A compact wide-band spectral imaging optical system

Abstract

The invention belongs to the technical field of spectral imaging. In order to solve the problem that the increase of working band and field of view of the existing spectral imaging technology will lead to difficulty in aberration correction of the system, a compact wide-band spectral imaging optical system is disclosed, comprising an immersion primary mirror, a correction lens and a convex grating; the immersion primary mirror is arranged as an optical element with positive optical focal length, which comprises a first surface and a second surface, wherein the first surface is on the object side and is arranged as a refractive surface, and the second surface is a reflective surface and is bent toward the object side; a reflective grating structure is arranged on the convex grating; the working band of the invention covers visible to short-wave infrared, and the system volume structure is compact.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral imaging, and relates to a spectral imaging optical system, and in particular to a wide-band, lightweight and compact spectral imaging optical system. Background Art

[0002] Spectral imaging technology can simultaneously obtain spatial information and spectral information of a scene, and has the advantage of "image and spectrum in one". It is widely used in remote sensing detection, mineral exploration, environmental monitoring, smart agriculture, food safety and other fields. According to different spectroscopic methods, spectral imaging systems can generally be divided into two types: dispersion type and interference type. According to the different spectroscopic elements used, the dispersion type can be divided into two types: prism type and grating type. The grating type spectral imaging system based on the Offner structure has the advantages of large relative aperture, small distortion, good imaging quality, and compact structure. It is one of the most common spectral imaging systems currently.

[0003] With the continuous development of spectral imaging technology and the increase in application requirements, spectral imaging systems are developing towards lightweight and high performance, requiring spectral imaging systems to have high imaging performance under conditions such as wide band, wide field of view, and large numerical aperture, while achieving lightweight and miniaturized system structure. However, the increase in working band and field of view will make it difficult to correct the aberration of the system, and will also cause the volume of the spectral imaging system to increase rapidly, which brings great difficulty to the design of spectral imaging systems. Summary of the invention

[0004] In order to solve the problem that the increase of working band and field of view of existing spectral imaging technology will lead to difficulty in aberration correction of the system, a compact wide-band spectral imaging optical system is provided, which has a working band covering visible to short-wave infrared and a compact system volume structure.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A compact wide-band spectral imaging optical system comprises an immersion primary mirror, a correction lens and a convex grating; the immersion primary mirror is configured as an optical element with positive optical power, comprising a first surface of the immersion primary mirror and a second surface of the immersion primary mirror, wherein the first surface of the immersion primary mirror is on the object side and is configured as a refractive surface, and the second surface of the immersion primary mirror is a reflective surface and is bent toward the object side; a reflective grating structure is configured on the convex grating;

[0007] The light emitted from the object surface passes through the correction lens and is refracted from the first surface of the immersion primary mirror to the second surface of the immersion primary mirror. The light reflected by the second surface of the immersion primary mirror passes through the first surface of the immersion primary mirror and the correction lens in sequence and is then reflected by the convex grating. The light reflected by the convex grating passes through the correction lens and is refracted from the first surface of the immersion primary mirror to the second surface of the immersion primary mirror again. After being reflected by the second surface of the immersion primary mirror, it passes through the first surface of the immersion primary mirror and the correction lens again, and a spectral image of the object is formed on the image plane.

[0008] A further optimization in the above solution is as follows: The radius of curvature R11 of the first surface of the immersion primary mirror and the radius of curvature R12 of the second surface of the immersion primary mirror satisfy the following conditions: 1.3 < R12 / R11 < 1.42; The correction lens is set as an optical element with a negative optical power, which includes a first surface of the correction lens and a second surface of the correction lens. The radius of curvature R21 of the first surface of the correction lens and the radius of curvature R22 of the second surface of the correction lens satisfy the following conditions: 0.77 < R22 / R21 < 0.82; The surface radius of curvature R3 of the convex grating and the radius of curvature R12 of the second surface of the immersion primary mirror satisfy the following conditions: 0.38 < R3 / R12 < 0.43.

[0009] Preferably, the first surface of the correction lens, the second surface of the correction lens, and the first surface of the immersion primary mirror are all aspherical surfaces.

[0010] Preferably, the Abbe number refractive index 55 < V < 69 of the optical materials used for the correction lens and the immersion primary mirror satisfies 1.4 < n < 1.6.

[0011] Preferably, the interval between the immersion primary mirror and the correction lens is 5.9 < d12 < 6.3.

