F-P spectral imaging system and method

Abstract

The invention provides an F-P spectral imaging system and method, and belongs to the technical field of spectral component measurement, and the system comprises a front lens which is used for collecting light energy and converting the light energy into emergent light meeting the limitation of the clear aperture of an F-P interferometer; the annular band optical filter comprises a central area and a plurality of concentric annular areas surrounding the central area, the bandwidth of each area is the same as the free spectral range of the F-P interferometer, and the annular band optical filter is used for eliminating level aliasing in emergent light of the front lens; the F-P interferometer is used for carrying out wavelength selection on emergent light of the annular band optical filter and outputting an interference field; the imaging mirror is used for projecting the interference field to the detector; and the detector is used for converting the projected optical signal into a digital electric signal. The F-P spectral imaging system which can maintain high spectral resolution and also can realize wide spectrum coverage is constructed by introducing the annular band optical filter which is accurately matched with the FSR of the F-P interferometer.

Description

Technical Field

[0001] This application relates to the field of spectral composition measurement technology, and in particular to an FP spectral imaging system and method. Background Technology

[0002] A Fabry-Pérot (FP) spectrometer is a spectroscopic analysis device based on the principle of a Fabry-Pérot interferometer, widely used in various scientific fields, including astronomy and atmospheric science. The core of this device is the Fabry-Pérot resonant cavity, which operates by utilizing the multi-beam interference effect between two partially transparent mirrors within the cavity. By adjusting the distance between the mirrors, high-resolution selection or filtering of light at specific wavelengths can be achieved, thus enabling precise analysis of the optical spectrum. According to the principle of the FP spectrometer, its performance is affected by the thickness *d* of the FP cavity and its reflectivity.

[0003] Based on the principle of FP multibeam interference, such as Figure 1 As shown, the optical path difference between adjacent beams is expressed as The phase difference is Where d is the distance between the two mirrors, the two reflectors of the FP interferometer are in medium 0 in front and behind them, and the refractive index is 0. n 0, the medium between the two reflecting surfaces is 1, refractive index n (usually air,) n ≈1). The transmission coefficient from medium 0 to medium 1 is t The transmittance coefficients of medium 1 to medium 0 are t The reflection coefficient within medium 1 to medium 0 is ' r Angle of incidence of light θ Its amplitude is u , v The frequency and intensity of light I 0( v )= u 2 The amplitude of each emitted beam can be expressed as... utt ' r 2m When the first emitted beam is considered to have zero phase, the complex amplitude of each emitted beam, considering phase, can be expressed as: utt '[ r 2 exp(- jδ FPI )] m Where m is the beam number; the total complex amplitude is The interference light intensity of the image plane is ,in, yes The complex conjugate of . Because of reflectivity R = r2 ,and The intensity distribution of the interference light emitted from the FP interferometer is as follows: ,in, It is the overall transmittance of the FP cavity. F =4 R / (1- R ) 2 This is the fineness coefficient. The interference intensity can be understood as the initial light passing through FP and undergoing transmission; the transmittance is expressed as... T FPI The (ν) curve is a periodic function of the wavenumber ν. When the incident angle θ of the light is fixed, that is, at a fixed position on the image plane of the FP spectrometer, the light intensity is as follows: Figure 2 The superposition of multiple wavenumber light intensities. If the spectral range is limited (e.g. Figure 2 (The orange area in the middle) ensures that only one wavenumber peak's energy is detected by the detector, thus achieving intensity detection for that wavenumber. Changing the incident angle θ shifts the wavenumber peak within the spectral range, enabling intensity detection at different wavenumbers, i.e., displaying the spectrum on the image plane. Within a confined spectral range, when δF-PI / 2=kπ, the intensity of the transmitted light equals the intensity of the incident light; this is the theoretical maximum value for transmitted light, where k is the interference order. Substituting δF-PI=4πνndcosθ, we obtain... This equation is known as the fundamental equation of the FP interferometer.

[0004] The performance of an FP spectrometer is determined by its free spectral range (FSR) and spectral resolution. (Analysis) F determines Wave number The width of the peak, i.e., spectral resolution. Spectral resolution describes the fineness of the output spectrum of an FP spectrometer in the wavelength dimension, specifically the full width at half maximum (FWHM) of the wavenumber peak. (FWHM is the relative half-intensity value.) kπ The phase difference is .make Solving for the full width at half maximum (FWHM) phase... .Will Substituting the values, the spectral resolution is calculated: Therefore, in order to achieve higher spectral resolution, it is necessary to increase the reflectance R of FP to increase F, while also increasing n and d.

[0005] To avoid interference from wavenumber peaks outside the restricted spectral range, the interferometric order k is restricted. Assume the... k The center wavelength of the interference peak is λ +Δ λ , No. k The center wavelength of the +1st order interference peak is λ ,but: Solve for Δ λand Δ v That is, the free spectral range and : In summary, to increase the free spectral range of the spectrometer, d and n need to be reduced. However, to improve spectral resolution, reflectivity needs to be increased, thus increasing n and d. There is a contradiction between these two approaches. Simply increasing F (i.e., increasing reflectivity) will cause losses on the reflective surface, leading to a significant decrease in the overall transmittance of the system.

