Aperture multiplexing super-wide spectrum freeform imaging method and device

Abstract

This invention relates to the field of curved surface imaging, specifically to an ultra-wideband freeform surface imaging method and apparatus with aperture multiplexing. The method and apparatus first divide the aperture of an Offner grating imaging spectrometer into at least two parts: one part for visible light imaging and the other for short-wave infrared imaging. A variable-line convex diffraction grating is also designed, which achieves different spectral resolutions in the two detection bands: visible light imaging and short-wave infrared imaging. This invention can achieve ultra-wideband spectral detection covering the visible to short-wave infrared bands, simultaneously obtaining spectral information from both visible and short-wave infrared wavelengths, exhibiting uniform spectral resolution in both bands, high imaging quality, and small size and volume.

Description

Technical Field

[0001] This invention relates to the field of curved surface imaging, and more specifically, to a method and apparatus for ultrawide-band freeform surface imaging with aperture multiplexing. Background Technology

[0002] In recent years, with the deepening of space exploration, imaging spectroscopy, which originated in the 1980s, has attracted much attention due to its ability to provide more information about matter. Dispersive spectrometers have become the preferred choice for many instruments due to their intuitive data and system stability. The Offner and Dyson structures are two classic structures in dispersive spectrometers. Among them, the Offner structure is the most widely used.

[0003] In the design of imaging spectrometers, the detection spectral band and spectral resolution are two crucial parameters. The visible to short-wave infrared band (400nm-2500nm) is a vital spectral range for remote sensing, containing rich information about material characteristics. Instruments capable of providing 2nm-5nm spectral resolution in the visible band and 5nm-10nm spectral resolution in the short-wave infrared band can meet most remote sensing needs. Imaging spectrometers with wide spectral band detection can provide richer spectral information, reducing the number of instruments and improving operational efficiency. Spectral resolution describes the spectrometer's spectral resolving power; different spectral bands require different resolutions due to varying material properties.

[0004] Currently, there are several main methods for achieving broadband detection: 1. Using a prism as a dispersive element, traditional methods are employed to obtain relatively good results over a wider wavelength range; 2. Designing multiple optical instruments and stitching together spectral bands to achieve broadband detection; 3. Using computational optics methods, relying on previously obtained partial wavelengths, to infer the nature of substances and thus obtain broadband computational spectral data (requires prior information). However, these methods suffer from problems such as large size, heavy weight, severe dispersive nonlinearity, and complex data processing, failing to meet the requirements of lightweight instruments, systematization, and real-time performance. The relevant terminology is explained below:

[0005] Freeform surfaces: Utilizing a third independent axis during the design process to create optical surfaces with asymmetric design features.

[0006] A spectrometer is a device that uses a photodetector to measure the energy intensity of spectral lines at different wavelengths. Its structure generally includes a converging lens, a slit, a dispersive system, an imaging lens, and a photodetector.

[0007] The spectrometer uses the Offner structure, which Lobb et al. applied in the 1980s to design spectrometers, enabling miniaturization and weight reduction. Replacing the secondary mirror of the Offner with a convex grating provides a deflection path while simultaneously achieving light dispersion. The specific operation is as follows: light exiting the slit is reflected by the primary mirror, undergoing its first deflection before reaching the secondary mirror. With the secondary mirror replaced by the convex grating, the light undergoes a second deflection at the secondary mirror, simultaneously achieving dispersion due to the grating. This dispersed light then reaches the third mirror. The dispersed light undergoes a third deflection at the third mirror, converging and ultimately being received by the detector located at the image plane.

[0008] There are already several existing technologies for achieving ultra-wideband spectral detection in molded spectrometers. Typical approaches include the following:

[0009] The first approach utilizes a prism as a dispersive element. For example... Figure 1 As shown, prisms are commonly used dispersive elements. In the visible to short-wave infrared band, most prism materials have high transmittance, which can meet the requirements of ultra-wideband detection. However, as... Figure 2 As shown, due to the different refractive indices of the prism material at different wavelengths, prism-type imaging spectrometers suffer from dispersive nonlinearity. For example... Figure 1 As shown, in the design, multiple prisms made of different materials are usually required for compensation to reduce the impact of dispersive nonlinearity on the instrument. However, prism materials cannot meet the design requirements for different spectral resolutions in visible light and short-wave infrared. While prism materials exhibit dispersive nonlinearity, their dispersive capability remains continuous, making it impossible to achieve discontinuous spectral resolution design requirements. Imaging spectrometers using prisms as dispersive elements are bulky and heavy, and are not the most efficient solution in designs with strict requirements for system size and weight.

