Snapshot imaging spectrometer

Abstract

The present application relates to a kind of snapshot imaging spectrometer, it includes for discrete sampling field integration element, off-axis three mirrors, dispersion and reflection assembly, folding mirror and focal plane detector, the field integration element, dispersion and reflection assembly, folding mirror and focal plane detector are located in the same side of the off-axis three mirrors, the off-axis three mirrors are symmetric about symmetry plane, the field integration element and the focal plane detector are located in the two sides of the symmetry plane;Wherein, light is incident by the field integration element, is reflected to the dispersion and reflection assembly by the off-axis three mirrors, is reflected back to the off-axis three mirrors by the dispersion and reflection assembly, after twice reflection by the off-axis three mirrors, light is imaged to the focal plane detector by the folding mirror.The present application is compact in volume, and light imaging performance is excellent, and spectral distortion is low, effectively improves atlas data fidelity.

Description

Technical Field

[0001] This invention relates to the field of imaging spectroscopy technology, and in particular to a snapshot imaging spectrometer. Background Technology

[0002] Imaging spectrometers can acquire both spatial and spectral information of a target, offering the advantage of integrated image and spectrum analysis. They are widely used in environmental monitoring, food hygiene, authenticity verification, light source detection, mineral exploration, agriculture, and forestry. Traditional imaging spectrometers typically acquire three-dimensional spectral information through time-division scanning.

[0003] Slit-based dispersive imaging spectrometers can simultaneously acquire one-dimensional spatial and spectral information along the slit direction. Spatial images perpendicular to the slit require push-broom or swing-broom scanning along that direction. These spectrometers are widely used in spaceborne and airborne platforms. Filter wheel-based imaging spectrometers can simultaneously acquire a two-dimensional spatial image at a specific wavelength. Information at different wavelengths requires changing filters, i.e., scanning wavelengths. These spectrometers are typically used in fixed ground-based environments. In recent years, with the increasing maturity of UAV technology, hyperspectral imaging technology has become widespread in industry applications. However, UAVs and other small, lightweight platforms are prone to vibration during operation, making it difficult for onboard scanning imaging spectrometers to obtain stable, high-quality spectral data. Snapshot imaging spectrometers can simultaneously acquire two-dimensional spatial and one-dimensional spectral information in a single exposure, resulting in a three-dimensional data cube. They are unaffected by vibration, have strong environmental adaptability, and are highly suitable for UAV hyperspectral remote sensing and hyperspectral imaging of moving targets.

[0004] In existing technologies, the collimating lens group and focusing lens group of snapshot imaging spectrometers are two independent components, distributed on both sides of the dispersive element. This coaxial structure is simple and easy to implement. However, under the requirements of large-field integrating elements, high spatial resolution, and high spectral resolution, the collimating lens group and focusing lens group also require long focal lengths. This will result in an excessively long and bulky system, limiting its use on UAV platforms. In addition, such coaxial optical systems using prisms or gratings as dispersive elements have difficulty eliminating spectral distortion. The acquired spectral data has residual spectral line bending and color distortion, affecting data fidelity. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a snapshot imaging spectrometer with a compact system size, excellent optical imaging performance, low spectral distortion, and effectively improve the fidelity of spectral data.

[0006] According to the technical solution provided by the present invention, the snapshot imaging spectrometer includes a field integrating element for discrete sampling, an off-axis three-mirror, a dispersion and reflection assembly, an off-axis three-mirror folding mirror, and a focal plane detector. The field integrating element, the dispersion and reflection assembly, the folding mirror, and the focal plane detector are located on the same side of the off-axis three-mirror. The plane where the field integrating element is located intersects the plane where the focal plane detector is located. The off-axis three-mirror is symmetrical about a plane of symmetry. The field integrating element and the focal plane detector are located on opposite sides of the plane of symmetry.

[0007] In this process, light is incident on the field integrating element, reflected by the off-axis three-mirror to the dispersion and reflection component, reflected back to the off-axis three-mirror by the dispersion and reflection component, and after a second reflection by the off-axis three-mirror, the light is imaged onto the focal plane detector by the folding mirror.

