Double-step Fabry-Perot interference snapshot imaging spectrometer

Abstract

The invention relates to the field of spectral imaging, in particular to a double-step Fabry-Perot interference snapshot imaging spectrometer, which comprises a telescopic system, a micro lens array, a Fabry-Perot array interference system and an area array detector, and is characterized in that the telescopic system is used for collecting a target light field and carrying out view field limitation and collimation on the target light field; the Fabry-Perot array interference system is used for modulating a target light field into an interference light field array, the Fabry-Perot array interference system comprises two step lenses which are orthogonal in the step direction, the highest steps of the two step lenses are tightly attached, and an air gap with the thickness changing in a checkerboard-shaped two-dimensional increasing mode is formed between the two step lenses; the microlens array is used for imaging the interference light field array onto the area array detector through each imaging channel; and the area array detector is used for receiving the transmission image field of the microlens array 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 double-step Fabry-Perot interference snapshot 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 Michelson interferometer system uses a high-precision precision moving mirror scanning mechanism to perform fine scanning of 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 double-step Fabry-Perot interferometer snapshot 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 double-step Fabry-Perot interferometer snapshot imaging spectrometer comprises a telescope system, a microlens array, a Fabry-Perot array interferometer system and a planar array detector; wherein: The telescope system is used to collect the target light field and to limit and collimate the target light field; The Fabry-Perot array interference system is located in the parallel optical path of the telescope system. The Fabry-Perot array interference system is used to modulate the target light field to form an interference light field array. The Fabry-Perot array interference system includes a first step lens and a second step lens with orthogonal step directions. The first step lens and the second step lens serve as a front interference plate and a rear interference plate of the Fabry-Perot array interference system respectively. The number of steps of the first step lens is M, the number of steps of the second step lens is N, the step height difference between any two adjacent steps of the first step lens is d, and the step height difference between any two adjacent steps of the second step lens is Md. The highest step of the first step lens is tightly fitted with the highest step of the second step lens, so that an air gap with a thickness that changes in a two-dimensional incremental manner in a checkerboard shape is formed between the first step lens and the second step lens. The thickness of each area of ​​the air gap corresponds to an optical path difference. The first step lens, the air gap and the second step lens form a FP resonant cavity array. The microlens array is located in the emission direction of the Fabry-Perot array interference system. The microlens array adopts an image-side telecentric optical path structure and is composed of M×N microlens units. Each microlens unit corresponds to a row of steps of the first step lens and a column of steps of the second step lens. Each microlens unit serves as an imaging channel. The microlens array is used to image the interference light field array onto the area array detector through each imaging channel. The area array detector is located at the image focal plane of the microlens array and is used to receive the transmission image field of each imaging channel of the microlens array to obtain an interference image array.

[0006] Furthermore, two opposite surfaces of the first step lens and the second step lens 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 first step lens and the second step lens respectively include a step substrate. When 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; when 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.

[0008] 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.

[0009] Furthermore, the thickness of the air gap is distributed in a two-dimensional increasing manner in a checkerboard pattern. m Direction d The step length increases successively, and the thickness increases along n Direction Md The step size increases successively. m , n ) steps corresponding to the thickness of the air gap of the FP resonant cavity h ( m , n )for: h ( m , n )=[( n -1) M + m -1] d .

[0010] Furthermore, for the incident broadband spectrum, the step height difference d of the first step lens 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 the incident narrowband spectrum, the step height difference d of the first step lens 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 .

