Polarization Imaging Spectrometer

Abstract

The present invention provides a 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 collimated into a parallel light field; the parallel light field is incident on the polarization modulation system; the parallel light field successively passes through the polarization modulation system to obtain a linearly polarized light field and is incident on the converging system; the converging system performs multiple imaging on the linearly polarized light field to form a multiple imaging light field array and is incident on the polarization interference system to obtain a right-handed circularly polarized light and a left-handed circularly polarized light; the left-handed circularly polarized light and the right-handed circularly polarized light are superposed and interfered to form a polarization interference image field array and are incident on an analyzer polarizing plate to obtain a linearly polarized light and are incident on the imaging system, and finally a polarization interference image array is obtained; by extracting the interferogram 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 further demodulated.

Description

Technical Field

[0001] The present invention relates to the field of spectral technology, and particularly to a polarization imaging 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. 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 the detailed features of the target 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 spectral band can detect, track, and identify targets all-weather and has more excellent advantages, the detection band is also expanding towards the longer-wavelength infrared direction. Fourier transform spectroscopy 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 emitters. It 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 spectral detection technology is in a rapid development stage. Most of the structures of polarization imaging spectral detection systems adopt the time-sharing detection or amplitude-splitting detection method. By rotating a polarizer or splitting into multiple polarization detection channels through a beam splitter, time-sharing detection cannot obtain all-dimensional transient information in real time, which restricts its detection of moving scenes or rapidly changing targets; while amplitude-splitting detection results in a very large volume and weight of the system. At the same time, in current research, most of its detection bands are located in the visible light band, and relatively few studies are conducted in the infrared band. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a polarization imaging spectrometer, which solves the problem of static, real-time, and integrated measurement of information in multiple dimensions of image, spectrum, and polarization by adopting the polarization modulation technology of a high-order phase retarder, combining the distributed phase modulation interference technology of a multi-stage micro-mirror, and the multiple imaging technology of a microlens array. By utilizing the high-order phase retardation characteristics of a birefringent crystal, the target light field passes through two birefringent crystals with different phase retardation amounts and the fast axis directions forming an angle of 45°, and after polarization by a polarizer, the Stokes parameters of the incident light are modulated into the light intensity signal. At the same time, a microlens array is used for multiple imaging, and a spatial modulation polarization interference system based on a polarization beam splitter, a quarter-wave plate, and a multi-stage micro-mirror is used to perform distributed phase modulation on the polarization image field, obtaining a polarization interference image array, and through channel filtering and Fourier transform, synchronous demodulation of polarization, image, and spectrum is achieved.

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

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

[0007] 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;

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

[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 then passes through the polarizer polarizing plate to obtain a linearly polarized light field and is incident on the converging system;

[0011] The converging system performs multiple imaging on the linearly polarized light field to form a multiple imaging light field array and is incident on the polarization interference system;

[0012] 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 polarizing plate;

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

[0014] Among them,

[0015] The s-polarized multiple 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 onto the transverse multi-level micro-mirror. The transverse multi-level 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 multiple image field. The p-polarized multiple image field passes through the polarization beam splitter to obtain a p-polarized multiple image field. The p-polarized multiple image field is vertically incident on the third quarter-wave plate and then becomes right-handed circularly polarized light;

[0016] The p-polarized multiple image field passes 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 onto the longitudinal multi-level micro-mirror. The longitudinal multi-level 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 multiple image field. The s-polarized multiple image field is reflected by the polarization beam splitter to obtain an s-polarized multiple image field. The s-polarized multiple image field is vertically incident on the third quarter-wave plate and then becomes left-handed circularly polarized light;

[0017] The third quarter-wave plate is used to transform the p-polarized multiple image field passing through the polarization beam splitter into right-handed circularly polarized light, and transform the s-polarized multiple image field reflected by the polarization beam splitter into left-handed circularly polarized light;

[0018] The left-handed circularly polarized light and the right-handed circularly polarized light are superimposed and interfered to form a polarization interference image field array with a specific optical path difference distribution characteristic and are incident on the analyzer polarizer;

[0019] The polarization interference image field array passes through the analyzer polarizer to obtain linearly polarized light and is incident on the imaging system to obtain a polarization interference image array;

[0020] 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.

[0021] Preferably, the telescopic system includes: a telescopic objective lens, a field stop, and a collimator;

[0022] 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 at the same time 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;

[0023] 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.

