Reflective Fabry-Perot etalon array snapshot interferometry spectrometer

Abstract

The present invention relates to the field of spectral imaging, and in particular to a reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer, comprising a telescope system, a microlens array, a beam splitter, a reflective Fabry-Perot etalon array, and a detection system. The telescope system is used to collect a target light field and perform field-of-view restriction and collimation on the target light field; the microlens array is used to perform array imaging on the collimated target light field; the beam splitter is used to transmit the array imaging light beam; the reflective Fabry-Perot etalon array is composed of a substrate and a plurality of Fabry-Perot etalon units with a two-dimensional linearly increasing dielectric cavity thickness, wherein the step height difference between any two adjacent Fabry-Perot etalon units is the same; and the detection system is used to image the interference light field modulated by the reflective Fabry-Perot etalon array to obtain an interference image array. The present invention has the advantages of small size, light weight, compact structure, static, stable, and reliable.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral imaging, and in particular relates to a reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer. Background Art

[0002] Fourier transform spectroscopy is a widely used measurement method for acquiring infrared spectra of target scenes. Its applications extend beyond the laboratory to remote sensing. Most Fourier transform spectrometers employ a time-modulated Michelson interferometer system. The system measures the time-modulated interference signal generated by the interaction of the incident spectrum with the Michelson interferometer, and then performs spectral demodulation via Fourier transform. In a Michelson interferometer-based Fourier transform infrared spectrometer, the interference pattern is temporally sampled using a moving mirror. This moving mirror splits the input beam, generating a time-varying optical path difference between the two beams. Under monochromatic light illumination, the detector responds to this time-varying optical path difference with a sinusoidal signal that varies with the optical path difference. By precisely measuring the change in optical path difference, typically using a reference laser signal, the wavelength information of the incident light can be recovered from the sampled interference signal. Multiple wavelengths of illumination produce a composite interference pattern, and the intensity of each wavelength, i.e., the spectral information, can be recovered using Fourier transform. Since the Michelson interferometer system uses a high-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, 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 to the Michelson interferometer system, the Fabry-Perot interferometer system has advantages such as compact structure, small size, and light weight, making it particularly suitable for applications such as those onboard drones and micro-nano satellites. Traditional Fabry-Perot interferometer systems are typically used as very narrow bandpass filters, achieving narrowband filtering through the use of very high reflectivity coatings. If a low reflectivity coating is used on the surface of the Fabry-Perot cavity, the spectral transmission is essentially sinusoidal, and the spectrum can be restored through Fourier transform. However, if the coating reflectivity 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 reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer to solve the technical problems of existing Fourier transform spectrometers based on Michelson interferometer systems, such as large size, heavy weight, difficulty in integration and susceptibility to external environmental influences.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] A reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer comprises a telescope system, a microlens array, a beam splitter, a reflective Fabry-Perot etalon array and a detection system; wherein,

[0007] The telescope system is used to collect the target light field and perform field-of-view limitation and collimation on the target light field;

[0008] The microlens array is located in the collimation direction of the telescope system. The micro-imaging mirror array adopts an image-side telecentric optical path structure and is composed of M×N microlens units. The micro-imaging mirror array is used to perform array imaging of the collimated target light field.

[0009] The beam splitter is located in the imaging light path of the microlens array and is used to transmit the array imaging light beam;

[0010] The reflective Fabry-Perot etalon array is located on the image-side focal plane of the microlens. The reflective Fabry-Perot etalon array consists of a substrate and M×N Fabry-Perot etalon units with dielectric cavities having a two-dimensional linearly increasing thickness. The thickness of each dielectric cavity corresponds to an optical path difference. The step height difference between any two adjacent Fabry-Perot etalon units in one direction is d, and the step height difference between any two adjacent Fabry-Perot etalon units in the other direction is Md. Each Fabry-Perot etalon unit corresponds to a microlens unit.

[0011] The detection system is located in the reflection direction of the beam splitter and is used to image the interference light field modulated by the reflective Fabry-Perot etalon array to obtain an interference image array.

[0012] Furthermore, the reflectivity of the two reflection interfaces of the dielectric cavity is 30% to 40%.

[0013] Furthermore, the substrate adopts a low-refractive-index substrate or a metal substrate, and the Fabry-Perot etalon unit adopts a high-refractive-index transparent dielectric layer; or, the substrate adopts a high-refractive-index substrate or a metal substrate, and the Fabry-Perot etalon unit adopts a low-refractive-index transparent dielectric layer, and a reflective film is plated on the upper surface of the low-refractive-index transparent dielectric layer; or, the substrate adopts an opaque glass or plastic substrate, and a reflective film is plated on the upper surface of the opaque glass or plastic substrate, and the Fabry-Perot etalon unit adopts a low-refractive-index transparent dielectric layer, and a reflective film is plated on the upper surface of the low-refractive-index transparent dielectric layer.