[0006] Therefore, how to simultaneously satisfy a wide free spectral range and high spectral resolution in FP interferometers has become an urgent technical problem to be solved. Summary of the Invention

[0007] This application provides an FP spectral imaging system and method to solve the problem of the contradiction between free spectral range and spectral resolution in the prior art, and the defect that the instrument cannot simultaneously meet the requirements of wide free spectral range and high spectral resolution.

[0008] This application provides an FP spectral imaging system, including a front mirror placed in sequence for collecting light energy and converting it into outgoing light that meets the aperture limit of the FP interferometer; The annular filter includes multiple regions, including a central region and multiple concentric annular regions surrounding the central region. The bandwidth of each region is the same as the free spectral range of the FP interferometer, and is used to eliminate order aliasing in the outgoing light of the front mirror. The FP interferometer is used to select the wavelength of the emitted light from the annular filter and output an interference field. An imaging mirror is used to project the interference field onto the detector; A detector is used to convert projected light signals into digital electrical signals.

[0009] According to the FP spectral imaging system provided in this application, the light transmission range of each region in the annular filter is determined based on the wavelength range corresponding to each order.

[0010] According to the FP spectral imaging system provided in this application, the center wavelength of each region in the annular filter is shifted sequentially according to the step size of the free spectral range, thereby covering the Doppler broadening of the target spectral lines.

[0011] According to the FP spectral imaging system provided in this application, the FP interferometer includes two plane mirrors placed relatively parallel to each other, and the flatness of the plane mirrors is higher than λ / 100.

[0012] According to the FP spectral imaging system provided in this application, the reflectivity of the plane mirror is higher than 97%.

[0013] According to the FP spectral imaging system provided in this application, the accuracy of the spacing between the plane mirrors is within 0.5 μm.

[0014] According to the FP spectral imaging system provided in this application, the front mirror is a focal-free optical system.

[0015] This application also provides a FP spectral imaging method, which applies any of the FP spectral imaging systems described above, including: The front mirror collects the light energy emitted from the target scene and converts it into outgoing light that meets the aperture limit of the FP interferometer; The annular filter allows one FP interference order to pass through in each region, eliminating order aliasing in the outgoing light of the front mirror; The FP interferometer performs wavelength selection on the outgoing light from the annular filter and outputs an interference field; The imaging mirror projects the interference field onto the detector; The detector converts the projected light signal into a digital electrical signal.

[0016] According to the FP spectral imaging method provided in this application, before the light energy emitted by the target scene is collected by the front mirror and converted into outgoing light that meets the aperture limit of the FP interferometer, the method further includes: The FP spectral imaging system was spectrally calibrated using a monochromator to obtain the wavelength-channel mapping relationship.

[0017] According to the FP spectral imaging method provided in this application, after the detector converts the projected light signal into a digital electrical signal, the method further includes: Based on the spectral response model and radiation correction parameters obtained from laboratory calibration, the digital electrical signal obtained from a single complete scan is standardized to obtain a standard data cube. After identifying and extracting the spectral signals of the same target in different bands from the standard data cube, the spectral signals are arranged in wavelength order based on the wavelength-channel mapping relationship to obtain the target spectral curve.