[0011] Furthermore, the preparation process of the step substrate of the first step lens is as follows: A1: providing a flat substrate with a lateral width of a and a longitudinal width of b, and polishing and cleaning the flat substrate; A2: Etching the flat substrate to form a two-step structure, with an etching depth of Md / 2 and an etching width of a / 2; A3: Etching the two-step structure to form a four-step structure, with an etching depth of Md / 4 and an etching width of a / 4, repeating step A3 to ensure that each etching depth is 1 / 2 of the previous etching depth and each etching width is 1 / 2 of the previous etching depth, until the step height difference is d and the step width is a / M; The preparation process of the step substrate of the second step lens is as follows: B1: providing a plane substrate with a lateral width of a and a longitudinal width of b, and polishing and cleaning the plane substrate; B2: Etching the flat substrate to form a two-step structure, with an etching depth of NMd / 2 and an etching width of b / 2; B3: Etch the two-step structure to form a four-step structure, with an etching depth of NMd / 4 and an etching width of b / 4. Repeat step B3 to ensure that the etching depth and width of each etching are 1 / 2 of the previous etching, until the step height difference is Md and the step width is b / N.

[0012] Furthermore, the telescope system includes a telescope objective lens, a field stop and a collimator lens; wherein, The telescope objective is used to collect the target light field and image the target light field at the field aperture; The field diaphragm is located on both the image-side focal plane of the telescope objective and the object-side focal plane of the collimator. The field diaphragm is used to limit the field of view of the imaging of the target light field. The collimator is used to collimate the divergent light emitted by the target light field located at the field stop into parallel light.

[0013] Furthermore, the planar array detector is also used to perform image segmentation on the interference image array, dividing the interference image array into interference image units corresponding to each FP resonant cavity; and arranging the interference image units in the order of the thickness of each FP resonant cavity to form an interference image data cube, and performing discrete Fourier transform operation on the interference image data cube with the optical path difference as the axis to obtain a spectral image data cube that varies with wavelength.

[0014] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention adopts two orthogonally placed step lenses with medium and low reflectivity to construct a Fabry-Perot array interference 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 two step lenses 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 interference system. Through the coupled modulation transmission of the light field by the Fabry-Perot array interference system and the microlens array, the synchronous measurement of the interference image data cube 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

[0015] 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 double-step Fabry-Perot interferometer snapshot imaging spectrometer described in Example 1 of the present invention.

[0016] Figure 2 Schematic diagram of the structure of the first step lens described in Example 1 of the present invention.

[0017] Figure 3 Schematic diagram of the spatial distribution of the thickness of the air gap between the first step lens and the second step lens described in Example 1 of the present invention.

[0018] Figure 4 It is a schematic diagram of the preparation process of the step substrate of the first step lens described in Example 1 of the present invention.

[0019] Figure 5 It is a schematic diagram of the process of image spectrum inversion described in Example 1 of the present invention.

[0020] Figure 6 It is a schematic diagram of the structure of the first step lens described in Example 2 of the present invention.

[0021] Description of the reference numerals of Example 1: telescope objective 10 , field stop 20 , collimator 30 , first step lens 40 , step substrate 401 , anti-reflection film 402 , second step lens 50 , microlens array 60 , planar array detector 70 .

[0022] Description of the reference numerals of Example 2: stepped substrate 403 , anti-reflection film 404 , high refractive index dielectric film 405 . DETAILED DESCRIPTION

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0028] The invention provides a double-step Fabry-Perot interference snapshot imaging spectrometer, comprising a telescope system, a microlens array, a Fabry-Perot array interference system and a planar array detector; wherein the telescope system is used to collect a target light field, and to limit and collimate the target light field; the Fabry-Perot array interference system is located in a parallel optical path of the telescope system, and is used to modulate the target light field to form an interference light field array; the microlens array is located in the emission direction of the Fabry-Perot array interference system, and the microlens array adopts an image-side telecentric optical path structure, and is composed of M×N microlens units, each of which corresponds to a row of steps of a first step lens and a column of steps of a second step lens, and each of which serves as an imaging channel, and the microlens array is used to image the interference light field array onto the planar array detector through each imaging channel; the planar array detector is located at the image-side focal plane of the microlens array, and is used to receive the transmission image field of each imaging channel of the microlens array to obtain an interference image array.