[0010] The second approach uses multiple optical instruments with different detection spectral bands, achieving ultra-wideband detection through spectral stitching. This method decomposes the ultra-wideband detection spectral band into several narrow-band imaging spectrometers that can be implemented using existing technologies. These instruments are responsible for spectral detection within a specific range, and by combining multiple instruments, overall ultra-wideband detection is achieved. This method has been used in many classic optical instruments, such as Germany's EnMAP, the European Space Agency's CO2M, and the United States' OCO-2 remote sensing instruments. Using this method can effectively reduce the design difficulty, but it increases the system's complexity and weight.

[0011] The third method uses computational optics to infer the composition of substances based on previously obtained partial wavelengths, thereby obtaining broadband computational spectral data. This method combines optical instruments with data processing algorithms, using a pre-constructed rich database to preprocess the observed substances. After classifying and organizing the spectral characteristics of the substances in the database, some spectral bands can be inferred based on existing prior information, thus obtaining broadband detection results without direct measurement. However, this method requires processing a large amount of data in the early stages and necessitates a database with rich spectral information. The obtained prior information is a key element in obtaining spectral data; however, in actual measurements, it is impossible to verify and correct this prior information. Therefore, the application of this type of method is still in the research stage and has not yet been widely adopted.

[0012] Existing technical solutions using prisms increase system size and weight, suffer from dispersion nonlinearity issues, and cannot meet the design requirements for variable spectral resolution. The multi-optical system spectral stitching method is essentially still a design approach for narrow detection bands, and it significantly increases the number of instruments, leading to a substantial increase in system size and weight. Computational optics methods require extensive preprocessing of material spectral databases; the resulting prior information cannot be verified or corrected in actual detection, and the accuracy and reliability of the data depend heavily on the quality of the algorithm.

[0013] Taking the first approach as an example, this involves using prisms as dispersive elements. Prisms are commonly used dispersive elements, and most prism materials have high transmittance in the visible to short-wave infrared band, meeting the requirements for ultra-wide spectral detection. However, because prism materials have different refractive indices at different wavelengths, prism-type imaging spectrometers suffer from dispersive nonlinearity. In the design, multiple prisms made of different materials are typically used for compensation to reduce the impact of dispersive nonlinearity on the instrument. Simultaneously, prism materials cannot meet the design requirements for different spectral resolutions in the visible and short-wave infrared bands. While prism materials exhibit dispersive nonlinearity, their dispersive capability remains continuous, failing to meet the design requirements for discontinuous spectral resolution. Imaging spectrometers using prisms as dispersive elements are bulky and heavy, making them less than the most efficient solution in designs with strict requirements for system size and weight.

[0014] Taking the second approach as an example, this method decomposes the ultrawide detection spectral band into several narrow-band imaging spectrometers that can be implemented using existing technologies. These instruments are only responsible for spectral detection within a certain range. By combining multiple instruments, overall ultrawide spectral detection can be achieved. This method has been used in many classic optical instruments, such as Germany's EnMAP, the European Space Agency's CO2M, and the United States' OCO-2 remote sensing instruments. Using this method can effectively reduce the design difficulty, but it increases the system's complexity and weight.

[0015] Taking the third approach as an example, this method combines optical instruments with data processing algorithms. It preprocesses the observed substances using a pre-built, rich database. After classifying and organizing the spectral characteristics of the substances in the database, some spectral bands can be inferred based on existing prior information, thus obtaining broad-spectrum detection results without direct measurement. However, this method requires processing a large amount of data in the early stages and necessitates a database with rich spectral information. The obtained prior information is a key element in acquiring spectral data; however, in actual measurements, it is impossible to verify and correct this prior information. Therefore, the application of this type of method is still in the research stage and has not yet been widely adopted. Summary of the Invention

[0016] This invention provides an ultrawide spectral freeform surface imaging method and apparatus with aperture multiplexing, which at least solves the technical problems of low imaging quality, large size and volume of existing surface imaging systems.

