Ultra-fast single-pixel polarization imaging system

Abstract

The present invention provides an ultrafast single-pixel polarization imaging system, including a laser, an imaging device, a polarization modulation module, and an information processing module. When the polarization modulation module is a first type of polarization modulation module, the polarization modulation module adjusts the polarization state of the laser signal provided by the laser, and sequentially uses the formed polarized light with different polarization states as measurement optical signals and transmits them to the imaging device; for each type of polarized light received in sequence, the imaging device divides the polarized light into multiple incident optical signals with different wavelengths, makes each incident optical signal perpendicularly incident on different positions of the target to be measured, and the spatial optical signals reflected or transmitted from different positions of the target to be measured are transmitted to the information processing module; the information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each type of polarized light, thereby realizing Stokes polarization imaging. The present invention can achieve real-time polarization imaging.

Description

Technical Field

[0001] The present invention belongs to the field of polarization imaging, and particularly relates to an ultrafast single-pixel polarization imaging system. Background Art

[0002] Existing polarization imaging systems usually utilize infrared polarization imaging detection technology. This technology calculates the Stokes vector of the polarization information of the target to be measured by obtaining infrared intensity images in different polarization directions, and then obtains parameters such as the degree of polarization or the polarization angle. However, the response time of infrared polarization imaging technology can only reach the order of milliseconds, with a slow response speed and unable to achieve real-time polarization imaging. Summary of the Invention

[0003] The present invention provides an ultrafast single-pixel polarization imaging system to solve the problem that the current polarization imaging system has a slow response speed and cannot achieve real-time polarization imaging.

[0004] According to the first aspect of the embodiment of the present invention, an ultrafast single-pixel polarization imaging system is provided, including a laser, an imaging device, a polarization modulation module, and an information processing module. When the polarization modulation module is a first type of polarization modulation module, the polarization modulation module adjusts the polarization state of the laser signal provided by the laser, and sequentially uses the formed polarized light with different polarization states as measurement optical signals and transmits them to the imaging device; the imaging device divides each type of polarized light received in sequence into multiple incident optical signals with different wavelengths, makes each incident optical signal perpendicularly incident on different positions of the target to be measured, and the spatial optical signals reflected or transmitted from different positions of the target to be measured are transmitted to the information processing module; the information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each type of polarized light, thereby realizing Stokes polarization imaging;

[0005] When the polarization modulation module is a second type of polarization modulation module, the imaging device uses the laser signal provided by the laser as a measurement optical signal, divides it into multiple incident optical signals with different wavelengths, makes each incident optical signal perpendicularly incident on different positions of the target to be measured, and the spatial optical signals reflected or transmitted from different positions of the target to be measured are transmitted to the polarization modulation module; the polarization modulation module adjusts the polarization state of the spatial optical signal to form multiple polarized lights with different polarization states and transmits them to the information processing module; the information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of each polarized light, thereby realizing Stokes polarization imaging.

[0006] In an alternative implementation, when the polarization modulation module is a first type of polarization modulation module, the information processing module includes a coupler, a dispersion module, a photodetector, an oscilloscope, a spectrometer, and a processor. For each type of polarized light, the coupler divides the spatial light signal corresponding to this type of polarized light into two paths, one path is transmitted to the spectrometer, and the spectrometer records the frequency-domain data. The other path is transmitted to the photodetector after being stretched in the time domain by the dispersion module. The photodetector converts the spatially optical signal after time-domain stretching into a spatial electrical signal and transmits the spatial electrical signal to the oscilloscope, and the oscilloscope records the time-domain data. For each type of polarized light provided in sequence by the polarization modulation module, the processor determines the wavelength of the spatial light signal reflected or transmitted from each position on the target to be measured according to the frequency-domain data of this type of polarized light, and determines the intensity of the spatial light signal corresponding to each position on the target to be measured under the action of this type of polarized light according to the wavelength magnitude of the spatial electrical signal in the time-domain data of this type of polarized light. According to the intensity of the spatial light signal corresponding to each position on the target to be measured, the Stokes parameters corresponding to each position on the target to be measured are determined, so as to realize Stokes polarization imaging;

[0007] When the polarization modulation module is a second type of polarization modulation module, it further includes a dispersion module. The dispersion module stretches the laser signal provided by the laser in the time domain and then transmits the time-domain stretched laser signal to the imaging device. The imaging device divides the time-domain stretched laser signal into multiple incident optical signals with different wavelengths, and makes each incident optical signal perpendicularly incident on different positions of the target to be measured.

[0008] In another alternative implementation, when the polarization modulation module is a second type of polarization modulation module, the polarization modulation module includes three beam splitters, a quarter-wave plate, four polarizers, and four couplers. The information processing module includes four photodetectors, an oscilloscope, and a processor. The first beam splitter is used to receive the spatial light signal and divides the spatial light signal into two paths, which are respectively transmitted to the second beam splitter and the third beam splitter. The second beam splitter divides the spatial light signal it receives into two paths. One path is connected to the oscilloscope through the first polarizer, the first coupler, and the first photodetector in sequence, and the other path is connected to the oscilloscope through the second polarizer, the second coupler, and the second photodetector in sequence. The third beam splitter divides the spatial light signal it receives into two paths. One path is connected to the oscilloscope through the third polarizer, the quarter-wave plate, the third coupler, and the third photodetector in sequence, and the other path is connected to the oscilloscope through the fourth polarizer, the fourth coupler, and the fourth photodetector in sequence.

[0009] The four polarizers adjust the polarization states of the received spatial optical signals to form polarized light with different polarization states. After the corresponding couplers couple and transmit the polarized light to the corresponding photodetectors, the four photodetectors respectively perform photoelectric conversion on the polarized light to form polarization signals. The quarter-wave plate converts the polarized light provided by the third polarizer into circularly polarized light or elliptically polarized light. The oscilloscope respectively records the time-domain data of the linearly polarized signals output by the four photodetectors. The processor determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each position on the target to be measured in the time-domain data, thereby realizing Stokes polarization imaging.

[0010] In another alternative implementation, the imaging device includes a first cylindrical mirror, a first reflector, a first virtual imaging phase array VIPA, a first transmission grating, a second transmission grating, a second VIPA, a second reflector, and a second cylindrical mirror. The target to be measured is located between the first transmission grating and the second transmission grating. After the measurement optical signal is focused by the first cylindrical mirror, it is transmitted to the first VIPA through the first reflector. The first VIPA performs spatial dispersion on the measurement optical signal to divide it into multiple incident optical signals with different wavelengths. After the multiple incident optical signals pass through the first transmission grating whose dispersion direction is orthogonal to the first VIPA, an incident optical signal array is formed. The incident optical signal array is perpendicularly incident on different positions of the target to be measured, thereby realizing area scanning of the target to be measured.