[0029] The telescope system includes a telescope objective, a field diaphragm and a collimator; wherein the telescope objective is used to collect a target light field and image the target light field at the field diaphragm; the field diaphragm is located on the image-side focal plane of the telescope objective and on the object-side focal plane of the collimator at the same time, and the field diaphragm is used to limit the field of view of the imaging of the target light field; the collimator is used to collimate the divergent light emitted by the target light field located at the field diaphragm into parallel light.

[0030] The Fabry-Perot array interference system comprises a first step lens and a second step lens orthogonal in step directions, the first step lens and the second step lens respectively serve as a front interference plate and a rear interference plate of the Fabry-Perot array interference system, the number of steps of the first step lens is M, the number of steps of the second step lens is N, the step height difference between any two adjacent steps of the first step lens is d, the step height difference between any two adjacent steps of the second step lens is Md, the highest step of the first step lens is closely fitted with the highest step of the second step lens, so that an air gap with a thickness that changes in a two-dimensional incremental manner in a checkerboard shape is formed between the first step lens and the second step lens, the thickness of each area of ​​the air gap corresponds to an optical path difference, and the first step lens, the air gap and the second step lens form a FP resonant cavity array.

[0031] The present invention images the target light field onto the field diaphragm through a telescope objective lens, and the field diaphragm limits the imaging field of view and then collimates it into parallel light through a collimator, which is incident on a Fabry-Perot array interference system. The Fabry-Perot array interference system is composed of two step lenses, which are placed face to face, and the step directions are orthogonal to each other, and the highest step surfaces of the two step lenses are in close contact, so that an air gap with a thickness that changes in a two-dimensional checkerboard shape is formed between the two step lenses. The two step lenses use silicon or germanium materials with high refractive index, so that the reflection interfaces on both sides of the air gap have medium and low reflectivity, forming a low-fineness Fabry-Perot interference array, so that the spectrum can be demodulated by Fourier transform. By reasonably designing the structural parameters of the double-step lens, the thickness of the air gap changes in a two-dimensional discrete linear increment, and different air gap thicknesses correspond to different optical path differences, thereby forming a spatial modulation of the optical path difference. Therefore, after the parallel light passes through the Fabry-Perot array interference system, an interference light field array modulated by different optical path differences is formed, and each interference light field unit corresponds to a specific optical path difference. The interference light field array is focused by using a microlens array, and each microlens unit corresponds to an interference light field unit with a specific optical path difference, so that the target light field is imaged onto a planar array detector, and an interference image array of the target light field corresponding to the optical path difference array is obtained on the planar array detector. After image segmentation and image registration of the interference image array, it is arranged into an interference image data cube in the order of the optical path difference, and then discrete Fourier transform is performed along the optical path difference dimension, so that the spectral information of each object point of the target scene can be demodulated, thereby realizing snapshot synchronous measurement of the scene target image information and spectral information. The present invention reduces the size of the Fourier transform infrared imaging spectrometer and has the advantages of compact structure, static, stable, reliable, etc.

[0032] Example 1 like Figure 1-Figure 5 As shown, the double-step Fabry-Perot interference snapshot imaging spectrometer provided in Example 1 of the present invention includes a telescope objective 10, a field aperture 20, a collimator 30, a first step lens 40, a second step lens 50, a microlens array 60 and a planar array detector 70 (using devices such as HgCdTe or InSb).

