Wide-spectrum common-caliber hyperspectral imaging device and method

Abstract

The invention discloses a wide-spectrum common-caliber hyperspectral imaging device and a wide-spectrum common-caliber hyperspectral imaging method, and belongs to the technical field of spectral imaging. The device comprises a collimation system (1), a color separation film (2), a visible near-infrared band light splitting element (3), a visible near-infrared band focusing lens group (4), a visible near-infrared band light filter (5), a short-wave infrared band light splitting element (6), a short-wave infrared band focusing lens group (7) and a short-wave infrared band light filter (8). After being collimated by the collimation system (1), a light beam is divided into a visible near-infrared path and a short-wave infrared path by the color separation film (2), the visible near-infrared path and the short-wave infrared path are subjected to light splitting through the visible near-infrared band light splitting element (3) combined by the transmission grating and the prism and the short-wave infrared band light splitting element (6) of the reflection grating respectively, and then the light beam is converged to a corresponding image surface through respective focusing lens groups (4 and 7). According to the invention, the synchronous acquisition of the 400-2500nm ultra-wide spectrum linear dispersion hyperspectrum is realized.

Description

Technical Field

[0001] This invention belongs to the field of spectral imaging technology, specifically relating to a broadband common-aperture hyperspectral imaging device and method. Background Technology

[0002] Spectral imaging technology can simultaneously acquire the spatial geometric features and spectral radiation characteristics of the target, and has important application value in fields such as resource exploration, environmental monitoring, and target identification. To achieve full-spectrum coverage from visible light to short-wave infrared, traditional technical approaches typically employ a combination of multiple discrete optical path systems, resulting in complex overall structures and large volumes, making them difficult to adapt to miniaturized aerial detection platforms and unmanned systems with extremely stringent requirements for payload size and mass.

[0003] To address the aforementioned shortcomings, existing technologies have proposed common-aperture spectral imaging schemes based on off-axis reflective structures. These schemes achieve a degree of system compactness by sharing a front-mounted optical system and a wide-band detector. However, such off-axis structures based on prism dispersion principles still face the following technical bottlenecks: First, the envelope size and mass of the optical system still significantly exceed the capacity of miniaturized platforms; second, the inherent nonlinear spectral broadening characteristics of prism dispersion lead to spectral line distortion, increasing the complexity of subsequent spectral calibration and radiometric processing, thus limiting the accuracy of quantitative applications.

[0004] Therefore, existing off-axis reflective co-aperture spectral imaging devices are insufficient in terms of miniaturization and weight reduction, and the nonlinear dispersion effect introduced by the prism beam splitter affects the accuracy of spectral data processing; while conventional grating-prism hybrid spectral imagers are difficult to achieve full-spectrum response coverage from visible light to short-wave infrared bands in a single device architecture. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a broadband common-aperture hyperspectral imaging device and method that, while achieving broadband detection capabilities from visible light to shortwave infrared, meets the constraints of geometric size, mass, and cost, and maintains linear sampling characteristics in the spectral dimension, thereby improving the convenience and accuracy of remote sensing data processing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A broadband common-aperture hyperspectral imaging device includes a collimation system, a dichroic filter, a visible and near-infrared band beam splitter, a visible and near-infrared band focusing lens assembly, a visible and near-infrared band filter, a short-wave infrared band beam splitter, a short-wave infrared band focusing lens assembly, and a short-wave infrared band filter. The collimation system consists of a slit, a plane mirror, and a spherical collimating lens. The slit and the plane mirror are fitted together, and a rectangular aperture is formed in the center of the plane mirror. The light beam emitted from the slit passes through the rectangular aperture to reach the spherical collimating lens. After passing through the dichroic mirror, the light beam is reflected into the dichroic filter. The beam is then split into two paths. The visible and near-infrared beam is reflected by the dichroic filter and split into the visible and near-infrared beam splitter, then focused by the visible and near-infrared focusing lens group, and finally reaches the visible and near-infrared image plane after passing through the visible and near-infrared filter. The short-wave infrared beam passes through the dichroic filter and is split into the short-wave infrared beam splitter, then focused by the short-wave infrared focusing lens group, and finally reaches the short-wave infrared image plane after passing through the short-wave infrared filter.

[0008] Furthermore, the visible and near-infrared band beam splitter consists of a transmission grating and a prism, with the prism positioned behind the transmission grating.

[0009] Furthermore, the short-wave infrared band beam splitter includes a reflective grating, which is set at an angle to the optical axis to automatically optimize and correct spherical aberration, spectral line curvature, and color distortion.

