A catadioptric shortwave infrared imaging spectrometer

Abstract

This invention provides a catadioptric shortwave infrared imaging spectrometer, comprising, in order of light incidence, an entrance slit, a plane mirror, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, a grating, and an imaging sensor. The plane mirror, together with the upper portions of the first, second, third, fourth, fifth, sixth, and seventh lenses, forms a collimation system. The grating, together with the lower portions of the seventh, sixth, fifth, fourth, third, second, and first lenses, and the imaging sensor, together form an imaging system. Collimation and imaging share a single lens group, resulting in a compact structure, easier aberration correction, simpler assembly and adjustment, better image quality, lower tolerance sensitivity, and reduced assembly difficulty.

Description

Technical Field

[0001] This utility model belongs to the field of spectral imaging technology, specifically relating to a catadioptric shortwave infrared imaging spectrometer. Background Technology

[0002] Shortwave infrared (SIR) has become a key band in remote sensing due to its unique spectral characteristics. SIR imaging spectrometers play a crucial role in remote sensing, their core value lying in their ability to simultaneously acquire spatial distribution and detailed spectral information of targets, enabling real-time monitoring and analysis of all remotely sensed targets. The miniaturization of platforms and the pursuit of high spectral resolution are important development directions. SIR imaging spectroscopy technology is not only widely used in remote sensing but also demonstrates significant application value in several important industries (scientific research, military reconnaissance, industrial classification, etc.). The core advantages of this technology are its ability to achieve non-destructive testing, rapid analysis, and wide-area coverage, thereby significantly improving the efficiency of target material composition identification and classification.

[0003] In recent years, with the increasing demand for applications such as UAV remote sensing and rapid laboratory testing, the need for lightweight, high-performance short-wave infrared imaging spectrometers has become increasingly urgent. Among traditional reflective spectrometers, the Offner-type structure has become a common design due to its large relative aperture, high dispersion linearity, compact structure, and excellent imaging quality. This structure typically consists of two concave mirrors and a convex grating. However, the high difficulty and cost of fabricating convex gratings, the limited variety of options, and the need for customized design result in poor versatility, restricting its application in miniaturized, low-cost spectrometers. Utility Model Content

[0004] This invention provides a large-range spectral confocal dispersive lens, which adopts a catadioptric system composed of transmission and reflection, to solve the problem of poor versatility of existing technologies and meet the needs of engineering applications.

[0005] According to a first aspect of the present invention, one or more embodiments of this application provide a catadioptric shortwave infrared imaging spectrometer:

[0006] According to the direction of light incidence, the system includes, in sequence, an entrance slit, a plane mirror, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, a grating, and an imaging sensor. The plane mirror and the upper parts of the first, second, third, fourth, fifth, sixth, and seventh lenses constitute a collimation system. The grating, together with the lower parts of the seventh, sixth, fifth, fourth, third, second, and first lenses, and the imaging sensor, constitute an imaging system.

[0007] Based on the above technical solution of this utility model, the following improvements can also be made:

[0008] The second and third lenses are closely joined to form a first cemented lens group, with the cementing surface of the first cemented lens group bent toward the image plane; the sixth and seventh lenses are closely joined to form a second cemented lens group, with the cementing surface of the second cemented lens group bent toward the grating.

[0009] The first lens is a meniscus lens with a concave incident surface and a convex exit surface.

[0010] The second lens is a biconvex lens, with a convex incident surface and a convex exit surface;

[0011] The third lens is a meniscus lens with a concave incident surface and a convex exit surface;

[0012] The fourth lens is a meniscus lens with a concave incident surface and a convex exit surface.

[0013] The fifth lens is a plano-convex lens, with a convex incident surface and a planar exit surface;

[0014] The sixth lens is a biconcave lens, with a concave incident surface and a concave exit surface;

[0015] The seventh lens is a meniscus lens with a convex incident surface and a concave exit surface.

[0016] The air gap between the entrance slit and the plane mirror is 17 mm.

[0017] The air gap between the plane mirror and the first lens is 6mm;

[0018] The air gap between the first lens and the first cemented lens group is 6.38 mm;

[0019] The air gap between the first cemented lens group and the fourth lens is 10mm;

[0020] The air gap between the fourth and fifth lenses is 1.36 mm;

[0021] The air gap between the fifth lens and the second cemented lens group is 1.21 mm;

[0022] The air gap between the second cemented lens group and the planar engraved diffraction grating is 5.5 mm.