[0018] The FP spectral imaging system and method provided in this application include a front mirror placed sequentially for collecting light energy and converting it into outgoing light that meets the aperture limit of the FP interferometer; and a ring filter comprising multiple regions, including a central region and multiple concentric ring regions surrounding the central region. The bandwidth of each region is the same as the free spectral range of the FP interferometer, used to eliminate order aliasing in the outgoing light from the front mirror. In other words, the ring filter is composed of multiple concentric rings, each ring corresponding to a narrow-bandpass filtering region with a specific center wavelength, and the passband width of each ring matching the aperture limit of the FP interferometer. The free spectral range, with each annular band having a one-to-one correspondence between its spatial position and the field of view or spatial position of the imaging system, allows light from different spatial regions (or different scanning times) to pass through their respective annular bands. Since each annular band only allows spectral components within one FSR width to pass through, the light entering the FP interferometer is confined to a single interference order in the wavelength dimension, fundamentally eliminating spectral aliasing between different orders. The FP interferometer is used to perform wavelength selection on the outgoing light from the annular band filters and output an interference field. An imaging mirror is used to project the interference field onto a detector. The detector is used to convert the projected optical signal into a digital electrical signal. This application introduces an annular filter before the FP interferometer. The annular filter acts as a pre-spectral preselector, ensuring that each beam of light entering the FP interferometer is within its current FSR window. Therefore, the interference signal output by the FP corresponds to only a unique wavelength range, avoiding spectral ambiguity caused by multi-order superposition, and ensuring uniqueness and accuracy in subsequent spectral reconstruction. The annular filter divides the broad spectrum into multiple sub-bands of FSR width, each sub-band independently entering the FP through its corresponding annular filter. This allows the FP to maintain high precision, while the overall system achieves broad spectral coverage through multi-annular filter stitching, overcoming the limitations of FSR and resolution. The inherent contradictions of the existing technology are addressed by employing a fixed-cavity FP interferometer, which eliminates the need for dynamic cavity adjustment and the high-precision piezoelectric drive device. Furthermore, since each frame corresponds to spectral information within a single FSR, the spectrum can be directly inverted through calibration relationships, avoiding complex Fourier transform and phase correction algorithms, thus improving system real-time performance and reliability. The spatial coding characteristics of the annular filter allow it to be used with a two-dimensional detector to acquire multi-band information in a single exposure, or combined with a scanning mechanism to improve the signal-to-noise ratio. The coordinated design of the front mirror and imaging mirror ensures efficient light transmission and meets the FP aperture requirements, guaranteeing system light throughput and imaging quality. In summary, this application, by introducing an annular filter precisely matched to the FP interferometer's FSR, constructs an FP spectral imaging system that maintains high spectral resolution while achieving wide spectral coverage. This effectively solves the core problems of existing technologies, such as order aliasing, FSR-resolution contradictions, high system complexity, and heavy data processing, improving the accuracy, practicality, and engineering feasibility of spectral imaging. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the principle of an FP interferometer in the existing technology; Figure 2 This is a schematic diagram of the variation curve of TF-PI with wavenumber ν in the existing technology; Figure 3 This is a schematic diagram of the FP spectral imaging system provided in this application; Figure 4 This is a schematic diagram of the structure of the annular filter provided in this application; Figure 5 This is a schematic diagram showing the relationship between different levels of incident angle and transmission center wavelength provided in this application; Figure 6 This is a schematic flowchart of the FP spectral imaging method provided in this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] It should be noted that in the description of the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The terms "upper," "lower," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly, for example, they can be fixed connections, detachable connections, or integral connections; they can be mechanical connections or electrical connections; they can be direct connections or indirect connections through an intermediate medium; and they can be internal connections between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] The terms "first," "second," etc., used in this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class, without limiting the number of objects; for example, a first object can be one or more. Furthermore, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects have an "or" relationship.

[0024] The following is combined with Figures 3-6 This application describes the FP spectral imaging system and method provided in the embodiments.

[0025] Figure 3 This is a schematic diagram of the FP spectral imaging system provided in this application, as shown below. Figure 3 As shown, the FP spectral imaging system includes front mirrors placed in sequence to collect light energy and convert it into outgoing light that meets the aperture limit of the FP interferometer; The annular filter includes multiple regions, including a central region and multiple concentric annular regions surrounding the central region. The bandwidth of each region is the same as the free spectral range of the FP interferometer, and is used to eliminate order aliasing in the outgoing light of the front mirror. The FP interferometer is used to select the wavelength of the emitted light from the annular filter and output an interference field. An imaging mirror is used to project the interference field onto the detector; A detector is used to convert projected light signals into digital electrical signals.

[0026] In this embodiment, the front mirror collects incident light energy from the target scene, typically far-field or near-field radiation, and collimates, focuses, or shapes the beam to meet the requirements of the subsequent FP interferometer for optical parameters such as incident beam aperture, divergence angle, and optical axis alignment.

[0027] In practical implementation, the front mirror can be composed of a lens group, a mirror, or a catadioptric optical system. Its numerical aperture (NA) and field of view (FOV) need to be matched with the spatial resolution and light flux requirements of the entire system. The output beam needs to be controlled within the effective aperture of the FP interferometer to avoid edge diffraction or energy loss.

[0028] In this embodiment, the annular filter consists of multiple regions. The central circle is one region, surrounded by multiple concentric annular regions, i.e., annular zones. Each region allows only one transmission peak. Each region corresponds to a filter with a different center wavelength. The passband width of each region is equal to the FSR of the FP interferometer, i.e., the wavelength interval between adjacent interference orders. The spatial distribution of the regions matches the field of view or pupil plane, allowing light from different spatial positions to pass through the corresponding wavelength filtering regions. This enables multiple regions to cover a wider spectral range and satisfy a wider spectral band detection. The annular filter is used to eliminate the aliasing problem caused by multi-order interference in the FP interferometer, ensuring that the light entering the FP interferometer contains only wavelength components within a single free spectral range.

[0029] Specifically, the transmission peaks of a FP interferometer repeat periodically, with intervals equal to the FSR (Free Speed ​​Reduction). If the input spectrum is wider than the FSR, different wavelengths may fall into the same interference order, causing aliasing. A ring filter pre-divides the broad spectrum into several sub-bands with FSR widths, allowing only one interference order to pass through each sub-band, thus achieving order separation. For example, if the FP interferometer's FSR is 10 nm, then each ring of the ring filter also has a bandwidth of 10 nm, such as 400–410 nm, 410–420 nm, and so on.

