Stokes Modulated Fourier Transform Polarization Imaging Spectrometer

Abstract

The present invention provides a Stokes modulation Fourier transform polarization imaging spectrometer, comprising: a telescopic system, a polarization modulation system, a converging system, a polarization interference system and an imaging system; the target light field emitted by the target scene is incident on the telescopic system, and after passing through the telescopic system, the target light field is collimated into a parallel light field and incident on the polarization modulation system; the parallel light field is subjected to polarization modulation by a high-order phase retarder to obtain a modulated light field, and then a linearly polarized light field is obtained after passing through a polarizer, and the linearly polarized light field is incident on the converging system; the converging system is used to converge the linearly polarized light field and then incident on the polarization interference system to obtain a polarization interference image; by performing a step scan on the target scene, each field point of the target scene sequentially traverses each step of the multi-level micromirror to obtain a polarization interference image data cube; by extracting the interferograms of each field point and performing a Fourier transform, the spectral information of each Stokes parameter in each field is finally demodulated.

Description

Technical Field

[0001] The present invention relates to the field of spectral technology, and particularly to a Stokes modulation Fourier transform polarization imaging spectrometer. Background Art

[0002] With the development of science and technology, the requirements for target detection and recognition in high-tech fields such as space exploration, aerial remote sensing, and military reconnaissance are getting higher and higher. Since imaging can obtain the scene information of the entire target, spectroscopy can reflect the composition and content information of each point in the target scene, and polarization can acquire target detail features and suppress the influence of complex environments, it has become an extremely urgent application requirement to combine imaging spectroscopy technology with polarization imaging technology to construct a multi-dimensional information synchronous measurement system. Since polarization imaging in the infrared band can detect, track, and recognize targets all-weather and has more excellent advantages, the detection band is also extended towards the longer-wavelength infrared direction. The Fourier transform spectroscopy technology has the advantages of multi-channel, high throughput, high wavenumber accuracy, low stray light, etc., and can achieve high-resolution detection and analysis of weak radiators, and is the most powerful spectral detection technology in the infrared band. However, the traditional Fourier transform infrared spectroscopy technology is restricted to a certain extent in terms of reliability, stability, and real-time performance due to the moving mirror scanning mechanism. Therefore, the infrared polarization imaging spectroscopy technology based on a static interference system has greater development potential and important application value.

[0003] At present, the polarization imaging spectroscopy detection technology is in a rapid development stage. Most of the structures of polarization imaging spectroscopy detection systems adopt the time-sharing detection or amplitude-division detection method. By rotating a polarizer or by splitting into multiple polarization detection channels through a beam splitter, time-sharing detection cannot obtain all-dimensional transient information in real time, and amplitude-division detection results in a very large volume and weight of the system. At the same time, in current research, most of the detection bands are located in the visible light band, and relatively few studies are carried out in the infrared band. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to propose a Stokes modulation Fourier transform polarization imaging spectrometer. By using a birefringent crystal as a high-order phase retarder to perform polarization modulation on the incident light field, all Stokes parameters are modulated onto the light intensity signal. At the same time, the phase modulation interference technology of a multi-stage micro-mirror is adopted to realize the distributed optical path difference modulation of the imaging light field, and an interference image of polarization modulation is obtained. And a polarization beam splitter and three quarter-wave plates are used to convert the polarization state of the polarization image field, so that all the light fields enter the detector after passing through the interference system, improving the utilization rate of the light field energy. Through interference pattern extraction, channel filtering and Fourier transform, synchronous measurement of the target image, spectrum and polarization is realized, solving the problem of simultaneous detection of polarization information, image information and spectrum information during the target detection process, and expanding the dimension of information detection. The system structure is compact, and at the same time has the characteristics of staticization and high stability, and is easy to realize miniaturization and integration. At the same time, the effective fusion of image, polarization and spectrum information can reconstruct a higher quality target scene, highlight the detailed features of the target, enhance the effect of target recognition, and improve the accuracy of target detection.

[0005] To achieve the above object, the present invention adopts the following specific technical solutions:

[0006] The present invention provides a Stokes modulation Fourier transform polarization imaging spectrometer, which sequentially includes: a telescopic system, a polarization modulation system, a converging system, a polarization interference system and an imaging system along the light beam propagation direction;

[0007] The target light field emitted by the target scene is incident on the telescopic system, and after passing through the telescopic system, the target light field is collimated into a parallel light field and incident on the polarization modulation system;

[0008] The polarization modulation system includes: a first high-order phase retarder, a second high-order phase retarder, and a polarizer;

[0009] The parallel light field is sequentially subjected to polarization modulation by the first high-order phase retarder and the second high-order phase retarder to obtain a modulated light field;

[0010] The modulated light field passes through the polarizer to obtain a linearly polarized light field, and the linearly polarized light field is incident on the converging system;

[0011] The converging system is used to converge the linearly polarized light field and then incident on the polarization interference system for imaging;

[0012] The polarization interference system includes: a polarization beam splitter, a plane mirror, a multi-stage micro-mirror, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, and an analyzer;

[0013] The polarization beam splitter is used to decompose the imaging light field of the linearly polarized light field into two s-polarized image fields and p-polarized image fields with equal amplitudes and perpendicular vibration directions;

[0014] Among them,

[0015] The s-polarized image field is reflected by the polarization beam splitter and then becomes left-handed circularly polarized light after passing through the first quarter-wave plate. The left-handed circularly polarized light is imaged on the plane mirror and then returns along the original path after being reflected by the plane mirror. After passing through the first quarter-wave plate again, it is transformed into a p-polarized image field. The p-polarized image field is transmitted through the polarization beam splitter and then vertically incident on the third quarter-wave plate and is transformed into right-handed circularly polarized light;