[0023] The first lens, the second lens, the fourth lens, the fifth lens, and the seventh lens are all negative optical power; the third lens and the sixth lens are both positive optical power.

[0024] Among them, the apertures of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are all less than 28mm.

[0025] The grating is a planar etched diffraction grating, and the planar etched diffraction grating has an aperture.

[0026] The size of the entrance slit is 10mm × 25μm.

[0027] The focal length of the first lens is 80.35 mm;

[0028] The focal length of the second lens is 49.66 mm;

[0029] The focal length of the third lens is 89.99 mm;

[0030] The focal length of the fourth lens is 76.91 mm;

[0031] The focal length of the fifth lens is 24.3 mm;

[0032] The focal length of the sixth lens is 12.44 mm;

[0033] The focal length of the seventh lens is 36.48 mm.

[0034] The total length of the catadioptric shortwave infrared spectrometer does not exceed 70 mm.

[0035] The beneficial effects of this invention are as follows: This invention provides a catadioptric short-wave infrared imaging spectrometer. From the direction of light incidence, the first lens has a negative optical power and a meniscus structure; the second lens has a negative optical power and a biconvex structure; the third lens has a positive optical power and a meniscus structure; the fourth lens has a negative optical power and a meniscus structure; the fifth lens has a negative optical power and a plano-convex structure; the sixth lens has a positive optical power and a biconcave structure; and the seventh lens has a negative optical power and a meniscus structure. The aperture stop is located on a planar etched diffraction grating. The system's light source enters from the upper entrance slit. The catadioptric architecture reduces size and makes the structure compact. Collimation and imaging share a single lens group. The direction of light from the planar mirror to the planar etched diffraction grating is the collimation system; the direction of light reflection from the planar etched diffraction grating to the imaging sensor is the imaging system. The image side, the planar mirror, and the entrance slit are on the same side. The first lens in this system helps correct field curvature; the second and third lenses are closely joined to form a first cemented lens group to correct monochromatic aberration; the sixth and seventh lenses are closely joined to form a second cemented lens group to correct monochromatic aberration; and the fourth and fifth lenses are split from a high-refractive-index biconvex lens to help correct aperture aberration. The system has a reasonable distribution of optical power. With a total length not exceeding 70mm, compared to traditional reflectance spectrometers, it offers more degrees of freedom, is more conducive to aberration correction, is easier to assemble and adjust, has a spectral resolution better than 1nm, an MTF close to the diffraction limit, good imaging quality, low tolerance sensitivity, and reduced assembly difficulty. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the catadioptric shortwave infrared imaging spectrometer according to an embodiment of the present invention.

[0037] Figure 2 This is a spectral resolution dot plot of an embodiment of the present invention.

[0038] Figure 3 This is an example of the relationship between the RMS dot plot and wavelength in an embodiment of this utility model.

[0039] Figure 4 The MTF curve of this utility model embodiment is shown in the 900nm band.

[0040] Figure 5 The MTF curve of this utility model embodiment is shown in the 1300nm band.

[0041] Figure 6 The MTF curve of this utility model embodiment is shown in the 1500nm band.

[0042] Figure 7 The MTF curve of this utility model embodiment is shown in the 1700nm band.

[0043] Figure 8 This is the energy concentration curve at 900 nm for an embodiment of this utility model.

[0044] Figure 9 This is the energy concentration curve at 1300nm for an embodiment of this utility model.

[0045] Figure 10 This is the energy concentration curve at 1500nm for an embodiment of this utility model.

[0046] Figure 11 This is the energy concentration curve at 1700nm for an embodiment of this utility model.

[0047] Explanation of reference numerals in the attached figures: 1. Plane mirror; 2. Entrance slit; 3. First lens G1; 4. Second lens G2; 5. Third lens G3; 6. Fourth lens G4; 7. Fifth lens G5; 8. Sixth lens G6; 9. Seventh lens G7; 10. Plane engraved diffraction grating; 11. Imaging sensor. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0049] It should be noted that, unless otherwise defined, the technical or scientific terms used in one or more embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in one or more embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0050] like Figures 1-11 As shown, one or more embodiments of this application disclose a catadioptric shortwave infrared imaging spectrometer.

