ridge-step fabry-perot interferometric imaging spectrometer

Abstract

The present application relates to the field of spectral imaging, and especially to a ridge stepped Fabry-Perot interferometric imaging spectrometer, comprising a scanning mirror, a telescope objective, a Fabry-Perot array interference system and a detection system, the scanning mirror is located on the object focal plane of the telescope objective, and performs lateral push scanning on a target light field; the telescope objective adopts an image far field optical path structure, and is used for collecting the target light field and imaging the target light field in an FP resonant cavity of the Fabry-Perot array interference system; the Fabry-Perot array interference system is located on the image focal plane of the telescope objective, and comprises parallel plates and a ridge stepped mirror, the step height of the ridge stepped mirror is in a decreasing distribution from the middle to both sides; the detection system is located in the exit direction of the Fabry-Perot array interference system, and is used for imaging the interference light field modulated by the Fabry-Perot array interference system to obtain an interference image array. The present application has the advantages of small volume, light weight, compact structure, static state, stability, reliability and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of spectral imaging technology, and particularly relates to a ridge stepped Fabry-Perot interferometric imaging spectrometer. BACKGROUND

[0002] Fourier transform spectroscopy is a widely used measurement method for obtaining the infrared spectrum of a target scene, and has a very wide range of applications, extending from the laboratory to remote sensing. Most Fourier transform spectrometers use a time-modulated Michelson interferometer system, measure the time-modulated interference signal generated by the interaction of the incident spectrum with the Michelson interferometer system, and perform spectral demodulation by Fourier transform. In the Fourier transform infrared spectrometer based on the Michelson interferometer system, a moving mirror is used to time-sample the interference pattern, and the moving mirror generates a time-varying optical path difference between the two beams by splitting the input beam. Under monochromatic light illumination, the response of the detector to this time-varying optical path difference is a sinusoidal signal that varies with the optical path difference. By accurately measuring the change in the optical path difference, the wavelength information of the incident light is recovered from the sampled interference signal, usually using a reference laser signal. Illumination with multiple wavelengths produces a combined interference pattern that is added together, and the intensity of each wavelength, i.e. the spectral information, can be recovered using Fourier transform. Since the Fourier transform spectrometer based on the Michelson interferometer system requires a beam splitter for beam splitting and combining of the incident light, and a high-precision precision moving mirror scanning mechanism for control of the optical path difference, the Fourier transform spectrometer based on the Michelson interferometer system has a large volume, a heavy weight, a high integration difficulty and is extremely susceptible to external environmental influences, making it difficult to meet the application requirements of new technologies such as unmanned aerial vehicle on-board and micro-nano satellite on-board.

[0003] The Fabry-Perot interferometer system has the advantages of compact structure, small volume and light weight compared to the Michelson interferometer system, and is therefore particularly suitable for application requirements such as unmanned aerial vehicle on-board and micro-nano satellite on-board. Traditional Fabry-Perot interferometer systems are usually used as very narrow bandpass filters, and narrow-band filtering is achieved by using very high reflectivity coatings. If the Fabry-Perot cavity surface uses a lower reflectivity coating, the spectral transmission is essentially sinusoidal, and the spectrum can be recovered by Fourier transform. However, too low a coating reflectivity will result in a reduction in fringe contrast, leading to interference failure. SUMMARY

[0004] In view of the above, the present application aims to provide a ridge stepped Fabry-Perot interferometric imaging spectrometer to solve the technical problems of the existing Fourier transform spectrometer based on the Michelson interferometer system, which has a large volume, a heavy weight, a high integration difficulty and is extremely susceptible to external environmental influences.

[0005] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0006] A roof ladder Fabry-Perot interferometric imaging spectrometer, comprising a scanning mirror, a telescope, a Fabry-Perot array interference system and a detection system; wherein,

[0007] The scanning mirror is located on the object focal plane of the telescope and performs lateral push scanning on the target light field.

[0008] The telescope adopts an image-side telecentric optical path structure and is used for collecting the target light field and imaging the target light field in the FP resonant cavity of the Fabry-Perot array interference system.