[0016] The p-polarized image field is transmitted through the polarization beam splitter and then becomes right-handed circularly polarized light after passing through the second quarter-wave plate. The right-handed circularly polarized light is imaged on the multi-stage micro mirror. The multi-stage micro mirror performs distributed phase modulation and reflection on the right-handed circularly polarized light and then returns along the original path. After passing through the second quarter-wave plate again, it is transformed into an s-polarized image field. The s-polarized image field is reflected by the polarization beam splitter and then vertically incident on the third quarter-wave plate and is transformed into left-handed circularly polarized light;

[0017] The left-handed circularly polarized light and the right-handed circularly polarized light are superimposed and interfered to form an interference image field with a specific optical path difference distribution characteristic and are incident on the analyzer polarizing plate; linearly polarized light with a vibration direction consistent with the transmission axis direction of the analyzer polarizing plate is obtained;

[0018] The linearly polarized light is incident on the imaging system after exiting the polarization interference system to obtain a polarization interference image;

[0019] By performing a step scan on the target scene, each field point of the target scene sequentially traverses each step of the multi-stage micro mirror to obtain a polarization interference image data cube; by extracting the interference patterns of each field point and performing a Fourier transform, the spectral information of each Stokes parameter in each field is finally demodulated.

[0020] Preferably, the telescopic system includes: a telescopic objective lens, a field stop, and a collimator;

[0021] The target light field is imaged at the field stop after passing through the telescopic objective lens. The field stop is located on the image-side focal plane of the telescopic objective lens and the object-side focal plane of the collimator, and is used to limit the field of view of the image of the target scene formed by the telescopic objective lens. The imaging light field passing through the field stop is collimated into a parallel light field by the collimator; the collimator is located on the object-side focal plane of the converging system.

[0022] Preferably, after the parallel light field passes through the polarization modulation system, all Stokes parameters S0, S1, S2, and S3 of it are modulated into the S0 component of the intensity parameter, so that the polarization state of the target light field is detected;

[0023] Let:

[0024] The Stokes vector of the target optical field is S in , and the Mueller matrix of the first high-order phase retarder is M R1 , and the Mueller matrix of the second high-order phase retarder is M R2 , and the Mueller matrix of the polarizer polarizing plate is M P .

[0025] Let:

[0026] The wavenumber of the target optical field is ν, and the refractive indices of the o-ray and e-ray of the crystals of the first high-order phase retarder and the second high-order phase retarder are respectively n o and n e ;

[0027] Then:

[0028] The optical path difference between the o-ray and e-ray emerging from the first high-order phase retarder is , and the phase retardation ;

[0029] The optical path difference between the o-ray and e-ray emerging from the second high-order phase retarder is , and the phase retardation ;

[0030] That is, the Stokes parameters S out of the linearly polarized optical field obtained after the target optical field passes through the polarization modulation system are:

[0031]

[0032] Therefore, in the S 0' parameter of the linearly polarized optical field, all the Stokes parameters of the target optical field are included, and each parameter is modulated by different modulation functions, that is:

[0033]

[0034] Preferably, the imaging system includes: a relay imaging lens, a narrowband filter, and a area array detector;

[0035] The relay imaging lens has an object-side telecentric optical path structure and is used to image the primary image field on the plane mirror and the multi-stage micro-mirror onto the area array detector;

[0036] The narrowband filter is used to filter the spectrum of the optical field, and its central wavelength corresponds to the central wavelength of the gas spectral line;

[0037] The area array detector is located on the image plane of the relay imaging mirror and is used to receive polarization interference images.

[0038] Preferably, the first quarter-wave plate is a birefringent crystal. The optical axis of the crystal is parallel to the surface, and the angle between the fast axis direction and the positive x-axis is 45°;

[0039] The second quarter-wave plate is a birefringent crystal. The optical axis of the crystal is parallel to the surface, and the angle between the fast axis direction and the positive x-axis is 45°;

[0040] The third quarter-wave plate is a birefringent crystal. The optical axis of the crystal is parallel to the surface, and the angle between the fast axis direction and the positive x-axis is 45°;

[0041] The crystal material of the birefringent crystal is quartz, calcite, magnesium fluoride, yttrium vanadate or barium metaborate.

[0042] Preferably, the plane mirror is located at the image-side focal plane of the imaging objective in the reflection optical path of the polarization beam splitter;

[0043] The multi-stage micro mirror is located at the image-side focal plane of the imaging objective in the transmission optical path of the polarization beam splitter, and is in a mirror-symmetrical position relative to the plane mirror with respect to the polarization beam splitter. It has a stepped structure and uses the stepped structure to perform distributed phase modulation on the incident polarized image field.

[0044] Preferably, let:

[0045] The number of steps of the multi-stage micro mirror is N The step height of the multi-stage micro mirror is h ;

[0046] The optical path difference corresponding to the interference image field formed by the n th step of the multi-stage micro mirror and the plane mirror is obtained as , and the phase difference is ;

[0047] For the high-resolution spectral line detection of gas spectra, when the bandwidth of the gas spectral line is BW, the step height h of the multi-stage micro mirror should satisfy the relationship .

[0048] Preferably, the target scene is scanned step by step, each step being one step, so that each field of view in the target scene sequentially traverses each step of the multi-stage micro mirror, and the collected polarization interference images form an interference image cube; the interference pattern signals of each field of view point are sequentially extracted along the direction of the optical path difference as:

[0049]

[0050] Using Euler's formula to expand it, the interference pattern signal is expressed as:

[0051]

[0052] Therefore, after being modulated by the polarization imaging spectrometer, the Stokes parameters of the target scene are modulated into seven parts centered on 0, ± φ 2, ±( φ 2 - φ 1), and ±( φ 2 + φ 1), forming an interferogram of seven channels.