[0017] According to an embodiment of the present invention, an ultrawideband freeform surface imaging method with aperture multiplexing is provided, comprising the following steps:

[0018] The aperture of the Offner grating imaging spectrometer is divided into at least two parts, one part for visible light imaging and the other part for short-wave infrared imaging.

[0019] A variable-curvature convex diffraction grating was designed, which achieves different spectral resolutions in two detection bands: visible light imaging and short-wave infrared imaging.

[0020] Furthermore, the aperture of the Offner grating imaging spectrometer can be divided into two or more parts according to actual needs, and the proportion of each part of the aperture can be accurately calculated according to the specific signal-to-noise ratio calculation method of the Offner grating imaging spectrometer.

[0021] Furthermore, in the variable-line convex diffraction grating, different aperture portions have different grating parameters, but the same grating parameters are used within the same aperture.

[0022] Furthermore, the variable-line convex diffraction grating is a convex diffraction grating with different structural parameters fabricated on a common substrate, thereby obtaining different spectral resolutions for visible light and short-wave infrared.

[0023] Furthermore, the Offner grating imaging spectrometer is:

[0024] The light emitted from the object point is reflected by the primary mirror and then diffracted by the convex grating. Part of the light is used for spectral detection in the visible light band, and part of the light is used for spectral detection in the short-wave infrared band. The diffracted light is reflected by the three mirrors and converges to the focal plane. The short-wave infrared band is imaged onto the short-wave focal plane after passing through the folding mirror. The angle and spatial distance formed by the two focal planes meet the actual detector installation requirements.

[0025] According to another embodiment of the present invention, an ultrawideband freeform surface imaging device with aperture multiplexing is provided, comprising:

[0026] Offner grating imaging spectrometer and a variable-convex diffraction grating; wherein:

[0027] The aperture of the Offner grating imaging spectrometer is divided into at least two parts, one part for visible light imaging and the other part for short-wave infrared imaging.

[0028] A variable-curvature convex diffraction grating was designed, which achieves different spectral resolutions in two detection bands: visible light imaging and short-wave infrared imaging.

[0029] Furthermore, it includes two freeform mirrors, a variable-curvature convex diffraction grating, and a folding mirror.

[0030] Furthermore, the XY polynomial is used to characterize the freeform surface in the system design;

[0031] The system slit direction is set to the X-axis direction. The entire system is symmetric about the YOZ plane. Therefore, the odd-order X term in the X-Y polynomial is set to 0, and the even-order term is used during optimization. The specific form is as follows:

[0032]

[0033] c is the curvature; r is the radius; k is the quadratic surface coefficient; a i It is the coefficient of the monomial.

[0034] Furthermore, the parameters of the Offner grating imaging spectrometer are as follows:

[0035] Spectral range: 0.4μm-2.5μm; numerical aperture: 0.167; slit length: 10mm; visible light spectral resolution better than 2.7nm, short-wave infrared spectral resolution better than 5nm.

[0036] Furthermore, the convex diffraction grating in the visible light band uses +1 diffraction order and has a grating ruling density of 100 lines / mm, while the convex diffraction grating in the short-wave infrared band uses +1 diffraction order and has a grating ruling density of 120 lines / mm.

[0037] A storage medium storing program files capable of implementing any of the above-mentioned aperture multiplexing ultrawide spectral freeform surface imaging methods.

[0038] A processor for running a program, wherein the program executes an aperture multiplexing ultrawide spectral freeform surface imaging method of any of the above.

[0039] The ultra-wideband freeform surface imaging method and apparatus with aperture multiplexing in this invention first divides the aperture of the Offner grating imaging spectrometer into at least two parts: one part for visible light imaging and the other part for short-wave infrared imaging. A variable-line convex diffraction grating is also designed, which achieves different spectral resolutions in the two detection bands: visible light imaging and short-wave infrared imaging. This invention can achieve ultra-wideband spectral detection covering the visible to short-wave infrared bands, simultaneously obtaining spectral information in both visible and short-wave infrared bands, exhibiting uniform spectral resolution in both bands, high imaging quality, and small size and volume. Attached Figure Description

[0040] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0041] Figure 1 This is a diagram of a prism dispersive imaging spectrometer.