[0010] Furthermore, both the visible and near-infrared focusing lens group and the short-wave infrared focusing lens group are composed of spherical lenses.

[0011] Furthermore, the visible and near-infrared band filter is coated with a long-pass cutoff filter film near the visible and near-infrared image plane surface, and the short-pass cutoff wavelength is 550nm.

[0012] Furthermore, the focal length ratio of the visible and near-infrared band focusing lens group to the collimation system achieves a zoom ratio of 0.733, and the focal length ratio of the short-wave infrared band focusing lens group to the collimation system achieves a zoom ratio of 1.

[0013] Furthermore, the angle between the transmission grating and the optical axis and the apex angle of the prism are determined by the spectral dimension length on the image plane, the number of grating line pairs, and the focal length of the focusing lens group in the visible and near-infrared bands. By increasing the air gap between the grating and the prism, the spectral line bending and color distortion caused by the prism and the grating are canceled out.

[0014] Furthermore, the visible and near-infrared band beam splitter and the visible and near-infrared band focusing lens group are coaxial in the optical axis direction, and the short-wave infrared band beam splitter and the short-wave infrared band focusing lens group are set at an angle.

[0015] Furthermore, a long-wave pass cutoff filter film is deposited on the surface of the short-wave infrared image plane near the short-wave infrared image plane, with a short-wave cutoff wavelength of 1300nm.

[0016] This invention also provides a broadband common-aperture hyperspectral imaging method, employing the aforementioned broadband common-aperture hyperspectral imaging device, comprising: a target beam incident through a slit, passing through a rectangular aperture of a plane mirror, being collimated by a spherical collimating mirror, and then refracted by a plane mirror before entering a dichroic filter; the dichroic filter splits the beam into a reflected visible and near-infrared beam and a transmitted short-wave infrared beam; the two beams respectively enter a visible and near-infrared beam splitter and a short-wave infrared beam splitter; the split beams pass through a visible and near-infrared focusing lens group and a short-wave infrared focusing lens group, and respectively pass through a visible and near-infrared filter coated with a long-pass cutoff filter and a short-wave infrared filter to eliminate secondary spectral aliasing, ultimately being imaged on the visible and near-infrared image plane and the short-wave infrared image plane, respectively, achieving simultaneous acquisition of linear dispersive hyperspectral data in the 400-2500nm ultra-wideband.

[0017] Beneficial effects:

[0018] 1. This invention uses a common aperture integrated design, which allows a single device to share a slit, collimating mirror and plane reflector, and uses a dichroic filter to achieve dual-band beam splitting of visible and near-infrared and short-wave infrared. It replaces the traditional dual-machine splicing scheme with a single device, which significantly reduces the system size and weight. The structure is compact and can meet the miniaturized detection requirements of small payload platforms such as UAVs.

[0019] 2. The collimating mirror of this invention uses a concave spherical reflector, and the focusing lens group uses spherical lenses throughout. Compared with the Offner curved prism solution, spherical elements have mature technology, are easier to manufacture, and have lower costs. In terms of spectral performance, this invention uses a grating as the core spectroscopic element, achieving linear dispersion and uniform spectral resolution distribution, greatly simplifying the remote sensing data processing workflow. The long-pass filters (cutoff wavelengths of 550nm and 1300nm) effectively eliminate secondary spectral aliasing. The dual-band independent matching of gratings with different line pairs and differentiated zoom ratios are optimized separately in the ultra-wide spectral range of 400-2500nm, balancing resolution and sensitivity.

[0020] 3. By optimizing the grating-prism air gap, correcting the dual-band independent focusing lens group, and automatically optimizing aberrations, the present invention controls spectral line curvature and chromatic aberration within a single pixel. The center wavelength MTF is greater than 0.65 at the Nyquist frequency, and the RMS spot size is better than the detector pixel size, resulting in excellent imaging quality.

[0021] In summary, this invention achieves ultra-wide spectral detection while simultaneously resolving the contradictions between miniaturization, high performance, and low cost. It also possesses environmental adaptability and parameter scalability, providing a technologically advanced and economical solution for lightweight hyperspectral payloads. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a broadband common aperture hyperspectral imaging device according to the present invention.

[0023] Figure 2 This is a schematic diagram of the collimation system.

[0024] Figure 3a This represents the optical modulation transfer function (MTF) at the center wavelength (700 nm) in the visible-near-infrared (VNIR) band under different slit heights, with a cutoff frequency of 45.5 lp / mm. Solid lines represent the meridional plane, dashed lines represent the sagittal plane, blue represents the MTF at a slit height of 0 mm, green represents the MTF at a slit height of 4.2 mm, and red represents the MTF at a slit height of 6 mm, and so on.