[0008] In one embodiment of the present invention, the off-axis three-mirror includes a primary mirror, a secondary mirror, and a third mirror, wherein the primary mirror and the third mirror are located on the same side of the secondary mirror, and the surface shape of the off-axis three-mirror is aspherical.

[0009] In one embodiment of the present invention, the dispersion and reflection component is a reflective diffraction grating.

[0010] In one embodiment of the present invention, the dispersion and reflection assembly includes a dispersion element and a plane mirror, the plane mirror being located at the pupil plane of the off-axis three-mirror.

[0011] In one embodiment of the present invention, the dispersive element is one of a single prism, a cemented prism, a split prism group, and a diffraction grating.

[0012] In one embodiment of the present invention, the field integration element is one of a slit array, a pinhole array, a microlens array, and an optical fiber array.

[0013] In one embodiment of the present invention, a focal plane detector is further included, which is connected to the focal plane, and the diagonal size of the focal plane detector is 5mm to 62mm.

[0014] In one embodiment of the present invention, the focal length of the off-axis three-lens structure is 25mm to 460mm.

[0015] In one embodiment of the present invention, the dispersion and reflection assembly includes a cemented prism and a plane mirror, the plane mirror being located at the pupil plane of the off-axis three-mirror, and the cemented prism including a first prism and a second prism, the second prism being located between the first prism and the plane mirror.

[0016] In one embodiment of the present invention, the first prism is made of ultraviolet fused silica material, and the second prism is made of H-F4 optical material.

[0017] The technical solution of the present invention has the following advantages over the prior art:

[0018] 1. The present invention adopts a dual-pass multiplexed off-axis three-reflector system to achieve a compact system volume. Under the same performance, the size of the conventional transmission optical path is reduced by at least 2 times.

[0019] 2. This invention utilizes the characteristics of an off-axis three-mirror system that can obtain large object and image planes. The system can distribute the field integration element and focal plane on both sides of the symmetry plane of the three-mirror system, and obtain large object and image planes that do not interfere with each other after folding the imaging optical path through a folding mirror.

[0020] 3. The distortion of the off-axis three-mirror system and the dispersive prism of this invention compensates for each other, realizing overall distortion elimination of the system, excellent spectroscopic imaging performance, low spectral distortion, and effectively improving the fidelity of spectral data.

[0021] 4. The snapshot imaging spectrometer of the present invention can obtain spectral data in a single exposure. Compared with the scanning imaging spectrometer, it has higher data acquisition efficiency, stronger anti-interference ability, and can acquire spectral data of moving targets, thus obtaining video hyperspectral images. Attached Figure Description

[0022] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the optical path of the imaging spectrometer of the present invention;

[0024] Figure 2 This is a top view of the imaging spectrometer of the present invention;

[0025] Figure 3 This is a three-dimensional view of the optical system of the imaging spectrometer of the present invention;

[0026] Figure 4 This is a schematic diagram of an existing slit array;

[0027] Figure 5 This is a schematic diagram of an existing pinhole array;

[0028] Figure 6 This is a schematic diagram of an existing microlens array;

[0029] Figure 7 This is a dot diagram of an optical system according to an embodiment of the present invention.

[0030] Explanation of reference numerals in the accompanying drawings: 1-Field integrator; 2-Light ray; 3-Primary mirror; 4-Secondary mirror; 5-Third mirror; 6-Cemented prism assembly; 6.1-First prism; 6.2-Second prism; 7-Plane mirror; 8-Folding mirror; 9-Focal plane detector; 10-Plane of symmetry. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0032] Reference Figure 1 As shown, in order to achieve a compact system size, excellent optical imaging performance, low spectral distortion, and effectively improve the fidelity of spectral data, this invention includes a field integrating element 1 for discrete sampling, an off-axis three-mirror system, a dispersion and reflection assembly, an off-axis three-mirror system, a folding mirror 8, and a focal plane detector 9. The field integrating element 1, the dispersion and reflection assembly, the folding mirror 8, and the focal plane detector 9 are located on the same side of the off-axis three-mirror system. The off-axis three-mirror system is symmetrical about a plane of symmetry 10, and the field integrating element 1 and the focal plane detector 9 are located on opposite sides of the plane of symmetry 10.