[0051] The system, arranged sequentially according to the direction of light incidence, includes an entrance slit 2, a plane mirror 1, a first lens G1, a second lens G2, a third lens G3, a fourth lens G4, a fifth lens G5, a sixth lens G6, a seventh lens G7, a grating, and an imaging sensor 4. The plane mirror 1, together with the upper portions of the first lens G1, second lens G2, third lens G3, fourth lens G4, fifth lens G5, sixth lens G6, and seventh lens G7, forms a collimation system. The grating, together with the lower portions of the seventh lens G7, sixth lens G6, fifth lens G5, fourth lens G4, third lens G3, second lens G2, and first lens G1, and the imaging sensor 4, together form an imaging system. The second lens G2 and the third lens G3 are closely joined to form a first cemented lens group, with the cementing surface of the first cemented lens group bent towards the image plane. The sixth lens G6 and the seventh lens G7 are closely joined to form a second cemented lens group, with the cementing surface of the second cemented lens group bent towards the grating. Its operating wavelength is 900nm-1700nm. The third lens G3 and the sixth lens G6 have positive optical power, while the first, second, fourth, fifth, and seventh lenses G7 have negative optical power. Collimation and imaging share a single lens group. The collimation system uses the upper half of the system, referring to the section of light from the plane mirror 1 to the plane-etched diffraction grating 3, specifically encompassing the upper halves of the first lens G1, second lens G2, third lens G3, fourth lens G4, fifth lens G5, sixth lens G6, and seventh lens G7. The imaging system uses the lower half of the system, referring to the section of light reflected from the plane-etched diffraction grating 3 to the imaging sensor 4, specifically encompassing the lower halves of the seventh lens G7, sixth lens G6, fifth lens G5, fourth lens G4, third lens G3, second lens G2, and first lens G1.

[0052] It is understood that in this embodiment, each lens is made of optical glass and each lens is a spherical lens.

[0053] In this embodiment, as an example, the specific lens parameter settings are as follows:

[0054] The first lens G1 is a meniscus lens with a focal length of 80.35mm, a concave incident surface, and a convex exit surface.

[0055] The second lens G2 is a biconvex lens with a focal length of 49.66 mm. The incident surface is convex, and the exit surface is convex.

[0056] The third lens, G3, is a meniscus lens with a focal length of 89.99 mm. The incident surface is concave, and the exit surface is convex.

[0057] The fourth lens, G4, is a meniscus lens with a focal length of 76.91 mm. The incident surface is concave, and the exit surface is convex.

[0058] The fifth lens G5 is a plano-convex lens with a focal length of 24.3 mm. The incident surface is convex and the exit surface is flat;

[0059] The sixth lens G6 is a double concave lens with a focal length of 12.44 mm. The incident surface is concave and the exit surface is concave;

[0060] The seventh lens G7 is a meniscus lens with a focal length of 36.48 mm. The incident surface is convex and the exit surface is concave;

[0061] The air gap between the incident slit 2 and the plane mirror 1 is 17 mm;

[0062] The air gap between the plane mirror 1 and the first lens G1 is 6 mm;

[0063] The air gap between the first lens G1 and the first cemented lens group is 6.38 mm;

[0064] The air gap between the first cemented lens group and the fourth lens G4 is 10 mm;

[0065] The air gap between the fourth lens G4 and the fifth lens G5 is 1.36 mm;

[0066] The air gap between the fifth lens G5 and the second cemented lens group is 1.21 mm;

[0067] The air gap between the second cemented lens group and the plane ruled diffraction grating 3 is 5.5 mm.

[0068] Among them, the apertures of the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, the sixth lens G6, and the seventh lens G7 are all less than 28 mm.

[0069] The refractive index n1 of the first lens G1 satisfies 1.8 < n1 < 1.85; the refractive index n2 of the second lens G2 satisfies 1.65 < n2 < 1.8; the refractive index n3 of the third lens G3 satisfies 1.6 < n3 < 1.7; the refractive index n4 of the fourth lens G4 satisfies 1.8 < n4 < 1.85; the refractive index n5 of the fifth lens G5 satisfies 1.9 < n5 < 2; the refractive index n6 of the sixth lens G6 satisfies 1.9 < n6 < 2; the refractive index n7 of the seventh lens G7 satisfies 1.64 < n7 < 1.84.

[0070] The Abbe number v1 of the first lens G1 satisfies 36 < v1 < 37.5; the Abbe number v2 of the second lens G2 satisfies 40 < v2 < 54; the Abbe number v3 of the third lens G3 satisfies 44.1 < v3 < 46.1; the Abbe number v4 of the fourth lens G4 satisfies 30 < v4 < 40; the Abbe number v5 of the fifth lens G5 satisfies 20 < v5 < 30; the Abbe number v6 of the sixth lens G6 satisfies 12 < v6 < 19; the Abbe number v7 of the seventh lens G7 satisfies 40 < v7 < 54.

