Low-fineness snapshot image surface interference imaging spectrometer

Abstract

The invention relates to the field of spectral imaging, in particular to a low-fineness snapshot image surface interference imaging spectrometer, which comprises a telescopic system, a micro-lens array, a Fabry-Perot array interference system and a detection system, 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 micro lens array is used for performing array imaging on the straightened target light field; the Fabry-Perot array interference system comprises a parallel flat plate and a checkerboard step mirror, the heights of steps are distributed in a checkerboard-shaped two-dimensional progressive decrease mode, the step height differences between every two adjacent steps are the same, the highest step is tightly attached to the parallel flat plate, and an air gap with the thickness changing in a two-dimensional progressive increase mode is formed between the highest step and the parallel flat plate. The thickness of each area of the air gap corresponds to one optical path difference; and the detection system is used for imaging the modulated interference light field 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 low-fineness snapshot image plane 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 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 low-fineness snapshot image plane interference 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 low-fineness snapshot image plane interference imaging spectrometer includes a telescope system, a microlens array, a Fabry-Perot array interference system and a detection system; wherein, The telescope system is used to collect the target light field and to limit and collimate the target light field; The microlens array is located in the collimation direction of the telescope system. The microlens array adopts an image-side telecentric optical path structure and is composed of M×N microlens units. The microlens array is used to perform array imaging of the collimated target light field. The Fabry-Perot array interference system is located in the imaging optical path of the microlens array. The Fabry-Perot array interference system includes a parallel plate and a checkerboard step mirror. The parallel plate serves as a front interference plate of the Fabry-Perot array interference system. The checkerboard step mirror is located on the image focal plane of the microlens array and serves as a rear interference plate of the Fabry-Perot array interference system. The number of steps of the checkerboard step mirror is M×N, and the step heights are distributed in a two-dimensional decreasing manner in a checkerboard shape. The step height difference between any two adjacent steps in one direction of the checkerboard step mirror is d, and the step height difference between any two adjacent steps in another direction of the checkerboard step mirror is Md. Each step corresponds to a microlens unit, and the highest step is tightly fitted with the parallel plate, so that an air gap with a thickness that changes in a two-dimensional increasing manner is formed between the parallel plate and the checkerboard 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 checkerboard 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, the two opposite surfaces of the parallel plate and the checkerboard 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 checkerboard step mirror, and the surface of the high refractive index plate facing the checkerboard 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 checkerboard step mirror, and a high refractive index dielectric film is evaporated on the surface of the low refractive index plate facing the checkerboard 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 checkerboard 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, assuming that the step height difference between two adjacent steps is d, the step height of the chessboard step mirror is distributed in a two-dimensional decreasing manner in a chessboard shape. m Direction d The step length decreases successively, and the height increases along n Direction Md The step size decreases successively. m , n ) steps height D ( m , n )for: D ( m , n )=-[( n -1) M + m -1] d .

[0012] Furthermore, assuming that the step height difference between two adjacent steps is d, 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 .

[0013] 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 corresponding to the maximum aperture 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; 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 .

[0014] Furthermore, the preparation process of the step substrate is as follows: S1: providing a plane substrate with a lateral width of a and a longitudinal width of b, and polishing and cleaning the plane substrate; S2: The planar substrate is longitudinally etched to form a longitudinal two-step structure, with an etching depth of NMd / 2 and an etching width of b / 2; S3: The longitudinal two-step structure is longitudinally etched to form a longitudinal four-step structure, the etching depth is NMd / 4, the etching width is b / 4, and step S3 is repeated to ensure that the etching depth each time is 1 / 2 of the previous etching, and the etching width each time is 1 / 2 of the previous etching, until the etching depth is Md and the etching width is b / N; S4: performing transverse etching on the longitudinal four-step structure to form a transverse two-step structure, with an etching depth of Md / 2 and an etching width of a / 2; S5: The lateral two-step structure is laterally etched to form a lateral four-step structure, with an etching depth of Md / 4 and an etching width of a / 4. Step S5 is repeated to ensure that the etching depth each time is 1 / 2 of the previous etching and the etching width each time is 1 / 2 of the previous etching until the etching depth is d and the etching width is a / M.