[0024] Preferably, the fast axis direction of the first high-order phase retarder forms an angle of 45° with the positive x-axis direction;

[0025] The fast axis direction of the second high-order phase retarder is along the positive x-axis direction;

[0026] 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;

[0027] The direction of the transmission axis of the polarizer polarizing plate forms an angle of 45° with the positive direction of the x-axis.

[0028] Preferably, 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 is detected;

[0029] Let:

[0030] The wave number of the target light field is ν, and the refractive indices of the ordinary light and extraordinary light of the crystals of the first high-order phase retarder and the second high-order phase retarder are n o and n e , the thickness of the first high-order phase retarder is d1, and the thickness of the second high-order phase retarder is d2;

[0031] Then:

[0032] The optical path difference of the light emerging from the first high-order phase retarder is L1 = (n e -n o )d1, and the phase retardation is

[0033] The optical path difference of the light emerging from the second high-order phase retarder is L2 = (n e -n o )d2, and the phase retardation is

[0034] The Stokes parameter S out of the linearly polarized light field is:

[0035]

[0036] Therefore, the S0' parameter in the linearly polarized light field 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:

[0037]

[0038] Preferably, the converging system includes: a microlens array, which is composed of the same number of row microlens units and column microlens units, and is used for multi-channel imaging of the linearly polarized light field.

[0039] Preferably, the fast axis directions of the first quarter-wave plate, the second quarter-wave plate, and the third quarter-wave plate form an angle of 45° with the x-axis. They are all birefringent crystals, and the crystal materials are quartz, calcite, magnesium fluoride, yttrium vanadate, or barium metaborate.

[0040] Preferably, the transverse multi-level micro-mirror is located on the image-side focal plane of the microlens array and has a stepped structure. The steps are along the x-axis, and each step corresponds to a row of microlens units in the microlens array;

[0041] The longitudinal multi-level micro-mirror is located on the image-side focal plane of the microlens array and has a stepped structure. The steps are along the y-axis, and each step corresponds to a column of microlens units in the microlens array.

[0042] Preferably, the imaging system includes: a relay imaging lens, a narrowband filter, and a planar array detector;

[0043] The relay imaging lens has an object-side telecentric optical path structure and is used to image the polarization imaging light field array onto the planar array detector;

[0044] The narrowband filter is used to filter the spectrum of the light field;

[0045] The planar array detector is located on the image plane of the relay imaging lens and is used to receive the polarization interference image array;

[0046] The linearly polarized light forms a polarization interference image array on the planar array detector after passing through the relay imaging lens and the narrowband filter.

[0047] Preferably, the process of extracting the interferogram signal is as follows:

[0048] Let:

[0049] The number of steps of both the transverse multi-level micro-mirror and the longitudinal multi-level micro-mirror is N. The step height of the transverse multi-level micro-mirror is h1. Then the step height of the longitudinal multi-level micro-mirror is h2 = N×h1. 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 transverse multi-level micro-mirror and the n-th step of the longitudinal multi-level micro-mirror are respectively:

[0050] Δ(m,n) = 2nh2 - 2mh1 = 2(nN - m)h1;

[0051]

[0052] Select a certain target point corresponding to the polarization interference image array, and sequentially extract the interferogram signal I of this target point along the direction of the optical path difference as:

[0053]

[0054] Preferably, expand the interferogram signal I using Euler's formula to obtain:

[0055]

[0056] Therefore, the Stokes parameters of the target optical field are modulated into interference patterns of seven channels centered at 0, and Each channel contains the information of one or two Stokes parameters;

[0057] Among them, 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 interference pattern channels are located at 0, ±L2, ±(L2 - L1), and ±(L2 + L1) respectively;

[0058] Perform band - pass filtering on the C0 interference pattern channel. The pass - band is located at Δ = [-(L2 - L1) / 2, (L2 - L1) / 2]. After Fourier transform, the spectrum of the S0 parameter is S0(ν) = 2FT[C0(Δ)];

[0059] Perform band - pass filtering on the C1 interference pattern channel. The pass - band is located at Δ = [(2L2 - L1) / 2, (2L2 + L1) / 2]. After Fourier transform, the spectrum of the S2 parameter is S2(ν) = 4FT[C1(Δ)]exp(j2πνL2);

[0060] Perform band - pass filtering on the C2 interference pattern channel. The pass - band is located at Δ = [(L2 - L1) / 2, (2L2 - L1) / 2]. After Fourier transform, the spectra of the S1 and S3 parameters are:

[0061] S1(ν) = 8Re{FT[C2(Δ)]exp[j2πν(L2 - L1)]}

[0062] S3(ν) = 8Im{FT[C2(Δ)]exp[j2πν(L2 - L1)]}

[0063] 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 to perform Fourier transform on the interference pattern signal I to obtain the spectral information of the four Stokes parameters of the target optical field:

[0064] S0(ν) = 2FT[C0(Δ)]

[0065]

[0066]

[0067]

[0068] Compared with the existing technology, the present invention has the following advantages:

[0069] 1. The present invention combines Fourier transform imaging spectroscopy technology with infrared polarization modulation technology, and can simultaneously obtain infrared image information, spectral information and polarization information of the target.

[0070] 2. The present invention uses a polarization interference system based on a multi-stage micro-mirror for distributed phase modulation, without moving parts, improving the reliability and real-time performance of information acquisition.

[0071] 3. The present invention uses a high-order phase retarder and a microlens array for polarization imaging modulation, without amplitude division, reducing the volume and weight of the system.

[0072] 4. The present invention can realize static, real-time and integrated measurement of information in multiple dimensions of image, spectrum and polarization, and can effectively solve the problems of large volume and weight of current polarization imaging spectrometers and inability to detect multi-dimensional information in real time. Description of the Drawings

[0073] Figure 1 is a schematic structural diagram of a polarization imaging spectrometer according to an embodiment of the present invention.

[0074] Figure 2 is a schematic optical path diagram of polarization modulation of each interference imaging channel in the main ray of the polarization imaging spectrometer according to an embodiment of the present invention.

[0075] 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.

[0076] 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.

[0077] Figure 5 is a schematic diagram of the crystal optical characteristics of the polarizer polarizing plate according to an embodiment of the present invention.

[0078] Figure 6 is a schematic diagram of the crystal optical characteristics of three quarter-wave plates in the polarization imaging spectrometer according to an embodiment of the present invention.

[0079] Figure 7 is a schematic structural diagram of the transverse multi-stage micro-mirror and the longitudinal multi-stage micro-mirror structure according to an embodiment of the present invention.

[0080] Figure 8It is a schematic diagram of the multi - level micro - mirror multiple imaging optical path by the microlens array provided according to an embodiment of the present invention.

[0081] Figure 9 It is a schematic diagram of the optical path difference modulation process of each interference imaging channel shown by the chief ray provided according to an embodiment of the present invention.

[0082] Figure 10 It is a schematic diagram of the Stokes parameter channel interference provided according to an embodiment of the present invention.

[0083] Figure 11 It is a schematic diagram of the Stokes parameter spectrum demodulation process provided according to an embodiment of the present invention.

[0084] 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, microlens array 7, polarization beam splitter 8, transverse multi - level micro - mirror 9, longitudinal multi - level 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;

[0085] Target light field K1, modulation light field K2, linearly polarized light field K3, s - polarized multiple image field K4, left - hand circularly polarized light K5, p - polarized multiple image field K6, p - polarized multiple image field K7, right - hand circularly polarized light K8, s - polarized multiple image field K9, s - polarized multiple image field K10, p - polarized multiple image field K11, left - hand circularly polarized light K12, right - hand circularly polarized light K13, polarization interference image field array K14, and linearly polarized light K15. Detailed implementation manners

[0086] 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.

[0087] 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, rather than to limit the present invention.

[0088] Figure 1 It shows a schematic structural diagram of a polarization imaging spectrometer provided according to an embodiment of the present invention.

[0089] Figure 2 It shows a schematic diagram of the optical path of polarization modulation of each interference imaging channel shown by the chief ray in the polarization imaging spectrometer provided according to an embodiment of the present invention.

[0090] As Figure 1-2 shown, the 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Figure 3 shows a schematic diagram of the crystal optical characteristics of the first high-order phase retarder provided by the embodiment of the present invention.

[0095] As Figure 3 shown, the first high-order phase retarder 4 is a birefringent crystal. 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 direction, and the direction of the slow axis (o-axis) forms an angle of 135° with the positive x-axis direction; 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.

[0096] Figure 4 shows a schematic diagram of the crystal optical characteristics of the second high-order phase retarder provided by the embodiment of the present invention.

