Roof step Fabry-Perot interference imaging spectrometer

Abstract

The invention relates to the field of spectral imaging, in particular to a ridge step Fabry-Perot interference imaging spectrometer, which comprises a scanning reflector, a telescope objective, a Fabry-Perot array interference system and a detection system, and is characterized in that the scanning reflector is positioned on an object space focal plane of the telescope objective and is used for transversely pushing and scanning a target light field; the telescope objective adopts an image space telecentric light path structure and is used for collecting a 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 an image space focal plane of the telescope objective and comprises parallel flat plates and a ridge-shaped step mirror, and the step height of the ridge-shaped step mirror is distributed in a manner that the step height decreases gradually from the middle to the two sides; and the detection system is positioned in the emergent 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 invention has the advantages of small volume, light weight, compact structure, static state, stability, reliability and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of spectral imaging, and in particular relates to a roof-step Fabry-Perot interference imaging spectrometer. Background Art

[0002] Fourier transform spectroscopy is a widely used measurement method for obtaining infrared spectra of target scenes. Its application range is very broad and has extended from the laboratory to the field of remote sensing. Most Fourier transform spectrometers use a time-modulated Michelson interferometer system to measure the time-modulated interference signal generated by the interaction between the incident spectrum and the Michelson interferometer system, and perform spectral demodulation through Fourier transform. In a Fourier transform infrared spectrometer based on a Michelson interferometer system, a moving mirror is used to sample the interference pattern in time. The moving mirror generates a time-varying optical path difference between the two beams by splitting the input beam. Under the illumination of monochromatic light, the detector responds to this time-varying optical path difference as a sinusoidal signal that changes with the optical path difference. By accurately measuring the change in the optical path difference, a reference laser signal is usually used to recover the wavelength information of the incident light from the sampled interference signal. The illumination of multiple wavelengths produces an added synthetic interference pattern, and the intensity of each wavelength, that is, the spectral information, can be recovered using Fourier transform. Since the Fourier transform spectrometer based on the Michelson interferometer system requires a beam splitter to split and combine the incident light beam, and a high-precision precision moving mirror scanning mechanism to control the optical path difference, the Fourier transform spectrometer based on the Michelson interferometer system is large in size, heavy in weight, difficult to integrate, and easily affected by the external environment, it is difficult to adapt to the application needs of new scientific and technological fields such as drones, micro-nano satellites, etc.

[0003] Compared with the Michelson interferometer system, the Fabry-Perot interferometer system has the advantages of compact structure, small size and light weight, so it is particularly suitable for applications such as drone-mounted and micro-nano satellite-mounted. Traditional Fabry-Perot interferometer systems are usually used as very narrow bandpass filters, and narrowband filtering is achieved by using very high reflectivity coatings. If a lower reflectivity coating is used on the surface of the Fabry-Perot cavity, the spectral transmission is essentially a sinusoidal curve, and the spectrum can be restored by Fourier transform. However, if the reflectivity of the coating is too low, the fringe contrast will be reduced, resulting in interference failure. Summary of the invention