[0015] 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.

[0016] Furthermore, the detection system includes a relay imaging mirror, a cold screen aperture and an array detector; wherein, The relay imaging mirror adopts an object-side telecentric optical path structure to image the interference light field modulated by the Fabry-Perot array interferometer system 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.

[0017] 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.

[0018] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention adopts a chessboard 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 chessboard 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 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

[0019] 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 structural diagram of the low-fineness snapshot image plane interference imaging spectrometer described in Example 1 of the present invention.

[0020] Figure 2 It is a schematic diagram of the structure of the checkerboard step mirror described in Example 1 of the present invention.

[0021] Figure 3 Schematic diagram of the spatial distribution of the thickness of the air gap between the parallel plate and the checkerboard step mirror described in Example 1 of the present invention.

[0022] Figure 4 It is a schematic diagram of the preparation process of the step substrate described in Example 1 of the present invention.

[0023] Figure 5 It is a schematic diagram of the process of image spectrum inversion described in Example 1 of the present invention.

[0024] Figure 6 It is a schematic diagram of the structure of the checkerboard step mirror described in Example 2 of the present invention.

[0025] Explanation of the figure marks of Example 1: telescope objective 10, field aperture 20, collimator 30, microlens array 40, parallel plate 50, checkerboard step mirror 60, step substrate 601, anti-reflection film 602, relay imaging mirror 70, cold screen aperture 80, and area array detector 90.

[0026] Description of the reference numerals of Example 2: stepped substrate 603 , anti-reflection film 604 , high refractive index dielectric film 605 . DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0032] The invention provides a low-fineness snapshot image plane interference imaging spectrometer, including a telescope system, a microlens array, a Fabry-Perot array interference system and a detection system; wherein the telescope system is used to collect a target light field, and to limit and collimate the target light field; the microlens array is located in the collimation direction of the telescope system, the microlens array adopts an image-side telecentric optical path structure, and is composed of M×N microlens units, and the microlens array is used to perform array imaging on the collimated target light field; the Fabry-Perot array interference system is located in the imaging optical path of the microlens array, and the Fabry-Perot array interference system includes a parallel plate and a checkerboard step mirror, the parallel plate serves as a front interference plate of the Fabry-Perot array interference system, and the checkerboard step mirror serves as a front interference plate of the Fabry-Perot array interference system. The checkerboard step mirror is located on the image focal plane of the microlens array. As the rear interference plate of the Fabry-Perot array interferometer system, the checkerboard step mirror has M×N steps, and the step heights are distributed in a two-dimensional decreasing manner in a checkerboard shape. The step height difference between any two adjacent steps is the same. Each step corresponds to a microlens unit, and the highest step fits tightly with the parallel plate, so that an air gap with a thickness that changes in a two-dimensional increasing manner is formed between the parallel plate and the checkerboard step mirror, and the thickness of each area of ​​the air gap corresponds to an optical path difference. The detection system is located in the emitting 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.

[0033] 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.

[0034] The detection system includes a relay imaging mirror, a cold screen aperture and an array detector; the relay imaging mirror adopts an object-side telecentric optical path structure, which is used to image the interference light field modulated by the Fabry-Perot array interferometer system onto the array detector; the cold screen aperture is located on the image-side focal plane of the relay imaging mirror, which is used to limit the object-side numerical aperture; the array detector is located at the image plane of the relay imaging mirror, which is used to perform photoelectric conversion on the interference light field to obtain an interference image array.

