Stokes-Fourier transform polarization spectrometer

Abstract

The present invention provides a Stokes-Fourier transform polarization spectrometer, comprising: a telescopic system, a polarization modulation 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 collimated into a parallel light field; the parallel light field is incident on the polarization modulation system to obtain a linearly polarized light field, and the linearly polarized light field is incident on the polarization interference system to obtain a polarization interference light field; the polarization interference light field passes through an analyzer polarizer to obtain a linearly polarized light incident on the imaging system to obtain a polarization interference image array; by extracting the interferogram signal from the polarization interference image array and performing Fourier transform processing, the spectral information of each Stokes parameter of the target light field in all fields of view is further demodulated. The present invention realizes the distributed phase modulation of the target light field in the transverse space, obtains an interferogram array of polarization modulation and processes it, realizes the demodulation of the spectra of all Stokes parameters, and improves the real-time performance of obtaining polarization and spectral information.

Description

Technical Field

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

[0002] With the development of technology, in high-tech fields such as space exploration, military reconnaissance, medical engineering, and resource remote sensing, the requirements for the accuracy and real-time performance of target detection and recognition are getting higher and higher. Therefore, combining spectral technology with polarization technology to construct a multi-dimensional information real-time detection system has become a very urgent application requirement. The polarization spectral information in the infrared band has the characteristics of all-weather and being unaffected by day and night changes, and has more unique advantages in complex environment application fields. Fourier transform spectral technology has the advantages of multi-channel, high throughput, high wavenumber accuracy, and low stray light, 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 spectral technology is limited in terms of reliability, stability, and real-time performance due to the moving mirror scanning mechanism. Therefore, the infrared polarization spectral technology based on a static interference system has greater development potential and important application value.

[0003] At present, the polarization spectral technology is in a rapid development stage. Most of the system structures adopt the time-sharing detection or amplitude-splitting detection method. Time-sharing detection cannot obtain all-dimensional transient information in real time, while amplitude-splitting detection results in a very large volume and weight of the system. At the same time, most of the detection bands are located in the visible light band, and there is less research on the infrared band. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to propose a Stokes-Fourier transform polarization spectrometer, which combines Fourier transform spectral technology with polarization modulation technology to simultaneously obtain the spectral information and polarization information of the target light field. A phase modulation is performed using an interference system based on a multi-stage micro-mirror, without moving parts, improving the reliability of the system and the real-time performance of information acquisition. A high-order phase retarder is used for polarization modulation, without amplitude splitting, reducing the volume and weight of the system. It can realize the integrated acquisition of spectral and polarization multi-dimensional information, and at the same time has the performance of miniaturization, multi-parameter, static, and snapshot detection.

[0005] To achieve the above purpose, the present invention adopts the following specific technical solutions: It is characterized in that, in the order of the light beam propagation direction, it includes: a telescopic system, a polarization modulation system, a polarization interference system, and an imaging system;

[0006] The target light field emitted by the target scene is incident on the telescopic system and collimated into a parallel light field; the parallel light field is incident on the polarization modulation system;

[0007] The polarization modulation system includes: a first high-order phase retarder, a second high-order phase retarder, and a polarizer.

[0008] The collimated light field passes through a first high-order phase retarder and a second high-order phase retarder in sequence for polarization modulation to obtain a modulated light field;

[0009] The modulated light field passes through a polarizer to obtain a linearly polarized light field, which is incident on a polarization interference system;

[0010] The polarization interference system includes: a polarization beam splitter, a transverse multi-stage micro-mirror, a longitudinal multi-stage micro-mirror, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, and an analyzer polarizer;

[0011] The polarization beam splitter is used to decompose the linearly polarized light field into two s-polarized light fields and p-polarized light fields with equal amplitudes and perpendicular vibration directions;

[0012] Among them,

[0013] The s-polarized light field is reflected by the polarization beam splitter and becomes a left-handed circularly polarized light after passing through the first quarter-wave plate. The left-handed circularly polarized light is imaged on the transverse multi-stage micro-mirror. The transverse multi-stage micro-mirror performs distributed phase modulation and reflection on the left-handed circularly polarized light and then returns along the original path. After passing through the first quarter-wave plate again, it is transformed into a p-polarized light field. The p-polarized light field is transmitted through the polarization beam splitter to obtain a p-polarized light field, and the p-polarized light field is vertically incident on the third quarter-wave plate and then transformed into a right-handed circularly polarized light;

[0014] The p-polarized light field is transmitted through the polarization beam splitter and becomes a right-handed circularly polarized light after passing through the second quarter-wave plate. The right-handed circularly polarized light is imaged on the longitudinal multi-stage micro-mirror. The longitudinal 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 light field. The s-polarized light field is reflected by the polarization beam splitter to obtain an s-polarized light field, and the s-polarized light field is vertically incident on the third quarter-wave plate and then transformed into a left-handed circularly polarized light;