[0025] Figure 3b The optical modulation transfer function (MTF) for the center wavelength (1750 nm) of the shortwave infrared (SWIR) band at different slit heights is given, with a cutoff frequency of 16.7 lp / mm.

[0026] Figure 4a The figures show the root-mean-square radius (RMS) and geometric radius (GEO) of the center wavelength (700 nm) in the visible-near-infrared (VNIR) band when the slit height is 0 mm, 4.2 mm, and 6 mm. In the upper left image, blue represents the image spot with a slit height of 0 mm; in the upper right image, green represents the image spot with a slit height of 4.2 mm; and in the lower image, red represents the image spot with a slit height of 6 mm, and so on.

[0027] Figure 4b The graph shows the root mean square radius (RMS) and geometric radius (GEO) of the center wavelength (1750 nm) in the shortwave infrared (SWIR) band when the slit surface height is 0 mm, 4.2 mm, and 6 mm. In the top left image, blue represents the spot pattern when the slit surface height is 0 mm; in the top right image, green represents the spot pattern when the slit surface height is 4.2 mm; and in the bottom image, red represents the spot pattern when the slit surface height is 6 mm.

[0028] The attached figures are labeled as follows: 1. Collimation system; 2. Color separator; 3. Visible and near-infrared band beam splitter; 4. Visible and near-infrared band focusing lens group; 5. Visible and near-infrared band filter; 6. Short-wave infrared band beam splitter; 7. Short-wave infrared band focusing lens group; 8. Short-wave infrared band filter; 9. Slit; 10. Plane mirror; 11. Spherical collimating lens. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] like Figure 1 As shown, a broadband common aperture spectral imaging device of the present invention includes a collimation system 1, a dichroic filter 2, a visible and near-infrared band beam splitter 3, a visible and near-infrared band focusing lens group 4, a visible and near-infrared band filter 5, a short-wave infrared band beam splitter 6, a short-wave infrared band focusing lens group 7, and a short-wave infrared band filter 8.

[0031] like Figure 2 As shown, the collimation system 1 consists of a slit 9, a plane mirror 10, and a spherical collimating mirror 11. The slit 9 and the plane mirror 10 are attached together, and the spherical collimating mirror 11 is a concave spherical mirror. To avoid chromatic aberration introduced by the broadband response, the slit 9 is machined. The plane mirror 10 has a rectangular hole in the middle, and its rear surface, except for the hole, is coated with a reflective film. The light beam emitted from the slit 9 passes through the rectangular hole of the plane mirror 10, is collimated by the spherical collimating mirror 11, and then reflected by the plane mirror 10 before entering the dichroic filter 2.

[0032] After passing through dichroic filter 2, the visible and near-infrared beam is reflected into the visible and near-infrared beam splitter 3. After being split by the visible and near-infrared beam splitter 3, it is converged by the visible and near-infrared focusing lens group 4. After the second-order spectrum is eliminated by the visible and near-infrared filter 5, it converges onto the visible and near-infrared image plane, completing the visible and near-infrared imaging process. The zoom ratio is 0.733. After being transmitted through dichroic filter 2, the short-wave infrared beam enters the short-wave infrared beam splitter 6. After being split by the short-wave infrared beam splitter 6, it is converged by the short-wave infrared focusing lens group 7. After the second-order spectrum is eliminated by the short-wave infrared filter 8, it converges onto the short-wave infrared image plane, completing the short-wave infrared imaging process. The zoom ratio is 1.

[0033] Preferably, the visible and near-infrared band beam splitter 3 consists of a transmission grating and a prism. The prism is placed behind the transmission grating. The angle between the transmission grating and the optical axis and the apex angle of the prism are determined by the spectral dimension length on the image plane, the number of grating line pairs, and the focal length of the visible and near-infrared band focusing lens group 4. The calculation process is as follows:

[0034] Calculate the grid horn:

[0035] ;

[0036] in, It is the Bragg wavelength. It is the refractive index of the grating material;

[0037] Calculate the external angle of incidence based on Snell's law

[0038] Based on grating character dispersion Dispersion with the plane of the image Relationship calculation of image equivalent focal length :

[0039] ;

[0040] in, It is the diffraction order of the grating. It is the number of grating lines. It is the dispersion width on the image plane. It refers to the spectral range;

[0041] According to the multiplication relationship Determine the focal length of the collimating lens ;

[0042] Apply central bundle and axial constraints, and numerically or analytically solve for the prism apex angle. Make it satisfy:

[0043] .