[0042] Figure 2 The graph shows the dispersion characteristics of the prism material.

[0043] Figure 3 This is a schematic diagram of the ultrawideband freeform surface imaging spectrometer in this invention;

[0044] Figure 4 This is a schematic diagram of the aperture reuse design in this invention;

[0045] Figure 5 This is a schematic diagram of the variable-spacing convex diffraction grating in this invention;

[0046] Figure 6 The MTF (modulation transfer function) curves for the visible light band at 0.4 μm and 1 μm in this invention are shown.

[0047] Figure 7 The MTF (modulation transfer function) curves for the shortwave infrared band at 1μm and 2.5μm in this invention are shown.

[0048] Figure 8 This is an energy curve diagram of the visible light band at 0.4μm and 1μm in this invention;

[0049] Figure 9 This is an energy curve diagram of the 1μm and 2.5μm shortwave infrared bands in this invention. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0051] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0052] Example 1

[0053] This invention, based on the Offner grating architecture, utilizes a single optical system to achieve the design requirements of an ultra-wide spectral band and variable spectral resolution. The invention aims to solve the aforementioned technical problems by designing a freeform Offner grating imaging spectrometer covering the visible to short-wave infrared bands through aperture multiplexing. In this structure, the aperture of the Offner grating imaging spectrometer is divided into two symmetrical parts: one part for visible light imaging and the other for short-wave infrared imaging. Simultaneously, this invention employs a specially designed variable-line convex diffraction grating, enabling different spectral resolutions in the two detection bands. The freeform surface corrects system aberrations and reduces the system's structure and size, meeting the design requirements of a wide spectral band, miniaturization, and lightweight design. Compared to traditional designs, this invention achieves an ultra-wide detection spectral band covering the visible to short-wave infrared bands, with a spectral resolution better than 2.7 nm in the visible band and a spectral resolution better than 5 nm in the short-wave infrared band.

[0054] In view of this, this invention proposes an ultra-wide spectral band freeform surface imaging method and system with aperture multiplexing. Based on the Offner grating imaging spectrometer, the system aperture is divided into two parts, used to obtain visible light spectral and short-wave infrared spectral information respectively. In practical design, the designer can reasonably allocate the ratio of the two aperture parts according to the system signal-to-noise ratio requirements. In addition, this invention designs a special variable-line convex diffraction grating, fabricating convex diffraction gratings with different structural parameters on a common substrate to obtain different spectral resolutions for visible light and short-wave infrared. The entire system consists of two freeform surface mirrors, one variable-line convex diffraction grating, and one folding mirror. Compared with traditional designs, this system can achieve ultra-wide spectral detection covering the visible to short-wave infrared band with only one instrument, simultaneously obtaining spectral information for visible light and short-wave infrared. The system has uniform spectral resolution in the visible and short-wave infrared bands, high imaging quality, and small size and volume.

[0055] The detailed description of the technical solution of this invention is as follows: Figure 3 As shown, traditional Offner grating imaging spectrometers use convex diffraction gratings as dispersive elements, providing uniform spectral resolution within a certain detection range. However, when achieving a wide spectral band design, traditional convex diffraction gratings struggle to achieve high diffraction efficiency over a broad spectral range. Therefore, it is typically necessary to design two or more traditional Offner grating imaging spectrometers with different spectral bands to achieve wide spectral detection. The key technologies of the ultra-wide spectral band imaging spectrometer proposed in this invention include: an aperture multiplexing method and a variable-line convex diffraction grating design method. Among them, such as Figure 4 As shown, traditional Offner grating imaging spectrometers have circular apertures, with all aperture rays used for a common detection spectral band. The aperture multiplexing method proposed in this invention can divide the aperture into two or more parts according to actual needs, and accurately calculate the proportion of each part based on the instrument's specific signal-to-noise ratio calculation method. Furthermore, to match the aperture multiplexing method and provide different spectral resolutions in different spectral bands, this invention also proposes a special variable-line convex diffraction grating. Unlike traditional convex diffraction gratings with constant grating parameters, or other forms of variable-line convex diffraction gratings whose grating parameters are variable functions, the variable-line convex diffraction grating designed in this invention requires different grating parameters in different aperture sections, but the same grating parameters within the same aperture. This method can achieve different dispersion capabilities in different spectral bands, while maintaining uniform spectral resolution within the same spectral band.