[0014] Furthermore, the low refractive index substrate is a quartz, calcium fluoride, magnesium fluoride or sapphire dielectric material; the high refractive index transparent dielectric layer uses a silicon dielectric material or a germanium dielectric material; the high refractive index substrate is a silicon dielectric material or a germanium dielectric material, the low refractive index transparent dielectric layer is any one of silicon dioxide, aluminum oxide, calcium fluoride, magnesium fluoride, yttrium fluoride, thorium fluoride, and cerium fluoride, and the reflective film is a silicon film or a germanium film.

[0015] Furthermore, the dielectric cavity thickness h(m,n) of the (m,n)th Fabry-Perot etalon unit is:

[0016] .

[0017] Furthermore, for the incident broadband spectrum, the step height difference d satisfies the following relationship:

[0018] ;

[0019] 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 dielectric cavity, J is the spectral harmonic order, and n0 is the medium refractive index of the Fabry-Perot etalon unit;

[0020] For the incident narrowband spectrum, the step height difference d satisfies the following relationship:

[0021] ;

[0022] 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 order of spectrum folding, and can be any integer less than or equal to .

[0023] Furthermore, the preparation process of the reflective Fabry-Perot etalon array is as follows:

[0024] S1: providing a substrate with a lateral width a and a longitudinal width b, and polishing and cleaning the substrate;

[0025] S2: evaporating a zero optical path difference dielectric layer of the dielectric cavity on the substrate, wherein the thickness of the zero optical path difference dielectric layer is close to zero, and the lateral width and longitudinal width of the zero optical path difference dielectric layer are respectively the same as the lateral width and longitudinal width of the substrate;

[0026] S3: vapor-depositing a longitudinal two-step dielectric layer of the dielectric cavity on the zero optical path difference dielectric layer, wherein the thickness of the longitudinal two-step dielectric layer is NMd / 2, the longitudinal width of the longitudinal two-step dielectric layer is b / 2, and the transverse width of the longitudinal two-step dielectric layer is a;

[0027] S4: Vapor-depositing a longitudinal four-step dielectric layer of the dielectric cavity on the longitudinal two-step dielectric layer, wherein the thickness of the longitudinal four-step dielectric layer is NMd / 4, the longitudinal width of the longitudinal four-step dielectric layer is b / 4, and the transverse width of the longitudinal four-step dielectric layer is a. Repeating step S4, in each evaporation process of the longitudinal step dielectric layer, the thickness of the longitudinal step dielectric layer is 1 / 2 of the previous one, and the longitudinal width of the longitudinal step dielectric layer is 1 / 2 of the previous one, until the step height difference of the longitudinal step dielectric layer is Md and the longitudinal width of the longitudinal step dielectric layer is b / N;

[0028] S5: evaporating a transverse two-step dielectric layer of the dielectric cavity on the longitudinal step dielectric layer, wherein the thickness of the transverse two-step dielectric layer is Md / 2, the transverse width of the transverse two-step dielectric layer is a / 2, and the longitudinal width of the transverse two-step dielectric layer is b;

[0029] S6: Evaporate a horizontal four-step dielectric layer of the dielectric cavity on the horizontal two-step dielectric layer, the thickness of the horizontal four-step dielectric layer is Md / 4, the horizontal width of the horizontal four-step dielectric layer is a / 4, and the vertical width of the horizontal four-step dielectric layer is b. Repeat step S6. In each evaporation process of the horizontal step dielectric layer, the thickness of the horizontal step dielectric layer is 1 / 2 of the previous time, and the horizontal width of the horizontal step dielectric layer is 1 / 2 of the previous time, until the step height difference of the horizontal step dielectric layer is d and the horizontal width of the horizontal step dielectric layer is a / M.

[0030] Furthermore, the telescope system includes a telescope objective lens, a field stop and a collimator lens; wherein,

[0031] The telescopic objective lens is used to collect the target light field and image the target light field at the field stop;

[0032] The field stop is located on both the image-side focal plane of the telescope objective and the object-side focal plane of the collimator. The field stop is used to limit the field of view of the imaging of the target light field.

[0033] The collimator is used to collimate the divergent light emitted by the target light field at the field stop into parallel light.