[0009] The Fabry-Perot array interference system is located on the image-side focal plane of the telescope, and the Fabry-Perot array interference system comprises a parallel plate and a roof ladder mirror, the parallel plate serving as a front interference plate of the Fabry-Perot array interference system, and the roof ladder mirror serving as a rear interference plate of the Fabry-Perot array interference system, the step heights of the roof ladder mirror decreasing from the middle to both sides, the step height difference between any two adjacent steps of the roof ladder mirror being the same, and the highest step in the middle of the roof ladder mirror being closely attached to the parallel plate, so that the parallel plate and the roof ladder mirror form an air gap with a step change in thickness, the thickness of each region of the air gap corresponding to an optical path difference, and the parallel plate, the air gap and the roof ladder mirror forming an FP resonant cavity array.

[0010] The detection system is located in the exit direction of the Fabry-Perot array interference system and is used for imaging the interference light field modulated by the Fabry-Perot array interference system to obtain an interference image array.

[0011] Further, the two surfaces of the parallel plate opposite to the roof ladder mirror respectively serve as reflective interfaces, and the two reflective interfaces and the air gap form FP resonant cavities, and the reflectivity of the two reflective interfaces is 30% to 40%.

[0012] Further, the parallel plate adopts a high-refractive plate, a antireflection film is deposited on the surface of the high-refractive plate away from the roof ladder mirror, and the surface of the high-refractive plate toward the roof ladder mirror is not coated, or the parallel plate adopts a low-refractive plate, an antireflection film is deposited on the surface of the low-refractive plate away from the roof ladder mirror, and a high-refractive dielectric film is deposited on the surface of the low-refractive plate toward the roof ladder mirror and serves as a reflective interface of the FP resonant cavity.

[0013] Further, the high-refractive plate adopts a silicon or germanium dielectric material, and the low-refractive plate adopts a quartz, calcium fluoride, magnesium fluoride or sapphire dielectric material.

[0014] Further, the roof-shaped stepped mirror comprises stepped bases, the stepped bases are made of high refractive index medium, the upper surface of the stepped base of the high refractive index medium is not coated and serves as the reflection interface of the FP resonant cavity, and the lower surface of the stepped base of the high refractive index medium is coated with an anti-reflection film; or, the stepped bases are made of low refractive index medium, the upper surface of the stepped base of the low refractive index medium is coated with a high refractive index medium film and serves as the reflection interface of the FP resonant cavity, and the lower surface of the stepped base of the low refractive index medium is coated with an anti-reflection film.

[0015] Further, the low refractive index medium is made of quartz, calcium fluoride, magnesium fluoride or sapphire medium material; the high refractive index medium is made of silicon or germanium medium material; and the high refractive index medium film is made of silicon film or germanium film.

[0016] Further, the height difference of the steps between any two adjacent steps on the roof-shaped stepped mirror is d, the thickness of the air gap corresponding to the first step is m h m

[0017] .

[0018] Further, for the incident broadband spectrum, the height difference d of the steps satisfies the following relationship:

[0019] ;

[0020] wherein λ min is the minimum wavelength of the broadband spectrum, θ max is the corresponding incident angle of the light ray in the FP resonant cavity at the maximum field of view angle, J is the spectral harmonic order, and n0 is the refractive index of the medium in the FP resonant cavity.

[0021] For the incident narrowband spectrum, the height difference d of the steps satisfies the following relationship:

[0022] ;

[0023] wherein λ S is the shortest wavelength of the narrowband spectrum, λ L is the longest wavelength of the narrowband spectrum, k is the spectral folding order, and is any integer less than or equal to .

[0024] Further, assuming that the step number of the roof-shaped stepped mirror is 2M, the preparation process of the stepped base is as follows:

[0025] S1: providing a planar base with a lateral width of 2a and a longitudinal width of 2a, and polishing and cleaning the planar base;

[0026] ​​​S2: two-way etching is performed on the planar substrate to form a two-step structure, the two-way etching depth is Md / 2, and the two-way etching width is a / 2;

[0027] S3: two-way etching is performed on the two-step structure to form a four-step structure, the two-way etching depth is Md / 4, and the two-way etching width is a / 4, step S3 is repeated, the depth and width of each two-way etching are ensured to be 1 / 2 of the last etching, until the step height difference is d and the step width is a / M.