[0015] The third quarter-wave plate is used to transform the p-polarized light field transmitted through the polarization beam splitter into a right-handed circularly polarized light, and transform the s-polarized light field reflected by the polarization beam splitter into a left-handed circularly polarized light;

[0016] The left-handed circularly polarized light and the right-handed circularly polarized light are superimposed and interfered to form a polarization interference light field with a specific optical path difference distribution characteristic, which is incident on the analyzer polarizer;

[0017] The polarization interference light field passes through the analyzer polarizer to obtain a linearly polarized light, which is incident on an imaging system to obtain a polarization interference image array;

[0018] By extracting the interference pattern signal and performing Fourier transform processing on the polarization interference image array, the spectral information of each Stokes parameter of the target light field in all fields of view is demodulated.

[0019] Preferably, the telescopic system includes: a telescopic objective lens, a field stop, and a collimator;

[0020] 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 also on 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.

[0021] Preferably, the first high-order phase retarder is a birefringent crystal, the fast-axis direction forms an angle of 45° with the positive x-axis direction, and the slow-axis direction forms an angle of 135° with the positive x-axis direction;

[0022] The second high-order phase retarder is a birefringent crystal, the fast-axis direction is along the positive x-axis direction, and the slow-axis direction is along the positive y-axis direction;

[0023] The crystal materials of the first high-order phase retarder and the second high-order phase retarder are quartz, calcite, magnesium fluoride, yttrium vanadate, or barium metaborate;

[0024] The direction of the transmission axis of the polarizer polarizing plate forms an angle of 45° with the positive x-axis direction.

[0025] Preferably, after the parallel light field passes through the polarization modulation system, all its 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;

[0026] Let:

[0027] The Stokes vector of the target light field is S in , the Mueller matrix of the first high-order phase retarder is M R1 , the Mueller matrix of the second high-order phase retarder is M R2 , the Mueller matrix of the polarizer polarizing plate is M P ;

[0028] Let:

[0029] The wave number of the target light 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 n o and n e respectively, the thickness of the first high-order phase retarder is d1, and the thickness of the second high-order phase retarder is d2;

[0030] Then the optical path difference of the first high-order phase retarder is L1 = (n e -n o )d1, and the phase retardation amount is

[0031] The optical path difference of the second high-order phase retarder is L2 = (n e-n o ) d2, the phase delay amount is

[0032] The Stokes parameter S of the linearly polarized light field out is:

[0033]

[0034] Therefore, all the Stokes parameters of the target light field are included in the S0' parameter in the linearly polarized light field, and each parameter in the target light field is modulated by different modulation functions, that is:

[0035]

[0036] Preferably, the transverse multi-stage micro-mirror is located on the reflection optical path of the polarization beam splitter; the longitudinal multi-stage micro-mirror is located on the transmission optical path of the polarization beam splitter, and the transverse multi-stage micro-mirror and the longitudinal multi-stage micro-mirror are placed in mirror symmetry with respect to the beam splitting surface of the polarization beam splitter; it has a stepped structure, and the stepped directions are orthogonal to each other.

[0037] Preferably, the imaging system includes: a beam reduction system, a narrow-band filter, and a planar array detector;

[0038] The beam reduction system is used to image the polarization interference light field onto the planar array detector;

[0039] The narrow-band filter is used to filter the spectrum of the polarization interference light field, and the planar array detector is used to receive the polarization interference image array;

[0040] The linearly polarized light forms a polarization interference pattern array on the planar array detector after passing through the beam reduction system and the narrow-band filter.

[0041] Preferably, the extraction process of the interference pattern signal is:

[0042] Let:

[0043] The number of steps of both the transverse multi-stage micro-mirror and the longitudinal multi-stage micro-mirror is N, and the step height of the transverse multi-stage micro-mirror is h1, then the step height of the longitudinal multi-stage micro-mirror is h2 = N×h1; thus, the optical path difference Δ and the phase difference corresponding to the interference light field unit formed by the m-th step of the transverse multi-stage micro-mirror and the n-th step of the longitudinal multi-stage micro-mirror are obtained respectively as:

[0044] Δ(m,n) = 2nh2 - 2mh1 = 2(nN - m)h1;

[0045]

[0046] Then the interference pattern signal I collected by the planar array detector is:

[0047]

[0048] Preferably, the interference pattern signal I is expanded using Euler's formula to obtain:

[0049]

[0050] Therefore, the Stokes parameters of the target optical field are modulated into interference patterns of seven channels centered at 0, and with each channel containing the information of one or two Stokes parameters;