[0053] Preferably, the interferogram channels of the seven channels include:

[0054] C 0 interferogram channel, with the central position at Δ = 0, only containing S 0 parameter;

[0055] C 1 interferogram channel, with the central position at Δ = L 2, only containing S 2 parameter;

[0056] C 2 interferogram channel, with the central position at Δ = L 2 - L 1, containing S 1 and S 3 parameters;

[0057] C 3 interferogram channel, with the central position at Δ = L 2 + L 1, containing S 1 and S 3 parameters;

[0058] C -1 interferogram channel, with the central position at Δ = - L 2, only containing S 2 parameter;

[0059] C -2 interferogram channel, with the central position at Δ = -( L 2 - L 1), containing S 1 and S 3 parameters;

[0060] C -3 interferogram channel, with the central position at Δ = -( L 2 + L 1), containing S 1 andS 3 parameters;

[0061] Among them, each channel contains one or two Stokes parameter information, C Channel 0 only contains S 0 parameter, C ±1 Channel only contains S 2 parameters, C ±2 and C ±3 Channel contains S 1 and S 3 parameters. The central positions of the interferogram channels are located at 0, ± L 2, ±( L 2 - L 1) and ±( L 2 + L 1), respectively.

[0062] Preferably, C The passband of the band - pass filtering of the 0 interferogram channel is located at Δ = [-( L 2 - L 1) / 2, ([[]] L 2 - L 1) / 2]. Then, through Fourier transform, the spectrum of S 0 parameter is ;

[0063] C The passband of the band - pass filtering of the 1 interferogram channel is located at Δ = [(2 L 2 - L 1) / 2, (2 L 2 + L 1) / 2]. Then, through Fourier transform, the spectrum of S 2 parameter is ;

[0064] C The passband of the band - pass filtering of the 2 interferogram channel is located at Δ = [( L 2 - L 1) / 2, (2 L 2 - L 1) / 2]. Then, through Fourier transform, the spectra of S 1 and S 3 parameters are respectively and ;

[0065] When the thickness ratio of the first high - order phase retarder and the second high - order phase retarder is d 1: d 2 = 1:2, the 7 channels of the interferogram C 0,C ±1 , C ±2 , C ±3 Separate from each other, select three independent channels, perform Fourier transform on the interference pattern, and obtain the spectral information of the four Stokes parameters of the target optical field as follows:

[0066]

[0067] Compared with the existing technology, the present invention combines Fourier transform imaging spectroscopy technology with infrared polarization modulation technology, can simultaneously obtain infrared image information, spectral information and polarization information of the target, and has the following advantages:

[0068] 1. The present invention uses an interference system based on a multi-stage micro-mirror for phase modulation, without moving parts, improving the reliability of the polarization imaging spectrometer system provided by the present invention and the real-time performance of information acquisition.

[0069] 2. The present invention uses a high-order phase retarder for polarization modulation, without beam splitting, reducing the volume and weight of the system.

[0070] 3. The present invention can realize the integrated acquisition of imaging, spectral and polarization multi-dimensional information, and at the same time has the performance of miniaturization and light weight, and can obtain multi-dimensional information of a long-distance target in a relatively harsh environment, and has an absolute advantage in suppressing background noise, increasing the detection distance, obtaining detail features and target camouflage recognition. Description of the Drawings

[0071] Figure 1 is a schematic optical path diagram of a Stokes modulation Fourier transform polarization imaging spectrometer according to an embodiment of the present invention.

[0072] Figure 2 is a schematic diagram of the polarization modulation process showing the principal ray of the zero field of view according to an embodiment of the present invention.

[0073] Figure 3 is a schematic diagram of the crystal optical characteristics of the first high-order phase retarder according to an embodiment of the present invention.

[0074] Figure 4 is a schematic diagram of the crystal optical characteristics of the second high-order phase retarder according to an embodiment of the present invention.

[0075] Figure 5 is a schematic diagram of the crystal optical characteristics of the polarizer polarizing plate according to an embodiment of the present invention.

[0076] Figure 6 is a schematic diagram of the crystal optical characteristics of three quarter-wave plates according to an embodiment of the present invention.

[0077] Figure 7 It is a schematic structural diagram of a multi-stage micro-mirror according to an embodiment of the present invention.

[0078] Figure 8 It is a schematic diagram of a telecentric imaging optical path of different fields of view on a multi-stage micro-mirror according to an embodiment of the present invention.

[0079] Figure 9 It is a schematic diagram of the optical path difference modulation of a multi-stage micro-mirror showing the chief rays of each field of view according to an embodiment of the present invention.

[0080] Figure 10 It is a schematic diagram of Stokes parameter channel interference according to an embodiment of the present invention.

[0081] Figure 11 It is a schematic diagram of the Stokes parameter spectral demodulation process according to an embodiment of the present invention.

[0082] The reference numerals therein include: telescopic objective lens 1, field stop 2, collimator 3, first high-order phase retarder 4, second high-order phase retarder 5, polarizer polarizing plate 6, imaging objective lens 7, polarization beam splitter 8, plane mirror 9, multi-stage micro-mirror 10, first quarter-wave plate 11, second quarter-wave plate 12, third quarter-wave plate 13, analyzer polarizing plate 14, relay imaging lens 15, narrow-band filter 16, and area array detector 17;

[0083] Target light field K1, modulation light field K2, linearly polarized light field K3, s-polarized image field K4, left-handed circularly polarized light K5, p-polarized image field K6, p-polarized image field K7, right-handed circularly polarized light K8, s-polarized image field K9, s-polarized image field K10, p-polarized image field K11, left-handed circularly polarized light K12, right-handed circularly polarized light K13, interference image field K14, and linearly polarized light K15. Detailed implementation manners

[0084] In the following, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are denoted by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, their detailed descriptions will not be repeated.