[0030] Figure 4 This is a schematic diagram of the structure of the annular filter provided in this application, as shown below. Figure 4 As shown, this is a 3-ring filter, which includes 3 zones: the first zone is the central area, the second zone is the annular area adjacent to the first zone, and the third zone is the annular area adjacent to the second zone.

[0031] In this embodiment, the FP interferometer acts as a tunable narrowband filter, performing high-resolution wavelength selection on the incident light and outputting an interference field with a specific wavelength (i.e., a spatially coherent interference pattern). The FP interferometer typically consists of two highly reflective, highly parallel mirrors, with a fixed or adjustable spacing between them. At a given mirror spacing, only wavelengths λ that satisfy the resonance condition are efficiently transmitted. By adjusting the cavity length, different wavelengths can be scanned, achieving hyperspectral imaging.

[0032] In this embodiment, the imaging mirror images the interference field (i.e., the spatial light intensity distribution with wavelength information) output by the FP interferometer onto the focal plane of the detector, maintaining a one-to-one correspondence between spatial information and spectral information.

[0033] Understandably, imaging mirrors need high transmittance and low aberrations to ensure that interference fringes or target images are not distorted, and the imaging magnification is matched with the detector pixel size to achieve the required spatial sampling rate.

[0034] In this embodiment, the detector receives the light signal projected by the imaging mirror and converts it into a digital electrical signal, thereby achieving the joint acquisition of two-dimensional spatial information and one-dimensional spectral information. The detector typically employs a CCD or CMOS area array detector.

[0035] Understandably, this application achieves multi-channel parallel design by using different regions of the ring filter to correspond to different wavelengths, thereby realizing single-exposure multispectral imaging.

[0036] In summary, the overall workflow of the FP spectral imaging system provided in this application is as follows: the target radiation light is collected and shaped by the front mirror to form a beam that meets the input requirements of the FP interferometer; the beam passes through the annular filter and is divided into multiple sub-spectral bands of FSR width to eliminate order aliasing; each sub-band light enters the FP interferometer, and only a narrow wavelength is allowed to pass through at a specific cavity length, forming an interference field; the interference field is projected onto the detector through the imaging mirror to form an image carrying spatial-spectral information. By adjusting the FP cavity length (or utilizing the multi-channel characteristics of the annular filter), the system can cover a wide spectral range while maintaining high spectral resolution.

[0037] The FP spectral imaging system provided in this application includes a front mirror placed sequentially for collecting light energy and converting it into outgoing light that meets the aperture limit of the FP interferometer; and a ring filter comprising multiple regions, including a central region and multiple concentric ring regions surrounding the central region. The bandwidth of each region is the same as the free spectral range of the FP interferometer, used to eliminate order aliasing in the outgoing light from the front mirror. In other words, the ring filter is composed of multiple concentric rings, each ring corresponding to a narrow-bandpass filtering region with a specific center wavelength, and the passband width of each ring matching the aperture limit of the FP interferometer. The free spectral range, with each annular band having a one-to-one correspondence between its spatial position and the field of view or spatial position of the imaging system, allows light from different spatial regions (or different scanning times) to pass through their respective annular bands. Since each annular band only allows spectral components within one FSR width to pass through, the light entering the FP interferometer is confined to a single interference order in the wavelength dimension, fundamentally eliminating spectral aliasing between different orders. The FP interferometer is used to perform wavelength selection on the outgoing light from the annular band filters and output an interference field. An imaging mirror is used to project the interference field onto a detector. The detector is used to convert the projected optical signal into a digital electrical signal. This application introduces an annular filter before the FP interferometer. The annular filter acts as a pre-spectral preselector, ensuring that each beam of light entering the FP interferometer is within its current FSR window. Therefore, the interference signal output by the FP corresponds to only a unique wavelength range, avoiding spectral ambiguity caused by multi-order superposition, and ensuring uniqueness and accuracy in subsequent spectral reconstruction. The annular filter divides the broad spectrum into multiple sub-bands of FSR width, each sub-band independently entering the FP through its corresponding annular filter. This allows the FP to maintain high precision, while the overall system achieves broad spectral coverage through multi-annular filter stitching, overcoming the limitations of FSR and resolution. The inherent contradictions of the existing technology are addressed by employing a fixed-cavity FP interferometer, which eliminates the need for dynamic cavity adjustment and the high-precision piezoelectric drive device. Furthermore, since each frame corresponds to spectral information within a single FSR, the spectrum can be directly inverted through calibration relationships, avoiding complex Fourier transform and phase correction algorithms, thus improving system real-time performance and reliability. The spatial coding characteristics of the annular filter allow it to be used with a two-dimensional detector to acquire multi-band information in a single exposure, or combined with a scanning mechanism to improve the signal-to-noise ratio. The coordinated design of the front mirror and imaging mirror ensures efficient light transmission and meets the FP aperture requirements, guaranteeing system light throughput and imaging quality. In summary, this application, by introducing an annular filter precisely matched to the FP interferometer's FSR, constructs an FP spectral imaging system that maintains high spectral resolution while achieving wide spectral coverage. This effectively solves the core problems of existing technologies, such as order aliasing, FSR-resolution contradictions, high system complexity, and heavy data processing, improving the accuracy, practicality, and engineering feasibility of spectral imaging.