[0011] The spatial optical signals transmitted from different positions of the target to be measured pass through the second transmission grating and the second VIPA in sequence and are aggregated into a beam of spatial optical signals. This beam of spatial optical signals passes through the second reflector and is transmitted to the information processing module after being dispersed by the second cylindrical mirror.

[0012] The first cylindrical mirror, the first reflector, the first VIPA, and the first transmission grating are symmetrically distributed with respect to the target to be measured with the second cylindrical mirror, the second reflector, the second VIPA, and the second transmission grating respectively.

[0013] In another alternative implementation, the imaging device includes a coupling mirror, a cylindrical mirror, a reflecting mirror, a VIPA, and a transmission grating connected in sequence. The first end of the coupling mirror is used to receive the measurement optical signal. After the measurement optical signal is focused by the cylindrical mirror, it is transmitted to the VIPA. The VIPA performs spatial dispersion on the measurement optical signal and divides it into multiple incident optical signals with different wavelengths. After the multiple incident optical signals pass through the transmission grating whose dispersion direction is orthogonal to that of the VIPA, an incident optical signal array is formed. The incident optical signal array is perpendicularly incident on different positions of the target to be measured, thereby realizing the surface scanning of the target to be measured; the spatial optical signals reflected from different positions of the target to be measured are transmitted back to the coupling mirror along the original path, and then transmitted by the coupling mirror to the information processing module.

[0014] In another alternative implementation, after the information processing module determines the Stokes parameters corresponding to each position on the target to be measured, taking the dispersion direction of the transmission grating as the column direction of the two-dimensional intensity matrix and the dispersion direction of the VIPA as the row direction of the two-dimensional intensity matrix, using the free spectral range FSR of the VIPA to define the number of columns of the two-dimensional intensity matrix, and using the free angular range FAR of the VIPA to define the number of rows of the two-dimensional intensity matrix, arranging the Stokes parameters corresponding to each position on the target to be measured in the two-dimensional intensity matrix, thereby forming a Stokes image and realizing Stokes polarization imaging.

[0015] In another alternative implementation, when the polarization modulation module is a first type of polarization modulation module, the polarization modulation module adjusts the polarization state of the laser signal provided by the laser to form horizontally polarized light, vertically polarized light, 45-degree linearly polarized light, 135-degree linearly polarized light, right-handed circularly polarized light, and left-handed circularly polarized light, and sequentially uses the formed polarized light with different polarization states as the measurement optical signal and transmits it to the imaging device;

[0016] The information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each type of polarized light, including: for each position on the target to be measured, obtaining the four Stokes parameters of this position according to the following formula, and using the four Stokes parameters to describe completely polarized light, partially polarized light, and natural light:

[0017] S0 = I 0° +I 90°

[0018] S1 = I 0° -I 90°

[0019] S2 = I 45° -I 135°

[0020] S3 = I R -I L

[0021] Wherein, I 0° 、I 90° respectively represent the horizontal linearly polarized light intensity and the vertical linearly polarized light intensity; I 45° 、I 135° respectively represent the 45-degree linearly polarized light intensity and the 135-degree linearly polarized light intensity; I R 、I L respectively represent the right-handed circularly polarized light intensity and the left-handed circularly polarized light intensity.

[0022] In another alternative implementation, when the polarization modulation module is a second type of polarization modulation module, the information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of each path of polarized light, including: for each position on the target to be measured, obtaining the four Stokes parameters of this position according to the following formula:

[0023] S0 = I0 + I2

[0024] S1 = I0 - I2

[0025] S2 = 2I1 - I0 - I2

[0026] S3 = 2I3 - I0 - I2

[0027] Wherein I0, I1, I2 and I3 respectively represent the light intensities of the four polarized lights output by the polarization modulation module.

[0028] In another alternative implementation, according to the two-dimensional intensity matrix in the Stokes polarization image, the polarization states of each position on the target to be measured are analyzed, so as to analyze the physical properties of each position on the target to be measured.

[0029] In another alternative implementation, the photodetector is a single-pixel photodetector, and the laser signal is an ultrafast pulsed laser with a pulse repetition frequency greater than megahertz.

[0030] The beneficial effects of the present invention are:

[0031] 1. The present invention utilizes the polarization-sensitive characteristics of the target to be measured. By using an imaging device to vertically incident measurement optical signals of different wavelengths onto different positions of the target to be measured, a one-to-one mapping relationship between the frequency domain and the spatial domain can be achieved. By using this mapping relationship, according to the intensities of the spatial optical signals reflected or transmitted from each position on the target to be measured, the Stokes parameters used to characterize its polarization state are determined. The entire process depends on the propagation of optical signals and does not need to rely on infrared polarization imaging technology. Compared with infrared polarization imaging, the propagation speed of optical signals is faster. Therefore, the present invention can improve the polarization imaging speed and achieve real-time polarization imaging.

[0032] 2. When the polarization modulation module is the first type of polarization modulation module, the dispersion module is arranged behind the imaging device and in front of the photodetector. Based on the dispersion Fourier transform (DFT), the spatial optical signal output by the imaging device can be stretched in the time domain. Thereafter, the photodetector can directly collect the spectral information of the spatial optical signal. Compared with traditional spectrometers, the present invention directly collects the spectral information using a photodetector, which can improve the polarization imaging response speed and further ensure the realization of real-time polarization imaging while ensuring the spectral resolution and increasing the sampling rate to the megahertz level. When the polarization modulation module is the second type of polarization modulation module, the dispersion module is arranged in front of the imaging device, which can avoid separately setting a dispersion module for each spatial optical signal in the polarization modulation module for time-domain stretching. Therefore, the device can be simplified and the cost can be reduced.

[0033] 3. When the polarization modulation module is the first type of polarization control module based on the time-division method, the present invention controls the polarization modulation module to generate several set polarization states, and obtains the polarization information of the target to be measured in multiple times. The device is simple, the cost is low, and system calibration is not required. When the polarization modulation module is the second type of polarization control module based on the amplitude-division method, the present invention controls the polarization modulation module to perform amplitude division on the spatial optical signal output by the imaging module, and can simultaneously measure all polarization parameters. And through matrix operation, the Stokes parameters used to represent the polarization states of all positions on the target to be measured can be obtained at one time.

[0034] 4. The present invention determines the number of columns and rows of the two-dimensional intensity matrix in the Stokes image by using the free spectral range (FSR) and the free angular range (FAR) of the VIPA. Then, the Stokes parameters corresponding to each position on the target to be measured are arranged in the two-dimensional intensity matrix to form a Stokes image. Based on the Stokes image for polarization state analysis, the polarization state of the corresponding position on the target to be measured can be obtained more intuitively and quickly, thereby further improving the polarization imaging speed.