[0044] In optical design, a series of initial parameters can be obtained by following the calculation method above. The optimization target of minimizing spectral line bending and color distortion can be set, and the air gap between the grating and the prism can be gradually increased to perform automatic optimization, so that the spectral line bending and color distortion caused by the prism and the grating can be offset, thereby minimizing spectral line bending and color distortion.

[0045] Preferably, the visible and near-infrared focusing lens group 4 consists of 6 lenses, namely a cemented doublet consisting of two lenses, a concave lens, a meniscus lens, and two convex lenses, which are used to converge the diffracted beam and correct aberrations. The visible and near-infrared beam splitter 3 and the visible and near-infrared focusing lens group 4 are coaxial in the optical axis direction, and the focal length of the visible and near-infrared focusing lens group 4 can be set to 47.65mm and the focal length of the collimation system 1 can be set to 65mm to meet the zoom ratio requirements.

[0046] Preferably, the short-wave infrared band beam splitter 6 includes a reflective grating with an angle to the optical axis and also with the short-wave infrared band focusing lens group 7 composed of spherical lenses. In the optical design, the reflective grating can be given an initial 45° rotation angle to set the optimization target of minimizing spectral line bending and color distortion. Then, automatic optimization is performed to achieve the functions of beam splitting, converging diffraction beams, correcting spherical aberration, spectral line bending, and color distortion. The focal length of the short-wave infrared band focusing lens group 7 and the collimation system 1 are both set to 65mm to meet the zoom ratio requirements.

[0047] Preferably, the short-wave infrared focusing lens group 7 consists of five lenses, which, from left to right, are a convex lens, a doublet consisting of two lenses, a convex lens, and a concave lens.

[0048] Since the dispersive element of the system is a grating, there will be a second-order spectrum. That is, the second-order diffraction light of 400-500nm will overlap with the spectral region of 800-1000nm on the image plane, and the second-order diffraction light of 1000-1250nm will overlap with the spectral region of 2000-2500nm on the image plane. In order to avoid spectral aliasing, a second-order filter needs to be placed in front of the visible and near-infrared image plane and the short-wave infrared image plane, namely the visible and near-infrared band filter 5 and the short-wave infrared band filter 8.

[0049] Preferably, the visible and near-infrared filter 5 has a long-pass cutoff filter film on the surface near the visible and near-infrared image plane, and the short-pass cutoff wavelength is 550nm. The visible and near-infrared secondary filter is placed in front of the visible and near-infrared image plane.

[0050] Preferably, the short-wave infrared filter 8 is coated with a long-wave pass cutoff filter film near the short-wave infrared image surface, the short-wave infrared cutoff wavelength is 1300nm, and the short-wave infrared secondary filter is placed in front of the short-wave infrared image surface.

[0051] The present invention also provides an imaging method for a broadband common aperture spectral imaging device, comprising:

[0052] The target beam is incident through the common slit 9, passes through the rectangular hole of the plane mirror 10, is collimated by the spherical collimating mirror 11, and then refracted by the plane mirror 10 into the dichroic filter 2; the dichroic filter 2 splits the beam into two paths - the visible and near-infrared band beam is reflected and the short-wave infrared band beam is transmitted. Two beams enter their respective beam splitters, namely the visible and near-infrared beam splitter 3 and the short-wave infrared beam splitter 6. The visible and near-infrared beam splitter 3 uses a combination of a transmission grating and a prism for diffraction, while the short-wave infrared beam splitter 6 uses a reflection grating for diffraction. The split beams are then converged by spherical focusing lens groups of the corresponding bands, namely the visible and near-infrared focusing lens group 4 and the short-wave infrared focusing lens group 7. Secondary spectral aliasing is eliminated by filters coated with long-pass cutoff filters (i.e., the visible and near-infrared filter 5 and the short-wave infrared filter 8), and finally converged to the visible and near-infrared image planes and the short-wave infrared image plane, respectively, to achieve simultaneous acquisition of linear dispersive hyperspectral data in the ultra-wide spectral range of 400-2500 nm.

[0053] Example:

[0054] A simulation experiment was conducted to demonstrate the operation of the aforementioned device. In this embodiment:

[0055] The system's first-order parameters are: spectral range 400-2500nm, covering the visible to short-wave infrared bands, slit length 12mm, F number 3, with visible and near-infrared pixel size 11μm, grating line pairs 300 lines / mm, and zoom ratio 0.733; short-wave infrared pixel size 30μm, grating line pairs 54.25 lines / mm, and zoom ratio 1; spectral line curvature and chromatic aberration are both less than one pixel.