[0004] In view of this, the present invention aims to provide a roof-step Fabry-Perot interferometer imaging spectrometer to solve the technical problems of the existing Fourier transform spectrometer based on the Michelson interferometer system, such as large size, heavy weight, great integration difficulty and being easily affected by the external environment.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows: A roof-step Fabry-Perot interferometer imaging spectrometer comprises a scanning reflector, a telescope objective lens, a Fabry-Perot array interferometer system and a detection system; wherein: The scanning reflector is located on the object focal plane of the telescope objective lens and performs horizontal push scanning of the target light field; The telescope objective adopts an image-side telecentric optical path structure, which is used to collect the target light field and image the target light field into the FP resonant cavity of the Fabry-Perot array interferometer system; The Fabry-Perot array interferometer system is located on the image focal plane of the telescope objective lens. The Fabry-Perot array interferometer system includes a parallel plate and a ridge-shaped step mirror. The parallel plate serves as a front interferometer of the Fabry-Perot array interferometer system, and the ridge-shaped step mirror serves as a rear interferometer of the Fabry-Perot array interferometer system. The step height of the ridge-shaped step mirror is distributed in a decreasing manner from the middle to both sides. The step height difference between any two adjacent steps on the ridge-shaped step mirror is the same. The highest step in the middle of the ridge-shaped step mirror fits tightly with the parallel plate, so that an air gap with a step-changing thickness is formed between the parallel plate and the ridge-shaped step mirror. The thickness of each area of ​​the air gap corresponds to an optical path difference. The parallel plate, the air gap and the ridge-shaped step mirror form a FP resonant cavity array. The detection system is located in the emission direction of the Fabry-Perot array interference system and is used to image the interference light field modulated by the Fabry-Perot array interference system to obtain an interference image array.

[0006] Furthermore, two opposite surfaces of the parallel plate and the roof-shaped step mirror are respectively used as reflection interfaces, and the two reflection interfaces and the air gap form a FP resonant cavity, and the reflectivity of the two reflection interfaces is 30% to 40%.

[0007] Furthermore, the parallel plate adopts a high refractive index plate, and an anti-reflection film is evaporated on the surface of the high refractive index plate away from the ridge-shaped step mirror, and the surface of the high refractive index plate facing the ridge-shaped step mirror is not coated, or the parallel plate adopts a low refractive index plate, and an anti-reflection film is evaporated on the surface of the low refractive index plate away from the ridge-shaped step mirror, and a high refractive index dielectric film is evaporated on the surface of the low refractive index plate facing the ridge-shaped step mirror and serves as a reflection interface of the FP resonant cavity.

[0008] Furthermore, the high refractive index plate is made of silicon or germanium dielectric material, and the low refractive index plate is made of quartz, calcium fluoride, magnesium fluoride or sapphire dielectric material.

[0009] Furthermore, the ridge-shaped step mirror includes a step substrate, the step substrate adopts a high refractive index medium, the upper surface of the step substrate of the high refractive index medium is not coated and serves as a reflection interface of the FP resonant cavity, and an anti-reflection film is evaporated on the lower surface of the step substrate of the high refractive index medium; or, the step substrate adopts a low refractive index medium, a high refractive index medium film is evaporated on the upper surface of the step substrate of the low refractive index medium and serves as a reflection interface of the FP resonant cavity, and an anti-reflection film is evaporated on the lower surface of the step substrate of the low refractive index medium.

[0010] Furthermore, the low refractive index medium is made of quartz, calcium fluoride, magnesium fluoride or sapphire; the high refractive index medium is made of silicon or germanium; and the high refractive index medium film is made of silicon film or germanium film.

[0011] Furthermore, the height difference between any two adjacent steps on the roof-shaped step mirror is d, then m The thickness of the air gap corresponding to the step h ( m )for: .

[0012] Furthermore, for the incident broadband spectrum, the step height difference d satisfies the following relationship: ; Among them, λ min is the minimum wavelength of the broadband spectrum, θ max is the incident angle of the light with the maximum field 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; For an incident narrowband spectrum, the step height difference d satisfies the following relationship: ; Among them, 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, which is less than or equal to Any integer of .

[0013] Furthermore, assuming that the number of steps of the roof-shaped step mirror is 2M, the preparation process of the step base is: S1: providing a flat substrate with a lateral width of 2a and a longitudinal width of 2a, and polishing and cleaning the flat substrate; S2: bidirectionally etching the planar substrate to form a two-step structure, the bidirectional etching depth is Md / 2, and the bidirectional etching width is a / 2; S3: Perform bidirectional etching on the two-step structure to form a four-step structure, with a bidirectional etching depth of Md / 4 and a bidirectional etching width of a / 4. Repeat 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.