[0071] The aperture stop is located on the plane ruled diffraction grating 3; among them, the first lens G1 is made of heavy lanthanum flint material, the second lens G2 is made of lanthanum flint material, the third lens G3 is made of titanium flint material, the fourth lens G4 is made of heavy lanthanum flint material, the fifth lens G5 is made of heavy lanthanum flint material, the sixth lens G6 is made of heavy flint material, and the seventh lens G7 is made of lanthanum flint material. Each lens uses domestic glass, which has the advantages of high production frequency, sufficient supply, and low cost.

[0072] The fifth lens G5 in this embodiment is a plano-convex lens, which is beneficial to reducing errors in the processing and assembly processes and improving mass production performance.

[0073] Among them, the aperture stop is located on the plane ruled diffraction grating 3. The light source of this system is incident from above through the slit 2, and it adopts a catadioptric architecture with a compact structure. The collimation and imaging functions are integrated through a shared lens group. The collimation optical path is from the plane mirror 1 to the plane ruled diffraction grating 3, and the imaging optical path is from the plane ruled diffraction grating 3 to the imaging sensor 4, realizing hyperspectral imaging. By introducing the plane mirror 1 to fold the optical path, not only the system volume is significantly reduced, but also the object-image distance is optimized, avoiding object-side and image-side interference. The imaging sensor 4, the plane mirror 1, and the incident slit 2 are on the left side of the lens group.

[0074] The first lens in this spectrometer is beneficial to correcting field curvature. The second and third lenses are closely cemented into the first cemented lens group, introducing a cemented surface to generate high-order aberrations to correct coma and astigmatism. The sixth and seventh lenses are closely cemented into the second cemented lens pair to correct monochromatic aberrations. The cemented lens has a weak optical power and is generally placed near the system aperture stop. The fourth and fifth lenses G5 are formed by splitting a positive lens with a large biconvex optical power, which helps to correct aperture aberrations, and the optical power of this system is reasonably distributed. The radius of curvature, lens thickness, air gap, glass material, etc. of all lenses are used for aberration correction.

[0075] To avoid the risk of delamination of cemented lenses over large temperature ranges, optical glass materials with similar coefficients of thermal expansion are selected for bonding. Here, ZEMAX software is used to replace materials, controlling the difference in the coefficients of thermal expansion of the cemented glass to within 2. Configuring such cemented lenses in the front and rear groups of the system not only effectively corrects the system's monochromatic aberration but also reduces tolerance sensitivity, maximizing its cost-effectiveness.

[0076] In this embodiment, the system has a relatively small numerical aperture F-number, effectively improving the system's light flux collection capability. Structurally, the design is highly compact, significantly reducing the system's size and weight. Compared to traditional Czerny-Turner and Offner system spectrometers, the collimating mirror, imaging mirror, plane mirror 1, and plane diffraction grating in this system are all common optical components with mature manufacturing processes. Assembly and debugging are simpler, requiring only minor adjustments to the detector's axial (optical axis) and vertical directions for alignment. This optical system, with its compact structure, strong light-gathering capability, and lightweight design, is suitable for applications with strict space constraints and weight sensitivity, such as airborne hyperspectral imaging systems.

[0077] This example describes a catadioptric shortwave infrared imaging spectrometer, such as... Figure 1 As shown. Operating wavelength range: 900nm-1700nm, numerical aperture NA 0.2, operating F-number 2.5, field of view 10mm, slit size 10mm×25μm, grating substrate material is float glass, planar engraved diffraction grating has a density of 300 lines / mm, diffraction order +1, and spectral resolution better than 1nm. An imaging sensor with 4 pixels of 15μm×15μm is selected.

[0078] The spectral resolution dot plot of this embodiment is as follows: Figure 2 As shown in the figure, the two light spots separated by 1 nm can be separated, indicating that the system resolution is better than 1 nm.

[0079] The root mean square (RMS) spot radius of this embodiment varies with wavelength, as follows: Figure 3 As shown in the figure, the RMS spot pattern of the five fields of view at the center and edges is less than 3 μm throughout the entire working band, and the imaging blur spots of each field of view can be accommodated by a 15*15 μm detector pixel. The results indicate that this catadioptric high-resolution shortwave infrared imaging spectrometer has good imaging quality.