[0028] Further, the detection system comprises a relay imaging mirror, a cold screen diaphragm and a surface array detector; wherein,

[0029] The relay imaging mirror is located in the exit direction of the Fabry-Perot array interference system, the relay imaging mirror adopts an object far field optical path structure, and is used for imaging the interference light field modulated by the reflective Fabry-Perot standard array to the surface array detector;

[0030] The cold screen diaphragm is located on the image side focal plane of the relay imaging mirror, and is used for limiting the object side numerical aperture;

[0031] The surface array detector is located at the image plane of the relay imaging mirror, and is used for photoelectric conversion of the interference light field to obtain an interference image array.

[0032] Further, a scanning mirror is used to linearly push scan the target light field along the step direction perpendicular to the ridge-shaped step mirror, the scanning step length of the scanning mirror is a field of view corresponding to a step width of the ridge-shaped step mirror, after completing a period of push scanning, an interference image data cube is obtained; the interference image data cube is cut along the step direction of the ridge-shaped step mirror to obtain interference image units corresponding to different interference orders, the interference image units corresponding to different time points of the zero optical path difference step are spliced in spatial order to obtain a panoramic image of the target, and the interference image units corresponding to different steps of the target are spliced in optical path difference order to obtain an interference image sequence of the target and perform discrete Fourier transform operation to obtain a restored spectrum.

[0033] Compared with the prior art, the application can achieve the following beneficial effects:

[0034] The ridge-shaped stepped mirror with low reflectivity is used to construct the Fabry-Perot array interference system, the beam splitter and the precise dynamic mirror scanning mechanism in the traditional Fourier transform imaging spectrometer are replaced, the optical and mechanical structure of the Fourier transform imaging spectrometer is simplified and lightened, the stability and robustness of the Fourier transform imaging spectrometer are improved, and the Fourier transform imaging spectrometer has the advantages of small size, light weight, compact structure, static, stable and reliable, etc.. Meanwhile, the incidence interface of the ridge-shaped stepped mirror adopts low reflectivity, the difficulty of spectrum recovery of the traditional Fabry-Perot interference system is reduced, the coupling modulation transmission of the light field is realized through the Fabry-Perot array interference system, the synchronous measurement of the interference image sequence is realized, and then the snapshot effective detection of the target scene image information and the spectrum information is realized, and the real-time of multi-dimensional information detection is improved. BRIEF DESCRIPTION OF DRAWINGS

[0035] The drawings constituting a part of this application provide a further understanding of the present application, the schematic embodiments of the present application and the description thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1 It is a structural schematic diagram of the ridge-shaped stepped Fabry-Perot interference imaging spectrometer according to the embodiment 1 of the present application.

[0037] Figure 2 It is a structural schematic diagram of the Fabry-Perot array interference system according to the embodiment 1 of the present application.

[0038] Figure 3 It is a structural schematic diagram of the ridge-shaped stepped mirror according to the embodiment 1 of the present application.

[0039] Figure 4 It is a preparation flowchart of the stepped base according to the embodiment 1 of the present application.

[0040] Figure 5 It is a collection process diagram of the interference image array according to the embodiment 1 of the present application.

[0041] Figure 6 It is a structural schematic diagram of the ridge-shaped stepped mirror according to the embodiment 2 of the present application.

[0042] The reference signs of the embodiment 1 are as follows: scanning mirror 10, telescope objective 20, parallel plate 30, ridge-shaped stepped mirror 40, stepped base 401, anti-reflection film 402, relay imaging mirror 50, cold shield diaphragm 60, and area array detector 70.

[0043] The reference signs of the embodiment 2 are as follows: stepped base 403, anti-reflection film 404, and high-refractive-index dielectric film 405. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is 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 and do not constitute a limitation of the present invention.

[0045] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0046] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0047] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0048] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0049] The present invention provides a roof-step Fabry-Perot interferometer imaging spectrometer, comprising a scanning reflector, a telescope objective lens, a Fabry-Perot array interferometer system and a detection system; wherein,