[0097] As Figure 4 shown, the second high-order phase retarder 5 is a birefringent crystal. The optical axis of the crystal is parallel to the surface. The direction of the fast axis (e-axis) is along the positive x-axis direction, and the direction of the slow axis (o-axis) 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, whose thickness satisfies a certain proportional relationship with the thickness of the first high-order phase retarder, such as d1:d2 = 1:2.

[0098] 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.

[0099] Figure 5 Shows a schematic diagram of the crystal optical characteristics of the polarizer polarizing film provided by an embodiment of the present invention.

[0100] As Figure 5 shown, the included angle between the light transmission axis direction of the polarizer polarizing film 6 and the positive x-axis direction is 45°, and it is formed by evaporating a layer of 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 included angle between the wire grid direction and the positive x-axis direction is 135°.

[0101] 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.

[0102] The modulated light field K2 passes through the polarizer polarizing film 6 to obtain a linearly polarized light field K3, and the included angle between the vibration direction of the linearly polarized light field K3 and the positive x-axis direction is 45°.

[0103] 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.

[0104] Let:

[0105] 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 .

[0106] Let:

[0107] 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;

[0108] Then:

[0109] The optical path difference between the o - light and e - light emitted from the first high - order phase retarder 4 is \(L1=(n e - n o )d1\), and the phase retardation amount is

[0110] The optical path difference between the o - light and e - light emitted from the second high - order phase retarder 5 is \(L2=(n e - n o )d2\), and the phase retardation amount is

[0111] After the target light field K1 passes through the polarization modulation system, the Stokes parameter S out of the linearly polarized light field K3 can be expressed as:

[0112]

[0113] Therefore, the S0' parameter in the linearly polarized light field K3 emitted from the polarization modulation system contains all the Stokes parameters of the target light field K1, and each parameter in the target light field K1 is modulated by different modulation functions, that is:

[0114]

[0115] The linearly polarized light field K3 emitted from the polarization modulation system is incident on the converging system after passing through the system.

[0116] The converging system includes: a microlens array 7, which is composed of multiple microlens units and performs multi - channel imaging on the incident linearly polarized light field K3.

[0117] The microlens array 7 performs multiple imaging on the linearly polarized light field K3 to form a multiple imaging light field array, which is incident on the polarization interference system.

[0118] The polarization interference system includes: a polarization beam splitter 8, a transverse multi - level micro - mirror 9, a longitudinal multi - level 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.

[0119] The polarization beam splitter 8 is used to decompose the above - mentioned multiple imaging light field array into two s - polarized multiple image fields K4 (vibration direction perpendicular to the paper plane) and p - polarized multiple image fields K7 (vibration direction parallel to the paper plane) with equal amplitudes and perpendicular vibration directions. The s - polarized multiple image field K4 is reflected after passing through the polarization beam splitter 8, and the p - polarized multiple image field K7 is transmitted after passing through the polarization beam splitter 8.

[0120] Figure 6Shows a schematic diagram of the crystal optical characteristics of three quarter-wave plates in a polarization imaging spectrometer according to an embodiment of the present invention.

[0121] As Figure 6 shown, the fast axis direction of the first quarter-wave plate 11 makes an angle of 45° with the x-axis, and the wavelength corresponds to the central wavelength of the gas spectral line. The s-polarized multiple image field K4 reflected by the polarization beam splitter 8 is converted into a p-polarized multiple image field K6 when returning.

[0122] The fast axis direction of the second quarter-wave plate 12 makes an angle of 45° with the x-axis, and the wavelength corresponds to the central wavelength of the gas spectral line. The p-polarized multiple image field K7 passing through the polarization beam splitter is converted into an s-polarized multiple image field K9 when returning.

[0123] The third quarter-wave plate 13 is located below the polarization beam splitter 8, and its fast axis direction makes an angle of 45° with the x-axis, and the wavelength corresponds to the central wavelength of the gas spectral line.

[0124] The materials of the first quarter-wave plate 11, the second quarter-wave plate 12, and the third quarter-wave plate 13 are all birefringent crystals. The optical axis of the crystal is parallel to the surface. The crystal materials include quartz, calcite, magnesium fluoride (MgF2), yttrium vanadate (YVO4), barium metaborate (α-BBO), etc.

[0125] Figure 7 Shows a schematic diagram of the structures of a transverse multi-level micro-mirror and a longitudinal multi-level micro-mirror according to an embodiment of the present invention.