[0035] 5. When correcting the optical field of the incident optical signal output by the VIPA, the present invention does not rely on the fixed uniform reflectivity within the VIPA, but instead uses a stepped reflectivity. The value of this stepped reflectivity changes in steps according to the different output positions of the corresponding incident optical signal from the VIPA (i.e., the different distances between the corresponding incident optical signal and the first incident optical signal), and it is a variable value. By adopting the stepped reflectivity and combining the above optical field correction formula to correct the optical field of the incident optical signal, the amplitudes of the incident optical signals output by the VIPA can be made approximately the same, the amplitude profile shape is closer to symmetry, and the coupling efficiency between the VIPA and the transmission grating can be improved. Thus, the present invention can solve the problems of mode mismatch between the VIPA and the transmission grating and crosstalk between adjacent channels of the VIPA. At a wavelength three times the 3dB bandwidth from the center wavelength, the crosstalk is reduced by at least half. In addition, the present invention can calculate the grating coupling efficiency of the stepped reflectivity model with stepped changes by using Fourier transform. Since the amplitudes of the incident optical signals output by the VIPA are approximately the same, there is a unified reference standard for the light signal intensities returned from various positions of the target to be measured. Therefore, when the present invention determines the Stokes parameters corresponding to various positions on the target to be measured based on the light intensity, the determination accuracy of the Stokes parameters can be improved. Brief Description of the Drawings

[0036] Figure 1 FIG. is a schematic structural diagram of an embodiment of an ultrafast single-pixel polarization imaging system when the polarization control module of the present invention is a first-type polarization control module;

[0037] Figure 2 FIG. is a schematic structural diagram of another embodiment of an ultrafast single-pixel polarization imaging system when the polarization control module of the present invention is a first-type polarization control module;

[0038] Figure 3 FIG. is a schematic structural diagram of an embodiment of an ultrafast single-pixel polarization imaging system when the polarization control module of the present invention is a second-type polarization control module;

[0039] Figure 4 FIG. is a schematic structural diagram of another embodiment of an ultrafast single-pixel polarization imaging system when the polarization control module of the present invention is a second-type polarization control module. Detailed Embodiments

[0040] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and make the above objects, features, and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] In the description of the present invention, unless otherwise specified and defined, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the communication inside two components. It can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meaning of the above terms can be understood according to specific situations.

[0042] The ultrafast single-pixel polarization imaging system of the present invention may include a laser, an imaging device, a polarization modulation module, and an information processing module. When the polarization modulation module is a first-type polarization modulation module, the polarization modulation module adjusts the polarization state of the laser signal provided by the laser, and sequentially uses the formed polarized light with different polarization states as measurement light signals and transmits them to the imaging device; for each type of polarized light received in sequence by the imaging device, the imaging device divides the polarized light into multiple incident light signals with different wavelengths, makes each incident light signal perpendicularly incident on different positions of the target to be measured, and the spatial light signals reflected or transmitted from different positions of the target to be measured are transmitted to the information processing module; the information processing module determines the Stokes parameters corresponding to each position of the target to be measured according to the intensity of the spatial light signal corresponding to each type of polarized light, so as to realize Stokes polarization imaging.

[0043] When the polarization modulation module is a second-type polarization modulation module, the imaging device uses the laser signal provided by the laser as a measurement light signal, divides it into multiple incident light signals with different wavelengths, makes each incident light signal perpendicularly incident on different positions of the target to be measured, and the spatial light signals reflected or transmitted from different positions of the target to be measured are transmitted to the polarization modulation module; the polarization modulation module adjusts the polarization state of the spatial light signal, forms multiple paths of polarized light with different polarization states and transmits them to the information processing module; the information processing module determines the Stokes parameters corresponding to each position of the target to be measured according to the intensity of each path of polarized light, so as to realize Stokes polarization imaging.

[0044] In this embodiment, the first-type polarization modulation module may be a polarization control module based on the time-sharing method, and the second-type polarization modulation module may be a polarization control module based on the amplitude-division method. When the polarization modulation module is a first-type polarization modulation module, the laser, the polarization modulation module, the imaging device, and the information processing module are connected in sequence. An embodiment of this ultrafast single-pixel polarization imaging system is as Figure 1As shown, the polarization control module may include a polarizer and two wave plates. The two wave plates are mounted on a hollow high-speed motor. The motor drives the wave plates to rotate by a corresponding angle to achieve arbitrary polarization state adjustment. Among them, the polarization control module adjusts the polarization state of the laser signal provided by the laser, and can form horizontally polarized light, vertically polarized light, 45-degree linearly polarized light, 135-degree linearly polarized light, right-handed circularly polarized light, and left-handed circularly polarized light. Then, the polarized light with different polarization states formed is used as the measurement optical signal in sequence and transmitted to the imaging device.

[0045] The imaging device may include a first cylindrical mirror, a first reflector, a first virtual imaging phase array VIPA, a first transmission grating, a second transmission grating, a second VIPA, a second reflector, and a second cylindrical mirror. The target to be measured is located between the first transmission grating and the second transmission grating. After the measurement optical signal is focused by the first cylindrical mirror, it is transmitted to the first VIPA through the first reflector. The first VIPA performs spatial dispersion on the measurement optical signal and divides it into multiple incident optical signals with different wavelengths. After the multiple incident optical signals pass through the first transmission grating whose dispersion direction is orthogonal to the first VIPA, an incident optical signal array is formed. The incident optical signal array is vertically incident on different positions of the target to be measured, thereby realizing the surface scanning of the target to be measured; the spatial optical signals transmitted from different positions of the target to be measured pass through the second transmission grating and the second VIPA in sequence and are aggregated into a beam of spatial optical signals. This beam of spatial optical signals passes through the second reflector and is transmitted to the information processing module after being dispersed by the second cylindrical mirror; the first cylindrical mirror, the first reflector, the first VIPA, and the first transmission grating are symmetrically distributed with respect to the target to be measured with the second cylindrical mirror, the second reflector, the second VIPA, and the second transmission grating respectively.