[0050] The scanning mirror is located on the object side focal plane of the telescope objective, and performs lateral push scanning on the target light field; the telescope objective adopts an image side telecentric optical path structure, and is used for collecting the target light field and imaging the target light field in the FP resonant cavity of the Fabry-Perot array interference system; the Fabry-Perot array interference system is located on the image side focal plane of the telescope objective, and the Fabry-Perot array interference system comprises a parallel plate and a hipped roof mirror, the parallel plate is used as the front interference plate of the Fabry-Perot array interference system, and the hipped roof mirror is used as the rear interference plate of the Fabry-Perot array interference system, the step height of the hipped roof mirror is arranged in a decreasing manner from the middle to both sides, the step height difference between any two adjacent steps of the hipped roof mirror is the same, the highest step in the middle of the hipped roof mirror is tightly attached to the parallel plate, so that the air gap with a step change in thickness is formed between the parallel plate and the hipped roof mirror, the thickness of each region of the air gap corresponds to an optical path difference, and the parallel plate, the air gap and the hipped roof mirror form the FP resonant cavity array; the detection system is located in the exit direction of the Fabry-Perot array interference system, and is used for imaging the interference light field modulated by the Fabry-Perot array interference system to obtain an interference image array.

[0051] The detection system comprises a relay imaging mirror, a cold screen diaphragm and a face array detector; wherein the relay imaging mirror is located in the exit direction of the Fabry-Perot array interference system, the relay imaging mirror adopts an object side telecentric optical path structure, and is used for imaging the interference light field modulated by the reflective Fabry-Perot standard array to the face array detector; the cold screen diaphragm is located on the image side focal plane of the relay imaging mirror, and is used for limiting the object side numerical aperture; and the face array detector is located at the image plane of the relay imaging mirror, and is used for photoelectric conversion of the interference light field to obtain an interference image array.

[0052] The target light field enters a telescope objective through a scanning mirror, the telescope objective adopts an image-side telecentric optical path structure, and the telescope objective images the target light field into a Fabry-Perot array interference system based on a roof-shaped echelon mirror. The Fabry-Perot array interference system is composed of a parallel flat plate and a roof-shaped echelon mirror, and the Fabry-Perot resonant cavity with a roof-shaped step change in thickness is formed by the close contact between the intermediate step surface of the parallel flat plate and the roof-shaped echelon mirror. The parallel flat plate and the roof-shaped echelon mirror are made of silicon or germanium materials with high refractive index, so that the reflection interfaces on both sides of the Fabry-Perot resonant cavity have a low reflectivity, thereby forming a low-fineness Fabry-Perot interferometer, so that the spectrum can be demodulated by Fourier transform. The roof-shaped echelon mirror structure causes the thickness of the Fabry-Perot resonant cavity to change discretely and linearly, and different thicknesses of the Fabry-Perot resonant cavity correspond to different optical path differences, so that the target light field forms an image modulated by interference fringes after passing through the Fabry-Perot array interference system. The modulated interference light field is imaged onto a surface array detector through a relay imaging mirror. The relay imaging mirror adopts an object-side telecentric optical path structure and is cold-stop matched with the cold shield diaphragm of the surface array detector. The scanning mirror is used to scan the target light field along the step direction perpendicular to the roof-shaped echelon mirror, and the scanning step is the field of view corresponding to one step width, so that an interference image data cube is obtained. By splicing the interference image units corresponding to different time instants at the zero optical path difference step, a panoramic image of the target is obtained; by splicing the interference image units corresponding to different steps of the same target, an interference image sequence of the target is obtained, and the spectrum information of the target is demodulated by performing discrete Fourier transform on the interference image sequence. The present application reduces the size of the Fourier transform infrared imaging spectrometer, has the advantages of compact structure, static, stable, reliable and the like.

[0053] Embodiment 1

[0054] As Figures 1-5 shown, the roof echelon Fabry-Perot interferometric imaging spectrometer provided by the embodiment 1 of the present application includes a scanning mirror 10, a telescope objective 20, a parallel flat plate 30, a roof-shaped echelon mirror 40, a relay imaging mirror 50, a cold shield diaphragm 60, and a surface array detector 70 (using HgCdTe or InSb devices).

[0055] The target light field first enters the telescope objective 20 through the scanning mirror 10. The telescope objective 20 adopts an image-side telecentric optical path structure. The target light field is imaged to a Fabry-Perot array interference system based on a roofed echelon mirror through the telescope objective 20, and is modulated into an interference light field. The Fabry-Perot array interference system is composed of a parallel flat plate 30 and a roofed echelon mirror 40. The parallel flat plate 30 is tightly attached to the roof surface (i.e. the middle step surface) of the roofed echelon mirror 40, so that an air gap with a gradually increasing thickness from the middle to both sides is formed between the parallel flat plate 30 and the roofed echelon mirror 40. Therefore, the interference signal is a function of the spatial position, and the zero optical path difference is achieved at the optical contact position of the parallel flat plate 30 and the roofed echelon mirror 40.