[0033] In this process, light ray 3 is incident on the field integrating element 1, reflected by the off-axis three-mirror to the dispersion and reflection component, reflected back to the off-axis three-mirror by the dispersion and reflection component, and after a second reflection by the off-axis three-mirror, light ray 2 is imaged onto the focal plane detector 9 by the folding mirror 8.

[0034] Specifically, the dispersion and reflection assembly can use a plane mirror 7 and a dispersion element to achieve the required dispersion and reflection functions. The dispersion element can be a single prism, a cemented prism, or a set of separate prisms. The dispersion element can also be a diffraction grating. When the dispersion element is a reflective diffraction grating, it can replace the plane mirror 7 and take into account both the dispersion and reflection light paths.

[0035] like Figure 2 As shown, in this embodiment of the invention, the dispersion and reflection component employs a cemented prism group 6 and a plane mirror 7. This invention uses the cemented prism group 6 and the plane mirror 7 as an example for explanation. The plane mirror 7 is located at the pupil plane of the off-axis three-mirror system. The cemented prism group 6 includes a first prism 6.1 and a second prism 6.2, with the second prism 6.2 located between the first prism 6.1 and the plane mirror 7. The off-axis three-mirror system includes a primary mirror 3, a secondary mirror 4, and a third mirror 5. The primary mirror 3 and the third mirror 5 are located on the same side of the secondary mirror 4. The primary mirror 3, secondary mirror 4, and third mirror 5 form an off-axis three-mirror structure. The working principle and specific details of the off-axis three-mirror structure are consistent with existing systems and are well-known to those skilled in the art, and will not be elaborated further here.

[0036] The working principle of the snapshot imaging spectrometer of this invention is as follows: The field integrator 1 is located on one side of the symmetry plane 10 of the off-axis three-mirror system. The light ray 2 entering from the field integrator 1 is collimated after passing through the off-axis three-mirror system and exiting. In the exit light path, it is dispersed by the cemented prism group 6 and then enters the plane mirror 7. The plane mirror 7 is located at the pupil plane of the off-axis three-mirror system, that is, the principal rays 2 of different fields of view intersect at a point on this plane. The plane mirror 7 reflects the light ray 2 back, and it passes through the dispersive prism, the off-axis three-mirror system, and the folding mirror again, finally forming an image on the focal plane detector 9, which is located on the other side of the symmetry plane 10. A folding mirror 8 is added in front of the focal plane detector 9 to fold the focal plane detector 9 outward, so that the focal plane detector 9 and the field integrator 1 are separated by a greater distance, which facilitates the installation of the focal plane detector 9 and can obtain a large object plane and image plane that do not interfere with each other. The object plane is formed on the field integrator 1. This invention employs a dual-pass multiplexed off-axis triple-reflector system to achieve a compact system size, reducing the size of conventional transmission optical paths by at least two times under the same specifications.

[0037] The field integrator 1 can be selected from field integrators such as slit arrays, pinhole arrays, microlens arrays, and fiber arrays according to actual needs. Field integrator 1 is used to segment and sample the image within the plane. The spectral image formed by the focal plane detector 9 is the spectral image of each segmented sampling point or region within field integrator 1, containing two-dimensional spatial information and one-dimensional spectral information. At this time, the three-dimensional spectral information of the target is acquired and unfolded on the two-dimensional focal plane detector 9, and a three-dimensional data cube can be obtained through spectral reconstruction.

[0038] Since the distortion generated by the prism is asymmetric, and the coaxial system is a rotationally symmetric system, it is impossible to generate complementary asymmetric distortion for compensation. However, the distortion generated by the off-axis three-mirror structure and the distortion generated by the dispersive prism are mutually compensated through optical design, achieving the overall distortion reduction effect of the system. This makes the spectroscopic imager of the present invention have excellent spectroscopic imaging performance, low spectral distortion, and effectively improve the fidelity of spectral data.