[0080] The MTF resolution curves of this embodiment under different fields of view are shown below. Figure 4 , Figure 5 , Figure 6 , Figure 7As shown in the figure, the horizontal axis represents the spatial frequency value in revolutions per millimeter (rpm), and the vertical axis represents the OTF modulus value, which is the MTF modulation transfer function (MTF). The MTF value is used to evaluate the image quality of the lens. A higher MTF value indicates better image quality, stronger ability to reproduce the true image, and better overlap of curves across different fields of view, representing better image quality consistency. The cutoff frequency of this system is 33.3 lp / mm. Analysis was conducted at four wavelengths: 900 nm, 1300 nm, 1500 nm, and 1700 nm. At the cutoff frequency of 33.3 lp / mm in each band, the MTF curve is close to the diffraction limit, indicating that the system has high image quality.

[0081] The energy curves of the enclosing circle in this embodiment under different fields of view are shown below. Figure 8 , Figure 9 , Figure 10 , Figure 11 As shown, over 90% of the energy across the entire field of view corresponding to each characteristic wavelength can be concentrated within the pixel size of the CCD detector. This result verifies that the designed optical system possesses excellent imaging performance and meets application requirements.

[0082] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0083] Obviously, those skilled in the art can make various modifications and variations to this utility model without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this utility model and their equivalents, this utility model also intends to include these modifications and variations.

Claims

1. A catadioptric shortwave infrared imaging spectrometer, characterized in that, According to the direction of light incidence, the system includes, in sequence, an entrance slit, a plane mirror, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, a grating, and an imaging sensor. The plane mirror and the upper parts of the first, second, third, fourth, fifth, sixth, and seventh lenses constitute a collimation system. The grating, together with the lower parts of the seventh, sixth, fifth, fourth, third, second, and first lenses, and the imaging sensor, constitute an imaging system.

2. The catadioptric shortwave infrared imaging spectrometer according to claim 1, characterized in that, The second and third lenses are closely joined to form a first cemented lens group, and the cementing surface of the first cemented lens group is bent toward the image plane; the sixth and seventh lenses are closely joined to form a second cemented lens group, and the cementing surface of the second cemented lens group is bent toward the grating.

3. The catadioptric shortwave infrared imaging spectrometer according to claim 1, characterized in that, The first lens is a meniscus lens with a concave incident surface and a convex exit surface; The second lens is a biconvex lens, with a convex incident surface and a convex exit surface; The third lens is a meniscus lens with a concave incident surface and a convex exit surface; The fourth lens is a meniscus lens with a concave incident surface and a convex exit surface. The fifth lens is a plano-convex lens, with a convex incident surface and a planar exit surface; The sixth lens is a biconcave lens, with a concave incident surface and a concave exit surface; The seventh lens is a meniscus lens with a convex incident surface and a concave exit surface.

4. The catadioptric shortwave infrared imaging spectrometer according to claim 2, characterized in that, The air gap between the entrance slit and the plane mirror is 17 mm; The air gap between the plane mirror and the first lens is 6mm; The air gap between the first lens and the first cemented lens group is 6.38 mm; The air gap between the first cemented lens group and the fourth lens is 10mm; The air gap between the fourth and fifth lenses is 1.36 mm; The air gap between the fifth lens and the second cemented lens group is 1.21 mm; The air gap between the second cemented lens group and the planar engraved diffraction grating is 5.5 mm.

5. The catadioptric shortwave infrared imaging spectrometer according to claim 1, characterized in that, The first lens, the second lens, the fourth lens, the fifth lens, and the seventh lens are all negative optical power; the third lens and the sixth lens are both positive optical power.

6. The catadioptric shortwave infrared imaging spectrometer according to claim 1, characterized in that, The apertures of the first, second, third, fourth, fifth, sixth, and seventh lenses are all less than 28 mm.

7. The catadioptric shortwave infrared imaging spectrometer according to claim 1, characterized in that, The grating is a planar etched diffraction grating, and the planar etched diffraction grating has an aperture.

8. The catadioptric shortwave infrared imaging spectrometer according to claim 1, characterized in that, The size of the entrance slit is 10mm × 25μm.

9. The catadioptric shortwave infrared imaging spectrometer according to claim 3, characterized in that, The focal length of the first lens is 80.35 mm; The focal length of the second lens is 49.66 mm; The focal length of the third lens is 89.99 mm; The focal length of the fourth lens is 76.91 mm; The focal length of the fifth lens is 24.3 mm; The focal length of the sixth lens is 12.44 mm; The focal length of the seventh lens is 36.48 mm.

10. The catadioptric shortwave infrared imaging spectrometer according to claim 1, characterized in that, The total length of the catadioptric shortwave infrared spectrometer does not exceed 70 mm.

Images