[0056] The two surfaces of the roofed echelon mirror 40 opposite to the parallel flat plate 30 serve as reflective interfaces and form distributed FP resonant cavities with the air gap. Each FP resonant cavity has a specific thickness, thereby having a fixed optical path difference. The light incident on the two reflective interfaces of the FP resonant cavity will be reflected multiple times in the FP resonant cavity, and interference will occur between the beams passing through the FP resonant cavity different times. The intensity of the interference signal of the light beam out of the FP resonant cavity depends on the thickness of the air gap between the two reflective interfaces, the reflectivity of the reflective interfaces, the light incidence angle, and the refractive index of the medium in the FP resonant cavity between the two reflective interfaces. The medium in the FP resonant cavity can be air or vacuum, or a low refractive index medium. The embodiment of the present application is implemented by using air. The reflective interfaces of the conventional Fabry-Perot interference system usually have very high reflectivity to generate a narrow transmission band, while the reflective interfaces of the Fabry-Perot array interference system in the present application have medium reflectivity to generate quasi-cosine interference signals that can be demodulated by Fourier transform.

[0057] The interference image signal formed by the FP resonant cavity corresponding to the mth step in the roofed echelon mirror 40 of the Fabry-Perot array interference system can be expressed as:

[0058] ;

[0059] wherein R1 and R2 are the reflectivities of the two reflective interfaces of the FP resonant cavity; v is the wave number, v = 1 / λ, λ is the wavelength, is the optical path difference of the FP resonant cavity corresponding to the mth step, and its expression is:

[0060] ;

[0061] wherein n0 is the refractive index of the medium in the FP resonant cavity, and n0 = 1 when the FP resonant cavity is filled with air; θ is the incidence angle of the light in the FP resonant cavity, corresponding to the field angle of the target scene; The gap thickness of the FP resonant cavity, due to the step structure, the gap thickness of the FP resonant cavity varies with the spatial position.

[0062] As can be seen from the interference image signal formula, when the reflectivity of the reflection interface is very low, the interference signal is a cosine function, but the modulation degree of the interference fringes is also very low;When the reflectivity of the reflection interface is very high, the interference fringes have very high modulation degree, but the interference signal is very narrow comb function. The traditional Fabry-Perot interferometer adopts a reflection interface with very high reflectivity, and uses resonance to generate very narrow interference characteristics. The Fourier transform spectrum of these very narrow comb-shaped interference signals will produce side lobes, which will take away the signal from the main frequency, causing the recovered spectrum to be distorted. In order to suppress the spectral distortion caused by harmonic signals and reduce the interference caused by the extension of side lobe signals to the main frequency signal, the maximum wave number of the incident spectrum should be less than or equal to twice the minimum wave number, that is, the maximum wavelength is less than or equal to twice the minimum wavelength, that is, the wavelength bandwidth of the incident spectrum is less than or equal to the minimum wavelength, or less than or equal to half of the maximum wavelength. For short-wave infrared 1-2 μm, medium-wave infrared 3-5 μm, long-wave infrared 8-14 μm, the application requirements can basically be met.

[0063] Therefore, the present application adopts a reflection interface with medium reflectivity to generate a cosine-like interference signal, at this time the spectral precision is low, and the roof-shaped step mirror 40 is close to double-beam interference, and the interference function can be approximately expressed as:

[0064] ;

[0065] Therefore, the spectral information of the incident light signal can be recovered from the interference signal by Fourier transform.

[0066] Although the lower the reflectivity, the closer the interference signal to the cosine function, and the higher the spectral recovery accuracy, but too low reflectivity will also reduce the modulation degree of the interference fringes, therefore, in order to realize effective demodulation of the spectrum by Fourier transform, the modulation degree of the fringes and the suppression of the spectral side lobes need to be balanced. By balancing the modulation degree of the interference pattern and the cosine degree of the interference signal, the reflectivity of the reflection interface is determined to minimize the spectral side lobes and maximize the modulation degree of the interference pattern. That is, by optimizing the reflectivity of the reflection interface, the maximum balance between the modulation degree of the interference fringes and the cosine characteristics is achieved. In the present application, the reflectivity of the two reflection interfaces of the FP resonant cavity is set to 30%-40%, which can achieve the best balance between the modulation degree of the interference pattern and the cosine characteristics. Therefore, each FP resonant cavity in the present application is a low-precision Fabry-Perot cavity that modulates the interference intensity of the interference pattern under a given optical path difference.

