens, a sixth single lens, a seventh single lens, a second cemented lens group, and an eighth single lens arranged sequentially along the exit direction of light; the first cemented lens group and the second cemented lens group have a symmetrical structure about the aperture stop.

5. The multispectral full polarization imaging device based on a rotating waveplate according to claim 1, characterized in that, The quarter-wave plate is an achromatic quarter-wave plate, and the rotary drive mechanism includes a stepper motor with a high-precision angle encoder and a controller. The controller is connected to the stepper motor, and the quarter-wave plate is connected to the stepper motor.

6. A method for correcting errors in multispectral full polarization imaging based on rotating waveplates, characterized in that, The method for the multispectral polarization imaging device based on a rotating waveplate according to any one of claims 1-5 includes: S1, a system calibration step: calibrating the system using a beam with known Stokes parameters to obtain calibration error parameters of the quarter-wave plate; S2, an image acquisition step: controlling the rotation drive mechanism to drive the quarter-wave plate to rotate to N different angular positions, and at each angular position, controlling the image sensor to acquire a target light intensity image under the current spectral channel to obtain N original light intensity images; where N is an integer greater than 4; S3, an error correction and parameter calculation step: for each pixel, based on its light intensity value sequence in the N original light intensity images, the calibration error parameters, and the incident angle information of the principal ray corresponding to the pixel, performing polarization measurement error correction, and calculating the corrected Stokes parameters; S4, an image generation step: generating a full Stokes polarization image of the corresponding spectral channel based on the Stokes parameters calculated for all pixels.

7. The multispectral full polarization imaging error correction method based on a rotating waveplate according to claim 6, characterized in that, In step S1, the calibration error parameters include at least the fast axis angle installation error of the quarter-wave plate and the deviation between the actual phase delay and the nominal value.

8. The multispectral full polarization imaging error correction method based on a rotating waveplate according to claim 6, characterized in that, In step S3, the polarization measurement error correction specifically includes: calculating the additional phase delay error caused by the beam incident at a non-perpendicular angle on the quarter-wave plate based on the incident angle information of the principal ray corresponding to the pixel, and superimposing the additional error with the calibration error parameter to construct the corrected polarization modulation model.

9. The multispectral full polarization imaging error correction method based on a rotating waveplate according to claim 6, characterized in that, In step S3, the corrected Stokes parameter is obtained by Fourier analysis. Specifically, the light intensity value sequence is expanded by Fourier series, its Fourier coefficients are extracted, and the Stokes parameter is calculated using the relationship between the Fourier coefficients and the Stokes parameter established based on the corrected polarization modulation model.

10. The multispectral full polarization imaging error correction method based on a rotating waveplate according to claim 6, characterized in that, The method further includes a spectral switching and fusion step: repeating steps S2 to S4 to sequentially obtain the full Stokes polarization image of each band in the plurality of predetermined spectral bands, and fusing the image data of different bands to generate a multispectral full polarization data cube.

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