[0051] Among them, the C0 channel only contains the S0 parameter, the C ±1 channel only contains the S2 parameter, and the C ±2 and C ±3 channels contain the S1 and S3 parameters. The central positions of the interference pattern channels are located at 0, ±L2, ±(L2 - L1), and ±(L2 + L1), respectively;

[0052] Perform band - pass filtering on the C0 interference pattern channel, with the pass - band located at Δ = [-(L2 - L1) / 2, (L2 - L1) / 2], and then obtain the spectrum of the S0 parameter S0(ν) = 2FT[C0(Δ)] through Fourier transform;

[0053] Perform band - pass filtering on the C1 interference pattern channel, with the pass - band located at Δ = [(2L2 - L1) / 2, (2L2 + L1) / 2], and then obtain the spectrum of the S2 parameter S2(ν) = 4FT[C1(Δ)]exp(j2πνL2) through Fourier transform;

[0054] Perform band - pass filtering on the C2 interference pattern channel, with the pass - band located at Δ = [(L2 - L1) / 2, (2L2 - L1) / 2], and then the spectra of the S1 and S3 parameters obtained through Fourier transform are:

[0055] S1(ν) = 8Re{FT[C2(Δ)]exp[j2πν(L2 - L1)]},

[0056] S3(ν) = 8Im{FT[C2(Δ)]exp[j2πν(L2 - L1)]};

[0057] When the thickness ratio of the first high - order phase retarder and the second high - order phase retarder is d1:d2 = 1:2, the seven channels C0, C ±1 、C ±2 、C ±3 of the interference pattern 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:

[0058] S0(ν) = 2FT[C0(Δ)]

[0059]

[0060]

[0061]

[0062] Compared with the existing technology, the present invention uses a birefringent crystal as a high-order phase retarder to perform polarization modulation on the incident light field, modulates all Stokes parameters onto the light intensity signal, and at the same time uses spatial modulation interference technology to achieve distributed phase modulation of the target light field in the transverse space, obtaining an array of polarization modulation interference patterns. And a polarization beam splitter and three quarter-wave plates are used to convert the polarization states of the polarized light 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. By performing Stokes channel filtering and Fourier transform on the polarization interference pattern array, the demodulation of the spectra of all Stokes parameters is realized, and the real-time performance of obtaining polarization and spectral information is improved. Description of the Drawings

[0063] Figure 1 is a schematic structural diagram of a Stokes-Fourier transform polarization spectrometer according to an embodiment of the present invention.

[0064] Figure 2 is a schematic optical path diagram of a Stokes-Fourier transform polarization spectrometer according to an embodiment of the present invention.

[0065] Figure 3 is a schematic diagram of the crystal optical characteristics of a first high-order phase retarder according to an embodiment of the present invention.

[0066] Figure 4 is a schematic diagram of the crystal optical characteristics of a second high-order phase retarder according to an embodiment of the present invention.

[0067] Figure 5 is a schematic diagram of the crystal optical characteristics of a polarizer polarizing plate according to an embodiment of the present invention.

[0068] Figure 6 is a schematic diagram of the crystal optical characteristics of a quarter-wave plate according to an embodiment of the present invention.

[0069] Figure 7 is a schematic structural diagram of a multi-stage micro mirror according to an embodiment of the present invention.

[0070] Figure 8 is a schematic diagram of the optical path difference modulation of a multi-stage micro mirror according to an embodiment of the present invention.

[0071] Figure 9It is a schematic diagram of Stokes parameter channel interference provided according to an embodiment of the present invention.

[0072] Figure 10 It is a schematic diagram of the Stokes parameter spectrum demodulation process provided according to an embodiment of the present invention.

[0073] 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, polarization beam splitter 7, transverse multi-stage micro mirror 8, longitudinal multi-stage micro mirror 9, first quarter-wave plate 10, second quarter-wave plate 11, third quarter-wave plate 12, analyzer polarizing plate 13, beam reducing system 14, narrowband filter 15 and area array detector 16;

[0074] Target light field K1, modulation light field K2, linearly polarized light field K3, s-polarized light field K4, left-handed circularly polarized light K5, p-polarized light field K6, p-polarized light field K7, right-handed circularly polarized light K8, s-polarized light field K9, s-polarized light field K10, p-polarized light field K11, left-handed circularly polarized light K12, right-handed circularly polarized light K13, polarization interference light field K14 and linearly polarized light K15. Detailed implementation manners

[0075] In the following, embodiments of the present invention will be described with reference to the 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.

[0076] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention.

[0077] Figure 1 It shows a schematic structural diagram of a Stokes-Fourier transform polarization spectrometer provided according to an embodiment of the present invention.