[0014] Furthermore, the detection system includes a relay imaging mirror, a cold screen aperture and an array detector; wherein, The relay imaging mirror is located in the emission direction of the Fabry-Perot array interferometer system. The relay imaging mirror adopts an object-side telecentric optical path structure and is used to image the interference light field modulated by the reflective Fabry-Perot etalon array onto the area array detector. The cold screen diaphragm is located on the image-side focal plane of the relay imaging mirror and is used to limit the object-side numerical aperture; The area array detector is located at the image plane of the relay imaging mirror and is used to perform photoelectric conversion on the interference light field to obtain an interference image array.

[0015] Furthermore, a scanning reflector is used to perform linear push scanning on the target light field along a step direction perpendicular to the ridge-shaped step mirror, and the scanning step length of the scanning reflector is the field of view corresponding to a step width of the ridge-shaped step mirror. After completing one cycle of push scanning, an interference image data cube is obtained; the interference image data cube is sheared into interference image units corresponding to different interference orders along the step direction of the ridge-shaped step mirror, and the interference image units at different moments corresponding to the zero optical path difference step are spliced ​​in spatial order to obtain a panoramic image of the target; the interference image units of different steps corresponding to the target are spliced ​​in order of optical path difference to obtain an interference image sequence of the target, and a discrete Fourier transform operation is performed to obtain a restored spectrum.

[0016] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention adopts a roof-shaped step mirror with medium and low reflectivity to construct a Fabry-Perot array interferometer system, replaces the beam splitter and precision moving mirror scanning mechanism in the traditional Fourier transform imaging spectrometer, simplifies and lightens the optical-mechanical structure of the Fourier transform imaging spectrometer, improves the stability and robustness of the Fourier transform imaging spectrometer, and has the advantages of small size, light weight, compact structure, static, stable, reliable, etc. At the same time, the incident interface of the roof-shaped step mirror adopts medium and low reflectivity, and the spectrum can be restored by Fourier transform, which reduces the difficulty of spectrum restoration in the traditional Fabry-Perot interferometer system. Through the coupled modulation transmission of the light field by the Fabry-Perot array interferometer system, the synchronous measurement of the interference image sequence can be realized, thereby realizing the snapshot-type effective detection of the target scene image information and the spectral information, and improving the real-time performance of multi-dimensional information detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 It is a schematic diagram of the structure of the roof-step Fabry-Perot interferometer imaging spectrometer described in Example 1 of the present invention.

[0018] Figure 2 It is a schematic diagram of the structure of the Fabry-Perot array interferometer system according to Example 1 of the present invention.

[0019] Figure 3 It is a schematic diagram of the structure of the roof-shaped step mirror described in Example 1 of the present invention.

[0020] Figure 4 It is a schematic diagram of the preparation process of the step substrate described in Example 1 of the present invention.

[0021] Figure 5 It is a schematic diagram of the acquisition process of the interference image array described in Example 1 of the present invention.

[0022] Figure 6 It is a schematic diagram of the structure of the roof-shaped step mirror described in Example 2 of the present invention.

[0023] Explanation of the reference numerals of Example 1: scanning reflector 10 , telephoto objective lens 20 , parallel plate 30 , roof-shaped step mirror 40 , step base 401 , anti-reflection film 402 , relay imaging mirror 50 , cold screen aperture 60 , and planar array detector 70 .

[0024] Description of the reference numerals of Example 2: stepped substrate 403 , anti-reflection film 404 , high refractive index dielectric film 405 . DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0026] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0027] 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 positions or positional relationships based on the positions 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", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. 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.