[0056] Furthermore, because the detection spectrum covers the visible to short-wave infrared band, the grating diffraction angle is relatively large in this system. To meet the design requirements of miniaturization and lightweighting, a freeform surface mirror is used in this invention to correct system aberrations. The ultra-wideband freeform surface imaging spectrometer proposed in this invention is as follows: Figure 3 As shown, the light rays emitted from the object point are reflected by the primary mirror and then diffracted by a convex grating. The upper portion of the light rays is used for spectral detection in the visible light band, while the lower portion is used for spectral detection in the short-wave infrared band. The diffracted light rays converge at the focal plane after reflection by three mirrors. The short-wave infrared light rays are imaged onto the short-wave focal plane after passing through a folding mirror. The two focal planes are positioned at a specific angle and spatial distance to meet the actual detector installation requirements.

[0057] Freeform surfaces can be represented in various ways, broadly categorized into parametric and polynomial methods. Parametric methods are primarily represented by Non-Uniform Rational B-Splines (NURBS); polynomial methods are mainly represented by Zernike polynomials and XY polynomials. Other representation methods are not listed here. Since spectrometers are optical systems for spectral analysis and have high image quality requirements, the continuous smoothness of optical element surfaces is necessary, hence the use of polynomial representation. Zernike polynomials possess strong surface fitting capabilities and orthogonality, with each term corresponding to a specific aberration. XY polynomials are another representation of freeform surfaces; during the design process, the surface shape obtained using Zernike polynomials needs to be converted to an XY polynomial representation for fabrication. Therefore, in the design of the freeform surface in this invention, XY polynomials are directly used to represent the surface.

[0058] The system is configured with the slit direction as the X-axis, therefore the entire system is symmetric about the YOZ plane. For this reason, the odd-order X terms in the X-Y polynomial are set to 0, and only the even-order terms are used during optimization, as shown below:

[0059]

[0060] c is the curvature; r is the radius; k is the quadratic surface coefficient; a i It is the coefficient of the monomial.

[0061] Design a spectrometer with a spectral range of 0.4μm-2.5μm, a numerical aperture of 0.167, a slit length of 10mm, and a visible light spectral resolution better than 2.7nm and a short-wave infrared spectral resolution better than 5nm. In conventional designs, it is difficult for designers to achieve such a wide spectral band and different spectral resolutions using the structure of an Offner grating spectrometer. According to the aperture multiplexing and variable-spacing convex diffraction grating design method proposed in this invention, the system's aperture is uniformly divided into two parts: one part for visible light band detection and the other for short-wave infrared band detection. Specifically, the convex diffraction grating for the visible light band uses a +1 diffraction order with a grating density of 100 lines / mm, and the convex diffraction grating for the short-wave infrared band uses a +1 diffraction order with a grating density of 120 lines / mm. Figure 4-5 As shown.

[0062] The system modulation transfer function curve is as follows: Figure 6 and Figure 7 As shown, the system's energy curve is as follows: Figure 8 and Figure 9 As shown, the use of ultra-wide spectral bands and variable-spacing gratings makes the system's aberrations very complex and varied. Good image quality can be obtained by relying on the powerful adjustment capabilities of freeform surfaces, which is the significance of their existence. MTF and energy curves for 0.4μm and 1μm in the visible light band and 1μm and 2.5μm in the short-wave infrared band were selected respectively. It can be observed that the MTF of the entire system meets the design requirements of the spectrometer system, the energy concentration of the system is above 90%, and the system has good image quality.

[0063] The key points and areas to be protected in this invention are as follows:

[0064] 1. The key point of this invention is the creative proposal of using aperture multiplexing in a freeform Offner grating spectrometer, which can solve the problem that the Offner grating spectrometer cannot achieve ultra-wide spectral detection and variable spectral resolution.