[0126] As Figure 7 shown, the transverse multi-level micro-mirror 9 is located on the image-side focal plane of the microlens array 7 and has a stepped structure. The steps are along the x-axis direction, and each step corresponds to a row of microlens units of the microlens array 7. The number of steps is N, and the step height

[0127] The longitudinal multi-level micro-mirror 10 is located on the image-side focal plane of the microlens array 7 and has a stepped structure. The steps are along the y-axis direction, and each step corresponds to a column of microlens units of the microlens array 7. The number of steps is N, and the step height h2 = N × h1.

[0128] Figure 8 Shows a schematic diagram of the multiple imaging optical path of a microlens array for a multi-level micro-mirror according to an embodiment of the present invention.

[0129] Figure 9 Shows a schematic diagram of the optical path difference modulation process of each interference imaging channel in the main ray schematic according to an embodiment of the present invention.

[0130] As Figure 8-9As shown, the interference imaging channel corresponding to the imaging channel O1 of the first step of the multi-level micro-mirror is O4;

[0131] The interference imaging channel corresponding to the imaging channel O2 on the third step of the multi-level micro-mirror is O5;

[0132] The interference imaging channel corresponding to the imaging channel O3 on the fifth step of the multi-level micro-mirror is O6.

[0133] The interference imaging channels R1 corresponding to the first step of the transverse multi-level micro-mirror and the first step of the longitudinal multi-level micro-mirror finally form the interference image unit (1);

[0134] The interference imaging channels R2 corresponding to the third step of the transverse multi-level micro-mirror and the first step of the longitudinal multi-level micro-mirror finally form the interference image unit (3);

[0135] The interference imaging channels R3 corresponding to the fifth step of the transverse multi-level micro-mirror and the first step of the longitudinal multi-level micro-mirror finally form the interference image unit (5);

[0136] The interference imaging channels R4 corresponding to the first step of the transverse multi-level micro-mirror and the third step of the longitudinal multi-level micro-mirror finally form the interference image unit (11);

[0137] The interference imaging channels R5 corresponding to the third step of the transverse multi-level micro-mirror and the third step of the longitudinal multi-level micro-mirror finally form the interference image unit (13);

[0138] The interference imaging channels R6 corresponding to the fifth step of the transverse multi-level micro-mirror and the third step of the longitudinal multi-level micro-mirror finally form the interference image unit (15);

[0139] The interference imaging channels R7 corresponding to the first step of the transverse multi-level micro-mirror and the fifth step of the longitudinal multi-level micro-mirror finally form the interference image unit (21);

[0140] The interference imaging channels R8 corresponding to the third step of the transverse multi-level micro-mirror and the fifth step of the longitudinal multi-level micro-mirror finally form the interference image unit (23);

[0141] The interference imaging channels R9 corresponding to the fifth step of the transverse multi-level micro-mirror and the fifth step of the longitudinal multi-level micro-mirror finally form the interference image unit (25).

[0142] Among them,

[0143] The s-polarized multiple 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 transverse multi-level micromirror 9. The transverse multi-level micromirror 9 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 11 again, it is transformed into a p-polarized multiple image field K6. The p-polarized multiple image field K6 is transmitted through the polarization beam splitter 8 to obtain a p-polarized multiple image field K11. The p-polarized multiple image field K11 is perpendicularly incident on the third quarter-wave plate 13 and then becomes right-handed circularly polarized light K13;

[0144] The p-polarized multiple image field K7 is transmitted through 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 longitudinal multi-level micromirror 10. The longitudinal multi-level micromirror 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 transformed into an s-polarized multiple image field K9. The s-polarized multiple image field K9 is reflected by the polarization beam splitter 8 to obtain an s-polarized multiple image field K10. The s-polarized multiple image field K10 is perpendicularly incident on the third quarter-wave plate 13 and then becomes left-handed circularly polarized light K12.

[0145] The s-polarized multiple image field K10 and the p-polarized multiple image field K11 pass through the third quarter-wave plate 13 at the exit position of the polarization beam splitter 8.

[0146] The third quarter-wave plate 13 is used to transform the p-polarized multiple image field K11 transmitted through the polarization beam splitter 8 into right-handed circularly polarized light K13, and transform the s-polarized multiple image field K10 reflected by the polarization beam splitter 8 into left-handed circularly polarized light K12.