[0085] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but do not constitute a limitation to the present invention.

[0086] Figure 1 Shows the optical path of a Stokes modulation Fourier transform polarization imaging spectrometer according to an embodiment of the present invention.

[0087] Figure 2 Shows the polarization modulation process of the chief ray of the zero field of view according to an embodiment of the present invention.

[0088] As Figure 1-2 shown, the Stokes modulation Fourier transform polarization imaging spectrometer provided by the embodiment of the present invention sequentially includes, along the light beam propagation direction: a telescopic system, a polarization modulation system, a converging system, a polarization interference system, and an imaging system.

[0089] The target light field K1 emitted from a distant target scene first enters the telescopic system. The polarization state of the target light field K1 is determined by the polarization characteristics of the target scene. The target light fields K1 emitted from different target scenes have different polarization characteristics. After passing through the telescopic system, the target light field K1 is collimated into a parallel light field.

[0090] The telescopic system includes: a telescopic objective lens 1, a field stop 2, and a collimating mirror 3; the target light field forms an image at the field stop 2 after passing through the telescopic objective lens 1. The field stop 2 is located on the image-side focal plane of the telescopic objective lens 1 and at the same time on the object-side focal plane of the collimating mirror 3, and is used to limit the field of view of the image of the target scene formed by the telescopic objective lens 1. The imaging light field passing through the field stop 2 is collimated into a parallel light field by the collimating mirror 3. The collimating mirror 3 serves as the aperture stop of the polarization imaging spectrometer provided by the present invention and is located on the object-side focal plane of the imaging objective lens 7. The collimated parallel light field is incident on the polarization modulation system.

[0091] Figure 3 Shows the crystal optical characteristics of the first high-order phase retarder according to an embodiment of the present invention.

[0092] Figure 4 Shows the crystal optical characteristics of the second high-order phase retarder according to an embodiment of the present invention.

[0093] Figure 5 Shows the crystal optical characteristics of the polarizer polarizing plate according to an embodiment of the present invention.

[0094] As Figure 3-5 shown, the polarization modulation system includes: a first high-order phase retarder 4, a second high-order phase retarder 5, and a polarizer polarizing plate 6;

[0095] The optical axis of the crystal of the first high-order phase retarder 4 is parallel to the surface, the fast axis (e-axis) direction forms an angle of 45° with the positive x-axis direction, the slow axis (o-axis) direction forms an angle of 135° with the positive x-axis direction, and the thickness is d 1, and the optical path difference generated by the e-light and o-light at the exit interface is .

[0096] The optical axis of the crystal of the second high-order phase retarder 5 is parallel to the surface, the fast axis (e-axis) direction is along the positive x-axis, the slow axis (o-axis) direction is along the positive y-axis, and the thickness is d 2, and the optical path difference generated by the e-light and o-light at the exit interface is .

[0097] The first high-order phase retarder 4 and the second high-order phase retarder 5 are used to adjust the phase difference of the outgoing light. The material is a birefringent crystal, including quartz, calcite, magnesium fluoride, yttrium vanadate, barium metaborate (α-BBO), etc.

[0098] The transmission axis direction of the polarizer polarizing film 6 forms an angle of 45° with the positive x-axis, and is formed by evaporating a micro-nano structured metal wire grid on the substrate. The substrate material is a medium such as calcium fluoride, zinc selenide, zinc sulfide, silicon, germanium, etc., and the wire grid material is a metal such as gold, aluminum, etc. Light with a polarization direction perpendicular to the wire grid direction can pass through, and light with a polarization direction parallel to the wire grid direction is blocked, that is, the wire grid direction forms an angle of 135° with the positive x-axis, and is used for transmitting linearly polarized light with a specific vibration direction.

[0099] The parallel light field passes through the first high-order phase retarder 4 and the second high-order phase retarder 5 in sequence for polarization modulation to obtain a modulated light field K2, which can be decomposed into two components with perpendicular vibration directions.

[0100] The modulated light field K2 passes through the polarizer polarizing film 6 to obtain a linearly polarized light field K3, and the vibration direction of the linearly polarized light field K3 forms an angle of 45° with the positive x-axis.

[0101] After the parallel light field passes through the polarization modulation system, all its Stokes parameters (S0, S1, S2, S3) are modulated into the intensity parameter S0 component, so that the polarization state of the target light field K1 is detected.

[0102] Let:

[0103] The Stokes vector of the target light field K1 is S in , the Mueller matrix of the first high-order phase retarder 4 is M R1 , the Mueller matrix of the second high-order phase retarder 5 is M R2 , the Mueller matrix of the polarizer polarizing film 6 is M P .

[0104] Let:

[0105] The wave number of the target light field K1 is ν, and the refractive indices of the o-light and e-light of the crystals of the first high-order phase retarder 4 and the second high-order phase retarder 5 are respectively n o and ne , the thickness of the first high-order phase retarder 4 is d 1, and the thickness of the second high-order phase retarder 5 is d 2.

[0106] Then:

[0107] The optical path difference between the o-ray and e-ray emerging from the first high-order phase retarder 4 is , and the phase retardation amount is ;

[0108] The optical path difference between the o-ray and e-ray emerging from the second high-order phase retarder 5 is , and the phase retardation amount is .

[0109] That is, after the target light field K1 passes through the polarization modulation system, the Stokes parameters of the linearly polarized light field K3 S out can be expressed as:

[0110]

[0111] Therefore, in the linearly polarized light field K3 emerging from the polarization modulation system, its S 0' parameter contains all the Stokes parameters of the target light field K1, and each parameter is modulated by different modulation functions, that is:

[0112]

[0113] The linearly polarized light field K3 enters the converging system after emerging from the polarization modulation system.