[0078] Figure 2 It shows a schematic optical path diagram of a Stokes-Fourier transform polarization spectrometer provided according to an embodiment of the present invention.

[0079] As Figure 1-2 shown, the Stokes-Fourier transform polarization spectrometer provided by the embodiment of the present invention sequentially includes, along the beam propagation direction: a telescopic system, a polarization modulation system, a polarization interference system, and an imaging system.

[0080] 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 by 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.

[0081] 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 also 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 collimated parallel light field is incident on the polarization modulation system.

[0082] 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.

[0083] Figure 3 It shows a schematic diagram of the crystal optical characteristics of the first high-order phase retarder provided according to an embodiment of the present invention.

[0084] Figure 4 It shows a schematic diagram of the crystal optical characteristics of the second high-order phase retarder provided according to an embodiment of the present invention.

[0085] Figure 5 It shows a schematic diagram of the crystal optical characteristics of the polarizer polarizing plate provided according to an embodiment of the present invention.

[0086] As Figure 3-5 shown, the first high-order phase retarder 4 is a birefringent crystal. The optical axis of the crystal is parallel to the surface. The angle between the fast axis (e-axis) direction and the positive x-axis direction is 45°, and the angle between the slow axis (o-axis) direction and the positive x-axis direction is 135°; the thickness is d1, and the optical path difference generated by the e-light and o-light at the exit interface is (n e -n o )d1;

[0087] The second high-order phase retarder 5 is a birefringent crystal. The optical axis of the crystal is parallel to the surface. The fast axis (e-axis) direction is along the positive x-axis direction, and the slow axis (o-axis) direction is along the positive y-axis direction. The thickness is d2, and the optical path difference generated by the e-light and o-light at the exit interface is (n e -n o )d2, and its thickness satisfies a certain proportional relationship with the thickness of the first high-order phase retarder, such as d1:d2 = 1:2.

[0088] The crystal materials of the first high-order phase retarder 4 and the second high-order phase retarder 5 include quartz, calcite, magnesium fluoride (MgF2), yttrium vanadate (YVO4), barium metaborate (α-BBO), etc.

[0089] The angle between the transmission axis direction of the polarizer polarizing plate 6 and the positive x-axis is 45°, and it is formed by evaporating a layer of micro-nano structured metal wire grid on a 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 angle between the wire grid direction and the positive x-axis is 135°.

[0090] 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 mutually perpendicular vibration directions.

[0091] The modulated light field K2 passes through the polarizer polarizing plate 6 to obtain a linearly polarized light field K3, and the angle between the vibration direction of the linearly polarized light field K3 and the positive x-axis is 45°.

[0092] After the parallel light field passes through the polarization modulation system, all its Stokes parameters (S0, S1, S2, S3) are modulated into the S0 component of the intensity parameter, so that the polarization state of the target light field K1 is detected.

[0093] Let:

[0094] 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 plate 6 is M P .

[0095] Let:

[0096] The wave number of the target light field K1 is ν, and the refractive indices of the o-ray and e-ray of the crystals of the first high-order phase retarder 4 and the second high-order phase retarder 5 are n o and n e , the thickness of the first high-order phase retarder 4 is d1, and the thickness of the second high-order phase retarder 5 is d2;

[0097] Then the optical path difference of the first high-order phase retarder 4 is L1 = (n e -n o )d1, and the phase retardation is

[0098] The optical path difference of the second high-order phase retarder 5 is L2 = (n e -n o )d2, and the phase retardation is

[0099] After the target optical field K1 passes through the polarization modulation system, the Stokes parameter S of the linearly polarized optical field K3 out can be expressed as:

[0100]

[0101] Therefore, the S0' parameter in the linearly polarized optical field K3 emerging from the polarization modulation system contains all the Stokes parameters of the target optical field K1, and each parameter in the target optical field K1 is modulated by different modulation functions, that is:

[0102]

[0103] The linearly polarized optical field K3 emerges from the polarization modulation system and then enters the polarization interference system.

[0104] The polarization interference system includes: a polarization beam splitter 7, a transverse multi-stage micro-mirror 8, a longitudinal multi-stage micro-mirror 9, a first quarter-wave plate 10, a second quarter-wave plate 11, a third quarter-wave plate 12, and an analyzer polarizer 13.

[0105] The polarization beam splitter 7 is used to decompose the above linearly polarized optical field K3 into two s-polarized optical fields K4 (vibration direction perpendicular to the paper plane) and p-polarized optical fields K7 (vibration direction parallel to the paper plane) with equal amplitudes and perpendicular vibration directions. The s-polarized optical field K4 is reflected after passing through the polarization beam splitter 8, and the p-polarized optical field K7 is transmitted after passing through the polarization beam splitter 8.