[0035] The present invention images the target light field onto the field diaphragm through a telescope objective lens. The field diaphragm limits the imaging field of view and then collimates it into parallel light through a collimator lens, which is incident on a microlens array. The microlens array performs array focusing on the incident light field, and images the multiple arrays of the target light field into a Fabry-Perot array interference system. The Fabry-Perot array interference system consists of a parallel plate and a checkerboard step mirror, and each step of the checkerboard step mirror corresponds to an imaging channel, that is, corresponds to a microlens unit. The parallel plate and the checkerboard step mirror are tightly fitted on the surface of the highest step, and an air gap with a thickness that changes linearly and incrementally in a checkerboard shape is formed between the parallel plate and the checkerboard step mirror. The parallel plate and the checkerboard step mirror are made of silicon or germanium materials with a 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. The step structure of the checkerboard step mirror causes the thickness of the air gap to vary in two-dimensional discrete linear fashion, and different air gap thicknesses correspond to different optical path differences, thereby modulating the optical path difference of the target light field incident therein, resulting in changes in interference intensity. Therefore, the target light field is modulated by the Fabry-Perot array interference system to form an interference light field array, and each interference light field unit corresponds to a specific optical path difference. The interference light field array is imaged onto a planar array detector after being transmitted by a relay imaging mirror, and an interference image array corresponding to the optical path difference array is obtained on the planar array detector. By performing image segmentation and image registration on the interference image array, and performing discrete Fourier transform along the optical path difference, the spectral information of each object point in the target scene can be restored, and snapshot measurement of the image information and spectral information of the target scene can be achieved. The present invention reduces the size of the Fourier transform infrared imaging spectrometer, and has the advantages of compact structure, static, stable, and reliable.

[0036] Example 1 like Figure 1-Figure 5 As shown, the low-fineness snapshot image plane interference imaging spectrometer provided by Example 1 of the present invention includes a telescope objective 10, a field aperture 20, a collimator 30, a microlens array 40, a parallel plate 50, a checkerboard step mirror 60, a relay imaging mirror 70, a cold screen aperture 80 and a planar array detector 90 (using devices such as HgCdTe or InSb).

[0037] The target light field is first imaged onto the field of view aperture 20 through the telescope objective 10. The field of view aperture 20 limits the imaging field of the target light field, thereby controlling the spatial sampling on the array detector 90 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 microlens array 40. The microlens array 40 is composed of M×N microlens units, which performs aperture segmentation and array imaging on the incident parallel light field. The microlens array 40 adopts an image-side telecentric optical path structure so that the main light of the array imaging beam is parallel to the optical axis. The microlens array 40 divides the incident light field into M×N sub-apertures, and images its array into the Fabry-Perot array interferometer system, forming interference in the FP resonant cavity of the Fabry-Perot array interferometer system. The interference plate of the Fabry-Perot array interference system is composed of a parallel plate 50 and a checkerboard step mirror 60. The parallel plate 50 serves as the front interference plate of the Fabry-Perot array interference system, and the checkerboard step mirror 60 serves as the rear interference plate of the Fabry-Perot array interference system. The checkerboard step mirror 60 includes a step base 601. The multiple steps of the step base 601 are arranged in a two-dimensional checkerboard shape. Each step has a specific thickness, thereby corresponding to an FP resonant cavity. Each FP resonant cavity corresponds to a specific microlens unit, and interference modulation is performed on each image field unit of the microlens array imaging. The two reflection interfaces of the Fabry-Perot array interference system use medium reflectivity to form a low-fineness interference cavity, which is close to double-beam interference, so that spectrum restoration can be performed through Fourier transform. The parallel plate 50 and the highest step of the checkerboard step mirror 60 are closely fitted, so that an air gap with a thickness that changes in a two-dimensional incremental manner is formed between the two, thereby forming an optical path difference that changes with the spatial position, and achieving zero optical path difference at the optical contact position of the two opposite surfaces of the parallel plate 50 and the checkerboard step mirror 60.

[0038] The two surfaces of the checkerboard step mirror 60 opposite to the parallel plate 50 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.

[0039] The interference image signal formed by the FP resonant cavity corresponding to the (m, n)th step in the checkerboard step mirror 60 of the Fabry-Perot array interferometer 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: ; Wherein, 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 different field angles of the target scene; h(m,n) is the gap thickness of the FP resonant cavity, which varies with the spatial position due to the checkerboard step structure.

[0040] 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.