[0114] The converging system includes: an imaging objective lens 7; the imaging objective lens 7 has an afocal telecentric optical path structure for converging the linearly polarized light field K3, and the linearly polarized light field K3 enters the polarization interference system for imaging after being converged by the imaging objective lens 7.

[0115] The polarization interference system includes: a polarization beam splitter 8, a plane mirror 9, a multi-stage micro mirror 10, a first quarter-wave plate 11, a second quarter-wave plate 12, a third quarter-wave plate 13, and an analyzer polarizer 14;

[0116] The polarization beam splitter 8 is used to decompose the imaging light field of the linearly polarized light field K3 into two s-polarized image fields K4 (vibration direction perpendicular to the paper surface) and p-polarized image fields K7 (vibration direction parallel to the paper surface) with equal amplitudes and perpendicular vibration directions. The s-polarized image field K4 is reflected after passing through the polarization beam splitter 8, and the p-polarized image field K7 is transmitted after passing through the polarization beam splitter 8.

[0117] The plane mirror 9 is located at the image-side focal plane of the imaging objective lens 7 in the reflection optical path of the polarization beam splitter 8.

[0118] Figure 6 Shows the crystal optical characteristics of three quarter-wave plates provided according to an embodiment of the present invention.

[0119] As Figure 6 shown,

[0120] The first quarter-wave plate 11 is located in front of the plane mirror 9, and the material is a birefringent crystal. The optical axis of the crystal is parallel to the surface. The direction of its fast axis (e-axis) forms an angle of 45° with the positive x-axis, and the direction of its slow axis (o-axis) forms an angle of 135° with the positive x-axis. The crystal materials include quartz, calcite, magnesium fluoride (MgF2), yttrium vanadate (YVO4), barium metaborate (α-BBO), etc. Its thickness is designed so that the optical path difference generated by the e-light and o-light at the exit interface of the wave plate is one-quarter wavelength, and the wavelength corresponds to the central wavelength of the gas spectral line. The s-polarized image field K4 reflected by the polarization beam splitter 8 is converted into a p-polarized image field K6 when returning.

[0121] The second quarter-wave plate 12 is located in front of the multi-stage micro mirror 10, and the material is a birefringent crystal. The optical axis of the crystal is parallel to the surface. The direction of its fast axis (e-axis) forms an angle of 45° with the positive x-axis, and the direction of its slow axis (o-axis) forms an angle of 135° with the positive x-axis. The crystal materials include quartz, calcite, magnesium fluoride (MgF2), yttrium vanadate (YVO4), barium metaborate (α-BBO), etc. Its thickness is designed so that the optical path difference generated by the e-light and o-light at the exit interface of the wave plate is one-quarter wavelength, and the wavelength corresponds to the central wavelength of the gas spectral line. The p-polarized image field K7 transmitted through the polarization beam splitter 8 is converted into an s-polarized image field K9 when returning.

[0122] The third quarter-wave plate 13 is located below the polarization beam splitter 8, and the material is a birefringent crystal. The optical axis of the crystal is parallel to the surface. The direction of its fast axis (e-axis) forms an angle of 45° with the positive x-axis, and the direction of its slow axis (o-axis) forms an angle of 135° with the positive x-axis. The crystal materials include quartz, calcite, magnesium fluoride (MgF2), yttrium vanadate (YVO4), barium metaborate (α-BBO), etc. Its thickness is designed so that the optical path difference generated by the e-light and o-light at the exit interface of the wave plate is one-quarter wavelength, and the wavelength corresponds to the central wavelength of the gas spectral line. The p-polarized image field K11 transmitted through the polarization beam splitter 8 is converted into a right-handed circularly polarized light K13, and the s-polarized image field K10 reflected by the polarization beam splitter 8 is converted into a left-handed circularly polarized light K12, and the two circularly polarized lights are superimposed to become a linearly polarized light K14.

[0123] Figure 7 Shows the structure of the multi-stage micro mirror provided according to an embodiment of the present invention.

[0124] Figure 8 Shows the telecentric imaging optical path of different fields of view on the multi-stage micro mirror provided according to an embodiment of the present invention.

[0125] Figure 9 Shows the optical path difference modulation of the main rays of each field of view provided according to an embodiment of the present invention by a multi-level micro-mirror.

[0126] As Figure 7-9 shown, the multi-level micro-mirror 10 is located at the image-side focal plane of the imaging objective 7 in the transmission optical path of the polarization beam splitter 8, and is in a mirror-symmetrical position relative to the plane mirror 9 with respect to the polarization beam splitter, having a stepped structure, the number of steps being N , the step height , and it uses the stepped structure to perform distributed phase modulation on the incident polarized image field.

[0127] The interference image field 4 corresponding to the field of view 1 corresponding to the first step of the multi-level micro-mirror 10, and the interference image field corresponds to the interference image unit (1);

[0128] The interference image field 5 corresponding to the field of view 2 on the third step of the multi-level micro-mirror 10, corresponding to the interference image unit (3);

[0129] The interference image field 6 corresponding to the field of view 3 on the fifth step of the multi-level micro-mirror 10, corresponding to the interference image unit (5).

[0130] The analyzer polarizer 14 allows the light along the polarization direction of the polarizer to pass through, and adjusts the direction of the transmission axis to make the initial phase difference of the interfering light zero.