[0106] Figure 6 Shows a schematic diagram of the crystal optical characteristics of a quarter-wave plate provided according to an embodiment of the present invention.

[0107] As Figure 6 shown, the first quarter-wave plate 10, the second quarter-wave plate 11, and the third quarter-wave plate 12 are all birefringent crystals. The optical axis of the crystal is parallel to the surface, the direction of the fast axis (e-axis) forms an angle of 45° with the positive x-axis, and the direction of the 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. Their thicknesses are designed so that the optical path difference generated by the e-light and o-light at the exit interface of the wave plate is a quarter of the wavelength, where the wavelength corresponds to the central wavelength of the detection gas spectral line.

[0108] Figure 7 Shows a schematic diagram of the structure of a multi-stage micro-mirror provided according to an embodiment of the present invention.

[0109] The transverse multi-level micro-mirror 8 is located on the reflection optical path of the polarization beam splitter 7; the longitudinal multi-level micro-mirror 9 is located on the transmission optical path of the polarization beam splitter 7. The transverse multi-level micro-mirror 8 and the longitudinal multi-level micro-mirror 9 are placed in a mirror image with respect to the beam splitting surface of the polarization beam splitter 7, and the stepped directions are orthogonal to each other. Both have a stepped structure. The number of steps of the transverse multi-level micro-mirror 8 is N, and the step height The number of steps of the longitudinal multi-level micro-mirror 9 is N, and the step height h2 = N×h1.

[0110] The transverse multi-level micro-mirror 8 and the longitudinal multi-level micro-mirror 9 respectively perform distributed phase modulation on the incident s-polarized light field K4 and p-polarized light field K7 in two directions by using their stepped structures.

[0111] Figure 8 The figure shows a schematic diagram of the optical path difference modulation of the multi-level micro-mirror provided by the embodiment of the present invention.

[0112] As Figure 8 shown, the interference light field R1 formed by the first step of the transverse multi-level micro-mirror and the first step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (1);

[0113] The interference light field R2 formed by the third step of the transverse multi-level micro-mirror and the first step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (3);

[0114] The interference light field R3 formed by the fifth step of the transverse multi-level micro-mirror and the first step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (5);

[0115] The interference light field R4 formed by the first step of the transverse multi-level micro-mirror and the third step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (11);

[0116] The interference light field R5 formed by the third step of the transverse multi-level micro-mirror and the third step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (13);

[0117] The interference light field R6 formed by the fifth step of the transverse multi-level micro-mirror and the third step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (15);

[0118] The interference light field R7 formed by the first step of the transverse multi-level micro-mirror and the fifth step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (21);

[0119] The interference light field R8 formed by the third step of the transverse multi-level micro-mirror and the fifth step of the longitudinal multi-level micro-mirror corresponds to the interference pattern array sampling unit (23);

[0120] The interference light field R9 formed by the 5th step of the horizontal multi-level micro-mirror and the 5th step of the vertical multi-level micro-mirror corresponds to the interference pattern array sampling unit (25).

[0121] Among them,

[0122] The s-polarized light field K4 is reflected by the polarization beam splitter 7 and then becomes left-handed circularly polarized light K5 after passing through the first quarter-wave plate 10. The left-handed circularly polarized light K5 is imaged onto the horizontal multi-level micro-mirror 8. The horizontal multi-level micro-mirror 8 performs distributed phase modulation and reflection on the left-handed circularly polarized light K5 and then returns along the original path. After passing through the first quarter-wave plate 10 again, it is transformed into a p-polarized light field K6. The p-polarized light field K6 is transmitted through the polarization beam splitter 7 to obtain a p-polarized light field K11. The p-polarized light field K11 is vertically incident on the third quarter-wave plate 12 and then transformed into right-handed circularly polarized light K13;

[0123] The p-polarized light field K7 is transmitted through the polarization beam splitter 7 and then becomes right-handed circularly polarized light K8 after passing through the second quarter-wave plate 11. The right-handed circularly polarized light K8 is imaged onto the vertical multi-level micro-mirror 9. The vertical multi-level micro-mirror 9 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 11 again, it is transformed into an s-polarized light field K9. The s-polarized light field K9 is reflected by the polarization beam splitter 7 to obtain an s-polarized light field K10. The s-polarized light field K10 is vertically incident on the third quarter-wave plate 12 and then transformed into left-handed circularly polarized light K12.

[0124] The third quarter-wave plate 12 is used to transform the p-polarized light field K11 transmitted through the polarization beam splitter 7 into right-handed circularly polarized light K13, and transform the s-polarized light field K10 reflected by the polarization beam splitter 7 into left-handed circularly polarized light K12.