[0033] The target light field is first imaged onto the field of view diaphragm 20 through the telescope objective 10. The field of view diaphragm 20 limits the imaging field of the target light field, thereby controlling the spatial sampling on the array detector 70 and the size of the imaging field of view, and suppressing the crosstalk of the imaging field of view between adjacent interference channels. Then it is collimated into parallel light by the collimator 30 and incident on the Fabry-Perot array interference system. Interference is formed in the FP resonant cavity of the Fabry-Perot array interference system. The interference plate of the Fabry-Perot array interference system is composed of a first step lens 40 and a second step lens 50. The first step lens 40 serves as the front interference plate of the Fabry-Perot array interference system, and the second step lens 50 serves as the rear interference plate of the Fabry-Perot array interference system. The first step lens 40 and the second step lens 50 are made of high refractive index materials such as silicon or germanium, and use the medium reflectivity of Fresnel reflection to form a low-fineness interference cavity to make it close to double-beam interference, so that spectral restoration can be performed through Fourier transform. The step surface of the first step lens 40 is orthogonal to the step surface of the second step lens 50 and the surfaces of the highest steps of the two are tightly fitted, so that an air gap with a thickness that changes in a two-dimensional chessboard-like incremental manner is formed between the first step lens 40 and the second step lens 50, thereby forming an optical path difference that changes with the spatial position, and achieving zero optical path difference at the position where the surfaces of the first step lens 40 and the second step lens 50 are in optical contact.

[0034] The step surfaces of the first step lens 40 and the second step lens 50 are used as reflective interfaces to form a distributed FP resonant cavity with the air gap. Each FP resonant cavity has a specific thickness and thus has a fixed optical path difference. The light incident on the reflective 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 reflective interfaces, the reflectivity of the reflective interface, the incident angle of the light, and the refractive index of the medium in the FP resonant cavity between the reflective 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 reflective interface of a traditional Fabry-Perot interference system usually adopts a very high reflectivity to produce a narrow transmission band, while the reflective 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.

[0035] The interference image signal formed by the FP resonant cavity corresponding to the m-th row step of the first step lens 40 and the n-th column step of the second step lens 50 of the Fabry-Perot array interference system can be expressed as: ; Among them, R1 and R2 are the reflectivities of the two reflection interfaces of the FP resonant cavity; ν is the wave number, ν=1 / λ, λ is the wavelength, and δ(m,n) is the optical path difference of the FP resonant cavity corresponding to the (m,n)th 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; h(m,n) is the air gap thickness of the FP resonant cavity, which varies with the spatial position due to the checkerboard step structure.

[0036] 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.

[0037] 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, the FP resonant cavity is close to double-beam interference, and 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.

[0038] 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.

[0039] 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 first step lens 40 and the second step lens 50 are made of high refractive index media such as silicon or germanium. The step surfaces of the first step lens 40 and the second step lens 50 are not coated. As the reflection interface of the FP resonant cavity, only the anti-reflection film 402 is evaporated on the plane of the first step lens 40 and the second step lens 50 to ensure high transmittance. The surfaces of the highest steps of the first step lens 40 and the second step lens 50 that are not coated are orthogonally and tightly fitted to achieve zero optical path difference at the optical contact surface.

[0040] An air gap with a gradually increasing thickness is formed between the first step lens 40 and the second step lens 50, thereby forming a spatially distributed modulation of the optical path difference. The height of each step is complementary to the thickness of the air gap of the FP resonant cavity. In order to form a continuous optical path difference sampling, let the step height difference between any two adjacent steps of the first step lens 40 be d, and the number of steps be M; let the step height difference between any two adjacent steps of the second step lens 50 be Md, and the number of steps be N. The air gap thickness h(m,n) of the (m,n)th FP resonant cavity formed by the mth step of the first step mirror and the nth step of the second step mirror is: .

[0041] 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, JFor 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.

[0042] For incident narrowband spectroscopy, 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, 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 .

[0043] The first stepped lens 40 includes a stepped substrate 401, the stepped substrate 401 has M steps, the height difference between any two adjacent steps is constant d, and the stepped substrate 401 is manufactured by etching, and the manufacturing process is as follows: A1: Provide a flat substrate with a lateral width of a and a longitudinal width of b, and polish and clean the flat substrate.

[0044] A2: The planar substrate is etched to form a two-step structure, with an etching depth of Md / 2 and an etching width of a / 2.