[0131] Among them,

[0132] The s-polarized image field K4 is reflected by the polarization beam splitter 8 and then becomes left-handed circularly polarized light K5 after passing through the first quarter-wave plate 11. The left-handed circularly polarized light K5 is imaged onto the plane mirror 9 and then returns along the original path after being reflected by the plane mirror 9. After passing through the first quarter-wave plate 11 again, it is converted into p-polarized image field K6. The p-polarized image field K6 is transmitted by the polarization beam splitter 8 to be p-polarized image field K11, and the p-polarized image field K11 is vertically incident on the third quarter-wave plate 13 and then converted into right-handed circularly polarized light K13;

[0133] The p-polarized image field K7 is transmitted by the polarization beam splitter 8 and then becomes right-handed circularly polarized light K8 after passing through the second quarter-wave plate 12. The right-handed circularly polarized light K8 is imaged onto the multi-level micro-mirror 10. The multi-level micro-mirror 10 performs distributed phase modulation and reflection on the right-handed circularly polarized light K8 and then returns along the original path. After passing through the second quarter-wave plate 12 again, it is converted into s-polarized image field K9. The s-polarized image field K9 is reflected by the polarization beam splitter 8 to be s-polarized image field K10, and the s-polarized image field K10 is vertically incident on the third quarter-wave plate 13 and then converted into left-handed circularly polarized light K12.

[0134] The left-handed circularly polarized light K12 and the right-handed circularly polarized light K13 are superimposed and interfered to become an interference image field K14, and the interference image field K14 is linearly polarized light.

[0135] The s-polarized image field and the p-polarized image field are respectively reflected by the plane mirror and the multi-stage micro-mirror and then pass through the quarter-wave plate again. Therefore, the two polarized image fields are equivalent to passing through a half-wave plate before returning to the polarization beam splitter. So the s-polarized image field becomes a p-polarized image field when returning and passes through the polarization beam splitter, while the p-polarized image field becomes an s-polarized image field when returning and is reflected by the polarization beam splitter. This makes the returned beam transmit in the direction of the detector and not return to the incident direction.

[0136] Due to the distributed phase modulation effect of the multi-stage micro-mirror on the polarized image field, the left-handed circularly polarized light K12 and the right-handed circularly polarized light K13 are superimposed and interfered to form an interference image field K14 with a specific optical path difference distribution characteristic. The interference image field K14 is incident on the analyzer polarizer, and only the light along the transmission axis direction of the polarizer passes through the analyzer. The interference image field K14 passes through the analyzer polarizer 14 to obtain linearly polarized light K15, and the vibration direction of the linearly polarized light K15 is consistent with the transmission axis direction of the analyzer polarizer.

[0137] The linearly polarized light K15 is incident on the imaging system after exiting the polarization interference system.

[0138] The imaging system includes: a relay imaging lens 15, a narrowband filter 16, and a planar array detector 17.

[0139] The relay imaging lens 15 has an object-side telecentric optical path structure and is used to image the primary image field on the plane mirror 9 and the multi-stage micro-mirror 10 onto the planar array detector 17.

[0140] The narrowband filter 16 is used to filter the spectrum of the light field, and the central wavelength corresponds to the central wavelength of the gas spectral line.

[0141] The planar array detector 17 is located on the image plane of the relay imaging lens 15 and receives the polarization interference image. The linearly polarized light K15 forms a polarization interference image on the planar array detector 17 after passing through the relay imaging lens 15 and the narrowband filter 16.

[0142] Adjust the transmission axis direction of the analyzer polarizer to adjust the initial phase difference between the two coherent image fields to zero.

[0143] Suppose:

[0144] The number of steps of the multi-stage micro-mirror is all N , and the step height of the multi-stage micro-mirror is h ; it can be obtained that the optical path difference corresponding to the interference image field formed by the n th step of the multi-stage micro-mirror and the plane mirror is , and the phase difference is 。

[0145] For the high-resolution spectral line detection of gas spectra, when the bandwidth of the gas spectral line is BW, the step height of the multi-stage micro-mirror h should satisfy the relationship 。

[0146] For gas spectral lines, their bandwidth BW is usually relatively narrow. Therefore, a relatively large step height can be used to sample the interferogram. At this time, the resolution of the restored spectrum is , so a relatively high spectral resolution can be obtained.

[0147] Using the polarization imaging spectrometer provided by the present invention to perform a step scan on the target scene, stepping one step each time, so that each field of view in the target scene traverses each step in turn, and the polarization interference images collected form an interference image cube. Sequentially extracting the interferogram signals of each field of view point along the direction of the optical path difference is:

[0148]

[0149] Expanding it using Euler's formula, the interferogram signal is expressed as:

[0150]

[0151] Therefore, through the modulation of the polarization imaging spectrometer provided by the present invention, the Stokes parameters of the target scene are modulated into seven parts centered on 0, ± φ 2, ±( φ 2 - φ 1) and ±( φ 2 + φ 1), forming interferograms of seven channels.

[0152] Figure 10 Shows the interference schematic diagram of the Stokes parameter channels provided by the embodiments of the present invention.

[0153] Figure 11 Shows the Stokes parameter spectral demodulation process provided by the embodiments of the present invention.

[0154] As Figure 10-11 shown,

[0155] C The 0 interferogram channel, the central position is at Δ = 0, and it only contains S the 0 parameter;

[0156] C The 1 interferogram channel, the central position is at Δ = L 2, and it only contains S the 2 parameter;

[0157] C 2 interferogram channels, with the central position at Δ = L 2 - L 1, including S 1 and S 3 parameters;

[0158] C 3 interferogram channels, with the central position at Δ = L 2 + L 1, including S 1 and S 3 parameters;

[0159] C -1 Interferogram channel, with the central position at Δ = - L 2, only including S 2 parameters;

[0160] C -2 Interferogram channel, with the central position at Δ = -( L 2 - L 1), including S 1 and S 3 parameters;

[0161] C -3 Interferogram channel, with the central position at Δ = -( L 2 + L 1), including S 1 and S 3 parameters;

[0162] Each channel contains one or two Stokes parameter information, C Channel 0 only contains S 0 parameters, C ±1 Channel only contains S 2 parameters, C ±2 And C ±3 Channel contains S 1 and S 3 parameters, and the central positions of the interferogram channels are respectively at 0, ± L 2, ±( L 2 - L 1) and ±( L 2 + L 1).