[0039] In this embodiment of the invention, the optical parameters of the snapshot imaging spectrometer are as follows:

[0040]

[0041] This invention employs a focal plane detector 9 with a pixel size of 7μm. The snapshot imaging spectrometer manufactured according to the aforementioned optical parameters has an image magnification ratio of 1:1, an off-axis three-mirror structure with a focal length range of 25mm to 460mm, and can be used in the ultraviolet, visible and near-infrared, short-wave infrared, mid-wave infrared, and long-wave infrared bands. Its spectral resolution ranges from 0.05nm to 300nm, and the system exhibits excellent spectroscopic imaging performance. The imaging spectrometer of this invention has an outer envelope size of 114mm × 106mm × 120mm and weighs less than 1kg, making it extremely lightweight and compact. The dot plot of this invention is shown below. Figure 6 As shown, the RMS radius (root mean square radius) of the dot plot is smaller than the Airy disk radius, indicating small spectral distortion of the system, less than 2.3 μm. Of course, other system optical parameters can also be selected, depending on actual needs; these will not be elaborated upon here.

[0042] This invention proposes a snapshot imaging spectrometer employing a dual-pass multiplexed off-axis three-mirror structure. The dual-pass structure compresses the system volume; the off-axis three-mirror structure enables a large object plane, and the field integrator 1 and focal plane detector 9 are arranged separately to obtain a large object plane and a large image plane; the inherent distortion of the off-axis three-mirror structure is used to compensate for the distortion of the dispersive prism, thus achieving spectral distortion reduction for the entire system. This solves the balance problem between size and performance, resulting in an imaging spectrometer system with a large object plane, high spatial resolution, high spectral resolution, excellent imaging performance, low spectral distortion, and a compact size, suitable for lightweight platforms such as UAVs.

[0043] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A snapshot imaging spectrometer, characterized in that... The system includes a field integrator for discrete sampling, an off-axis three-mirror system, a dispersion and reflection assembly, a folding mirror, and a focal plane detector. The field integrator, dispersion and reflection assembly, folding mirror, and focal plane detector are located on the same side of the off-axis three-mirror system. The off-axis three-mirror system is symmetrical about a plane of symmetry, and the field integrator and the focal plane detector are located on opposite sides of the plane of symmetry. In this process, light is incident on the field integrating element, reflected by the off-axis three-mirror to the dispersion and reflection component, reflected back to the off-axis three-mirror by the dispersion and reflection component, and after a second reflection by the off-axis three-mirror, the light is imaged onto the focal plane detector by the folding mirror. The field integration element is one of a slit array, a pinhole array, a microlens array, and a fiber array; The dispersion and reflection assembly includes a cemented prism and a plane mirror. The plane mirror is located at the pupil plane of the off-axis three-mirror. The cemented prism includes a first prism and a second prism. The second prism is located between the first prism and the plane mirror. Furthermore, the asymmetric distortion generated by the off-axis three-mirror and the asymmetric distortion generated by the cemented prism compensate for each other to achieve overall spectral distortion elimination of the system.

2. The snapshot imaging spectrometer according to claim 1, characterized in that: The off-axis three-mirror system includes a primary mirror, a secondary mirror, and a third mirror. The primary mirror and the third mirror are located on the same side of the secondary mirror, and the surface of the off-axis three-mirror system is aspherical.

3. The snapshot imaging spectrometer according to claim 1, characterized in that: It also includes a focal plane detector, which is connected to the focal plane, and the diagonal size of the focal plane detector is 5mm to 62mm.

4. The snapshot imaging spectrometer according to claim 1, characterized in that: The focal length of the off-axis three-lens structure is 25mm~460mm.

5. The snapshot imaging spectrometer according to claim 1, characterized in that: The first prism is made of ultraviolet fused silica material, and the second prism is made of H-F4 optical material.

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