[0065] 2. The core technology of this invention lies in the design method of aperture multiplexing and variable spectral resolution. Aperture multiplexing technology allows a single pupil of the optical system to be divided into different detection bands, thereby achieving the design goal of ultra-wideband detection. The variable-spacing convex diffraction grating, designed to match the aperture multiplexing method, can achieve different constant spectral resolutions in its respective bands. This satisfies the requirement for different spectral resolutions in different detection bands, and also ensures that the spectral resolution does not change linearly or nonlinearly within its respective band, greatly facilitating system calibration.

[0066] This invention uses an Offner-type freeform surface spectrometer as the initial structure and proposes an aperture reuse design method to achieve ultra-wideband detection and variable spectral resolution. In traditional designs, the optical aperture is used for only a single detection band, and the width of this band determines the overall detection spectral range of the system. In this design, limitations in the fabrication of ultra-wideband dispersive elements and spectral resolution prevent designers from achieving an ultra-wideband design covering the visible to short-wave infrared range. This invention proposes an aperture reuse design method, creatively introducing a method for segmented aperture detection and variable spectral resolution, abandoning the traditional method of single aperture corresponding to a single detection band. The visible and short-wave infrared bands require different spectral resolutions. This invention achieves a special variable-spacing convex diffraction grating by designing the dispersive element in different regions, while maintaining a constant spectral resolution within each band. The aperture reuse and variable spectral resolution design methods enable the Offner grating imaging spectrometer to simultaneously meet different spectral detection capabilities in both the 0.4μm-1μm and 1μm-2.5μm dual-band environments. This invention combines this with a freeform surface spectrometer, relying on the multiple design degrees of freedom of the freeform surface to complete the system's complex aberration correction. The designed ultra-wideband freeform surface imaging spectrometer has an ultra-wide detection spectral range of 4μm-2.5μm, with a spectral resolution of 2.7nm in the 0.4μm-1μm band and a spectral resolution better than 5nm in the 1μm-2.5μm band. Currently, no patents or literature report the design result of simultaneously achieving different spectral detection capabilities in the 0.4μm-2.5μm ultra-wideband using a single Offner grating imaging spectrometer.

[0067] Currently, there are several mainstream approaches to ultra-wideband detection in the visible to short-wave infrared range: 1. Using prisms as dispersive elements; 2. Designing multiple optical instruments and achieving wideband detection through spectral band stitching; 3. Using computational optics methods to infer substances based on obtained partial bands, thereby obtaining wideband computational spectral data. The first approach utilizes the high transmittance of prisms in the visible to short-wave infrared range, which can meet the requirements of ultra-wideband detection. However, the dispersive characteristics of prism materials exhibit nonlinearity, with spectral resolutions for short and long wavelengths differing by more than 10 times. This not only complicates instrument calibration but also increases the difficulty of system design. In the design process, designers typically add more prisms of different materials for compensation and correction to minimize the instrument's dispersive nonlinearity. This method results in a large instrument size and weight, failing to meet the design requirements for lightweight instruments. The second approach essentially still focuses on designing a narrow detection band. Ultra-wideband detection systems composed of multiple instruments are large in size, weight, and complexity. The third approach relies on the characteristics of computational optics algorithms to obtain ultra-wideband detection results. This method requires a large amount of data for model training to obtain prior information, while simultaneously calculating spectral information. It cannot be verified in practice, which limits the wide application of this type of method.

[0068] The starting point of this invention is as follows: 1. It proposes a design method for aperture reuse and variable spectral resolution. Based on the structural characteristics of the Offner grating spectrometer, a variable-spacing convex diffraction grating is designed, which can provide different spectral resolutions for the visible light band and the short-wave infrared band respectively. 2. The aperture reuse method can not only be used in the model introduced in this invention, but can even achieve a wider detection band on a planar grating. This invention focuses on the main remote sensing detection band of 0.4μm-2.5μm, so the design example shown is also the design result for this band. Through the design method of aperture reuse and variable-spacing convex diffraction grating, a narrower band can be divided, thereby obtaining different spectral resolutions within each band.