[0163] C 0 interferogram channel is band - pass filtered, and the passband is at Δ = -( L 2 -L 1) / 2, ([ L 2 - L 1) / 2], Fourier transform to obtain S the spectrum of the 0 parameter ;

[0164] C Band - pass filter the interference pattern of the 1st channel, the pass - band is located at Δ = [(2 L 2 - L 1) / 2, (2 L 2 + L 1) / 2], Fourier transform to obtain S the spectrum of the 2 parameter ;

[0165] C Band - pass filter the interference pattern of the 2nd channel, the pass - band is located at Δ = [( L 2 - L 1) / 2, (2 L 2 - L 1) / 2], Fourier transform to obtain S the spectra of the 1 and S 3 parameters and ;

[0166] By reasonably designing the thickness ratio of the two high - order phase retarders, when the thickness ratio is d 1: d 2 = 1:2, the 7 channels of the above - mentioned interference pattern ( C 0, C ±1 , C ±2 , C ±3 ) are separated from each other, and the separation distance is related to the phase retardation amount φ (φ1, φ2) of the high - order phase retarders. Select three independent channels, perform Fourier transform on the interference pattern, and the spectral information of the four Stokes parameters of the target optical field K1 can be obtained:

[0167]

[0168] Although the embodiments of the present invention have been shown and described above, it can be understood that the above - mentioned embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above - mentioned embodiments within the scope of the present invention.

[0169] The above - mentioned specific embodiments of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A Stokes modulation Fourier transform polarization imaging spectrometer, characterized in that, Along the propagation direction of the light beam, it includes: a telescope system, a polarization modulation system, a convergence system, a polarization interference system and an imaging system; The target light field emitted by the target scene is incident on the telescopic system, and after passing through the telescopic system, the target light field is collimated into a parallel light field and is incident on the polarization modulation system; The polarization modulation system comprises: a first high-order phase retarder, a second high-order phase retarder, and a polarizer polarizer; The parallel light field is sequentially polarized by the first high-order phase retarder and the second high-order phase retarder to obtain a modulated light field; The modulated light field then passes through a polarizer polarizer to obtain a linearly polarized light field, and the linearly polarized light field is incident on a converging system; The converging system is used to converge the linearly polarized light field and then inject it into the polarization interference system for imaging; The polarization interference system comprises: a polarization beam splitter, a plane reflector, a multi-stage micro reflector, a first quarter wave plate, a second quarter wave plate, a third quarter wave plate, and an analyzer polarizer; The polarization beam splitter is used to decompose the imaging light field of the linearly polarized light field into two beams of s-polarized image field and p-polarized image field with equal amplitudes and mutually perpendicular vibration directions; in, The s-polarized image field is reflected by the polarization beam splitter and then passes through the first quarter wave plate to become left-handed circularly polarized light. The left-handed circularly polarized light is imaged onto the plane reflector and then reflected by the plane reflector and then returns along the original path. It is transformed into a p-polarized image field after passing through the first quarter wave plate again. The p-polarized image field is transmitted through the polarization beam splitter and vertically incident on the third quarter wave plate and then transformed into right-handed circularly polarized light. The p-polarized image field is transmitted through the polarization beam splitter and then converted into right-handed circularly polarized light through the second quarter-wave plate. The right-handed circularly polarized light is imaged onto the multi-stage micro-reflector. The multi-stage micro-reflector performs distributed phase modulation and reflection on the right-handed circularly polarized light and then returns to the original path. The right-handed circularly polarized light is converted into an s-polarized image field through the second quarter-wave plate again. The s-polarized image field is reflected by the polarization beam splitter and then vertically incident on the third quarter-wave plate and then converted into left-handed circularly polarized light. The left-handed circularly polarized light and the right-handed circularly polarized light are superimposed and interfered to form an interference image field with a specific optical path difference distribution characteristic, which is incident on the analyzer polarizer; and linearly polarized light whose vibration direction is consistent with the transmission axis direction of the analyzer polarizer is obtained; The linearly polarized light is emitted from the polarization interference system and then incident on the imaging system to obtain a polarization interference image; By performing step-scanning on the target scene, each field of view point of the target scene sequentially traverses each step of the multi-stage micro-reflector to obtain a polarization interference image data cube; by extracting the interference pattern of each field of view point and performing Fourier transform, the spectral information of each Stokes parameter under each field of view is finally demodulated.

2. The telescopic Stokes modulation Fourier transform polarization imaging spectrometer according to claim 1, characterized in that, The telescope system comprises: a telescope objective lens, a field stop, and a collimator lens; The target light field forms an image at the field stop after passing through the telescopic objective lens. The field stop is located on the image-side focal plane of the telescopic objective lens and the object-side focal plane of the collimator, and is used to limit the field of view of the image of the target scene formed by the telescopic objective lens. The imaging light field passing through the field stop is collimated into a parallel light field by the collimator; the collimator is located on the object-side focal plane of the converging system.