[0067] For infrared materials, silicon and germanium materials have high refractive index, thus have moderate reflectivity. For silicon material, its refractive index is 3.4, and the surface reflectivity is 30%; for germanium material, its refractive index is 4.0, and the surface reflectivity is 36%. Therefore, the parallel plate 30 is made of high refractive index medium such as silicon or germanium, and an antireflection film is evaporated on the surface of the parallel plate 30 facing away from the ridge-shaped echelon mirror 40, while the surface of the parallel plate 30 facing toward the ridge-shaped echelon mirror 40 is not coated. The step base 401 can be made of high refractive index medium such as silicon or germanium, and the surface of the step base 401 facing toward the parallel plate 50 is not coated, so that the reflection interface has low reflectivity to achieve low fineness, and an antireflection film 402 is evaporated on the surface of the step base 401 facing away from the parallel plate 50 to ensure high transmittance. The step (i.e. the ridge surface) in the middle of the step base 401 is in contact with the uncoated side of the parallel plate 30, and zero optical path difference is achieved on the optical contact surface.

[0068] An air gap with thickness increasing from the middle to both sides is formed between the ridge-shaped echelon mirror 40 and the parallel plate 30, thereby constituting a spatial distribution modulation of optical path difference. The ridge-shaped echelon mirror 40 adopts a symmetrical echelon structure, with a ridge in the middle and steps decreasing in turn on both sides. The height of each step is complementary to the thickness of the air gap of the FP resonant cavity. Assuming that the height difference of the echelon of the ridge-shaped echelon mirror 40 is d, and the height of the mth step is ±md, then the thickness of the FP resonant cavity corresponding to the mth step is ±md, i.e. the gap thickness of the mth step of the FP resonant cavity is:

[0069] .

[0070] In order to achieve effective spectral restoration, the echelon height difference d should satisfy the Nyquist sampling theorem. In order to suppress the spectral aliasing caused by Fourier transform of high-order side lobe signals, the cut-off frequency of the sampled signal is expanded to J times the harmonic order (generally, J 3 can meet the requirements). For the incident broadband spectrum, the echelon height difference d should satisfy the following relationship:

[0071] ;

[0072] wherein λ min is the minimum wavelength of the broadband spectrum, θ max is the incident angle of the light ray corresponding to the maximum field of view angle in the FP resonant cavity, J is the spectral harmonic order, and n0 is the refractive index of the medium in the FP resonant cavity.

[0073] For the incident narrowband spectrum, especially for gas detection, in order to achieve high spectral resolution, the echelon height difference d should satisfy the following relationship:

[0074] ;

[0075] wherein λ S is the shortest wavelength of the narrowband spectrum, λ L is the longest wavelength of the narrowband spectrum, k is the spectral folding order, taking any integer less than or equal to .

[0076] The step base 401 is composed of 2M steps, the height difference between any two adjacent steps on the step base 401 is constant d, and the step base 401 is manufactured by etching, and the manufacturing process is as follows:

[0077] S1: providing a planar substrate with a lateral width of 2a and a longitudinal width of 2a, and polishing and cleaning the planar substrate.

[0078] S2: forming a two-step structure on the planar substrate by bidirectional etching, the bidirectional etching depth is Md / 2, and the bidirectional etching width is a / 2.

[0079] S3: forming a four-step structure on the two-step structure by bidirectional etching, the bidirectional etching depth is Md / 4, and the bidirectional etching width is a / 4, repeating step S3, ensuring that the depth and width of each bidirectional etching are 1 / 2 of the last etching, until the step height difference is d and the step width is a / M, thereby completing the manufacture of the ridge-shaped stepped mirror with a step height of ±d and a step number of 2M.