[0041] 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 checkerboard step mirror 60 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.

[0042] 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.

[0043] 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 50 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 50 away from the checkerboard step mirror 60, and no film is applied on the surface of the parallel plate 50 facing the checkerboard step mirror 60. The step substrate 601 can be made of a high refractive index medium material such as silicon or germanium, and the surface of the step substrate 601 facing the parallel plate 50 is not coated, so that the reflection interface has a medium-low reflectivity to achieve low fineness. The surface of the step substrate 601 away from the parallel plate 50 is evaporated with an anti-reflection film 602 to ensure high transmittance, and the highest step of the step substrate 601 is in contact with the uncoated side of the parallel plate 50 to achieve zero optical path difference on the optical contact surface.

[0044] An air gap with increasing thickness is formed between the checkerboard step mirror 60 and the parallel plate 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. Assuming that the step height difference of the checkerboard step mirror 60 is d, and the number of steps is M×N, in order to form continuous optical path difference sampling, the thickness of the air gap of the FP resonant cavity corresponding to the (m,n)th step is: .

[0045] 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 aperture 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.

[0046] 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, 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 .

[0047] The step base 601 is composed of M×N steps, the step height difference between any two adjacent steps in one direction of the step base 601 is constant d, and the step height difference between any two adjacent steps in another direction of the step base 601 is constant Md. The step base 601 is manufactured by etching, and the manufacturing process is as follows: S1: providing a plane substrate with a lateral width of a and a longitudinal width of b, and polishing and cleaning the plane substrate.

[0048] S2: The planar substrate is longitudinally etched to form a longitudinal two-step structure, with an etching depth of NMd / 2 and an etching width of b / 2.

[0049] S3: The longitudinal two-step structure is longitudinally etched to form a longitudinal four-step structure, with an etching depth of NMd / 4 and an etching width of b / 4. Step S3 is repeated to ensure that the etching depth each time is 1 / 2 of the previous etching, and the etching width each time is 1 / 2 of the previous etching, until the etching depth is Md and the etching width is b / N.

[0050] S4: performing transverse etching on the longitudinal four-step structure to form a transverse two-step structure, with an etching depth of Md / 2 and an etching width of a / 2.

[0051] S5: The lateral two-step structure is laterally etched to form a lateral four-step structure, with an etching depth of Md / 4 and an etching width of a / 4. Step S5 is repeated to ensure that the etching depth each time is 1 / 2 of the previous etching and the etching width each time is 1 / 2 of the previous etching until the etching depth is d and the etching width is a / M.

[0052] After the imaging light field is modulated by the Fabry-Perot array interference system, it is imaged onto the area array detector 90 at a certain reduction ratio through the relay imaging mirror 70. The relay imaging mirror 70 samples the object-side telecentric optical path structure, and its image-side focal plane matches the cold screen aperture 80 of the area array detector 90. In other words, the cold screen aperture 80 of the area array detector 90 is located on the image-side focal plane of the relay imaging mirror 70. The Fabry-Perot array interference system and the area array detector 90 satisfy the object-image conjugate relationship relative to the relay imaging mirror 70. The relay imaging mirror 70 relays the interference light field modulated by the Fabry-Perot array interference system onto the area array detector 90 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 dielectric thickness of 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 90 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 pattern 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 pattern sequence corresponding to each spatial pixel. Discrete Fourier transform operation is performed on the interference pattern sequence of each spatial pixel to obtain the spectral information corresponding to each spatial pixel, 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.

[0053] Example 2 The difference between Example 2 and Example 1 is only that the structure of the chessboard step mirror is different. Figure 6 As shown, the step substrate 603 of the checkerboard 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 605 such as silicon or germanium is evaporated on the step surface of the step substrate 603 so that the reflection interface has a medium-low reflectivity to achieve low fineness, and an anti-reflection film 604 is evaporated on the lower surface (i.e., the bottom plane) of the step substrate 603 to ensure high transmittance.

[0054] 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.