3. The telescopic system Stokes modulation Fourier transform polarization imaging spectrometer according to claim 2, characterized in that After the parallel light field passes through the polarization modulation system, all Stokes parameters S0, S1, S2, and S3 are modulated into the S0 component of the intensity parameter, so that the polarization state of the target light field is detected; Let: The Stokes vector of the target optical field is S in , and the Mueller matrix of the first high-order phase retarder is M R1 , and the Mueller matrix of the second high-order phase retarder is M R2 , and the Mueller matrix of the polarizer of the polarizer is M P ; Let ： The wave number of the target optical field is ν, and the refractive indices of the o-ray and e-ray of the first high-order phase retarder and the second high-order phase retarder crystal are respectively n o and n e ; Then: The optical path difference between the o-ray and the e-ray emitted by the first high-order phase retarder is , and the phase retardation amount ; The optical path difference between the o-ray and the e-ray emerging from the second high-order phase retarder is , and the phase retardation ; That is, the Stokes parameters of the linearly polarized light field obtained after the target light field passes through the polarization modulation system S out are as follows: Therefore, in the S 0' parameter, all Stokes parameters of the target optical field are included, and each parameter is modulated by a different modulation function, that is: 。 4. The telescopic Stokes modulation Fourier transform polarization imaging spectrometer according to claim 3, wherein The imaging system includes: a relay imaging lens, a narrow-band filter, and a area array detector; The relay imaging lens has an object-side telecentric optical path structure and is used to image the primary image field on the plane mirror and the multi-stage micro-mirror onto the area array detector; The narrow-band filter is used to filter the spectrum of the light field, and its central wavelength corresponds to the central wavelength of the gas spectral line; The area array detector is located on the image plane of the relay imaging lens and is used to receive the polarization interference image.

5. The telescopic system Stokes modulation Fourier transform polarization imaging spectrometer according to claim 4, characterized in that The first quarter-wave plate is a birefringent crystal, the optical axis of the crystal is parallel to the surface, and the fast axis direction forms an angle of 45° with the positive x-axis; The second quarter-wave plate is a birefringent crystal, the optical axis of the crystal is parallel to the surface, and the fast axis direction forms an angle of 45° with the positive x-axis; The third quarter-wave plate is a birefringent crystal, the optical axis of the crystal is parallel to the surface, and the fast axis direction forms an angle of 45° with the positive x-axis; The crystal material of the birefringent crystal is quartz, calcite, magnesium fluoride, yttrium vanadate, or barium metaborate.

6. The telescopic system Stokes modulation Fourier transform polarization imaging spectrometer according to claim 5, characterized in that The plane mirror is located at the image-side focal plane of the imaging objective lens in the reflection optical path of the polarization beam splitter; The multi-stage micro-mirror is located at the image-side focal plane of the imaging objective lens in the transmission optical path of the polarization beam splitter, and is in a mirror symmetry position with respect to the plane mirror relative to the polarization beam splitter. It has a stepped structure and uses the stepped structure to perform distributed phase modulation on the incident polarization image field.

7. The telescopic system Stokes modulation Fourier transform polarization imaging spectrometer according to claim 6, characterized in that Let: The number of steps of the multi-level micro mirror is N , and the step height of the multi-level micro mirror is h ; Obtaining the optical path difference corresponding to the interference image field formed by the n th step of the multi-level micro-mirror and the planar mirror is , and the phase difference is ; For the high-resolution spectral line detection of a gas spectrum, when the bandwidth of the gas spectral line is BW, the step height of the multi-stage micro-mirror h should satisfy the relationship .

8. The telescopic system Stokes modulation Fourier transform polarization imaging spectrometer according to claim 7, characterized in that Perform a step scan on the target scene, stepping one step each time, so that each field of view in the target scene sequentially traverses each step of the multi-stage micro-mirror. The acquired polarization interference images form an interference image cube; the interference signal of each field point is sequentially extracted along the direction of the optical path difference as: Expand it using Euler's formula, then the interference signal is expressed as: Therefore, after being modulated by the polarization imaging spectrometer, the Stokes parameters of the target scene are modulated into seven parts centered at 0, ± φ 2, ±( φ 2 - φ 1), and ±( φ 2 + φ 1), forming interference patterns of seven channels.

9. The telescopic Stokes modulation Fourier transform polarization imaging spectrometer according to claim 8, characterized in that The interference pattern channels of the seven channels include: C 0 interference pattern channel, with the central position at Δ = 0, only containing S 0 parameter; C 1 interference pattern channel, with the central position at Δ = L 2, only containing S 2 parameters; C 2 interference pattern channels, with the central position at Δ = L 2 - L 1, including S 1 and S 3 parameters; C 3 interference pattern channels, with the central position at Δ = L 2 + L 1, including S 1 and S 3 parameters; C -1 Interference pattern channel, with the center position at Δ = - L 2, containing only S 2 parameters; C -2 Interference pattern channel, with the center position at Δ = -( L 2 - L 1), including S 1 and S 3 parameters; C -3 Interference pattern channel, with the center position at Δ = -( L 2 + L 1), including S 1 and S 3 parameters; Among them, each channel contains one or two Stokes parameter information, C Channel 0 only contains S parameter 0, C ±1 Channel only contains S parameter 2, C ±2 and C ±3 Channel contains S parameters 1 and S 3. The central positions of the interferogram channels are located at 0, ± L 2, ±( L 2 - L 1), and ±( L 2 + L 1), respectively.

10. The telescopic system Stokes modulation Fourier transform polarization imaging spectrometer according to claim 9, characterized in that C 0 The passband of the interferogram channel bandpass filter is located at Δ = [-( L 2 - L 1) / 2, ( L 2 - L 1) / 2], then the spectrum of the S 0 parameter is ; C 1 The passband of the interference pattern channel bandpass filter is located at Δ = [(2 L 2 - L 1) / 2, (2 L 2 + L 1) / 2], then the spectrum of the S 2 parameters is ; C The passband of the band - pass filter for the two - interference - pattern channels is located at Δ = [( L 2 - L 1) / 2, (2 L 2 - L 1) / 2]. Then, through Fourier transform, the spectra of the S 1 and S 3 parameters are respectively and ; When the thickness ratio of the first high-order phase retarder and the second high-order phase retarder is d 1: d 2 = 1:2, the seven channels of the interference pattern C 0, C ±1 , C ±2 , C ±3 are separated from each other. Select three independent channels, perform Fourier transform on the interference pattern, and obtain the spectral information of the four Stokes parameters of the target optical field as follows:

Images