[0046] Among them, the virtual image imaging phase array VIPA is equivalent to an inclined etalon, which can perform spatial dispersion in the incident plane. The light longitudinally stretched by the VIPA passes through a transmission grating with a dispersion direction orthogonal to the VIPA to achieve transverse dispersion stretching. The combination of the VIPA and the transmission grating can be called a two-dimensional spatial disperser. The entire beam control process can be regarded as a one-to-one mapping between the wavelength and the spatial coordinates on the imaging plane. The two-dimensional spatial disperser composed of the VIPA and the transmission grating with orthogonal dispersion directions can achieve area array scanning. Its basic principle is that under far-field Fraunhofer diffraction, the frequency-domain information of an ultrafast laser with broad spectral characteristics is mapped to the spatial domain through the two-dimensional area array beam generated by the two-dimensional spatial disperser. On the surface of the target to be measured, two-dimensional plane information with different transmittances is loaded into the spectrum of the laser, and two-dimensional spatial information is encoded into the spectrum of the laser. Further through the second diffraction process, the spatial domain information is mapped to the frequency domain. The present invention combines the VIPA and the transmission grating, which can disperse the measurement optical signal transversely and longitudinally to form an area array light spot, so as to directly illuminate the two-dimensional plane to be measured, realize the one-to-one mapping between the frequency domain and the spatial domain, and since area scanning can be achieved, the polarization imaging efficiency can be further improved.

[0047] The information processing module may include a coupler, a dispersion module, a photodetector, an oscilloscope, a spectrometer, and a processor. For each type of polarized light sequentially provided by the imaging device, the coupler divides the spatial optical signal corresponding to this type of polarized light into two paths, one path is transmitted to the spectrometer, and the spectrometer records the frequency-domain data. The other path is transmitted to the photodetector after time-domain stretching by the dispersion module. The photodetector converts the spatially optical signal after time-domain stretching into a spatial electrical signal and transmits the spatial electrical signal to the oscilloscope, and the oscilloscope records the time-domain data; for each type of polarized light sequentially provided by the polarization modulation module, the processor determines the wavelength of the spatially optical signal reflected or transmitted from each position on the target to be measured according to the frequency-domain data of this type of polarized light, and determines the intensity of the spatially optical signal corresponding to each position on the target to be measured under the action of this type of polarized light according to the wavelength magnitude of the spatial electrical signal in the time-domain data of this type of polarized light. According to the intensity of the spatially optical signal corresponding to each position on the target to be measured, the Stokes parameters corresponding to each position on the target to be measured are determined, so as to realize Stokes polarization imaging. Projection

[0048] Among them, the dispersion module can map the spatial domain information of another spatial optical signal provided by the coupler to the frequency domain. Thereafter, the spatial optical signal in the form of a pulse propagates in a medium with group velocity dispersion. When losses are ignored and only second-order dispersion is considered, there is a one-to-one correspondence between the frequency domain information and the time domain information of the spatial optical signal itself, and thus the corresponding relationship between wavelength and time is obtained. When the polarization modulation module in the present invention is a first type of polarization modulation module, the dispersion module is disposed after the imaging device and before the photodetector, and time-domain stretching can be performed on the spatial optical signal output by the imaging device based on the dispersion Fourier transform (DFT). Thereafter, the photodetector can directly collect the spectral information of the spatial optical signal. Compared with traditional spectrometers, the present invention directly collects spectral information using a photodetector, which can increase the sampling rate to the megahertz level while ensuring spectral resolution, thereby improving the polarization imaging response speed and further ensuring the realization of real-time polarization imaging.

[0049] Since the polarization state of light can be represented by Stokes parameters, when the information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each type of polarized light, it may include: for each position on the target to be measured, obtain the four Stokes parameters of this position according to the following formula, and use the four Stokes parameters to describe completely polarized light, partially polarized light, and natural light:

[0050] S0 = I 0° + I 90°

[0051] S1 = I 0° - I 90°

[0052] S2 = I 45° - I 135°

[0053] S3 = I R - I L

[0054] Among them, I 0° and I 90° respectively represent the horizontal linearly polarized light intensity and the vertical linearly polarized light intensity; I 45° and I 135° respectively represent the 45-degree linearly polarized light intensity and the 135-degree linearly polarized light intensity; I R and I L respectively represent the right-handed circularly polarized light intensity and the left-handed circularly polarized light intensity.

[0055] After determining the Stokes parameters corresponding to each position on the target to be measured, the information processing module uses the dispersion direction of the transmission grating as the column direction of the two-dimensional intensity matrix, and the dispersion direction of the VIPA (i.e., the first VIPA and the second VIPA in this embodiment) as the row direction of the two-dimensional intensity matrix. It defines the number of columns of the two-dimensional intensity matrix using the free spectral range FSR of the VIPA, and defines the number of rows of the two-dimensional intensity matrix using the free angular range FAR of the VIPA. It arranges the Stokes parameters corresponding to each position on the target to be measured in the two-dimensional intensity matrix, thereby forming a Stokes image and realizing Stokes polarization imaging. Among them, the free spectral range FSR of the VIPA is determined by the parameters of the VIPA itself (such as thickness, incident angle, etc.), and the free angular range FAR is defined by the maximum scanning range in the dispersion direction of the VIPA. Since in the above description, four Stokes parameters are calculated for each position on the target to be measured, four two-dimensional intensity matrices can be formed and four Stokes parameter images can be reconstructed. After determining the two-dimensional intensity matrix in the Stokes image, based on the two-dimensional intensity matrix in the Stokes polarization image, the polarization states at each position on the target to be measured are analyzed, so as to analyze the physical properties of each position on the target to be measured. The corresponding relationship between the polarization state and the two-dimensional intensity matrix can be pre-stored in the information processing module. The present invention uses the free spectral range FSR and the free angular range FAR of the VIPA to determine the number of columns and rows of the two-dimensional intensity matrix in the Stokes image, and then arranges the Stokes parameters corresponding to each position on the target to be measured in the two-dimensional intensity matrix, thereby forming a Stokes image. Based on the Stokes image for polarization state analysis, the polarization state at the corresponding position of the target to be measured can be obtained more intuitively and quickly, thereby further improving the polarization imaging speed.

[0056] When the polarization modulation module is a first-type polarization modulation module, another embodiment of the ultrafast single-pixel polarization imaging system is as Figure 2 shown Figure 2 as Figure 1 shown in the embodiment, the difference between the two embodiments is that the structures of the imaging devices in the two embodiments are different. Figure 2In the described embodiment, the imaging device may include a coupling mirror, a cylindrical mirror, a reflecting mirror, a VIPA, and a transmission grating connected in sequence. The first end of the coupling mirror is used to receive the measurement optical signal. After the measurement optical signal is focused by the cylindrical mirror, it is transmitted to the VIPA. The VIPA performs spatial dispersion on the measurement optical signal to divide it into multiple incident optical signals with different wavelengths. After the multiple incident optical signals pass through the transmission grating whose dispersion direction is orthogonal to the VIPA, an incident optical signal array is formed. The incident optical signal array is perpendicularly incident on different positions of the target to be measured, thereby realizing the surface scanning of the target to be measured; the spatial optical signals reflected back from different positions of the target to be measured are transmitted back to the coupling mirror along the original path, and then transmitted by the coupling mirror to the information processing module. When the polarization modulation module is a first type of polarization control module based on the time-sharing method, the present invention controls the polarization modulation module to generate several set polarization states, and obtains the polarization information of the target to be measured in multiple times. The device is simple, the cost is low, and no system calibration is required.