[0034] Furthermore, the detection system includes a relay imaging mirror, a cold screen aperture and an array detector; wherein,

[0035] The relay imaging mirror is located in the reflection direction of the beam splitter. The relay imaging mirror adopts an object-space telecentric optical path structure and is used to image the interference light field modulated by the reflective Fabry-Perot etalon array onto the area array detector.

[0036] 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;

[0037] 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.

[0038] Furthermore, 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 Fabry-Perot etalon unit; and arranging the interference image units in the order of the thickness of each Fabry-Perot etalon unit to form an interference image data cube, and performing a 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.

[0039] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0040] The present invention uses a Fabry-Perot etalon unit with a two-dimensional linearly increasing dielectric cavity thickness to construct a reflective Fabry-Perot etalon array, replacing the precision moving mirror scanning mechanism in the traditional Fourier transform imaging spectrometer, simplifying and lightweighting the optical-mechanical structure of the Fourier transform imaging spectrometer, improving the stability and robustness of the Fourier transform imaging spectrometer, and having the advantages of small size, light weight, compact structure, static, stable, and reliable. At the same time, the incident interface of the reflective Fabry-Perot etalon array adopts a medium-low reflectivity, and the spectrum can be restored by Fourier transform, reducing the difficulty of spectrum restoration in the traditional Fabry-Perot interferometer system. Through the coupled modulation transmission of the light field by the reflective Fabry-Perot etalon array and the microlens array, the synchronous measurement of the interference image data cube can be achieved, thereby realizing the snapshot-type effective detection of the target scene image information and spectral information, and improving the real-time performance of multi-dimensional information detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0042] Figure 1 1 is a schematic structural diagram of the reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer according to Example 1 of the present invention.

[0043] Figure 2 Schematic diagram of the structure of a reflective Fabry-Perot etalon array based on a high-refractive-index dielectric cavity according to Example 1 of the present invention.

[0044] Figure 3 Schematic diagram of the spatial distribution of the dielectric cavity thickness of the reflective Fabry-Perot etalon array according to Example 1 of the present invention.

[0045] Figure 41 is a schematic diagram of the preparation process of the reflective Fabry-Perot etalon array described in Example 1 of the present invention.

[0046] Figure 5 1 is a flow chart of the image spectrum inversion process according to Example 1 of the present invention.

[0047] Figure 6 Schematic diagram of the structure of a reflective Fabry-Perot etalon array based on a low-refractive-index dielectric cavity according to Example 2 of the present invention.

[0048] Figure 7 3 is a schematic structural diagram of a reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer according to Example 3 of the present invention.

[0049] Description of the reference numerals of Example 1: telescope objective lens 10, field aperture 20, collimator 30, microlens array 40, beam splitter 50, reflective Fabry-Perot etalon array 60, substrate 601, high refractive index transparent medium layer 602, relay imaging mirror 70, cold screen aperture 80, and area array detector 90.

[0050] Description of the reference numerals of Example 2: substrate 603 , low-refractive-index transparent medium layer 604 , and reflective film 605 .

[0051] Description of the reference numerals of Example 3: substrate 606 , low refractive index transparent medium layer 607 , and reflective film 608 . DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0053] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0054] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second" and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0055] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0056] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0057] The present invention provides a reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer, comprising a telescope system, a microlens array, a beam splitter, a reflective Fabry-Perot etalon array, 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 micro-imaging mirror array adopts an image-side telecentric optical path structure and is composed of M×N microlens units; the micro-imaging mirror array is used to perform array imaging on the collimated target light field; the beam splitter is located in the imaging optical path of the microlens array and is used to limit and collimate the array imaging light field; The optical beam is transmitted; the reflective Fabry-Perot etalon array is located on the image focal plane of the microlens. The reflective Fabry-Perot etalon array consists of a substrate and M×N Fabry-Perot etalon units with dielectric cavities whose thickness increases linearly in two dimensions. The thickness of each dielectric cavity corresponds to an optical path difference. The step height difference between any two adjacent Fabry-Perot etalon units is the same. Each Fabry-Perot etalon unit corresponds to a microlens unit. The detection system is located in the reflection direction of the beam splitter and is used to image the interference light field modulated by the reflective Fabry-Perot etalon array to obtain an interference image array.

[0058] The telescope system includes a telescope objective, a field diaphragm and a collimator. The telescope objective is used to collect the target light field and image the target light field at the field diaphragm. 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 at the field diaphragm into parallel light.