[0038] In an optional embodiment, the light transmittance range of each region in the annular filter is determined based on the wavelength range corresponding to each order.

[0039] In this embodiment, the light transmission band (i.e., passband) of each annular region in the annular filter is pre-divided and set according to the wavelength range corresponding to different interference orders m of the FP interferometer.

[0040] The transmission condition of the FP interferometer is the resonance condition 2ndcosθ=mλ. For a fixed cavity length d, the FP interferometer will generate transmission peaks at a series of discrete wavelengths. The wavelength interval between adjacent transmission peaks is defined as the free spectral range. Since the transmission function of the FP is periodic, if the input spectral width is greater than the FSR, different wavelengths may fall into the response range of the same interference order, causing order aliasing.

[0041] To address the aforementioned issues, this application's embodiments divide the entire working spectral range into several sub-intervals. The width of each sub-interval is equal to the local FSR of the FP interferometer in that band. Each sub-interval corresponds to an interference order m. The k-th region of the annular filter (corresponding to a certain angle or spatial position in the field of view) is coated to transmit only λ. k The narrowband filter film of the wavelength band has its spatial arrangement matched with the entrance pupil or field of view of the optical system, so that light from different field of view passes through the corresponding band of the ring.

[0042] The FP spectral imaging system provided in this application precisely sets the light transmission range of each region of the annular filter to the wavelength range corresponding to each interference order of the FP interferometer, thereby cutting off the coupling path of different order spectral components from the physical source, effectively eliminating order aliasing, ensuring the uniqueness and accuracy of spectral information, realizing unambiguous high-spectral resolution imaging, while maintaining high throughput and wide spectral coverage.

[0043] In an optional embodiment, the center wavelength of each region in the annular filter is shifted sequentially according to the step size of the free spectral range, thereby covering the Doppler broadening of the target spectral line.

[0044] In this embodiment, the center wavelength of each region of the annular filter is shifted sequentially according to the free spectral range of the FP interferometer, and all annular zones together cover the expected Doppler broadening range of the target spectral line.

[0045] In practical implementation, the annular filter consists of N regions, each of which is a narrowband filter with a bandwidth approximately equal to the FSR (or slightly less than the FSR to allow for a safety margin). The total wavelength range covered by all annular zones is greater than or equal to the Doppler broadening width of the target spectral line.

[0046] The FP spectral imaging system provided in this application, by designing the center wavelength sequence of the ring filter with the free spectral range of the FP interferometer as the step size, and making it cover the Doppler broadening range of the target spectral line, can capture the entire Doppler profile without aliasing in a single exposure or rapid scan, significantly improving dynamic range, spectral integrity and speed performance.

[0047] In an optional embodiment, the FP interferometer includes two plane mirrors placed parallel to each other, the flatness of which is greater than λ / 100.

[0048] In this embodiment, the FP interferometer consists of two high-precision plane mirrors placed strictly parallel to each other to form a resonant cavity. The surface flatness of each plane mirror is better than λ / 100 (where λ is the operating wavelength; for example, in the visible light band, λ = 632.8 nm, then the flatness is better than 6.3 nm). This structure forms a multi-beam interference system. The incident light is reflected multiple times between the two mirrors, and the transmitted portions coherently superimpose each time, producing constructive interference at a specific wavelength and forming a sharp transmission peak.

[0049] The FP spectral imaging system provided in this application uses a parallel plane mirror with a flatness better than λ / 100 in the FP interferometer. This effectively suppresses phase noise and interference fringe degradation caused by surface topography errors from a physical mechanism perspective, significantly improving the contrast, resolution and stability of the instrument, and providing a reliable hardware foundation for high-precision optical measurement.

[0050] In an optional embodiment, the reflectivity of the plane mirror is higher than 97%.

[0051] In this embodiment, the reflectivity R of the two plane mirrors of the FP interferometer is further achieved by using a high-reflectivity dielectric film.

[0052] The distance d between two highly reflective plane mirrors is calculated by the following formula: ; in, The working center wavelength; Free spectral range (FSR) refers to the wavelength interval between transmission peaks of adjacent interference orders. For precision.

[0053] The FP spectral imaging system provided in this application uses a high-reflectivity plane mirror with a reflectivity higher than 97% and a flatness of λ / 100 level, which physically improves the system's precision, resolution, light field enhancement capability, and background suppression capability.