[0057] When the polarization modulation module is a second type of polarization modulation module, a dispersion module is further included. The laser, the dispersion module, the imaging device, the polarization modulation module, and the information processing module are connected in sequence. An embodiment of this ultrafast single-pixel polarization imaging system is as Figure 3 shown. After the dispersion module performs time-domain stretching on the laser signal provided by the laser, it transmits the time-domain stretched laser signal to the imaging device; the imaging device divides the time-domain stretched laser signal into multiple incident optical signals with different wavelengths, and makes each incident optical signal perpendicularly incident on different positions of the target to be measured. A collimator may also be provided between the dispersion module and the imaging device for collimating the time-domain stretched laser signal and then transmitting it to the imaging device. When the polarization modulation module is a second type of polarization modulation module in the present invention, placing the dispersion module before the imaging device can avoid separately setting a dispersion module for time-domain stretching for each spatial optical signal in the polarization modulation module, so that the device can be simplified and the cost can be reduced.

[0058] The imaging device may include a first cylindrical mirror, a first reflector, a first virtual imaging phase array VIPA, a first transmission grating, a second transmission grating, a second VIPA, a second reflector, and a second cylindrical mirror. The target to be measured is located between the first transmission grating and the second transmission grating. After the measurement optical signal is focused by the first cylindrical mirror, it is transmitted to the first VIPA through the first reflector. The first VIPA spatially disperses the measurement optical signal into multiple incident optical signals with different wavelengths. After the multiple incident optical signals pass through the first transmission grating whose dispersion direction is orthogonal to the first VIPA, an incident optical signal array is formed. The incident optical signal array is perpendicularly incident on different positions of the target to be measured, thereby realizing area scanning of the target to be measured. The spatial optical signals transmitted from different positions of the target to be measured sequentially pass through the second transmission grating and the second VIPA and are aggregated into a beam of spatial optical signal. This beam of spatial optical signal passes through the second reflector and is transmitted to the information processing module after being dispersed by the second cylindrical mirror. The first cylindrical mirror, the first reflector, the first VIPA, and the first transmission grating are symmetrically distributed with respect to the target to be measured with the second cylindrical mirror, the second reflector, the second VIPA, and the second transmission grating respectively.

[0059] The polarization control module may include three beam splitters, a quarter-wave plate, four polarizers, and four couplers. The information processing module may include four photodetectors, an oscilloscope, and a processor. The first beam splitter is used to receive the spatial optical signal and split it into two paths, which are respectively transmitted to the second beam splitter and the third beam splitter. The second beam splitter splits the spatial optical signal it receives into two paths. One path is sequentially connected to the oscilloscope through the first polarizer, the first coupler, and the first photodetector. The other path is sequentially connected to the oscilloscope through the second polarizer, the second coupler, and the second photodetector. The third beam splitter splits the spatial optical signal it receives into two paths. One path is sequentially connected to the oscilloscope through the third polarizer, the quarter-wave plate, the third coupler, and the third photodetector. The other path is sequentially connected to the oscilloscope through the fourth polarizer, the fourth coupler, and the fourth photodetector. The four polarizers adjust the polarization states of the spatial optical signals they receive to form polarized light with different polarization states. The quarter-wave plate converts the polarized light provided by the third polarizer into circularly polarized light or elliptically polarized light. After the four couplers respectively couple and transmit the polarized light they receive to the corresponding photodetectors, the four photodetectors respectively perform photoelectric conversion on the polarized light to form polarization signals. The oscilloscope respectively records the time-domain data of the linearly polarized signals output by the four photodetectors. The processor determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each position on the target to be measured in the time-domain data, thereby realizing Stokes polarization imaging.

[0060] For amplitude-splitting imaging, the beam splitter in the polarization modulation module divides the spatial light signal carrying the information of the target to be measured into four paths, and the light intensity of each path is detected by a photodetector. Therefore, the output polarization state can be represented by the intensity vectors of these four parameters as:

[0061] I = (I0, I1, I2, I3) T

[0062] Where I0, I1, I2, and I3 respectively represent the intensities of the four polarization signals detected by the photodetector after the polarization states of the four paths of spatial light signals divided by the polarization modulation module are adjusted. When the polarization modulation module is a second-type polarization modulation module, the information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of each path of polarized light, which may include: for each position on the target to be measured, the four Stokes parameters of this position are obtained according to the following formula:

[0063] S0 = I0 + I2

[0064] S1 = I0 - I2

[0065] S2 = 2I1 - I0 - I2

[0066] S3 = 2I3 - I0 - I2

[0067] Where I0, I1, I2, and I3 respectively represent the light intensities of the four polarized lights output by the polarization modulation module. The light intensity of each path can be expressed as a linear combination of the four Stokes vectors:

[0068] I0 = a 01 S0 + a 02 S1 + a 03 S2 + a 04 S3

[0069] I1 = a 11 S0 + a 12 S1 + a 13 S2 + a 14 S3

[0070] I2 = a 21 S0 + a 22 S1 + a 23 S2 + a 24 S3

[0071] I3 = a 31 S0 + a 32 S1 + a 33 S2 + a 34 S3

[0072] That is:

[0073] Among them: A i =(a i1 ,a i2 ,a i3 ,a i4 )

[0074] When the determinant of the system matrix |A| is not equal to zero, there exists an inverse matrix A -1 :

[0075] S=A -1 I

[0076] The system matrix A is determined by the Stokes vector of each wavelength of the input laser and the output intensity. When measuring the detection intensity of four channels, the intensity I and the inverse matrix A of the system matrix can be used to calculate the system matrix A. -1 A Stokes matrix S for representing the polarization state of each wavelength is calculated. After determining the two-dimensional intensity matrix in the Stokes image, the physical characteristics of each position on the target to be measured are analyzed according to the polarization state at each position on the target to be measured, wherein the corresponding relationship between the polarization state and the two-dimensional intensity matrix can be pre-stored in the information processing module.

[0077] For example, the four channel light intensities detected by the photodetector in the polarization control module are set to be:

[0078] a) 0 degree linear polarization, polarization direction parallel to ox axis, light intensity is

[0079] b) 45 degree linear polarization, the polarization direction is 45 degrees to the ox axis, and the light intensity is

[0080] c) 90 degree linear polarization, polarization direction parallel to oy axis, light intensity is

[0081] d) Left-handed circularly polarized light, polarization direction parallel to the ox axis, phase difference is π / 4, light intensity is

[0082]

[0083] After determining the Stokes parameters corresponding to each position on the target to be measured, the information processing module uses the dispersion direction of the transmission grating as the column direction of the two-dimensional intensity matrix, and the dispersion direction of the VIPA (i.e., the first VIPA and the second VIPA in this embodiment) as the row direction of the two-dimensional intensity matrix. The number of columns of the two-dimensional intensity matrix is defined by the free spectral range FSR of the VIPA, and the number of rows of the two-dimensional intensity matrix is defined by the free angular range FAR of the VIPA. The Stokes parameters corresponding to each position on the target to be measured are arranged in the two-dimensional intensity matrix, thereby realizing Stokes polarization imaging.