[0012] Preferably, the interval between the correction lens and the convex grating is 22.8 < d23 < 23.2.

[0013] By adopting the immersion primary mirror in the present invention, the incident angle of light on the surface of the element is reduced, effectively compressing the size of the wide-band spectral imaging optical system; by adding a correction lens, the correction ability of the system astigmatism is further increased; by making the surfaces of the immersion primary mirror and the correction lens aspherical, the aberration correction ability of the system is further improved, and the imaging quality is improved.

[0014] By adopting the solution of the present invention, the volume of the wide-band spectral imaging optical system can be effectively reduced, and the compactness of the system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0016] Figure 1 It is a structural schematic diagram of the optical system of the present invention;

[0017] Figure 2a It is a spot diagram at a wavelength of 2.5um of the embodiment;

[0018] Figure 2b This is the spot diagram of the embodiment at a wavelength of 1.45um

[0019] Figure 2c The spot diagram at 0.4um wavelength of the embodiment is shown in FIG.

[0020] Figure 3a It is the MTF curve at 2.5um wavelength of the embodiment;

[0021] Figure 3b MTF curve at 1.45um wavelength in the embodiment

[0022] Figure 3c It is the MTF curve at 0.4um wavelength of the embodiment;

[0023] Among them: 1 is the immersion primary mirror 1, 11 is the first surface of the immersion primary mirror, 12 is the second surface of the immersion primary mirror, 2 is the correction lens, 21 is the first surface of the correction lens, 22 is the second surface of the correction lens, and 3 is the convex grating. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0025] Embodiment 1:

[0026] like Figure 1 As shown, a compact wide-band spectral imaging optical system comprises an immersion primary mirror 1, a correction lens 2 and a convex grating 3; the immersion primary mirror is configured as an optical element with positive optical focal length, comprising a first surface 11 of the immersion primary mirror and a second surface 12 of the immersion primary mirror, wherein the first surface of the immersion primary mirror is on the object side and is configured as a refractive surface, and the second surface of the immersion primary mirror is a reflective surface and is bent toward the object side; a reflective grating structure is configured on the convex grating; light emitted from the object surface is transmitted through the correction lens and then refracted from the first surface of the immersion primary mirror to the second surface of the immersion primary mirror, light reflected from the second surface of the immersion primary mirror is transmitted through the correction lens and then reflected by the convex grating, light reflected by the convex grating is transmitted through the correction lens and then refracted from the first surface of the immersion primary mirror to the second surface of the immersion primary mirror again, and then transmitted through the first surface of the immersion primary mirror and the correction lens again to form a spectral image of the object on the image plane.

[0027] Embodiment two:

[0028] The radius of curvature R11 of the first surface of the immersion primary mirror and the radius of curvature R12 of the second surface of the immersion primary mirror satisfy the following conditions: 1.3 < R12 / R11 < 1.42; the correction lens is set as an optical element with negative optical power, which includes a first surface of the correction lens and a second surface of the correction lens. The radius of curvature R21 of the first surface of the correction lens and the radius of curvature R22 of the second surface of the correction lens satisfy the following conditions: 0.77 < R22 / R21 < 0.82; the radius of curvature R3 of the surface of the convex grating and the radius of curvature R12 of the second surface of the immersion primary mirror satisfy the following conditions: 0.38 < R3 / R12 < 0.43.

[0029] Preferred solution: The immersion primary mirror 1 is an optical element with positive optical power, which is used for the convergence of the object-side incident light beam and the image-side outgoing light beam. The immersion primary mirror can effectively compress the volume of the spectral imaging system, and its first surface 11 can increase the aberration correction ability after aspherization.

[0030] The correction lens 2 is an optical element with negative optical power. The light beam passes through the off-axis part of the correction lens four times in the optical path, effectively correcting the astigmatism of the system. After the first surface and the second surface of the correction lens are aspherized, the residual aberration of the system can be further corrected.

[0031] The convex grating 3 is used for beam splitting and providing partial optical power.

[0032] Figure 1 It is a schematic structural diagram of an imaging lens showing an exemplary embodiment according to the present invention. The elements and light rays in the figure are all schematic, and there are certain differences from the actual surface shape and actual light rays.

[0033] The first surface 11 of the immersion primary mirror, the first surface 21 of the correction lens, and the second surface 22 of the correction lens are all aspherical surfaces, and the mathematical expressions of their surface shapes satisfy the following formula:

[0034]

[0035] Where z is the distance from the vertex of the lens to the optical axis direction, c is the basic curvature of the lens, r is the distance from the optical axis along the direction perpendicular to the optical axis, K is the quadratic constant, and A, B, C, and D are aspherical coefficients.