[0125] The s-polarized light field and the p-polarized light field pass through the quarter-wave plate, are reflected by the multi-level micro-mirror, and then pass through the quarter-wave plate again. Therefore, both beams of light pass through the quarter-wave plate at a 45° angle twice before returning to the polarization beam splitter, which is equivalent to passing through a half-wave plate. So the s light reflected by the polarization beam splitter becomes p light when returning and passes through the polarization beam splitter, while the p light transmitted through the polarization beam splitter becomes s light when returning and is reflected by the polarization beam splitter. This makes the returning beam transmit in the direction of the detector and not return to the incident direction.

[0126] The s-polarized light field K10 and the p-polarized light field K11 pass through the third quarter-wave plate 13 at the exit position of the polarization beam splitter 8.

[0127] The left-handed circularly polarized light K12 and the right-handed circularly polarized light K13 are superimposed at the exit position of the third and fourth quarter-wave plates 12 and then become a linearly polarized light field. Due to the distributed phase modulation effects of the transverse multi-level micromirror 8 and the longitudinal multi-level micromirror 9 on the s-polarized light field and the p-polarized light field, the two beams of light are superimposed and interfere to form a polarization interference light field K14 with a specific optical path difference distribution characteristic and is incident on the analyzer polarizer 13;

[0128] Only the light along the polarization direction of the analyzer polarizer 13 can pass through the analyzer polarizer 13.

[0129] The polarization interference light field K14 passes through the analyzer polarizer 13 to obtain a 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 13.

[0130] The linearly polarized light K15 is incident into the imaging system after exiting the polarization interference system.

[0131] The imaging system includes: a beam reducing system 14, a narrowband filter 15, and a planar array detector 16. The beam reducing system 14 is used to image the polarization interference light field K14 onto the planar array detector 16. The narrowband filter 15 is used to filter the spectrum of the polarization interference light field, and the central wavelength corresponds to the central wavelength of the gas spectral line. The planar array detector 16 is used to receive the polarization interference image array.

[0132] The linearly polarized light K15 passes through the beam reducing system 14 and the narrowband filter 15, and a polarization interference pattern array is formed on the planar array detector 16. The central wavelength of the narrowband filter 15 corresponds to the central wavelength of the detected gas spectral line.

[0133] Provide adjustment of the transmission axis direction of the analyzer polarizer 13, so as to adjust the initial phase difference between the two coherent light beams from the two multi-level micromirrors to zero.

[0134] Suppose:

[0135] The number of steps of the two multi-level micromirrors is both N. Among them, the step height of the transverse multi-level micromirror 8 is h1, then the step height of the longitudinal multi-level micromirror 9 is h2 = N×h1; thus, the optical path difference Δ and the phase difference corresponding to the interference light field unit formed by the m-th step of the transverse multi-level micromirror 8 and the n-th step of the longitudinal multi-level micromirror 9 Are respectively:

[0136] Δ(m,n) = 2nh2 - 2mh1 = 2(nN - m)h1,

[0137]

[0138] For the high-resolution spectral line detection of the gas spectrum, when the bandwidth of the gas spectral line is BW, the step height h1 of the transverse multi-level micromirror 8 should satisfy the relationship

[0139] 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 Therefore, a relatively high spectral resolution can be obtained.

[0140] Since the signal collected by the area array detector 16 is the total light intensity signal of the outgoing light, the interferogram signal I finally collected by the area array detector 16 is:

[0141]

[0142] Expand the interferogram signal I using Euler's formula to obtain:

[0143]

[0144] Therefore, through the modulation of the polarization spectrometer, the Stokes parameters of the target light field K1 are modulated into 7 parts centered on 0, and forming an interferogram of 7 channels on the detector.

[0145] Figure 9 Shows the interference schematic diagram of the Stokes parameter channels provided by the embodiment of the present invention.

[0146] As Figure 9 shown: The central position of the C0 interferogram channel is at Δ = 0, and only contains the S0 parameter;

[0147] The central position of the C1 interferogram channel is at Δ = L2, and only contains the S2 parameter;

[0148] The central position of the C2 interferogram channel is at Δ = L2 - L1, and contains the S1 and S3 parameters;

[0149] The central position of the C3 interferogram channel is at Δ = L2 + L1, and contains the S1 and S3 parameters;

[0150] C -1 The central position of the interferogram channel is at Δ = -L2, and only contains the S2 parameter;

[0151] C -2 The central position of the interferogram channel is at Δ = -(L2 - L1), and contains the S1 and S3 parameters;

[0152] C -3 The central position of the interferogram channel is at Δ = -(L2 + L1), and contains the S1 and S3 parameters.

[0153] Each channel contains one or two Stokes parameter information. The C0 channel only contains the S0 parameter, and the C ±1 channel only contains the S2 parameter, and the C ±2 and C ±3 channels contain the S1 and S3 parameters. The central positions of the interferogram channels are located at 0, ±L2, ±(L2 - L1), and ±(L2 + L1) respectively.