[0028] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0029] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0030] The 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: The scanning reflector is located on the object focal plane of the telescope objective lens and performs horizontal push scanning on the target light field. The telescope objective lens adopts an image-side telecentric optical path structure to collect the target light field and image the target light field in the FP resonant cavity of the Fabry-Perot array interferometer system. The Fabry-Perot array interferometer system is located on the image-side focal plane of the telescope objective lens. The Fabry-Perot array interferometer system includes a parallel plate and a ridge-shaped step mirror. The parallel plate serves as the front interferometer of the Fabry-Perot array interferometer system, and the ridge-shaped step mirror serves as the rear interferometer of the Fabry-Perot array interferometer system. The step height of the ridge-shaped step mirror is in the middle direction. The two sides are distributed in a decreasing manner, and the step height difference between any two adjacent steps on the ridge-shaped step mirror is the same. The highest step in the middle of the ridge-shaped step mirror fits tightly with the parallel plate, so that an air gap with a step-changing thickness is formed between the parallel plate and the ridge-shaped step mirror. The thickness of each area of ​​the air gap corresponds to an optical path difference. The parallel plates, the air gap and the ridge-shaped step mirror constitute a FP resonant cavity array. The detection system is located in the exit direction of the Fabry-Perot array interferometer system, and is used to image the interference light field modulated by the Fabry-Perot array interferometer system to obtain an interference image array.

[0031] The detection system includes a relay imaging mirror, a cold screen aperture and an array detector; wherein the relay imaging mirror is located in the emitting direction of the Fabry-Perot array interferometer system, and the relay imaging mirror adopts an object-side telecentric optical path structure, and is used to image the interference light field modulated by the reflective Fabry-Perot etalon array onto the array detector; the cold screen aperture is located on the image-side focal plane of the relay imaging mirror, and is used to limit the object-side numerical aperture; the array detector is located at the image plane of the relay imaging mirror, and is used to perform photoelectric conversion on the interference light field to obtain an interference image array.

[0032] The target light field enters the telescope objective through the scanning reflector. The telescope objective adopts the image-side telecentric optical path structure. The telescope objective images the target light field into the Fabry-Perot array interferometer system based on the ridge-shaped step mirror. The Fabry-Perot array interferometer system consists of a parallel plate and a ridge-shaped step mirror. The parallel plate and the middle step surface of the ridge-shaped step mirror are in close contact, so that the FP resonant cavity with a ridge-shaped step change in thickness is formed. The parallel plate and the ridge-shaped step mirror are made of silicon or germanium materials with high refractive index, so that the reflection interface on both sides of the FP resonant cavity has a medium-low reflectivity, thereby forming a low-fineness Fabry-Perot interferometer, so that the spectrum can be demodulated by Fourier transform. The ridge-shaped step mirror structure causes the thickness of the FP resonant cavity to change discretely and linearly, and different thicknesses of the FP 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 interferometer system. The modulated interference light field is the superposition of the target scene and the interferometer fringes. The modulated interference light field is imaged onto the area array detector through the relay imaging mirror. The relay imaging mirror adopts an object-side telecentric optical path structure, and matches it with the cold screen aperture of the area array detector. The target light field is scanned along the step direction perpendicular to the roof-shaped step mirror by using a scanning reflector, and the scanning step length is a field of view corresponding to the width of a step, and an interference image data cube is obtained. By splicing the interference image units corresponding to the zero optical path difference step at different times, 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 interference image sequence is subjected to discrete Fourier transform to demodulate the spectral information of the target. The present invention reduces the size of the Fourier transform infrared imaging spectrometer and has the advantages of compact structure, static, stable and reliable.

[0033] Example 1 like Figure 1-Figure 5 As shown, the roof-step Fabry-Perot interferometer imaging spectrometer provided in Example 1 of the present invention includes a scanning reflector 10, a telescope objective lens 20, a parallel plate 30, a roof-shaped step mirror 40, a relay imaging mirror 50, a cold screen aperture 60, and a planar array detector 70 (using devices such as HgCdTe or InSb).