[0054] In an optional embodiment, the accuracy of the spacing between the plane mirrors is within 0.5 μm.

[0055] The distance between the mirrors directly determines the position of the resonant wavelength and the free spectral range. If d is not precisely controlled, the resonant peak will deviate completely from the target wavelength, causing the system to fail. Therefore, in this embodiment, the control accuracy of the distance between the two plane mirrors is further limited to within ±0.5μm, which can be achieved by piezoelectric ceramics, micro-displacement platforms or precision mechanical structures.

[0056] The FP spectral imaging system provided in this application embodiment has an FP interferometer that limits the plane mirror spacing accuracy to within ±0.5μm. This can control the resonant wavelength drift within the transmission peak width, effectively avoiding detuning caused by assembly or temperature drift. It ensures that the performance advantages brought by high reflectivity and high flatness can be practically realized, and significantly improves the system's stability, repeatability, and engineering practicality.

[0057] In an optional embodiment, the front mirror is an afocal optical system.

[0058] A focal-free type refers to a front lens composed of two or more optical elements, with an overall focal length of infinity (i.e., no focal point). When parallel light is input, the output is still parallel light, only changing the beam aperture and divergence angle (i.e., achieving angular magnification or compression).

[0059] In this embodiment, the front mirror receives the diverging beam from the target, converts it into a collimated beam, and controls the diameter and maximum incident angle of the emitted beam to precisely match the aperture and angular acceptance range of the FP interferometer. The afocal system does not focus, therefore it does not form a real image plane in front of the FP, avoiding the introduction of additional aberrations or thermal damage caused by energy concentration.

[0060] The FP spectral imaging system provided in this application uses a focal-free front mirror, which can achieve angle-aperture transformation of the incident beam without introducing focusing, thereby precisely controlling the divergence angle and aperture of the beam entering the FP interferometer, significantly improving the contrast of interference fringes, spectral resolution and system flux uniformity, while avoiding thermal damage and stray light.

[0061] In summary, the FP spectral imaging system provided in this application uses a focal-free, large-aperture, long-focal-length optical system as the front mirror. This system is mainly used to collect light energy and compress the incident light beam and amplify the field of view. It ensures that the incident beam aperture meets the limit of the FP interferometer's aperture, while also ensuring that light rays from different fields of view enter the interferometer as required. This allows for interference filtering of different wavelengths of light rays from different fields of view, resulting in different spectral distributions at different image plane positions after passing through the imaging mirror.

[0062] Considering the optical characteristics of the FP interferometer, light rays with different incident angles transmit at different wavelengths. Therefore, traditional imaging lenses cannot meet the requirements for beam splitting. A specially designed optical system with afocal characteristics is needed to convert the light rays from targets in different fields of view into parallel light rays that are incident on the FP interferometer and then imaged onto the detector by the object-side afocal imaging system, ensuring that the images in different fields of view correspond to different wavelengths.

[0063] Based on the fundamental equations of the FP interferometer, the relationship between the incident angles of different orders and the transmission center wavelength was calculated, such as... Figure 5 As shown, taking a 3-filter FP interferometer as an example, when parallel light is incident on the FP interferometer at a certain incident angle, due to the expanded free spectral range, there are three wavenumber transmission peaks at that detection angle. At this time, the filters are used to filter different orders of the spectrum in different fields, ensuring that each region has only one order of transmission peak. By using filters, the field of view of the spectrometer is expanded, increasing the spectral detection range without reducing the spectral resolution. Figure 5 The red transmission wavelength is combined to cover the entire detection band and a wider field of view. To match the incident angle of the beam entering the FP interferometer, the incident angle of the target entering the optical system needs to be magnified or reduced during the pre-optical design.

[0064] The aperture of an FP interferometer is theoretically unlimited, but due to limitations in manufacturing and assembly processes, the aperture cannot be made very large, constrained by the following factors: First, the flatness requirement for flat glass is better than λ / 600. With current testing and manufacturing processes, it is very difficult to achieve the above precision. Therefore, it can only be achieved within a limited diameter. Secondly, in order to achieve high spectral resolution, the flat glass of the FP interferometer needs to be coated with a high-reflectivity film, which is usually required to be better than 97%. However, the coating process will cause changes in the surface shape of the flat glass, so the coating of the flat glass is also a challenge. Third, the spacing and parallelism of the two flat glass plates are required to be very high, and the spacing accuracy is usually required to be controlled within 0.5μm.

[0065] According to technical research, the FP interferometer that can currently achieve the above-mentioned accuracy requirements, while ensuring the accuracy of flatness, reflectivity, and spacing of the flat glass, can achieve an aperture of about 20mm.

[0066] The FP spectral imaging method provided in the embodiments of this application is described below. The FP spectral imaging method described below can be referred to in correspondence with the FP spectral imaging system described above.