[0045] A3: Etch the two-step structure to form a four-step structure, with an etching depth of Md / 4 and an etching width of a / 4. Repeat step A3 to ensure that the etching depth and width of each etching are 1 / 2 of the previous etching, until the step height difference is d and the step width is a / M.

[0046] The second step lens 50 has N steps, and the height difference between any two adjacent steps is constant Md. The step base of the second step lens 50 is also manufactured by etching, and the manufacturing process is as follows: B1: Provide a flat substrate with a lateral width of a and a longitudinal width of b, and polish and clean the flat substrate.

[0047] B2: The planar substrate is etched to form a two-step structure, with an etching depth of NMd / 2 and an etching width of b / 2.

[0048] B3: Etch the two-step structure to form a four-step structure, with an etching depth of NMd / 4 and an etching width of b / 4. Repeat step B3 to ensure that the etching depth and width of each etching are 1 / 2 of the previous etching, until the step height difference is Md and the step width is b / N.

[0049] The target light field is modulated by the Fabry-Perot array interference system and enters the microlens array 60. The microlens array 60 is composed of M×N microlens units, which perform aperture segmentation and array imaging on the incident parallel light field. The microlens array 60 adopts an image-side telecentric optical path structure to make the main light of the array imaging light beam parallel to the optical axis. Each microlens unit corresponds to a FP resonant cavity of a specific thickness, that is, a specific row step of the first step lens 40 and a specific column step of the second step lens 50, respectively. Therefore, the microlens array 60 has the same unit spacing as the first step lens 40 and the second step lens 50. The surface array detector 70 is placed on the focal plane of the microlens array 60. The microlens array 60 images the interference light field array onto the surface array detector 70 through various imaging channels to obtain a set of interference image arrays. Each interference image unit in the interference image array corresponds to a FP resonant cavity of a specific gap thickness in the Fabry-Perot array interference system, thereby corresponding to an inherent optical path difference δ. In the present invention, each interference image unit in the interference image array is a copy of the same field of view, and is intensity modulated by the corresponding FP resonant cavity. The area array detector 70 performs image segmentation on the interference image array, divides the interference image array into interference image units corresponding to each specific FP resonant cavity, and arranges the divided interference image units into an interference image data cube according to the thickness order of the FP resonant cavity. The thickness of each FP resonant cavity corresponds to a specific optical path difference δ, and after image registration, the interference image of each target point can be extracted. Each spatial pixel of the two-dimensional image plane in the interference image data cube is extracted, and the interference light intensity of each optical path difference corresponding to the spatial pixel is extracted along the optical path difference δ axis, so as to obtain the interference image sequence corresponding to each spatial pixel. Discrete Fourier transform operation is performed on the interference image sequence of each spatial pixel, and the spectral information corresponding to each spatial pixel is obtained, thereby obtaining a spectral image data cube that changes with the wavelength λ, thereby demodulating the spectral information of each point of the target scene, and realizing the snapshot measurement of the image information and spectral information of the target scene.

[0050] Example 2 The difference between Example 2 and Example 1 is that the structures of the first step lens and the second step lens of Example 2 are different from those of the first step lens and the second step lens of Example 1. Figure 6As shown, the step substrate 403 of the first step lens 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 high 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. The structure of the second step lens can be obtained in the same way.