[0147] The s-polarized multiple image field and the p-polarized multiple image field pass through the quarter-wave plate again after being reflected by the multi-level micromirror. Both beams of light pass through the quarter-wave plate twice before returning to the polarization beam splitter. Therefore, it is equivalent to passing through a half-wave plate. So the s-polarized multiple image field becomes a p-polarized multiple image field when returning and is transmitted through the polarization beam splitter 8, while the p-polarized multiple image field becomes an s-polarized multiple image field when returning and is reflected by the polarization beam splitter 8. This enables the returned light beam to be transmitted in the direction of the detector without returning to the incident direction.

[0148] Due to the distributed phase modulation effect of the multi-level micromirror on the multiple image field, the left-handed circularly polarized light K12 and the right-handed circularly polarized light K13 are superimposed and interfere to form a polarization interference image field array K14 with a specific optical path difference distribution characteristic. The polarization interference image field array K14 is incident on the analyzer polarizer 14, and only the light along the polarization direction of the analyzer polarizer 14 can pass through the analyzer polarizer 14.

[0149] The polarization interference image field array 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 14.

[0150] After the linearly polarized light K15 exits from the polarization interference system, it is incident into the imaging system.

[0151] The imaging system includes: a relay imaging lens 15, a narrow-band filter 16, and a planar array detector 17.

[0152] The relay imaging lens 15 has an object-side telecentric optical path structure and is used to image the polarization imaging light field array onto the planar array detector 17.

[0153] The narrow-band 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.

[0154] The planar array detector 17 is located on the image plane of the relay imaging lens 15 and receives the polarization interference image array. The linearly polarized light K15 forms a polarization interference image array on the planar array detector 17 after passing through the relay imaging lens 15 and the narrow-band filter 16.

[0155] By adjusting the transmission axis direction of the analyzer polarizer 14, the initial phase difference between the two coherent light beams from the two multi-stage micro-mirrors is adjusted to zero.

[0156] Let:

[0157] The number of steps of both the transverse multi-stage micro-mirror 9 and the longitudinal multi-stage micro-mirror 10 is N, and the step height of the transverse multi-stage micro-mirror 9 is h1. Then the step height of the longitudinal multi-stage micro-mirror 10 is h2 = N×h1. 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 transverse multi-stage micro-mirror 9 and the n-th step of the longitudinal multi-stage micro-mirror 10 are respectively:

[0158] Δ(m,n) = 2nh2 - 2mh1 = 2(nN - m)h1;

[0159]

[0160] 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-stage micro-mirror 9 should satisfy the relationship

[0161] For the gas spectral line, its bandwidth BW is usually relatively narrow. Therefore, a relatively large step height can be used to sample the interference pattern. At this time, the resolution of the restored spectrum is Therefore, a relatively high spectral resolution can be obtained.

[0162] Select a certain target point corresponding to the above polarization interference image array, and sequentially extract the interference signal I of this target point along the direction of the optical path difference as follows:

[0163]

[0164] Expand the above interference signal I using Euler's formula to obtain:

[0165]

[0166] Therefore, through the modulation of the polarization imaging spectrometer provided by the present invention, the Stokes parameters of the target light field K1 are modulated into 7 parts centered on 0, and to form interference patterns of 7 channels.

[0167] Figure 10 shows a schematic diagram of the interference of Stokes parameter channels according to an embodiment of the present invention.

[0168] Figure 11 shows a schematic diagram of the spectral demodulation process of Stokes parameters according to an embodiment of the present invention.

[0169] As Figure 10-11 shown:

[0170] The central position of the C0 interference pattern channel is at Δ = 0, and it only contains the S0 parameter;

[0171] The central position of the C1 interference pattern channel is at Δ = L2, and it only contains the S2 parameter;

[0172] The central position of the C2 interference pattern channel is at Δ = L2 - L1, and it contains the S1 and S3 parameters;

[0173] The central position of the C3 interference pattern channel is at Δ = L2 + L1, and it contains the S1 and S3 parameters;

[0174] C -1 The central position of the interference pattern channel is at Δ = -L2, and it only contains the S2 parameter;

[0175] C -2 The central position of the interference pattern channel is at Δ = -(L2 - L1), and it contains the S1 and S3 parameters;

[0176] C -3 The central position of the interference pattern channel is at Δ = -(L2 + L1), and it contains the S1 and S3 parameters;

[0177] 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 The channels contain S1 and S3 parameters, and the central positions of the interferogram channels are located at 0, ±L2, ±(L2 - L1), and ±(L2 + L1) respectively.