[0067] Figure 6 This is a schematic flowchart of the FP spectral imaging method provided in this application, as shown below. Figure 6 As shown, the FP spectral imaging method may include the following steps: S610, the front mirror collects the light energy emitted by the target scene and converts it into outgoing light that meets the aperture limit of the FP interferometer; S620, the annular filter allows one FP interference order to pass through in each region, eliminating order aliasing in the outgoing light of the front mirror; S630, the FP interferometer performs wavelength selection on the outgoing light from the annular filter and outputs an interference field; S640, the imaging mirror projects the interference field onto the detector; The S650 detector converts the projected light signal into a digital electrical signal.

[0068] In this embodiment, the target under test enters the FP spectral imaging system at different angles and is incident on the FP interferometer as the system scans. During the scanning process, the incident angle changes, and the beam emitted from the FP interferometer is imaged on the detector image plane through the imaging mirror. The same target is imaged in different regions of the detector at different times as the system scans. The light intensity obtained by the target in different regions of the detector is stitched together to obtain the complete spectral curve of the target.

[0069] Specifically, the FP spectral imaging system moves smoothly along a preset trajectory within the detection area and systematically scans its coverage area. During the scanning process, the FP spectral imaging system performs multiple consecutive images at a high frequency, capturing information about the target in both spatial and spectral dimensions with each image. These images, acquired at different spatial locations and in different spectral bands, are registered and fused to form a three-dimensional data cube. This data cube contains two spatial dimensions (X, Y) and one spectral dimension (λ), comprehensively and precisely reflecting the spectral characteristics of each point in the detection area, providing a complete data foundation for subsequent quantitative analysis and identification.

[0070] The FP spectral imaging method provided in this application introduces a ring-shaped filter before the FP interferometer. This ring-shaped filter acts as a pre-spectral preselector, ensuring that each beam of light entering the FP interferometer is within its current FSR window. Therefore, the interference signal output by the FP corresponds to only a unique wavelength range, avoiding spectral ambiguity caused by multi-order superposition, and ensuring uniqueness and accuracy in subsequent spectral reconstruction. The ring-shaped filter divides the broad spectrum into multiple sub-bands of FSR width, each sub-band independently entering the FP through its corresponding ring-shaped filter. This allows the FP to maintain high precision, while the overall system achieves broad spectral coverage through multi-ring-shaped filter stitching, overcoming the limitations of FSR filters. The inherent contradiction between R and resolution is addressed by employing a fixed-cavity FP interferometer, eliminating the need for dynamic cavity adjustment and the high-precision piezoelectric drive device. Furthermore, since each frame corresponds to spectral information within a single FSR, the spectrum can be directly inverted through calibration relationships, avoiding complex Fourier transform and phase correction algorithms, thus improving system real-time performance and reliability. The spatial coding characteristics of the annular filter allow it to be used with a two-dimensional detector to acquire multi-band information in a single exposure, or combined with a scanning mechanism to improve the signal-to-noise ratio. The coordinated design of the front mirror and imaging mirror ensures efficient light transmission and meets the FP aperture requirements, guaranteeing system light throughput and imaging quality. In summary, this application, by introducing an annular filter precisely matched to the FP interferometer's FSR, constructs an FP spectral imaging system that maintains high spectral resolution while achieving wide spectral coverage. This effectively solves core problems in existing technologies such as order aliasing, FSR-resolution contradictions, high system complexity, and heavy data processing, improving the accuracy, practicality, and engineering feasibility of spectral imaging.

[0071] In an optional embodiment, before the light energy emitted by the target scene is collected by the front mirror and converted into outgoing light that meets the aperture limit of the FP interferometer, the method further includes: The FP spectral imaging system was spectrally calibrated using a monochromator to obtain the wavelength-channel mapping relationship.

[0072] In this embodiment, a monochromator is used to calibrate the instrument. The corresponding pixels on the image plane are recorded. Based on the detection principle, different monochromator wavelengths correspond to different pixel positions. By scanning the entire wavelength range with the monochromator, the response wavelength of each pixel on the image plane is calibrated.

[0073] Specifically, the monochromator, as a tunable, high-precision wavelength source, outputs narrowband monochromatic light with a known center wavelength. The monochromator wavelength is adjusted. The output light from the monochromator is injected into the entrance pupil position (i.e., the input end of the front mirror) of the FP spectral imaging system to simulate the radiation of a real target, while keeping the rest of the system (front mirror, FP cavity, imaging mirror, and detector) in normal working condition. The monochromator is controlled to output a series of reference wavelengths covering the system's operating band in sequence. For each wavelength, the detector image frame output by the FP system under a fixed cavity length is recorded. For each image frame, the interference bright spot or the maximum response pixel region is located, and the spatial position (such as row number, column number) or logical channel number of the response on the detector is recorded. A wavelength-channel mapping table is constructed.