[0154] Figure 10 FIG. shows a schematic diagram of the Stokes parameter spectrum demodulation process provided according to an embodiment of the present invention.

[0155] As Figure 10 shown, band - pass filtering is performed on the C0 interferogram channel, and the pass - band is located at Δ = [-(L2 - L1) / 2, (L2 - L1) / 2]. Then, through Fourier transform, the spectrum of the S0 parameter is obtained as S0(ν) = 2FT[C0(Δ)];

[0156] Band - pass filtering is performed on the C1 interferogram channel, and the pass - band is located at Δ = [(2L2 - L1) / 2, (2L2 + L1) / 2]. Then, through Fourier transform, the spectrum of the S2 parameter is obtained as S2(ν) = 4FT[C1(Δ)]exp(j2πνL2);

[0157] Band - pass filtering is performed on the C2 interferogram channel, and the pass - band is located at Δ = [(L2 - L1) / 2, (2L2 - L1) / 2]. Then, through Fourier transform, the spectra of the S1 and S3 parameters are:

[0158] S1(ν) = 8Re{FT[C2(Δ)]exp[j2πν(L2 - L1)]},

[0159] S3(ν) = 8Im{FT[C2(Δ)]exp[j2πν(L2 - L1)]}.

[0160] By reasonably designing the thickness ratio of the first high - order phase retarder 4 and the second high - order phase retarder 5, for example, the thickness ratio can be designed as d1:d2 = 1:2, so that the 7 channels (C0, C ±1 , C ±2 , C ±3 ) of the interferogram are separated from each other, and the separation distance is related to the phase retardation amount of the high - order phase retarder. Select three independent channels, perform Fourier transform on the interferogram signal I, and obtain the spectral information of the four Stokes parameters of the target optical field K1:

[0161] S0(ν) = 2FT[C0(Δ)]

[0162]

[0163]

[0164]

[0165] The present invention adopts the polarization modulation technology of a high-order phase retarder and combines it with the spatial modulation interference technology using a multi-stage micro-mirror to solve the problem of synchronous measurement of Stokes parameter spectra. By utilizing the high-order phase retardation characteristics of a birefringent crystal, light is made to pass through two birefringent crystals with different phase retardation amounts and the fast-axis directions forming an angle of 45°. After polarization by a polarizer, the Stokes parameters of the target light field are modulated into the light intensity signal. At the same time, a spatial modulation polarization interference system based on a polarization beam splitter, a quarter-wave plate, and a multi-stage micro-mirror is adopted to perform distributed polarization phase modulation on the incident polarized light field, realizing distributed interference modulation of each Stokes parameter, obtaining an array of polarization interference patterns of the Stokes parameter channels, and through channel filtering and Fourier transform, realizing synchronous demodulation of the spectra of each Stokes parameter.

[0166] Although the embodiments of the present invention have been shown and described above, it can be understood that the above 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 embodiments within the scope of the present invention.

[0167] The above 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 within the protection scope of the claims of the present invention.

Claims

1. A Stokes-Fourier transform polarization spectrometer, characterized in that, Along the beam propagation direction, it includes: telescope system, polarization modulation system, polarization interference system and imaging system; The target light field emitted by the target scene is incident on the telescopic system and is collimated into a parallel light field; the parallel light field 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 the polarizer polarizer to obtain a linearly polarized light field which is incident on a polarization interference system; The polarization interference system comprises: a polarization beam splitter, a transverse multi-stage micro-reflector, a longitudinal 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 linearly polarized light field into two beams of s-polarized light field and p-polarized light field with equal amplitudes and mutually perpendicular vibration directions; in, The s-polarized light 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 transverse multi-stage micro-reflector, the transverse multi-stage micro-reflector performs distributed phase modulation and reflection on the left-handed circularly polarized light and then returns to the original path, and then passes through the first quarter wave plate again to become a p-polarized light field, the p-polarized light field is transmitted through the polarization beam splitter to obtain a p-polarized light field, and the p-polarized light field is vertically incident on the third quarter wave plate and then converted into right-handed circularly polarized light; The p-polarized light 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 longitudinal multi-stage micro-reflector. The longitudinal 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 light field through the second quarter-wave plate again. The s-polarized light field is reflected through the polarization beam splitter to obtain an s-polarized light field. The s-polarized light field is vertically incident on the third quarter-wave plate and then converted into left-handed circularly polarized light. The third quarter wave plate is used to convert the p-polarized light field transmitted through the polarization beam splitter into right-handed circularly polarized light, and to convert the s-polarized light field reflected by the polarization beam splitter 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 a polarized interference light field having a specific optical path difference distribution characteristic, which is incident on the analyzer polarizer; The polarized interference light field is incident on the imaging system to obtain a polarized interference image array by passing through the analyzer polarizer to obtain linearly polarized light; By performing interference pattern signal extraction and Fourier transform processing on the polarization interference image array, the spectral information of each Stokes parameter of the target light field in all fields of view is demodulated.