[0069] Example 2

[0070] A storage medium storing program files capable of implementing any of the above-mentioned aperture multiplexing ultrawide spectral freeform surface imaging methods.

[0071] Example 3

[0072] A processor for running a program, wherein the program executes an aperture multiplexing ultrawide spectral freeform surface imaging method of any of the above.

[0073] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0074] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0075] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The system embodiments described above are merely illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection of units or modules may be electrical or other forms.

[0076] The units described as separate components may or may not be physically separate. Similarly, the components shown as units may or may not be physical units; they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0077] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0078] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for imaging ultrawideband freeform surfaces with aperture multiplexing, characterized in that, Includes the following steps: The aperture of the Offner grating imaging spectrometer is divided into at least two parts, one part for visible light imaging and the other part for short-wave infrared imaging. A variable-curvature convex diffraction grating was designed, which obtained different spectral resolutions in two detection bands: visible light imaging and short-wave infrared imaging. The variable-line convex diffraction grating is a convex diffraction grating with different structural parameters fabricated on a common substrate to obtain different spectral resolutions in visible light and short-wave infrared. Among them, the convex diffraction grating in the visible light band uses +1 diffraction order and the grating ruling density is 100 lines / mm, while the convex diffraction grating in the short-wave infrared band uses +1 diffraction order and the grating ruling density is 120 lines / mm. The light emitted from the object point is reflected by the first freeform surface mirror and then diffracted by the variable-convex surface diffraction grating. Part of the light is used for spectral detection in the visible light band, and part of the light is used for spectral detection in the short-wave infrared band. The diffracted light is reflected by the second freeform surface mirror and converges to the focal plane. The short-wave infrared band is imaged on the short-wave focal plane after passing through the folding mirror. The angle and spatial distance formed by the two focal planes meet the actual detector installation requirements.

2. The ultrawideband freeform surface imaging method with aperture multiplexing according to claim 1, characterized in that, Depending on the actual needs, the aperture of the Offner grating imaging spectrometer can be divided into two or more parts, and the proportion of each part of the aperture can be accurately calculated according to the specific signal-to-noise ratio calculation method of the Offner grating imaging spectrometer.

3. The ultrawideband freeform surface imaging method with aperture multiplexing according to claim 1, characterized in that, In a variable-diameter convex diffraction grating, different aperture portions have different grating parameters, but the grating parameters are the same within the same aperture.

4. An ultrawideband freeform surface imaging system with aperture multiplexing, characterized in that, The system employs an ultrawide spectral band freeform surface imaging method with aperture multiplexing as described in any one of claims 1-3; the system includes: an Offner grating imaging spectrometer; wherein: the Offner grating imaging spectrometer includes a first freeform surface mirror, a variable-line convex surface diffraction grating, a second freeform surface mirror, and a folding mirror; The aperture of the Offner grating imaging spectrometer is divided into at least two parts, one part for visible light imaging and the other part for short-wave infrared imaging. A variable-curvature convex diffraction grating was designed, which achieves different spectral resolutions in two detection bands: visible light imaging and short-wave infrared imaging.

5. The aperture-multiplexing ultrawideband freeform surface imaging system according to claim 4, characterized in that, The XY polynomial is used to characterize the freeform surface in the system design; The system slit direction is set to the X-axis direction, and the entire system is symmetric about the YOZ plane. Therefore, the odd-order X term in the XY polynomial is set to 0, and the even-order term is used during optimization, as shown in the following form: It is curvature; It is the radius; These are the coefficients of the quadratic surface; It is the coefficient of the monomial.

6. The aperture-multiplexing ultrawideband freeform surface imaging system according to claim 4, characterized in that, The parameters for the Offner grating imaging spectrometer are: Spectral range: 0.4μm-2.5μm; numerical aperture: 0.167; slit length: 10mm; visible light spectral resolution better than 2.7nm, short-wave infrared spectral resolution better than 5nm.

7. The aperture-multiplexing ultrawideband freeform surface imaging system according to claim 4, characterized in that, The convex diffraction grating in the visible light band uses +1 diffraction order and has a grating density of 100 lines / mm. The convex diffraction grating in the short-wave infrared band uses +1 diffraction order and has a grating density of 120 lines / mm.

Images