[0084] When the polarization modulation module is a second type of polarization modulation module, another embodiment of the ultrafast single-pixel polarization imaging system is as follows Figure 4 shown Figure 4 and Figure 3 The difference from the embodiment shown is that the structures of the imaging devices in the two embodiments are different. Figure 4 In the embodiment shown, the imaging device may include a coupling mirror, a cylindrical mirror, a reflector, a VIPA, and a transmission grating connected in sequence. The first end of the coupling mirror is used to receive the measurement optical signal. After the measurement optical signal is focused by the cylindrical mirror, it is transmitted to the VIPA. The VIPA performs spatial dispersion on the measurement optical signal, dividing it into multiple incident optical signals with different wavelengths. After the multiple incident optical signals pass through the transmission grating whose dispersion direction is orthogonal to the VIPA, an incident optical signal array is formed. The incident optical signal array is perpendicularly incident on different positions of the target to be measured, thereby realizing the area scanning of the target to be measured. The spatial optical signals reflected from different positions of the target to be measured are transmitted back to the coupling mirror along the original path, and then transmitted by the coupling mirror to the information processing module. When the polarization modulation module is a second type of polarization control module based on the amplitude division method, the present invention controls the polarization modulation module to perform amplitude division on the spatial optical signal output by the imaging module, and can simultaneously measure all polarization parameters. And through matrix operation, the Stokes parameters used to represent the polarization states of all positions on the target to be measured can be obtained at one time.

[0085] In addition, in the above four embodiments, the laser signal provided by the laser can be: an ultrafast pulsed laser with a spectral range of more than a dozen nanometers and a pulse repetition frequency greater than megahertz. The photodetector can be a single-pixel photodetector and can be a high-speed photodetector. The data acquisition time of the present invention mainly depends on the repetition frequency of the pulsed laser and the response time of the high-speed single-pixel photodetector converter. By making the photodetector an ultrafast single-pixel photodetector and the laser signal provided by the laser an ultrafast pulsed laser with a pulse repetition frequency greater than megahertz, the data acquisition response time can reach the nanosecond level, thereby further improving the polarization imaging speed.

[0086] The transmission spectrum of the VIPA shows multiple resonance peaks at intervals of the free spectral range (FSR), which is multi-beam interference. The output beam of the VIPA is periodically aliased, so it is necessary to combine the VIPA with a transmission grating to expand the spectrum two-dimensionally, thus realizing a one-to-one mapping of different wavelengths and different positions in space. Compared with the transmission grating, the VIPA can generate a larger angular dispersion, and its wavelength resolution is also one order of magnitude higher. The field of view size of the system of the present invention is jointly determined by the dispersion ability of the two-dimensional spatial disperser, the focal length of the lens, and the spectral bandwidth of the pulsed laser. The specific parameters are mainly affected by the cavity length of the VIPA, the number of lines of the transmission grating, the focal length of the lens, and the spectral bandwidth. The imaging resolution ability of the system is mainly affected by the spectral resolution and the spatial resolution. For the two-dimensional reconstructed image, the influencing factors of the longitudinal (Y-direction) imaging resolution ability and the transverse (X-direction) imaging resolution ability are different. For the Y-direction, the imaging resolution is mainly affected by the spectral resolution, angular dispersion, and focal length of the VIPA; for the X-direction, the imaging resolution is mainly affected by the free spectral range of the VIPA and the angular dispersion of the diffraction grating. Therefore, when realizing spectral imaging through two-dimensional mapping, both of them need to be considered simultaneously to achieve the best imaging effect. The system scanning rate is mainly determined by the pulse frequency of the light source. Usually, the pulse frequency of an ultrafast laser is greater than megahertz, so the scanning rate can reach the nanosecond / microsecond level.

[0087] It should be noted that: the present invention is particularly suitable for rapidly detecting polarization-sensitive samples (such as biological tissues, metals, etc.). By obtaining polarization information, the tiny target can be magnified and clearly presented, and within the ultra-transient time, the stress, optical rotation, birefringence and other material properties and their changes of the target can be reflected in real time. This is crucial for understanding polarization dynamics, the microscopic dynamic process of biological tissues, etc. In addition, an optical amplifier can be provided after the laser for amplifying the laser signal before outputting the laser signal provided by the laser to the polarization modulation module or the imaging device.

[0088] Although the present invention combines a VIPA and a transmission grating, it can disperse the measured optical signal both transversely and longitudinally to form a planar array of light spots, thereby being able to directly illuminate a two-dimensional plane to be measured, achieve planar scanning, and improve the polarization imaging efficiency. However, since the optical signal incident on the VIPA may be reflected multiple times within the VIPA before being transmitted to the transmission grating, and the power of the optical signal output from the VIPA will decay exponentially with the increase in the number of reflections (i.e., the beam profile output along the surface of the VIPA is exponential), the exponential beam profile output from the VIPA forms a Lorentz profile on the fiber coupling surface. The Lorentz beam profile coupled from the VIPA to the transmission grating will cause mode mismatch between the VIPA and the transmission grating and crosstalk between adjacent channels of the VIPA. The loss caused by the mode mismatch between the VIPA and the transmitted beam is usually 1 dB, and the lower limit of the crosstalk between adjacent channels of the VIPA is approximately -25 dB.