[0059] The detection system includes a relay imaging mirror, a cold screen aperture and an area array detector; among them, the relay imaging mirror is located in the reflection direction of the beam splitter, and the relay imaging mirror adopts an object-side telecentric optical path structure, which is used to image the interference light field modulated by the reflective Fabry-Perot etalon array onto the area 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 area 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.

[0060] The present invention uses a telescope objective lens to image the target light field onto a field diaphragm. The field diaphragm limits the imaging field of view and then collimates it into parallel light through a collimator. The light is then incident on a microlens array, which focuses the incident light field. The microlens array then transmits the light through a beam splitter, and the multiple arrays are imaged onto a reflective Fabry-Perot etalon array. The reflective Fabry-Perot etalon array consists of a substrate and multiple Fabry-Perot etalon units located on the substrate. Each Fabry-Perot etalon unit is equivalent to a phase plate. The multiple phase plates and the bottom substrate form a checkerboard-shaped, stepped phase reflector. Each step corresponds to an imaging channel, that is, a microlens unit. By designing the height of each step, the step height distribution changes linearly and incrementally in a two-dimensional checkerboard pattern. That is, the dielectric cavity thickness of the reflective Fabry-Perot etalon array changes linearly and incrementally in two dimensions. Each dielectric cavity thickness corresponds to a specific optical path difference, thereby modulating the optical path difference of the incident imaging light field and generating changes in the intensity of the interference image. Therefore, the imaging light field array is modulated by the reflective Fabry-Perot etalon array 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 reflected by the beam splitter and transmitted by the relay imaging mirror, and then imaged onto the area array detector. The interference image array corresponding to the optical path difference array is obtained on the area 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 target scene image information and spectral information 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.

[0061] Example 1

[0062] like Figure 1-Figure 5As shown, the reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer provided in Example 1 of the present invention includes a telescope objective 10, a field stop 20, a collimator 30, a microlens array 40, a beam splitter 50, a reflective Fabry-Perot etalon array 60, a relay imaging mirror 70, a cold screen stop 80 and a planar array detector 90.

[0063] The target light field is first imaged onto the field stop 20 through the telescope objective 10. The field stop 20 limits the imaging field of the target light field, thereby controlling the spatial sampling and the size of the imaging field of view on the area array detector 90 and suppressing the crosstalk of the imaging field of view between adjacent interference channels. It is then 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 perform 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 after transmission through the beam splitter 50, the array is imaged onto the reflective Fabry-Perot etalon array 60. The reflective Fabry-Perot etalon array 60 is located on the image focal plane of the microlens array 40 . Each Fabry-Perot etalon unit corresponds to a specific microlens unit and performs interferometric modulation on each image field unit of the microlens array 40 .

[0064] The reflective Fabry-Perot etalon array 60 consists of a substrate 601 and Fabry-Perot etalon units at different heights located on the substrate 601. The Fabry-Perot etalon units at different heights form steps between them and are arranged in a checkerboard pattern. Each step corresponds to a Fabry-Perot etalon unit, and each Fabry-Perot etalon unit forms a dielectric cavity. Each dielectric cavity has a specific thickness, thereby forming a two-dimensional, incrementally varying thickness distribution that exhibits a checkerboard pattern between the reflective interfaces on both sides of the dielectric cavity, thereby forming an optical path difference that varies with spatial position. The thickness of the first step is controlled to approach zero optical path difference. The reflective Fabry-Perot etalon array 60 utilizes the moderate reflectivity of Fresnel reflection in high-refractive-index media to form a low-fineness interference cavity, similar to two-beam interference, thus enabling spectral restoration via Fourier transform.

[0065] A distributed FP resonant cavity is formed between the reflective interfaces on both sides of the dielectric cavity. Each FP resonant cavity has a specific cavity length and thus a fixed optical path difference. Light incident on the front and rear reflective interfaces will be reflected multiple times within 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 through the FP resonant cavity depends on the thickness of the medium between the front and rear reflective interfaces of the dielectric cavity, 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. The medium in the FP resonant cavity can be a low-refractive index medium or a high-refractive index medium, and different medium types correspond to different reflective interface structures. The reflective interface of a traditional Fabry-Perot interferometer system usually adopts a very high reflectivity to produce a narrow transmission band, while the reflective interface of the reflective Fabry-Perot etalon array 60 in the present invention adopts a medium reflectivity to produce a quasi-cosine interference signal that can be demodulated using Fourier transform.