[0178] The C0 interferogram channel is band-pass filtered, and the passband is located at Δ = [-(L2 - L1) / 2, (L2 - L1) / 2]. After Fourier transform, the spectrum of the S0 parameter is obtained as S0(ν) = 2FT[C0(Δ)];

[0179] The C1 interferogram channel is band-pass filtered, and the passband is located at Δ = [(2L2 - L1) / 2, (2L2 + L1) / 2]. After Fourier transform, the spectrum of the S2 parameter is obtained as S2(ν) = 4FT[C1(Δ)]exp(j2πνL2);

[0180] The C2 interferogram channel is band-pass filtered, and the passband is located at Δ = [(L2 - L1) / 2, (2L2 - L1) / 2]. After Fourier transform, the spectra of the S1 and S3 parameters are as follows:

[0181] S1(ν) = 8Re{FT[C2(Δ)]exp[j2πν(L2 - L1)]}

[0182] S3(ν) = 8Im{FT[C2(Δ)]exp[j2πν(L2 - L1)]}

[0183] By reasonably designing the thickness ratio of the two high-order phase retarders, 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:

[0184] S0(ν) = 2FT[C0(Δ)]

[0185]

[0186]

[0187]

[0188] In the present invention, a birefringent crystal is used as a high-order phase retarder to perform polarization modulation on the target light field, and all Stokes parameters are modulated onto the light intensity signal. At the same time, the multiple imaging of a microlens array and the spatial phase modulation interference technology of a multi-stage micro-mirror are adopted to realize the array imaging of the target light field and the distributed phase modulation of each imaging unit, and an interference image array after polarization modulation of the target scene is obtained. Moreover, a polarization beam splitter and three quarter-wave plates are used to convert the polarization state of the polarized light field, so that all of the target light field enters the detector after passing through the interference system, improving the utilization rate of the light field energy.

[0189] By performing Stokes channel filtering and Fourier transform on the polarization interference image, the synchronous measurement of the target image, spectrum and polarization is realized, expanding the dimension of information detection. The system structure is compact, and at the same time has the characteristics of being static and having 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.

[0190] 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.

[0191] 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 shall be included in the protection scope of the claims of the present invention.

Claims

1. A polarization imaging spectrometer, characterized in that, It successively 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; 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; The polarization modulation system includes: a first high-order phase retarder, a second high-order phase retarder, and a polarizer; The parallel light field successively passes through the first high-order phase retarder and the second high-order phase retarder for polarization modulation to obtain a modulated light field; The modulated light field passes through the polarizer to obtain a linearly polarized light field and is incident on the converging system; The converging system performs multiple imaging on the linearly polarized light field to form a multiple imaging light field array and is incident on the polarization interference system; 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; The polarization beam splitter is used to decompose the multiple imaging light field array into two s-polarized multiple image fields and p-polarized multiple image fields with equal amplitudes and perpendicular vibration directions; Wherein, The s-polarized multiple image field is reflected by the polarization beam splitter and becomes 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 returns along the original path. After passing through the first quarter-wave plate again, it is transformed into a p-polarized multiple image field. The p-polarized multiple image field is transmitted through the polarization beam splitter to obtain a p-polarized multiple image field. The p-polarized multiple image field is vertically incident on the third quarter-wave plate and is transformed into right-handed circularly polarized light; The p-polarized multiple image field is transmitted through the polarization beam splitter and becomes 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 returns along the original path. After passing through the second quarter-wave plate again, it is transformed into an s-polarized multiple image field. The s-polarized multiple image field is reflected by the polarization beam splitter to obtain an s-polarized multiple image field. The s-polarized multiple image field is vertically incident on the third quarter-wave plate and is transformed into left-handed circularly polarized light; The third quarter-wave plate is used to transform the p-polarized multiple image field transmitted through the polarization beam splitter into right-handed circularly polarized light, and transform the s-polarized multiple image 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 polarization interference image field array with a specific optical path difference distribution characteristic and are incident on the analyzer; The polarization interference image field array passes through the analyzer to obtain linearly polarized light and is incident on the imaging system to obtain a polarization interference image array; 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.

2. The polarization imaging spectrometer according to claim 1, wherein The telescopic system includes: a telescopic objective lens, a field stop, and a collimating mirror; 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 also on the object-side focal plane of the collimator lens, 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 lens; the collimator lens is located on the object-side focal plane of the converging system.