[0089] To solve the above-mentioned problems of mode mismatch and crosstalk between adjacent channels of the VIPA, assume that the optical signal when the measured optical signal is directly output from the incident window on the VIPA is the first incident optical signal provided by the VIPA to the transmission grating, and the optical signal output after the measured optical signal is reflected i times within the VIPA is the i-th incident optical signal. The distance between the i-th incident optical signal and the first incident optical signal is y i , where i is an integer greater than 0. The present invention corrects the optical field of the incident optical signal output from the VIPA to make the amplitudes of all incident optical signals the same. Specifically, for the i-th incident optical signal, its optical field is corrected to:

[0090] where E i+1 (y i+1 ) represents the optical field of the (i + 1)-th incident optical signal output after being reflected i + 1 times within the VIPA, F -1 represents the inverse Fourier transform; represents the propagation phase factor of the i-th incident optical signal, F represents the Fourier transform, R A (y i ) represents the stepwise reflectivity of the i-th incident optical signal output after being reflected i times within the VIPA, E i (y i ) represents the optical field of the i-th incident optical signal output after being reflected i times within the VIPA; where exp{} represents the exponential function with the natural constant e as the base, i is the number of reflections within the VIPA, λ represents the wavelength of the measured optical signal, t represents the thickness of the VIPA, represents the spatial frequency of the i-th incident optical signal, n represents the refractive index of the output surface of the VIPA; R A (y i ) = 1 - k * yi , where k represents any value greater than 0 and less than 1 (k can be 0.5), and y i represents the spacing between the i-th incident optical signal and the starting incident optical signal. The amplitude transmittance of the i-th incident optical signal output after reflecting i times in the VIPA can be T A (y i ) = 1 - k * y i . To make the amplitude transmittance change proportionally with the spacing y between the corresponding incident optical signal and the first incident optical signal, it can be achieved by gradually changing the reflectivity of the VIPA output surface, thereby realizing the optical field correction of the incident optical signal output by the VIPA.

[0091] When the present invention corrects the optical field of the incident optical signal output by the VIPA, it does not rely on a fixed uniform reflectivity within the VIPA, but adopts a stepped reflectivity. The value of this stepped reflectivity changes stepwise with the different output positions of the corresponding incident optical signal from the VIPA (i.e., the different spacings between the corresponding incident optical signal and the first incident optical signal), and it is a variable value. By adopting the stepped reflectivity and combining the above optical field correction formula to correct the optical field of the incident optical signal, the amplitudes of the incident optical signals output by the VIPA can be made approximately the same, the amplitude profile shape is closer to symmetry, and the coupling efficiency between the VIPA and the transmission grating can be improved. Therefore, the present invention can solve the problems of mode mismatch between the VIPA and the transmission grating and crosstalk between adjacent channels of the VIPA. At a wavelength 3 times the 3dB bandwidth from the center wavelength, the crosstalk is reduced by at least half; in addition, the present invention can calculate the grating coupling efficiency of the stepped reflectivity model with stepped changes by using Fourier transform; since the amplitudes of the incident optical signals output by the VIPA are approximately the same, there is a unified reference standard for the light signal intensities returned from various positions of the target to be measured. Therefore, when the present invention determines the Stokes parameters corresponding to various positions on the target to be measured based on the light intensity, the determination accuracy of the Stokes parameters can be improved.

[0092] As can be seen from the above four embodiments, the present invention utilizes the polarization-sensitive characteristics of the target to be measured, and uses an imaging device to vertically incident measurement optical signals of different wavelengths on different positions of the target to be measured, so as to achieve a one-to-one mapping relationship between the frequency domain and the spatial domain. By using this mapping relationship, according to the intensities of the spatial optical signals reflected or transmitted from various positions on the target to be measured, the corresponding Stokes parameters for characterizing its polarization state are determined. The entire process depends on the propagation of optical signals and does not need to rely on infrared polarization imaging technology. Compared with infrared polarization imaging, the propagation speed of optical signals is faster. Therefore, the present invention can improve the polarization imaging speed and achieve real-time polarization imaging.

[0093] Other embodiments of the present invention will be readily apparent to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include known common knowledge or conventional technical means in the technical field not disclosed herein. The specification and examples are only considered exemplary, and the true scope and spirit of the invention are pointed out by the following claims.

[0094] It should be understood that the present invention is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only governed by the appended claims.

Claims

1. An ultrafast single-pixel polarization imaging system, characterized in that, It includes a laser, an imaging device, a polarization modulation module, and an information processing module. When the polarization modulation module is a first type of polarization modulation module, the polarization modulation module adjusts the polarization state of the laser signal provided by the laser, and sequentially uses the polarized light with different polarization states formed as measurement optical signals and transmits them to the imaging device; for each type of polarized light received in sequence by the imaging device, the imaging device divides the polarized light into multiple incident optical signals with different wavelengths, makes each incident optical signal perpendicularly incident on different positions of the target to be measured, and the spatial optical signals reflected or transmitted from different positions of the target to be measured are transmitted to the information processing module; the information processing module determines the Stokes parameters corresponding to each position of the target to be measured according to the intensity of the spatial optical signal corresponding to each type of polarized light, thereby realizing Stokes polarization imaging; When the polarization modulation module is a second type of polarization modulation module, the imaging device uses the laser signal provided by the laser as a measurement optical signal, divides it into multiple incident optical signals with different wavelengths, makes each incident optical signal perpendicularly incident on different positions of the target to be measured, and the spatial optical signals reflected or transmitted from different positions of the target to be measured are transmitted to the polarization modulation module; The polarization modulation module adjusts the polarization state of the spatial optical signal, forms multiple paths of polarized light with different polarization states and transmits them to the information processing module; The information processing module determines the Stokes parameters corresponding to each position of the target to be measured according to the intensity of each path of polarized light, thereby realizing Stokes polarization imaging; The imaging device includes a first cylindrical mirror, a first reflector, a first VIPA, a first transmission grating, a second transmission grating, a second VIPA, a second reflector, and a second cylindrical mirror. The target to be measured is located between the first transmission grating and the second transmission grating. After the measurement optical signal is focused by the first cylindrical mirror, it is transmitted to the first VIPA through the first reflector. The first VIPA performs spatial dispersion on the measurement optical signal and divides it into multiple incident optical signals with different wavelengths. After the multiple incident optical signals pass through the first transmission grating whose dispersion direction is orthogonal to that of the first VIPA, an incident optical signal array is formed. The incident optical signal array perpendicularly irradiates different positions of the target to be measured, thereby realizing the area scan of the target to be measured; The spatial optical signals transmitted from different positions of the target to be measured sequentially pass through the second transmission grating and the second VIPA and are aggregated into a beam of spatial optical signals. This beam of spatial optical signals passes through the second reflector and is transmitted to the information processing module after being dispersed by the second cylindrical mirror; The first cylindrical mirror, the first reflector, the first VIPA, and the first transmission grating are symmetrically distributed with respect to the target to be measured with the second cylindrical mirror, the second reflector, the second VIPA, and the second transmission grating respectively.