[0034] The target light field first enters the telescope objective lens 20 through the scanning reflector 10. The telescope objective lens 20 adopts an image-side telecentric optical path structure. The target light field is imaged into the Fabry-Perot array interferometer system based on the roof step mirror through the telescope objective lens 20 and modulated into an interference light field. The Fabry-Perot array interferometer system is composed of a parallel plate 30 and a roof step mirror 40. The parallel plate 30 and the roof surface (i.e., the middle step surface) of the roof step mirror 40 are tightly fitted, so that an air gap with a thickness gradually increasing from the middle to both sides is formed between the parallel plate 30 and the roof step mirror 40. Therefore, the interference signal is a function that changes with the spatial position, and zero optical path difference is achieved at the optical contact position between the parallel plate 30 and the roof step mirror 40.

[0035] The two surfaces of the ridge-shaped step mirror 40 opposite to the parallel plate 30 serve as reflection interfaces, and together with the air gap, form a distributed FP resonant cavity. Each FP resonant cavity has a specific thickness, and thus has a fixed optical path difference. Light incident on the reflection interfaces on both sides of the FP resonant cavity will be reflected multiple times in the FP resonant cavity, and interference will occur between the light beams that pass through the FP resonant cavity at different times. The intensity of the interference signal emitted by the light beam through the FP resonant cavity depends on the thickness of the air gap between the two reflection interfaces, the reflectivity of the reflection interface, the incident angle of the light, and the refractive index of the medium in the FP resonant cavity between the reflection interfaces on both sides. The medium in the FP resonant cavity can be air or vacuum, or a low refractive index medium. The present invention is described using an air embodiment. The reflection interface of a traditional Fabry-Perot interference system usually adopts a very high reflectivity to produce a narrow transmission band, while the reflection interface of the Fabry-Perot array interference system in the present invention adopts a medium reflectivity to produce a quasi-cosine interference signal that can be demodulated by Fourier transform.

[0036] The interference image signal formed by the FP resonant cavity corresponding to the mth step in the roof-shaped step mirror 40 of the Fabry-Perot array interferometer system can be expressed as: ; Where R1 and R2 are the reflectivity of the two reflection interfaces of the FP resonant cavity; ν is the wave number, ν=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: ; Where n0 is the refractive index of the medium in the FP resonant cavity. When the FP resonant cavity is air, n0=1; θ is the incident angle of the light in the FP resonant cavity, corresponding to the different field of view angles of the target scene; is 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.

[0037] It can be seen from the interference image signal formula that when the reflectivity of the reflection interface is very low, the interference signal is a cosine function, but the modulation of the interference fringes is also very low; when the reflectivity of the reflection interface is very high, the interference fringes have a very high modulation, but the interference signal is an extremely narrow comb function. The traditional Fabry-Perot interferometer uses a reflection interface with a very high reflectivity and uses resonance to produce very narrow interference features. These very narrow comb-shaped interference signals will produce side lobes in the Fourier transform spectrum, which will take away the signal from the main frequency and cause the restored spectrum to be distorted. In order to suppress the spectral distortion caused by harmonic signals and reduce the interference caused by the side lobe signal extending 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 should be less than or equal to the minimum wavelength, or less than or equal to half of the maximum wavelength. For short-wave infrared 1μm-2μm, medium-wave infrared 3μm-5μm, and long-wave infrared 8μm-14μm, they can basically meet the application requirements.

[0038] Therefore, the present invention uses a reflective interface with medium reflectivity to generate a cosine-like interference signal. At this time, the spectral fineness is low, and the roof-shaped step mirror 40 is close to double-beam interference. The interference pattern function can be approximately expressed as: ; Therefore, the spectral information of the incident light signal can be restored from the interference signal through Fourier transform.