[0080] The interference light field modulated by the Fabry-Perot array interference system is the superposition of the target scene and the interferometer fringes, and a relay imaging mirror 50 is used to image the interference light field onto a plane array detector 70 with a certain reduction ratio. The relay imaging mirror 50 samples the object far field optical path structure, and its image focal plane matches the cold shield diaphragm 60 of the plane array detector 70. That is, the cold shield diaphragm 60 of the plane array detector 70 is located on the image focal plane of the relay imaging mirror 50. The single-frame interferogram collected by the Fourier transform imaging spectrometer based on the ridge-shaped stepped FP cavity array is a panoramic image modulated by different interference orders, which contains both two-dimensional image information and one-dimensional interference information.

[0081] As shown in Figure 5 , t1-t7 correspond to different time points, A-G correspond to different targets, and different squares correspond to different optical path differences, i.e., different steps, and the middle column of squares correspond to zero optical path difference. The scanning direction of the scanning mirror 10 is perpendicular to the step direction, and the field of view is stepped by one step width each time.

[0082] The target light field is linearly pushed and scanned using the scanning reflector 10 along the step direction perpendicular to the ridge-shaped step mirror 40 to acquire an interference image sequence. The scanning step size is set to the field of view corresponding to the width of one step of the ridge-shaped step mirror 40. Then, each time a step scan is performed, the intermediate image point on each step of the ridge-shaped step mirror 40 will move to the corresponding position on the adjacent step. After one scanning cycle, the intermediate image field of each object point in the target light field will traverse each step in the opposite direction of the push-scan direction, thereby forming an interference image data cube. Each frame of the collected interference image is cut into interference image units corresponding to different interference levels along the step direction; the interference image units corresponding to the zero optical path difference step at different times are spliced ​​in spatial order to obtain a panoramic image of the target; and the interference image units corresponding to different steps of the same target are spliced ​​in order of optical path difference to obtain an interference image sequence. By performing a discrete Fourier transform operation on the interference image sequence, the restored spectral information of each object point can be demodulated.

[0083] Example 2

[0084] The difference between Example 2 and Example 1 is only that the structure of the roof-shaped stepped mirror is different, such as Figure 6 As shown, the step base 403 of the roof-shaped step mirror of Example 2 is made of a low-refractive-index transparent dielectric material such as quartz, calcium fluoride, magnesium fluoride, or sapphire to ensure a high transmittance at the interface. A high-refractive-index dielectric film 405 such as silicon or germanium is evaporated on the step surface of the step base 403 so that the reflective interface has a medium-low reflectivity to achieve low finesse. An anti-reflection film 404 is evaporated on the lower surface (i.e., the bottom plane) of the step base 403 to ensure high transmittance.

[0085] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0086] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A roof-staircase Fabry-Perot interferometric imaging spectrometer, characterized in that, The system comprises a scanning mirror, a telescope, a Fabry-Perot array interference system and a detection system. The scanning mirror is located on the object focal plane of the telescope and performs lateral push scanning on the target light field. The telescope adopts an image-side telecentric optical path structure and is used for collecting the target light field and imaging the target light field in the FP resonant cavity of the Fabry-Perot array interference system. The Fabry-Perot array interference system is located on the image focal plane of the telescope and comprises a parallel plate and a hipped stepped mirror. ； where λ min is the minimum wavelength of the broadband spectrum, θ max is the corresponding incidence angle of the maximum field of view angle light in the FP resonant cavity, J is the spectral harmonic order, and n0 is the refractive index of the medium in the FP resonant cavity. The parallel plate is used as the front interference plate of the Fabry-Perot array interference system, and the hipped stepped mirror is used as the rear interference plate of the Fabry-Perot array interference system. ； where λ S is the shortest wavelength of the narrowband spectrum, λ L is the longest wavelength of the narrowband spectrum, k is the spectral folding order, taking any integer less than or equal to ​ The step height of the hipped stepped mirror decreases from the middle to both sides.

2. The roof-staircase Fabry-Perot imaging spectrometer of claim 1, wherein, The step height difference between any two adjacent steps of the hipped stepped mirror is the same.

3. The roof-staircase Fabry-Perot imaging spectrometer of claim 2, wherein, The highest step in the middle of the hipped stepped mirror is closely combined with the parallel plate, so that the air gap with a step change in thickness is formed between the parallel plate and the hipped stepped mirror.

4. The roof-staircase Fabry-Perot imaging spectrometer of claim 1, wherein, The thickness of each region of the air gap corresponds to an optical path difference.