[0066] The interference image signal formed by the FP resonant cavity corresponding to the (m, n)th step in the reflective Fabry-Perot etalon array 60 can be expressed as:

[0067] ;

[0068] Where R1 and R2 are the reflectivities of the two reflective interfaces of the dielectric 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, which is expressed as:

[0069] ;

[0070] Where n0 is the refractive index of the medium in the FP resonant cavity; θ is the incident angle of the light in the FP resonant cavity, corresponding to different aperture angles of the target light field; h(m,n) is the thickness of the medium in the FP resonant cavity, which varies with the spatial position.

[0071] The interference image signal formula shows that when the reflectivity of the reflective 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 reflective interface is very high, the interference fringes have a high modulation, but the interference signal is an extremely narrow comb function. Traditional Fabry-Perot interferometers use reflective interfaces with very high reflectivity, leveraging resonance to produce very narrow interference features. These very narrow comb-like interference signals produce sidelobes in the Fourier transform spectrum, which detract from the main frequency signal and distort the recovered spectrum. To suppress spectral distortion caused by harmonic signals and reduce the interference caused by sidelobe signals extending into the main frequency signal, the maximum wavenumber of the incident spectrum should be less than or equal to twice the minimum wavenumber, meaning the maximum wavelength should be less than or equal to twice the minimum wavelength. In other words, the wavelength bandwidth of the incident spectrum should be less than or equal to the minimum wavelength, or less than or equal to half the maximum wavelength. For shortwave infrared (1μm-2μm), mediumwave infrared (3μm-5μm), and longwave infrared (8μm-14μm), this generally meets application requirements.

[0072] Therefore, the present invention uses a reflective interface with a medium reflectivity to generate a cosine-like interference signal. In this case, the spectral finesse is low, and the reflective Fabry-Perot etalon array 60 is close to double-beam interference. The interference pattern function can be approximately expressed as:

[0073] ;

[0074] Therefore, the spectral information of the incident light signal can be restored from the interference signal through Fourier transform.

[0075] 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 spectral demodulation through Fourier transform, a trade-off between fringe modulation and spectral sidelobe suppression is required. By balancing the interferogram modulation and the cosine degree of the interference signal, the reflectivity of the reflective interface is determined, minimizing the spectral sidelobes and maximizing the interferogram modulation. In other words, by optimizing the reflectivity of the reflective 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 reflective interfaces of the dielectric cavity is set to 30% to 40%, which can achieve the optimal trade-off between the interferogram modulation and the cosine characteristic. Therefore, each Fabry-Perot etalon unit 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.

[0076] For infrared materials, silicon and germanium have relatively high refractive indices, resulting in relatively moderate reflectivity. Silicon has a refractive index of 3.4 and a surface reflectivity of 30%, while germanium has a refractive index of 4.0 and a surface reflectivity of 36%. Therefore, substrate 601 can be a low-refractive-index substrate made of a low-refractive-index medium such as quartz, calcium fluoride, magnesium fluoride, or sapphire. This low-refractive-index substrate supports the Fabry-Perot etalon unit above. A high-refractive-index transparent dielectric layer 602 (i.e., the Fabry-Perot etalon unit) is fabricated on the low-refractive-index substrate using a high-refractive-index dielectric material such as silicon or germanium. The top surface of high-refractive-index transparent dielectric layer 602 is uncoated, and the thickness of the first step is controlled to ensure near-zero optical path difference. A metal substrate can also be used for substrate 601. A high-refractive-index transparent medium layer 602 with a two-dimensional stepped checkerboard pattern is made of high-refractive-index medium materials such as silicon or germanium on a metal substrate. Similarly, the upper surface of the high-refractive-index transparent medium layer 602 is not coated, and the thickness of the first step is controlled to make it close to zero optical path difference.

[0077] The dielectric thickness distribution between the two reflective interfaces of a two-dimensional, checkerboard-patterned step phase plate constitutes a spatially distributed modulation of the optical path difference. The total height of each step corresponds to the dielectric thickness in the FP resonant cavity. Assuming the step height difference of the two-dimensional, checkerboard-patterned step phase plate is d, and the number of steps is M×N, then to achieve continuous optical path difference sampling, the dielectric thickness of the (m,n)th FP resonant cavity is:

[0078] ;

[0079] In order to achieve effective spectrum restoration, the step height d should satisfy the Nyquist sampling theorem. In order to suppress the spectrum 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:

[0080] ;

[0081] 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 of the Fabry-Perot etalon unit.

[0082] 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:

[0083] ;

[0084] 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.