[0039] Although the lower the reflectivity, the closer the interference signal is to the cosine function, and thus the higher the spectral restoration accuracy, too low a reflectivity will also reduce the modulation of the interference fringes. Therefore, in order to achieve effective demodulation of the spectrum through Fourier transform, it is necessary to balance the fringe modulation and spectral sidelobe suppression. By balancing the interference pattern modulation and the cosine degree of the interference signal, the reflectivity of the reflection interface is determined, the spectral sidelobes are minimized and the interference pattern modulation is maximized. In other words, by optimizing the reflectivity of the reflection interface, the maximum trade-off between the interference fringe modulation and the cosine characteristic is achieved. In the present invention, the reflectivity of the two reflection interfaces of the FP resonant cavity is set at 30% to 40%, which can achieve the best trade-off between the interference pattern modulation and the cosine characteristic. Therefore, each FP resonant cavity in the present invention is a low-fineness Fabry-Perot cavity that modulates the interference intensity of the interference image under a given optical path difference.

[0040] For infrared materials, silicon and germanium materials have a higher refractive index and thus have a relatively moderate reflectivity. For silicon material, its refractive index is 3.4 and its surface reflectivity is 30%; for germanium material, its refractive index is 4.0 and its surface reflectivity is 36%. Therefore, the parallel plate 30 is made of a high refractive index medium such as silicon or germanium, and an anti-reflection film is evaporated on the surface of the parallel plate 30 away from the ridge-shaped step mirror 40, and no film is applied on the surface of the parallel plate 30 facing the ridge-shaped step mirror 40. The step substrate 401 can be made of a high refractive index medium material such as silicon or germanium, and the surface of the step substrate 401 facing the parallel plate 50 is not coated, so that the reflection interface has a medium-low reflectivity to achieve low fineness, and the surface of the step substrate 401 facing the parallel plate 50 is evaporated with an anti-reflection film 402 to ensure high transmittance, and the step (i.e., the ridge surface) in the middle of the step substrate 401 is in contact with the uncoated side of the parallel plate 30, so as to achieve zero optical path difference on the optical contact surface.

[0041] An air gap with a thickness that increases from the middle to the sides is formed between the ridge-shaped step mirror 40 and the parallel plate 30, thereby forming a spatially distributed modulation of the optical path difference. The ridge-shaped step mirror 40 adopts a symmetrical step structure, with the ridge in the middle and the steps on both sides decreasing in sequence, and the height of each step is complementary to the thickness of the air gap of the FP resonant cavity. Assuming that the step height difference of the ridge-shaped step 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, that is, the gap thickness corresponding to the mth step of the FP resonant cavity is: .

[0042] In order to achieve effective spectral restoration, the step height difference d should satisfy the Nyquist sampling theorem. In order to suppress the spectral aliasing caused by the Fourier transform of high-order sidelobe signals, the sampled signal cutoff frequency is extended to J Subharmonics (generally, J For the incident broadband spectrum, the step height difference d should satisfy the following relationship: ; Among them, λ min is the minimum wavelength of the broadband spectrum, θ max is the incident angle of the maximum field 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.

[0043] For incident narrowband spectra, especially for gas detection, in order to achieve high spectral resolution, the step height difference d should satisfy the following relationship: ; Among them, λ S is the shortest wavelength of the narrowband spectrum, λL is the longest wavelength of the narrowband spectrum, k is the spectral folding order, which is less than or equal to Any integer of .

[0044] The step substrate 401 is composed of 2M steps, and the height difference between any two adjacent steps on the step substrate 401 is constant d. The step substrate 401 is manufactured by etching, and the manufacturing process is as follows: S1: providing a flat substrate with a lateral width of 2a and a longitudinal width of 2a, and polishing and cleaning the flat substrate.

[0045] S2: bidirectionally etching the planar substrate to form a two-step structure, the bidirectional etching depth is Md / 2, and the bidirectional etching width is a / 2.

[0046] S3: Perform bidirectional etching on the two-step structure to form a four-step structure. The bidirectional etching depth is Md / 4 and the bidirectional etching width is a / 4. Repeat 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. The production of a ridge-shaped step mirror with a step height of ±d and a step number of 2M is completed.