5. The roof-staircase Fabry-Perot imaging spectrometer of claim 1 wherein, The thickness of the air gap corresponding to the first step is d. m The thickness of the air gap corresponding to the first step is d. h m The thickness of the air gap corresponding to the first step is d.​ 。 6. The roof-staircase Fabry-Perot imaging spectrometer of claim 1, wherein, The parallel plate, the air gap and the hipped stepped mirror form the FP resonant cavity array. The two surfaces of the parallel plate and the hipped stepped mirror opposite to each other are used as the reflecting interfaces. The two reflecting interfaces and the air gap form the FP resonant cavity. The reflectivity of the two reflecting interfaces is 30%-40%. The step base of the hipped stepped mirror adopts a high refractive index medium. The upper surface of the step base of the high refractive index medium is not coated and is used as the reflecting interface of the FP resonant cavity. The lower surface of the step base of the high refractive index medium is coated with an antireflection film. Alternatively, the step base adopts a low refractive index medium. The upper surface of the step base of the low refractive index medium is coated with a high refractive index film and is used as the reflecting interface of the FP resonant cavity. The lower surface of the step base of the low refractive index medium is coated with an antireflection film. For the incident broadband spectrum, the step height difference d satisfies the following relationship: For the incident narrowband spectrum, the step height difference d satisfies the following relationship: The detection system is located in the exit direction of the Fabry-Perot array interference system and is used for imaging the interference light field modulated by the Fabry-Perot array interference system to obtain an interference image array. The parallel plate adopts a high refractive index plate. The surface of the high refractive index plate away from the hipped stepped mirror is coated with an antireflection film. The surface of the high refractive index plate toward the hipped stepped mirror is not coated. Alternatively, the parallel plate adopts a low refractive index plate. The surface of the low refractive index plate away from the hipped stepped mirror is coated with an antireflection film. The surface of the low refractive index plate toward the hipped stepped mirror is coated with a high refractive index film and is used as the reflecting interface of the FP resonant cavity. The high refractive index plate adopts a silicon or germanium medium material. The low refractive index plate adopts a quartz, calcium fluoride, magnesium fluoride or sapphire medium material. The high refractive index medium adopts a silicon or germanium medium material. The high refractive index film adopts a silicon film or a germanium film. Supposing that the step number of the hipped stepped mirror is 2M, the preparation process of the step base is as follows: S1: providing a planar base with a lateral width of 2a and a longitudinal width of 2a and polishing and cleaning the planar base; S2: performing bidirectional etching on the planar substrate to form a two-step structure, the bidirectional etching depth being Md / 2 and the bidirectional etching width being a / 2; S3: performing bidirectional etching on the two-step structure to form a four-step structure, the bidirectional etching depth being Md / 4 and the bidirectional etching width being a / 4, repeating step S3 to ensure that the depth and width of each bidirectional etching are 1 / 2 of the previous etching until the step height difference is d and the step width is a / M.

7. The roof-staircase Fabry-Perot imaging spectrometer of claim 1, wherein, The detection system comprises a relay imaging mirror, a cold screen diaphragm and a face array detector, wherein, The relay imaging mirror is located in the exit direction of the Fabry-Perot array interference system, adopts an object far field optical path structure and is used for imaging the interference light field modulated by the reflective Fabry-Perot etalon array to the face array detector; The cold screen diaphragm is located on the image side focal plane of the relay imaging mirror and is used for limiting the object numerical aperture; The face array detector is located at the image plane of the relay imaging mirror and is used for photoelectric conversion of the interference light field to obtain an interference image array.

8. The roof-staircase Fabry-Perot imaging spectrometer of claim 1, wherein, The scanning mirror is used for linear push-broom of the target light field along the step direction perpendicular to the ridge-shaped step mirror, the scanning step length of the scanning mirror is the field of view corresponding to one step width of the ridge-shaped step mirror, after one cycle of push-broom, an interference image data cube is obtained; the interference image data cube is cut along the step direction of the ridge-shaped step mirror to obtain interference image units corresponding to different interference orders, the interference image units corresponding to different time instants of the zero optical path difference step are spliced in spatial order to obtain a panoramic image of the target, the interference image units corresponding to different steps of the target are spliced in optical path difference order to obtain an interference image sequence of the target and perform discrete Fourier transform operation to obtain a restored spectrum.

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