[0085] The height difference between any two adjacent steps in one direction of the two-dimensional stepped phase plate is constant d, and the height difference between any two adjacent steps in the other direction is constant Md. The two-dimensional stepped phase plate consists of M×N steps and is manufactured by coating. The manufacturing process is as follows:

[0086] S1: providing a substrate with a lateral width a and a longitudinal width b, and polishing and cleaning the substrate;

[0087] S2: evaporating a zero optical path difference dielectric layer of the dielectric cavity on the substrate, wherein the thickness of the zero optical path difference dielectric layer is close to zero, and the lateral width and longitudinal width of the zero optical path difference dielectric layer are respectively the same as the lateral width and longitudinal width of the substrate;

[0088] S3: vapor-depositing a longitudinal two-step dielectric layer of the dielectric cavity on the zero optical path difference dielectric layer, wherein the thickness of the longitudinal two-step dielectric layer is NMd / 2, the longitudinal width of the longitudinal two-step dielectric layer is b / 2, and the transverse width of the longitudinal two-step dielectric layer is a;

[0089] S4: Vapor-depositing a longitudinal four-step dielectric layer of the dielectric cavity on the longitudinal two-step dielectric layer, wherein the thickness of the longitudinal four-step dielectric layer is NMd / 4, the longitudinal width of the longitudinal four-step dielectric layer is b / 4, and the transverse width of the longitudinal four-step dielectric layer is a. Repeating step S4, in each evaporation process of the longitudinal step dielectric layer, the thickness of the longitudinal step dielectric layer is 1 / 2 of the previous one, and the longitudinal width of the longitudinal step dielectric layer is 1 / 2 of the previous one, until the step height difference of the longitudinal step dielectric layer is Md and the longitudinal width of the longitudinal step dielectric layer is b / N;

[0090] S5: evaporating a transverse two-step dielectric layer of the dielectric cavity on the longitudinal step dielectric layer, wherein the thickness of the transverse two-step dielectric layer is Md / 2, the transverse width of the transverse two-step dielectric layer is a / 2, and the longitudinal width of the transverse two-step dielectric layer is b;

[0091] S6: Evaporate a horizontal four-step dielectric layer of the dielectric cavity on the horizontal two-step dielectric layer, the thickness of the horizontal four-step dielectric layer is Md / 4, the horizontal width of the horizontal four-step dielectric layer is a / 4, and the vertical width of the horizontal four-step dielectric layer is b. Repeat step S6. In each evaporation process of the horizontal step dielectric layer, the thickness of the horizontal step dielectric layer is 1 / 2 of the previous time, and the horizontal width of the horizontal step dielectric layer is 1 / 2 of the previous time, until the step height difference of the horizontal step dielectric layer is d and the horizontal width of the horizontal step dielectric layer is a / M.

[0092] After being modulated by the reflective Fabry-Perot etalon array 60, the imaging light field is reflected back to the beam splitter 50 and, after being reflected by the beam splitter 50, is imaged onto the area array detector 90 at a specific reduction factor via 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 reflective Fabry-Perot etalon array 60 and the area array detector 90 satisfy an object-image conjugate relationship relative to the relay imaging mirror 70. The relay imaging mirror 70 relays and images the interference light field modulated by the reflective Fabry-Perot etalon array 60 onto the area array detector 90, generating a set of interference image arrays. Each interference image element corresponds to a Fabry-Perot etalon element of a specific dielectric thickness in the reflective Fabry-Perot etalon array 60, and thus corresponds to an inherent optical path difference δ. In the present invention, each interference image element in the interference image array is a replica of the same field of view and is intensity modulated by the corresponding Fabry-Perot etalon element. The area array detector 90 performs image segmentation on the interference image array, dividing it into interference image elements corresponding to specific Fabry-Perot etalon elements. These segmented interference image elements are arranged in order of Fabry-Perot etalon element thickness to form an interference image data cube. The thickness of each Fabry-Perot etalon element corresponds to a specific optical path difference δ. After image registration, the interference pattern of each target point can be extracted. Each spatial pixel in the two-dimensional image plane of the interference image data cube is extracted, and the interference light intensity corresponding to each optical path difference corresponding to the spatial pixel is extracted along the optical path difference δ axis, thereby obtaining the interference pattern sequence corresponding to each spatial pixel. A discrete Fourier transform is performed on the interference pattern sequence for each spatial pixel to obtain the spectral information corresponding to each spatial pixel, thereby obtaining a spectral image data cube that varies with wavelength λ. The spectral information of each point in the target scene is then demodulated, achieving snapshot measurement of the target scene's image and spectral information.