2. The ultrafast single-pixel polarization imaging system according to claim 1, characterized in that When the polarization modulation module is a first type of polarization modulation module, the information processing module includes a coupler, a dispersion module, a photodetector, an oscilloscope, a spectrometer, and a processor. For each type of polarized light, the coupler divides the spatial light signal corresponding to this type of polarized light into two paths. One path is transmitted to the spectrometer, and the spectrometer records the frequency-domain data. The other path is transmitted to the photodetector after time-domain stretching by the dispersion module. The photodetector converts the spatially light signal after time-domain stretching into a spatial electrical signal and transmits the spatial electrical signal to the oscilloscope, and the oscilloscope records the time-domain data. For each type of polarized light provided in sequence by the polarization modulation module, the processor determines the wavelength of the spatial light signal reflected or transmitted from each position on the target to be measured according to the frequency-domain data of this type of polarized light, and determines the intensity of the spatial light signal corresponding to each position on the target to be measured according to the wavelength magnitude of the spatial electrical signal in the time-domain data of this type of polarized light. According to the intensity of the spatial light signal corresponding to each position on the target to be measured, the Stokes parameters corresponding to each position on the target to be measured are determined, thereby realizing Stokes polarization imaging; When the polarization modulation module is a second type of polarization modulation module, a dispersion module is further included. The dispersion module performs time-domain stretching on the laser signal provided by the laser and then transmits the time-domain stretched laser signal to the imaging device. The imaging device divides the time-domain stretched laser signal into multiple incident light signals with different wavelengths, and makes each incident light signal perpendicularly incident on different positions of the target to be measured.

3. The ultrafast single-pixel polarization imaging system according to claim 1, wherein When the polarization modulation module is a second type of polarization modulation module, the polarization modulation module includes three beam splitters, a quarter-wave plate, four polarizers, and four couplers. The information processing module includes four photodetectors, an oscilloscope, and a processor. The first beam splitter is used to receive the spatial light signal and divides the spatial light signal into two paths, which are respectively transmitted to the second beam splitter and the third beam splitter. The second beam splitter divides the spatial light signal it receives into two paths. One path is connected to the oscilloscope through the first polarizer, the first coupler, and the first photodetector in sequence, and the other path is connected to the oscilloscope through the second polarizer, the second coupler, and the second photodetector in sequence. The third beam splitter divides the spatial light signal it receives into two paths. One path is connected to the oscilloscope through the third polarizer, the quarter-wave plate, the third coupler, and the third photodetector in sequence, and the other path is connected to the oscilloscope through the fourth polarizer, the fourth coupler, and the fourth photodetector in sequence; The four polarizers adjust the polarization states of the received spatial optical signals to form polarized light with different polarization states. After the corresponding couplers couple and transmit the polarized light to the corresponding photodetectors, the four photodetectors respectively perform photoelectric conversion on the polarized light to form polarization signals; the quarter-wave plate converts the polarized light provided by the third polarizer into circularly polarized light or elliptically polarized light; the oscilloscope respectively records the time-domain data of the linearly polarized signals output by the four photodetectors; the processor determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each position in the time-domain data, so as to realize Stokes polarization imaging.

4. The ultrafast single-pixel polarization imaging system according to claim 1, wherein After the information processing module determines the Stokes parameters corresponding to each position on the target to be measured, taking the dispersion direction of the transmission grating as the column direction of the two-dimensional intensity matrix and the dispersion direction of the VIPA as the row direction of the two-dimensional intensity matrix, using the free spectral range FSR of the VIPA to define the number of columns of the two-dimensional intensity matrix, and using the free angular range FAR of the VIPA to define the number of rows of the two-dimensional intensity matrix, arranging the Stokes parameters corresponding to each position on the target to be measured in the two-dimensional intensity matrix, so as to form a Stokes polarization image and realize Stokes polarization imaging.

5. The ultrafast single-pixel polarization imaging system according to claim 1 or 2, characterized in that, When the polarization control module is a first-type polarization control module, the polarization control module adjusts the polarization state of the laser signal provided by the laser to form horizontally polarized light, vertically polarized light, 45-degree linearly polarized light, 135-degree linearly polarized light, right-handed circularly polarized light and left-handed circularly polarized light, and sequentially uses the formed polarized light with different polarization states as measurement optical signals and transmits them to the imaging device; The information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of the spatial optical signal corresponding to each type of polarized light, including: for each position on the target to be measured, obtaining the four Stokes parameters of this position according to the following formula, and using the four Stokes parameters to describe completely polarized light, partially polarized light and natural light: S0 = I 0° +I 90° S1 = I 0° -I 90° S2 = I 45° -I 135° S3 = I R -I L Among them, I0° and I 90 ° represent the horizontal linearly polarized light intensity and the vertical linearly polarized light intensity respectively; I 45 °, I 135 ° represent the 45-degree linearly polarized light intensity and the 135-degree linearly polarized light intensity respectively; I R , I L represent the right-handed circularly polarized light intensity and the left-handed circularly polarized light intensity respectively.

6. The ultrafast single-pixel polarization imaging system according to claim 1 or 3, characterized in that When the polarization control module is a second-type polarization control module, the information processing module determines the Stokes parameters corresponding to each position on the target to be measured according to the intensity of each path of polarized light, including: for each position on the target to be measured, obtaining the four Stokes parameters of this position according to the following formula: S0 = I0 + I2 S1 = I0 - I2 S2 = 2I1 - I0 - I2 S3 = 2I3 - I0 - I2 Where I0, I1, I2 and I3 respectively represent the light intensities of the four polarized lights output by the polarization control module.

7. The ultrafast single-pixel polarization imaging system according to claim 4, wherein Analyze the polarization states of each position on the target to be measured according to the two-dimensional intensity matrix in the Stokes polarization image, so as to analyze the physical properties of each position on the target to be measured.

8. The ultrafast single-pixel polarization imaging system according to claim 1, characterized in that, Let the optical signal when the measured optical signal directly outputs from the incident window on the VIPA be the first incident optical signal provided by the VIPA to the transmission grating. The optical signal output after the measured optical signal is reflected i times in the VIPA is the i-th incident optical signal. The spacing between the i-th incident optical signal and the first incident optical signal is y i , where i is an integer greater than 0. The optical field of the incident optical signal output by the VIPA is corrected so that the amplitudes of all incident optical signals are the same: for the i-th incident optical signal, its optical field is corrected to: Among which E i+1 (y i+1 ) represents the optical field of the (i + 1)-th incident optical signal output after (i + 1) reflections in the VIPA, F -1 represents the inverse Fourier transform; represents the propagation phase factor of the i-th incident optical signal, F represents the Fourier transform, R A (y i ) represents the stepped reflectivity of the i-th incident optical signal output after i reflections in the VIPA, E i (y i ) represents the optical field of the i-th incident optical signal output after i reflections in the VIPA; Among which exp{} represents the exponential function with the natural constant e as the base, i is the number of reflections in the VIPA, λ represents the wavelength of the measured optical signal, t represents the thickness of the VIPA, represents the spatial frequency of the i-th incident optical signal, n represents the refractive index of the output surface of the VIPA; R A (y i ) = 1 - k * y i , where k represents any value greater than 0 and less than 1, y i represents the spacing between the i-th incident optical signal and the starting incident optical signal.

Images