[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 double-step Fabry-Perot interferometer snapshot imaging spectrometer, characterized in that: It includes a telescope system, a microlens array, a Fabry-Perot array interferometer system and a planar array detector; among them, The telescope system is used to collect the target light field and to limit and collimate the target light field; The Fabry-Perot array interference system is located in the parallel optical path of the telescope system. The Fabry-Perot array interference system is used to modulate the target light field to form an interference light field array. The Fabry-Perot array interference system includes a first step lens and a second step lens with orthogonal step directions. The first step lens and the second step lens serve as a front interference plate and a rear interference plate of the Fabry-Perot array interference system respectively. The number of steps of the first step lens is M, the number of steps of the second step lens is N, the step height difference between any two adjacent steps of the first step lens is d, and the step height difference between any two adjacent steps of the second step lens is Md. The highest step of the first step lens is tightly fitted with the highest step of the second step lens, so that an air gap with a thickness that changes in a two-dimensional incremental manner in a checkerboard shape is formed between the first step lens and the second step lens. The thickness of each area of ​​the air gap corresponds to an optical path difference. The first step lens, the air gap and the second step lens form a FP resonant cavity array. The microlens array is located in the emission direction of the Fabry-Perot array interference system. The microlens array adopts an image-side telecentric optical path structure and is composed of M×N microlens units. Each microlens unit corresponds to a row of steps of the first step lens and a column of steps of the second step lens. Each microlens unit serves as an imaging channel. The microlens array is used to image the interference light field array onto the area array detector through each imaging channel. The area array detector is located at the image focal plane of the microlens array and is used to receive the transmission image field of each imaging channel of the microlens array to obtain an interference image array.

2. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 1, characterized in that: The two opposite surfaces of the first step lens and the second step lens 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%.

3. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 1, characterized in that: The first step lens and the second step lens respectively include a step substrate. When 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. When 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.

4. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 3, 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.

5. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 1, characterized in that: The thickness of the air gap is distributed in a two-dimensional increasing manner in a checkerboard pattern. m Direction d The step length increases successively, and the thickness increases along n Direction Md The step size increases successively. m , n ) steps corresponding to the thickness of the air gap of the FP resonant cavity h ( m , n )for: h ( m , n )=[( n -1) M + m -1] d 。 6. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 1, characterized in that: For the incident broadband spectrum, the step height difference d of the first step lens 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 the incident narrowband spectrum, the step height difference d of the first step lens 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 .

7. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 3, characterized in that: The preparation process of the step substrate of the first step lens is: A1: providing a flat substrate with a lateral width of a and a longitudinal width of b, and polishing and cleaning the flat substrate; A2: Etching the flat substrate to form a two-step structure, with an etching depth of Md / 2 and an etching width of a / 2; A3: Etching the two-step structure to form a four-step structure, with an etching depth of Md / 4 and an etching width of a / 4, repeating step A3 to ensure that each etching depth is 1 / 2 of the previous etching depth and each etching width is 1 / 2 of the previous etching depth, until the step height difference is d and the step width is a / M; The preparation process of the step substrate of the second step lens is as follows: B1: providing a plane substrate with a lateral width of a and a longitudinal width of b, and polishing and cleaning the plane substrate; B2: Etching the flat substrate to form a two-step structure, with an etching depth of NMd / 2 and an etching width of b / 2; B3: Etch the two-step structure to form a four-step structure, with an etching depth of NMd / 4 and an etching width of b / 4. Repeat step B3 to ensure that the etching depth and width of each etching are 1 / 2 of the previous etching, until the step height difference is Md and the step width is b / N.

8. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 1, characterized in that: The telescope system includes a telescope objective lens, a field stop and a collimator lens; among them, The telescope objective is used to collect the target light field and image the target light field at the field aperture; The field diaphragm is located on both the image-side focal plane of the telescope objective and the object-side focal plane of the collimator. The field diaphragm is used to limit the field of view of the imaging of the target light field. The collimator is used to collimate the divergent light emitted by the target light field located at the field stop into parallel light.

9. The double-step Fabry-Perot interferometer snapshot imaging spectrometer according to claim 1, characterized in that: The area array detector is also used to perform image segmentation on the interference image array, dividing the interference image array into interference image units corresponding to each FP resonant cavity; and arranging the interference image units in the order of the thickness of each FP resonant cavity to form an interference image data cube, and performing discrete Fourier transform operation on the interference image data cube with the optical path difference as the axis to obtain a spectral image data cube that varies with wavelength.

Images