[0056] Depend on Figure 3a , Figure 3b As can be seen, the optical modulation transfer function (MTF) values ​​at their center wavelengths (700 nm and 1750 nm) in both the visible and near-infrared bands are greater than 0.65 at the Nyquist frequency. Here, OTF represents the optical transfer function, which is a complex function containing both amplitude and phase information. Figure 4a , Figure 4b It can be seen that the root mean square radius (RMS) of the light spot can be well confined within a single pixel.

[0057] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A broadband common-aperture hyperspectral imaging device, characterized in that, The system includes a collimation system, a dichroic filter, a visible and near-infrared (VIN) band beam splitter, a VIN band focusing lens assembly, a VIN band filter, a short-wave infrared (SWI) band beam splitter, a SWIe focusing lens assembly, and a SWIe filter. The collimation system consists of a slit, a plane mirror, and a spherical collimating mirror. The slit and plane mirror are fitted together, and a rectangular aperture is formed in the center of the plane mirror. A light beam emitted from the slit passes through the rectangular aperture, is collimated by the SWIe, and then reflected by the plane mirror into the dichroic filter. The beam is split into two paths by the dichroic filter. The VIN band beam is reflected by the dichroic filter, split by the VIN band beam splitter, then converged by the VIN band focusing lens assembly, and finally passes through the VIN band filter to reach the VIN image plane. The SWIe beam passes through the dichroic filter, is split by the SWIe, then converged by the SWIe focusing lens assembly, and finally passes through the SWIe filter to reach the SWIe image plane.

2. The broadband common-aperture hyperspectral imaging device according to claim 1, characterized in that, The visible and near-infrared band beam splitter consists of a transmission grating and a prism, with the prism positioned behind the transmission grating.

3. The broadband common-aperture hyperspectral imaging device according to claim 1 or 2, characterized in that, The short-wave infrared band beam splitter includes a reflective grating, which is set at an angle to the optical axis and automatically optimizes and corrects spherical aberration, spectral line curvature, and color distortion.

4. The broadband common-aperture hyperspectral imaging device according to claim 1, characterized in that, Both the visible and near-infrared focusing lens group and the short-wave infrared focusing lens group are composed of spherical lenses.

5. The broadband common-aperture hyperspectral imaging device according to claim 1, characterized in that, The visible and near-infrared band filter is coated with a long-pass cutoff filter film near the visible and near-infrared image plane surface, and the short-pass cutoff wavelength is 550nm.

6. The broadband common-aperture hyperspectral imaging device according to claim 1, characterized in that, The focal length ratio of the visible and near-infrared band focusing lens group to the collimation system achieves a zoom ratio of 0.733, and the focal length ratio of the short-wave infrared band focusing lens group to the collimation system achieves a zoom ratio of 1.

7. The broadband common-aperture hyperspectral imaging device according to claim 2, characterized in that, The angle between the transmission grating and the optical axis and the apex angle of the prism are determined by the spectral dimension length on the image plane, the number of grating line pairs, and the focal length of the focusing lens group in the visible and near-infrared bands. The spectral line bending and color distortion caused by the prism and grating are canceled out by increasing the air gap between the grating and the prism.

8. The broadband common-aperture hyperspectral imaging device according to claim 4, characterized in that, The visible and near-infrared band beam splitter and the visible and near-infrared band focusing lens group are coaxial in the optical axis direction, while the short-wave infrared band beam splitter and the short-wave infrared band focusing lens group are set at an angle.

9. The broadband common-aperture hyperspectral imaging device according to claim 5, characterized in that, The short-wave infrared band filter has a long-wave pass cutoff filter film deposited on the surface near the short-wave infrared image plane, with a short-wave cutoff wavelength of 1300nm.

10. A broadband common-aperture hyperspectral imaging method, characterized in that, The broadband common-aperture hyperspectral imaging device according to any one of claims 1 to 9 includes: a target beam is incident through a slit, passes through the rectangular aperture of a plane mirror, is collimated by a spherical collimating mirror, and then refracted by the plane mirror into a dichroic filter; the dichroic filter splits the beam into a reflected visible and near-infrared beam and a transmitted short-wave infrared beam; the two beams enter the visible and near-infrared beam splitter and the short-wave infrared beam splitter, respectively; the split beams pass through the visible and near-infrared focusing lens group and the short-wave infrared focusing lens group, and respectively pass through the visible and near-infrared filter coated with a long-pass cutoff filter and the short-wave infrared filter to eliminate secondary spectral aliasing, and are finally imaged on the visible and near-infrared image plane and the short-wave infrared image plane, respectively, to achieve simultaneous acquisition of linear dispersive hyperspectral data in the ultra-wide spectral range of 400-2500 nm.

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