[0074] The FP spectral imaging method provided in this application establishes a precise wavelength-channel mapping relationship through monochromator calibration, effectively compensating for manufacturing tolerances, assembly errors, and environmental drift in the FP system, and transforming the original pixel response into physically meaningful spectral coordinates, thereby ensuring the accuracy and repeatability of subsequent spectral analysis.

[0075] In an optional embodiment, after the detector converts the projected light signal into a digital electrical signal, the method further includes: Based on the spectral response model and radiation correction parameters obtained from laboratory calibration, the digital electrical signal obtained from a single complete scan is standardized to obtain a standard data cube. After identifying and extracting the spectral signals of the same target in different bands from the standard data cube, the spectral signals are arranged in wavelength order based on the wavelength-channel mapping relationship to obtain the target spectral curve.

[0076] In this embodiment, the raw data cube obtained from scanning is standardized based on the spectral response model and radiometric correction parameters obtained from laboratory calibration. The spectral signals of the same target in different wavelength bands are automatically identified and extracted from the data cube. These signals are then aligned and arranged in wavelength order, ultimately integrating them into a continuous and complete spectral curve.

[0077] Specifically, the original digital signal is corrected using a pre-calibrated spectral response model and radiometric correction parameters (such as dark current, gain, and non-uniformity correction coefficients) in the laboratory. All corrected data are then registered and fused according to their spatial location to generate a standard data cube. Within the standard data cube, the target region of interest is identified using spatial masks or target detection algorithms (such as threshold segmentation or deep learning segmentation). For all pixels within the region (or by taking the mean / median), their radiometric values ​​in each band are extracted. Using the wavelength-channel mapping relationship obtained through monochromator calibration, the discrete channel index k is converted into the physical wavelength. The extracted spectral signals are then arranged in ascending order of physical wavelength to form a continuous (or high-density sampled) target spectral curve.

[0078] The FP spectral imaging method provided in this application transforms the original digital signal into a physically consistent, wavelength-ordered target spectral curve through radiation normalization and wavelength rearrangement based on laboratory calibration. This eliminates the influence of system response deviation and channel order disorder, providing a reliable data foundation for high-precision spectral identification, component inversion, and multi-temporal comparison.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An FP spectral imaging system, characterized in that, It includes front mirrors placed in sequence to collect light energy and convert it into outgoing light that meets the aperture limit of the FP interferometer; The annular filter includes multiple regions, including a central region and multiple concentric annular regions surrounding the central region. The bandwidth of each region is the same as the free spectral range of the FP interferometer, and is used to eliminate order aliasing in the outgoing light of the front mirror. The FP interferometer is used to select the wavelength of the emitted light from the annular filter and output an interference field. An imaging mirror is used to project the interference field onto the detector; A detector is used to convert projected light signals into digital electrical signals.

2. The FP spectral imaging system according to claim 1, characterized in that, The light transmission range of each region in the annular filter is determined based on the wavelength range corresponding to each level.

3. The FP spectral imaging system according to claim 2, characterized in that, The center wavelength of each region in the annular filter shifts sequentially according to the step size of the free spectral range, covering the Doppler broadening of the target spectral lines.

4. The FP spectral imaging system according to claim 1, characterized in that, The FP interferometer includes two plane mirrors placed parallel to each other, and the flatness of the plane mirrors is higher than λ / 100.

5. The FP spectral imaging system according to claim 4, characterized in that, The reflectivity of the plane mirror is higher than 97%.

6. The FP spectral imaging system according to claim 4 or 5, characterized in that, The accuracy of the spacing between the plane mirrors is within 0.5 μm.

7. The FP spectral imaging system according to claim 1, characterized in that, The front mirror is an afocal optical system.

8. A FP spectral imaging method, characterized in that, The FP spectral imaging system as described in any one of claims 1-7 includes: The front mirror collects the light energy emitted from the target scene and converts it into outgoing light that meets the aperture limit of the FP interferometer; The annular filter allows one FP interference order to pass through in each region, eliminating order aliasing in the outgoing light of the front mirror; The FP interferometer performs wavelength selection on the outgoing light from the annular filter and outputs an interference field; The imaging mirror projects the interference field onto the detector; The detector converts the projected light signal into a digital electrical signal.

9. The FP spectral imaging method according to claim 8, characterized in that, Before the light energy emitted by the target scene is collected by the front mirror and converted into outgoing light that meets the aperture limit of the FP interferometer, the following steps are also included: The FP spectral imaging system was spectrally calibrated using a monochromator to obtain the wavelength-channel mapping relationship.

10. The FP spectral imaging method according to claim 9, characterized in that, After the detector converts the projected light signal into a digital electrical signal, the following steps are also included: Based on the spectral response model and radiation correction parameters obtained from laboratory calibration, the digital electrical signal obtained from a single complete scan is standardized to obtain a standard data cube. After identifying and extracting the spectral signals of the same target in different bands from the standard data cube, the spectral signals are arranged in wavelength order based on the wavelength-channel mapping relationship to obtain the target spectral curve.

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