2. The Stokes-Fourier transform polarization spectrometer according to claim 1, wherein The telescope system includes: telescope objective lens, field diaphragm, and collimator; 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 simultaneously on 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.

3. The Stokes-Fourier transform polarization spectrometer according to claim 2, characterized in that, The first high-order phase retarder is a birefringent crystal. The fast-axis direction makes an angle of 45° with the positive x-axis direction, and the slow-axis direction makes an angle of 135° with the positive x-axis direction. The second high-order phase retarder is a birefringent crystal. The fast-axis direction is along the positive x-axis direction, and the slow-axis direction is along the positive y-axis direction. The crystal materials of the first high-order phase retarder and the second high-order phase retarder are quartz, calcite, magnesium fluoride, yttrium vanadate, or barium metaborate. The transmission axis direction of the polarizer polarizing plate makes an angle of 45° with the positive x-axis direction.

4. The Stokes-Fourier transform polarization spectrometer according to claim 3, wherein After the parallel light field passes through the polarization modulation system, all its 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 light 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 , the thickness of the first high-order phase retarder is d 1, and the thickness of the second high-order phase retarder is d 2; Then the optical path difference of the first high-order phase retarder is , and the phase retardation amount is ; The optical path difference of the second high-order phase retarder is , and the phase retardation amount is ; The Stokes parameters of the linearly polarized light field S out are as follows: Therefore, in the linearly polarized light field S the 0' parameter contains all the Stokes parameters of the target light field, and each parameter in the target light field is modulated by different modulation functions, that is: 。 5. The Stokes-Fourier transform polarization spectrometer according to claim 4, characterized in that, The transverse multi-stage micro-mirror is located on the reflection optical path of the polarization beam splitter; the longitudinal multi-stage micro-mirror is located on the transmission optical path of the polarization beam splitter. The transverse multi-stage micro-mirror and the longitudinal multi-stage micro-mirror are placed in a mirror image with respect to the beam splitting surface of the polarization beam splitter; they have a stepped structure, and the stepped directions are orthogonal to each other.

6. The Stokes-Fourier transform polarization spectrometer according to claim 5, wherein The imaging system includes: a beam reducing system, a narrowband filter, and a planar array detector. The beam reducing system is used to image the polarization interference light field onto the planar array detector. The narrowband filter is used to filter the spectrum of the polarization interference light field, and the planar array detector is used to receive the polarization interference image array. The linearly polarized light forms a polarization interference pattern array on the planar array detector after passing through the beam reducing system and the narrowband filter.

7. The Stokes-Fourier transform polarization spectrometer according to claim 6, characterized in that, The process of extracting the interference pattern signal is as follows: Let: The number of steps of both the horizontal multi - level micro - mirror and the vertical multi - level micro - mirror is N , the step height of the horizontal multi - level micro - mirror is h 1, then the step height of the vertical multi - level micro - mirror is h 2 = N × h 1; thus, the optical path difference Δ and the phase difference φ corresponding to the interference light - field unit formed by the m th step of the horizontal multi - level micro - mirror and the n th step of the vertical multi - level micro - mirror are respectively: ； ； Then the interference pattern signal I collected by the planar array detector is: 。 8. The Stokes-Fourier transform polarization spectrometer according to claim 7, characterized in that, Expand the interference pattern signal I using Euler's formula to obtain: Therefore, the Stokes parameters of the target optical field are modulated into interference patterns of seven channels centered on 0, ± φ 2, ±( φ 2 - φ 1) and ±( φ 2 + φ 1), and each channel contains one or two Stokes parameter information; Among them, 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); Perform band-pass filtering on the C 0 interference pattern channels, with the passband located at Δ = [-( L 2 - L 1) / 2, ( L 2 - L 1) / 2], and then obtain the S 0 parameter spectrum ; Perform band-pass filtering on the C 1 interference pattern channel, with the passband located at Δ = [(2 L 2 - L 1) / 2, (2 L 2 + L 1) / 2], and then obtain the S spectrum of the 2 parameters ; Perform band - pass filtering on the C two interference - pattern channels, with the pass - band located at Δ = [( L 2 - L 1) / 2, (2 L 2 - L 1) / 2], and then obtain the S 1 and S spectra of the three parameters as follows: ， ； 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 a Fourier transform on the interference pattern, and obtain the spectral information of the four Stokes parameters of the target optical field as follows: 。

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