[0036] Embodiment 3:

[0037] A compact wide-band spectral imaging optical system based on Embodiment 1. The F / # of the optical system is 3.4, its field of view is 28 mm, the working band covers 400 - 2500 nm, and the spectral surface width is 4.2 mm; the specific parameters of the immersion primary mirror, the correction lens, and the convex grating are shown in the table;

[0038]

[0039] In the embodiment, the distance between the immersion primary mirror and the correction lens is 6.113 mm, and the distance between the correction lens and the convex grating is 23.04 mm.

[0040] In the embodiment, the first surface of the correction lens, the second surface of the correction lens and the first surface of the immersion primary mirror are aspherical surfaces. The aspherical surface system is shown in the following table.

[0041] Coefficient B Coefficient C Coefficient D Correction lens first surface 21 4.10e-011 3.49e-013 1.20e-016 Correction lens second surface 22 1.72e-010 2.01e-013 2.17e-016 Immersion primary mirror first surface 11 1.62e-010 -0.87e-014 8.1e-017

[0042] Figure 2a -c is the spot diagram of different fields of view at 0.4um, 1.45um and 2.5um in Example 1, and the specific spot diagram radius is shown in the following table. It can be seen from the figure that the size of the spot diagram is basically smaller than the size of a single pixel, and the imaging quality at each wavelength is good.

[0043]

[0044] Figure 3a -c is the modulation transfer function curve of the on-axis point of Example 1 at 0.4um, 1.45um and 2.5um, and the specific modulation transfer function values ​​under different fields of view are shown in the following table. It can be seen from the data in the table that the modulation transfer function values ​​of Example 1 are all greater than 0.68, and the imaging quality is close to the diffraction limit.

[0045]

[0046] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A compact wide - band spectral imaging optical system, characterized in that: It includes an immersion primary mirror, a correction lens, and a convex grating; the immersion primary mirror is set as an optical element with positive optical power, which includes an immersion primary mirror first surface and an immersion primary mirror second surface, where the immersion primary mirror first surface is the object - side and is set as a refractive surface, and the immersion primary mirror second surface is a reflective surface and bends towards the object - side; the convex grating is set with a reflective grating structure; The light emitted from the object surface passes through the correction lens and then refracts from the immersion primary mirror first surface to the immersion primary mirror second surface. The light reflected by the immersion primary mirror second surface passes through the immersion primary mirror first surface and the correction lens in sequence and is then reflected by the convex grating. The light reflected by the convex grating passes through the correction lens and then refracts from the immersion primary mirror first surface to the immersion primary mirror second surface again. After being reflected by the immersion primary mirror second surface, it passes through the immersion primary mirror first surface and the correction lens again, and a spectral image of the object is formed on the image surface.

2. The compact wide - band spectral imaging optical system according to claim 1, characterized in that, The radius of curvature R11 of the immersion primary mirror first surface and the radius of curvature R12 of the immersion primary mirror second surface satisfy the following conditions: 1.3 < R12 / R11 < 1.42; The correction lens is set as an optical element with negative optical power, which includes a correction lens first surface and a correction lens second surface. The radius of curvature R21 of the correction lens first surface and the radius of curvature R22 of the correction lens second surface satisfy the following conditions: 0.77 < R22 / R21 < 0.82; The surface radius of curvature R3 of the convex grating and the radius of curvature R12 of the immersion primary mirror second surface satisfy the following conditions: 0.38 < R3 / R12 < 0.

43.

3. The compact wide - band spectral imaging optical system according to claim 1, characterized in that, The correction lens first surface, the correction lens second surface, and the immersion primary mirror first surface are all aspherical surfaces.

4. The compact wide - band spectral imaging optical system according to claim 1, characterized in that, The Abbe number refractive index of the optical materials used for the correction lens and the immersion primary mirror satisfies 55 < V < 69 and 1.4 < n < 1.

6.

5. The compact wide - band spectral imaging optical system according to claim 1, characterized in that, The interval between the immersion primary mirror and the correction lens is 5.9 < d12 < 6.

3.

6. The compact wide - band spectral imaging optical system according to claim 1, characterized in that, The interval between the correction lens and the convex grating is 22.8 < d23 < 23.2.

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