[0093] Example 2

[0094] The difference between Example 2 and Example 1 is only the structure of the reflective Fabry-Perot etalon array. Figure 6As shown, the base 603 of the reflective Fabry-Perot etalon array of Example 2 uses a high-refractive-index substrate made of a high-refractive-index dielectric material such as silicon or germanium. The upper surface of the high-refractive-index substrate serves as the lower reflection interface of the Fabry-Perot etalon unit. A low-refractive-index transparent dielectric layer 604 with a checkerboard-shaped two-dimensional step pattern is made of a low-refractive-index transparent material such as silicon dioxide, aluminum oxide, calcium fluoride, magnesium fluoride, yttrium fluoride, thorium fluoride, or cerium fluoride on the high-refractive-index substrate. A silicon film or a germanium film of a certain thickness is evaporated on the upper surface of the low-refractive-index transparent dielectric layer 604 as a reflective film 605. The reflective film 605 serves as the upper reflection interface of the Fabry-Perot etalon unit, and the thickness of the first step is controlled to be close to zero optical path difference. Alternatively, a low-refractive-index transparent material such as silicon dioxide, aluminum oxide, calcium fluoride, magnesium fluoride, yttrium fluoride, thorium fluoride, or cerium fluoride may be used on a metal reflective substrate to produce a two-dimensional stepped low-refractive-index transparent medium layer 604 with a checkerboard pattern. A silicon film or germanium film of a certain thickness may be evaporated on the upper surface of the low-refractive-index transparent medium layer 604 as a reflective film 605, and the thickness of the first step may be controlled to be close to zero optical path difference.

[0095] Example 3

[0096] The only difference between Example 3 and Example 1 and Example 2 is the structure of the reflective Fabry-Perot etalon array. Figure 7 As shown, the reflective Fabry-Perot etalon array of Example 3 has an opaque glass or plastic substrate as its substrate 606. A silicon film or germanium film of a certain thickness is evaporated on the surface of the opaque glass or plastic substrate as a lower metal film 608. The silicon film or germanium film can also be replaced by a metal film such as silver, gold, or aluminum. The lower metal film 608 serves as the lower reflection interface of the Fabry-Perot etalon unit. Then, a two-dimensional, step-shaped, low-refractive-index transparent dielectric layer 607 with a checkerboard pattern is fabricated on the lower metal film 608 using a low-refractive-index transparent material such as silicon dioxide, aluminum oxide, calcium fluoride, magnesium fluoride, yttrium fluoride, thorium fluoride, or cerium fluoride. A silicon film or germanium film of a certain thickness is evaporated on the upper surface of the low-refractive-index transparent dielectric layer 607 as an upper reflection film 609. The upper reflection film 609 serves as the upper reflection interface of the Fabry-Perot etalon unit. The thickness of the first step is controlled to be close to zero optical path difference.

[0097] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0098] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer, characterized in that: It includes a telescope system, a microlens array, a beam splitter, a reflective Fabry-Perot etalon array and a detection system; among which, The telescope system is used to collect the target light field and perform field-of-view limitation and collimation on the target light field; The microlens array is located in the collimation direction of the telescope system. The micro-imaging mirror array adopts an image-side telecentric optical path structure and is composed of M×N microlens units. The micro-imaging mirror array is used to perform array imaging of the collimated target light field. The beam splitter is located in the imaging light path of the microlens array and is used to transmit the array imaging light beam; The reflective Fabry-Perot etalon array is located on the image focal plane of the microlens array. The reflective Fabry-Perot etalon array consists of a substrate and M×N Fabry-Perot etalon units with a dielectric cavity thickness that increases linearly in two dimensions. The thickness of each dielectric cavity corresponds to an optical path difference. The step height difference between any two adjacent Fabry-Perot etalon units in one direction is d, and the step height difference between any two adjacent Fabry-Perot etalon units in the other direction is Md. Each Fabry-Perot etalon unit corresponds to a microlens unit. The reflectivity of the two reflection interfaces of the dielectric cavity is 30%~40%. The substrate adopts a low-refractive-index substrate or a metal substrate, and the Fabry-Perot etalon unit adopts a high-refractive-index transparent dielectric layer. Alternatively, the substrate adopts a high-refractive-index substrate or a metal substrate, and the Fabry-Perot etalon unit adopts a high-refractive-index transparent dielectric layer. The etalon unit adopts a low-refractive-index transparent dielectric layer, and a reflective film is plated on the upper surface of the low-refractive-index transparent dielectric layer; or the substrate adopts an opaque glass or plastic substrate, and a reflective film is plated on the upper surface of the opaque glass or plastic substrate; the Fabry-Perot etalon unit adopts a low-refractive-index transparent dielectric layer, and a reflective film is plated on the upper surface of the low-refractive-index transparent dielectric layer; the low-refractive-index substrate is quartz, calcium fluoride, magnesium fluoride or sapphire dielectric material; the high-refractive-index transparent dielectric layer adopts silicon dielectric material or germanium dielectric material; the high-refractive-index substrate is silicon dielectric material or germanium dielectric material, the low-refractive-index transparent dielectric layer is any one of silicon dioxide, aluminum oxide, calcium fluoride, magnesium fluoride, yttrium fluoride, thorium fluoride, and cerium fluoride, and the reflective film is a silicon film or a germanium film; 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 dielectric cavity, J is the spectral harmonic order, and n0 is the medium refractive index of the Fabry-Perot etalon unit; For the incident narrowband spectrum, the step height difference d satisfies the following relationship: ； Among them, λs 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 ; The detection system is located in the reflection direction of the beam splitter and is used to image the interference light field modulated by the reflective Fabry-Perot etalon array to obtain an interference image array.