[0047] The interference light field modulated by the Fabry-Perot array interference system is a superposition of the target scene and the interferometer fringes. The interference light field is imaged onto the array detector 70 at a certain reduction ratio using the relay imaging mirror 50. The relay imaging mirror 50 samples the object-side telecentric optical path structure, and its image-side focal plane matches the cold screen aperture 60 of the array detector 70. In other words, the cold screen aperture 60 of the array detector 70 is located on the image-side focal plane of the relay imaging mirror 50. The single-frame interference image collected each time by the Fourier transform imaging spectrometer based on the roof-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.

[0048] like Figure 5 As shown, t1-t7 correspond to different moments, A-G correspond to different targets, different squares correspond to different optical path differences, that is, to different steps, and the middle row of squares corresponds to zero optical path difference. The scanning direction of the scanning reflector 10 is perpendicular to the step direction, and each step advances into a field of view with a step width.

[0049] The target light field is linearly pushed and scanned by the scanning reflector 10 along the step direction perpendicular to the ridge-shaped step mirror 40 to collect an interference image sequence. The scanning step length 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 a 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-scanning 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 the order of optical path difference to obtain an interference image sequence. By performing discrete Fourier transform operations on the interference image sequence, the restored spectral information of each object point can be demodulated.

[0050] Example 2 The difference between Example 2 and Example 1 is that the structure of the roof-shaped step mirror is different. Figure 6 As shown, the step substrate 403 of the roof-shaped step mirror of Example 2 is made of a low-refractive-index transparent medium material such as quartz, calcium fluoride, magnesium fluoride, sapphire, etc. to ensure a higher transmittance at the interface, and a high-refractive-index medium film 405 such as silicon or germanium is evaporated on the step surface of the step substrate 403 so that the reflection interface has a medium-low reflectivity to achieve low fineness, and an anti-reflection film 404 is evaporated on the lower surface (i.e., the bottom plane) of the step substrate 403 to ensure high transmittance.

[0051] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0052] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A roof-step Fabry-Perot interferometer imaging spectrometer, characterized in that: It includes a scanning reflector, a telescope objective lens, a Fabry-Perot array interferometer system and a detection system; among which, The scanning reflector is located on the object focal plane of the telescope objective lens and performs horizontal push scanning of the target light field; The telescope objective lens adopts an image-side telecentric optical path structure, which is used to collect the target light field and image the target light field into the FP resonant cavity of the Fabry-Perot array interferometer system; The Fabry-Perot array interferometer system is located on the image focal plane of the telescope objective lens. The Fabry-Perot array interferometer system includes a parallel plate and a ridge-shaped step mirror. The parallel plate serves as a front interferometer of the Fabry-Perot array interferometer system, and the ridge-shaped step mirror serves as a rear interferometer of the Fabry-Perot array interferometer system. The step height of the ridge-shaped step mirror is distributed in a decreasing manner from the middle to both sides. The step height difference between any two adjacent steps on the ridge-shaped step mirror is the same. The highest step in the middle of the ridge-shaped step mirror fits tightly with the parallel plate, so that an air gap with a step-changing thickness is formed between the parallel plate and the ridge-shaped step mirror. The thickness of each area of ​​the air gap corresponds to an optical path difference. The parallel plate, the air gap and the ridge-shaped step mirror form a FP resonant cavity array. The detection system is located in the emission direction of the Fabry-Perot array interference system and is used to image the interference light field modulated by the Fabry-Perot array interference system to obtain an interference image array.

2. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 1, characterized in that: The two opposite surfaces of the parallel plate and the ridge-shaped step mirror serve as reflection interfaces respectively. The two reflection interfaces and the air gap form a FP resonant cavity, and the reflectivity of the two reflection interfaces is 30%~40%.

3. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 1 or 2, characterized in that: A high refractive index plate is used as a parallel plate, and an anti-reflection film is evaporated on the surface of the high refractive index plate away from the ridge-shaped step mirror, and the surface of the high refractive index plate facing the ridge-shaped step mirror is not coated. Alternatively, a low refractive index plate is used as a parallel plate, and an anti-reflection film is evaporated on the surface of the low refractive index plate away from the ridge-shaped step mirror, and a high refractive index dielectric film is evaporated on the surface of the low refractive index plate facing the ridge-shaped step mirror and serves as a reflection interface of the FP resonant cavity.

4. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 3, characterized in that: The high refractive index plate is made of silicon or germanium dielectric material, and the low refractive index plate is made of quartz, calcium fluoride, magnesium fluoride or sapphire dielectric material.

5. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 1, characterized in that: The ridge-shaped step mirror comprises a step substrate, wherein the step substrate adopts a high refractive index medium, the upper surface of the step substrate of the high refractive index medium is not coated and serves as a reflection interface of the FP resonant cavity, and an anti-reflection film is evaporated on the lower surface of the step substrate of the high refractive index medium; or, the step substrate adopts a low refractive index medium, a high refractive index medium film is evaporated on the upper surface of the step substrate of the low refractive index medium and serves as a reflection interface of the FP resonant cavity, and an anti-reflection film is evaporated on the lower surface of the step substrate of the low refractive index medium.

6. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 5, characterized in that: The low refractive index medium adopts quartz, calcium fluoride, magnesium fluoride or sapphire medium material; the high refractive index medium adopts silicon or germanium medium material; and the high refractive index medium film adopts silicon film or germanium film.

7. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 1, characterized in that: The height difference between any two adjacent steps on the roof-shaped step mirror is d, then m The thickness of the air gap corresponding to the step h ( m )for: 。 8. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 1, characterized in that: For an incident broadband spectrum, the step height difference d satisfies the following relationship: ； Among them, λ min is the minimum wavelength of the broadband spectrum, θ max is the incident angle of the light with the maximum field 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; For an incident narrowband spectrum, the step height difference d satisfies the following relationship: ； Among them, 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, which is less than or equal to Any integer of .

9. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 5, characterized in that: Assuming the number of steps of the roof-shaped step mirror is 2M, the preparation process of the step base is: S1: providing a flat substrate with a lateral width of 2a and a longitudinal width of 2a, and polishing and cleaning the flat substrate; S2: bidirectionally etching the planar substrate to form a two-step structure, the bidirectional etching depth is Md / 2, and the bidirectional etching width is a / 2; S3: Perform bidirectional etching on the two-step structure to form a four-step structure, with a bidirectional etching depth of Md / 4 and a bidirectional etching width of a / 4. Repeat 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.

10. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 1, characterized in that: The detection system includes a relay imaging mirror, a cold screen aperture and an array detector; among them, The relay imaging mirror is located in the emission direction of the Fabry-Perot array interferometer system. The relay imaging mirror adopts an object-side telecentric optical path structure and is used to image the interference light field modulated by the reflective Fabry-Perot etalon array onto the area array detector. The cold screen diaphragm is located on the image-side focal plane of the relay imaging mirror and is used to limit the object-side numerical aperture; The area array detector is located at the image plane of the relay imaging mirror and is used to perform photoelectric conversion on the interference light field to obtain an interference image array.

11. The roof step Fabry-Perot interferometer imaging spectrometer according to claim 1, characterized in that: A scanning reflector 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 reflector is the field of view corresponding to the step width of the ridge-shaped step mirror. After completing one cycle of push-scanning, an interference image data cube is obtained; the interference image data cube is sheared into interference image units corresponding to different interference orders along the step direction of the ridge-shaped step mirror, and the interference image units at different times corresponding to the zero optical path difference step are spliced ​​in spatial order to obtain a panoramic image of the target; the interference image units of different steps corresponding to the target are spliced ​​in order of optical path difference to obtain an interference image sequence of the target and a discrete Fourier transform operation is performed to obtain a restored spectrum.

Images