[0055] 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 low-fineness snapshot image plane interference imaging spectrometer, characterized in that: It includes telescope system, microlens array, Fabry-Perot array interferometer system and detection system; among them, The telescope system is used to collect the target light field and to limit and collimate the target light field; The microlens array is located in the collimation direction of the telescope system. The microlens array adopts an image-side telecentric optical path structure and is composed of M×N microlens units. The microlens array is used to perform array imaging of the collimated target light field. The Fabry-Perot array interference system is located in the imaging optical path of the microlens array. The Fabry-Perot array interference system includes a parallel plate and a checkerboard step mirror. The parallel plate serves as a front interference plate of the Fabry-Perot array interference system. The checkerboard step mirror is located on the image focal plane of the microlens array and serves as a rear interference plate of the Fabry-Perot array interference system. The number of steps of the checkerboard step mirror is M×N, and the step heights are distributed in a two-dimensional decreasing manner in a checkerboard shape. The step height difference between any two adjacent steps in one direction of the checkerboard step mirror is d, and the step height difference between any two adjacent steps in another direction of the checkerboard step mirror is Md. Each step corresponds to a microlens unit, and the highest step is tightly fitted with the parallel plate, so that an air gap with a thickness that changes in a two-dimensional increasing manner is formed between the parallel plate and the checkerboard 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 checkerboard 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 low-fineness snapshot image plane interference imaging spectrometer according to claim 1, characterized in that: The two opposite surfaces of the parallel plate and the chessboard 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%~40%.

3. The low-fineness snapshot image plane interference 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 checkerboard step mirror, and the surface of the high refractive index plate facing the checkerboard 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 checkerboard step mirror, and a high refractive index dielectric film is evaporated on the surface of the low refractive index plate facing the checkerboard step mirror and serves as the reflection interface of the FP resonant cavity.

4. The low-fineness snapshot image plane interference 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 low-fineness snapshot image plane interference imaging spectrometer according to claim 1, characterized in that: The checkerboard 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 low-fineness snapshot image plane interference 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 low-fineness snapshot image plane interference imaging spectrometer according to claim 1, characterized in that: The step height of the chessboard step mirror is distributed in a two-dimensional decreasing manner in a chessboard shape. m Direction d The step length decreases successively, and the height increases along n Direction Md The step size decreases successively. m , n ) steps height D ( m , n )for: D ( m , n )=-[( n -1) M + m -1] d 。 8. The low-fineness snapshot image plane interference imaging spectrometer according to claim 7, 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 。 9. The low-fineness snapshot image plane interference 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 corresponding to the maximum aperture 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; 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 .

10. The low-fineness snapshot image plane interference imaging spectrometer according to claim 5, characterized in that: The preparation process of the step substrate is: S1: providing a plane substrate with a lateral width of a and a longitudinal width of b, and polishing and cleaning the plane substrate; S2: The planar substrate is longitudinally etched to form a longitudinal two-step structure, with an etching depth of NMd / 2 and an etching width of b / 2; S3: The longitudinal two-step structure is longitudinally etched to form a longitudinal four-step structure, the etching depth is NMd / 4, the etching width is b / 4, and step S3 is repeated to ensure that the etching depth each time is 1 / 2 of the previous etching, and the etching width each time is 1 / 2 of the previous etching, until the etching depth is Md and the etching width is b / N; S4: performing transverse etching on the longitudinal four-step structure to form a transverse two-step structure, with an etching depth of Md / 2 and an etching width of a / 2; S5: The lateral two-step structure is laterally etched to form a lateral four-step structure, with an etching depth of Md / 4 and an etching width of a / 4. Step S5 is repeated to ensure that the etching depth each time is 1 / 2 of the previous etching and the etching width each time is 1 / 2 of the previous etching until the etching depth is d and the etching width is a / M.

11. The low-fineness snapshot image plane interference 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.

12. The low-fineness snapshot image plane interference 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 adopts an object-side telecentric optical path structure to image the interference light field modulated by the chessboard step mirror 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.

13. The low-fineness snapshot image plane interference imaging spectrometer according to claim 12, 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