2. The reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer according to claim 1, wherein: The dielectric cavity thickness h(m,n) of the (m,n)th Fabry-Perot etalon unit is: 。 3. The reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer according to claim 1, wherein: The preparation process of the reflection Fabry-Perot etalon array is as follows: S1: providing a substrate with a lateral width a and a longitudinal width b, and polishing and cleaning the substrate; S2: evaporating a zero optical path difference dielectric layer of the dielectric cavity on the substrate, wherein the thickness of the zero optical path difference dielectric layer is close to zero, and the lateral width and longitudinal width of the zero optical path difference dielectric layer are respectively the same as the lateral width and longitudinal width of the substrate; S3: vapor-depositing a longitudinal two-step dielectric layer of the dielectric cavity on the zero optical path difference dielectric layer, wherein the thickness of the longitudinal two-step dielectric layer is NMd / 2, the longitudinal width of the longitudinal two-step dielectric layer is b / 2, and the transverse width of the longitudinal two-step dielectric layer is a; S4: Vapor-depositing a longitudinal four-step dielectric layer of the dielectric cavity on the longitudinal two-step dielectric layer, wherein the thickness of the longitudinal four-step dielectric layer is NMd / 4, the longitudinal width of the longitudinal four-step dielectric layer is b / 4, and the transverse width of the longitudinal four-step dielectric layer is a. Repeating step S4, in each evaporation process of the longitudinal step dielectric layer, the thickness of the longitudinal step dielectric layer is 1 / 2 of the previous one, and the longitudinal width of the longitudinal step dielectric layer is 1 / 2 of the previous one, until the step height difference of the longitudinal step dielectric layer is Md and the longitudinal width of the longitudinal step dielectric layer is b / N; S5: evaporating a transverse two-step dielectric layer of the dielectric cavity on the longitudinal step dielectric layer, wherein the thickness of the transverse two-step dielectric layer is Md / 2, the transverse width of the transverse two-step dielectric layer is a / 2, and the longitudinal width of the transverse two-step dielectric layer is b; S6: Evaporate a horizontal four-step dielectric layer of the dielectric cavity on the horizontal two-step dielectric layer, the thickness of the horizontal four-step dielectric layer is Md / 4, the horizontal width of the horizontal four-step dielectric layer is a / 4, and the vertical width of the horizontal four-step dielectric layer is b. Repeat step S6. In each evaporation process of the horizontal step dielectric layer, the thickness of the horizontal step dielectric layer is 1 / 2 of the previous time, and the horizontal width of the horizontal step dielectric layer is 1 / 2 of the previous time, until the step height difference of the horizontal step dielectric layer is d and the horizontal width of the horizontal step dielectric layer is a / M.

4. The reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer according to claim 1, wherein: The telescope system includes a telescope objective lens, a field stop and a collimator lens; among them, The telescopic objective lens is used to collect the target light field and image the target light field at the field stop; The field stop is located on both the image-side focal plane of the telescope objective and the object-side focal plane of the collimator. The field stop 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 at the field stop into parallel light.

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

6. The reflective Fabry-Perot etalon array snapshot interferometric imaging spectrometer according to claim 5, 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 Fabry-Perot etalon unit; and arranging the interference image units in the order of the thickness of each Fabry-Perot etalon unit to form an interference image data cube, and performing a 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