3. The polarization imaging spectrometer according to claim 2, wherein The fast axis direction of the first high-order phase retarder makes an angle of 45° with the positive x-axis direction. The fast axis direction of the second high-order phase retarder is along the positive x-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 direction of the transmission axis of the polarizer polarizing plate makes an angle of 45° with the positive x-axis direction.

4. The polarization imaging spectrometer according to claim 3, wherein After the parallel light field passes through the polarization modulation system, all the 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 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 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; Then: The optical path difference of the light emitted by the first high-order phase retarder is L1 = (n e - n o )d1, and the phase retardation amount is The optical path difference of the light emitted from the second high-order phase retarder is L2 = (n e - n o )d2, and the phase retardation amount is The Stokes parameter S of the linearly polarized light field out is as follows: Therefore, the S0' parameter in the linearly polarized light field 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 polarization imaging spectrometer according to claim 4, wherein The converging system includes: a microlens array, which is composed of an equal number of row microlens units and column microlens units, and is used for multi-channel imaging of the linearly polarized light field.

6. The polarization imaging spectrometer according to claim 5, characterized in that, The fast axis directions of the first quarter-wave plate, the second quarter-wave plate, and the third quarter-wave plate make an angle of 45° with the x-axis, and they are all birefringent crystals, and the crystal materials are quartz, calcite, magnesium fluoride, yttrium vanadate or barium metaborate.

7. The polarization imaging spectrometer according to claim 6, wherein The transverse multi-level micro-mirror is located on the image-side focal plane of the microlens array, has a stepped structure, the steps are along the x-axis direction, and each step corresponds to a row of microlens units of the microlens array. The longitudinal multi-level micro-mirror is located on the image-side focal plane of the microlens array, has a stepped structure, the steps are along the y-axis direction, and each step corresponds to a column of microlens units of the microlens array.

8. The polarization imaging spectrometer according to claim 7, wherein, The imaging system includes: a relay imaging lens, a narrowband filter, and a planar array detector. The relay imaging lens has an object-side telecentric optical path structure and is used to image the polarization imaging light field array onto the planar array detector. The narrowband filter is used to filter the spectrum of the light field. The planar array detector is located on the image plane of the relay imaging lens and is used to receive the polarization interference image array. The linearly polarized light forms a polarization interference image array on the planar array detector after passing through the relay imaging lens and the narrowband filter.

9. The polarization imaging spectrometer according to claim 8, characterized in that, The process of extracting the interferogram 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 h1, then the step height of the vertical multi-level micro-mirror is h2 = N×h1, so as to obtain the optical path difference Δ and the phase difference 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 They are respectively: Δ(m,n) = 2nh2 - 2mh1 = 2(nN - m)h1; Select a certain target point corresponding to the polarization interference image array, and sequentially extract the interferogram signal I of this target point along the direction of the optical path difference as:

10. The polarization imaging spectrometer according to claim 9, wherein Use Euler's formula to expand the interferogram signal I to obtain: Therefore, the Stokes parameters of the target optical field are modulated into interference patterns of seven channels centered on 0, and Each channel contains information on one or two Stokes parameters; Among them, the C0 channel only contains the S0 parameter, and the C ±1 channel only contains the S2 parameter, and the C ±2 and the C ±3 channel contains the S1 and S3 parameters, and the central positions of the interferogram channels are located at 0, ±L2, ±(L2 - L1), and ±(L2 + L1) respectively; Perform band-pass filtering on the C0 interferogram channel. The passband is located at Δ = [-(L2 - L1) / 2, (L2 - L1) / 2]. After Fourier transform, the spectrum of the S0 parameter is S0(ν) = 2FT[C0(Δ)]; Perform band-pass filtering on the C1 interferogram channel. The passband is located at Δ = [(2L2 - L1) / 2, (2L2 + L1) / 2]. After Fourier transform, the spectrum of the S2 parameter is S2(ν) = 4FT[C1(Δ)]exp(j2πνL2); Perform band-pass filtering on the C2 interferogram channel. The passband is located at Δ = [(L2 - L1) / 2, (2L2 - L1) / 2]. After Fourier transform, the spectra of the S1 and S3 parameters are: S1(ν) = 8Re{FT[C2(Δ)]exp[j2πν(L2 - L1)]} S3(ν) = 8Im{FT[C2(Δ)]exp[j2πν(L2 - L1)]} 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. Three independent channels are selected to perform Fourier transform on the interference pattern signal I to obtain the spectral information of the four Stokes parameters of the target optical field: S0(ν) = 2FT[C0(Δ)]

Images