Freeform surface based imaging spectrometer telescope system

Abstract

The application provides a free-form surface-based imaging spectrometer telescope system, which comprises six optical lenses in sequence in the light incidence direction, namely a concave lens, a concave lens, a convex lens, a convex lens, a convex lens and a concave lens; the focal length of the lens is 7.6 mm, the F number is 2.0, the working wavelength range is 400 nm-700 nm, the visible light wavelength range is 400 nm-700 nm, the field of view angle is 47.5°, and the total optical length of the system is 100 mm; the free-form surface optical system is designed as an image-side telecentric optical path structure and can be used as a telescope lens of a free-form surface imaging spectrometer; the free-form surface technology represented by Zernike polynomials is adopted in the design process of the optical system, one of the six lenses is a free-form surface lens, all aberrations are corrected in the optimization process, and finally the lens has the advantages of excellent image quality, large relative aperture, large field of view angle and image-side telecentricity.

Description

Technical Field

[0001] This invention relates to the field of optical design technology, and in particular to an imaging spectrometer telescope system based on freeform surfaces. Background Technology

[0002] Imaging spectrometers are a fusion of imaging and spectral technologies, enabling the analysis of target areas using a combination of images and spectra. They are comprehensive optical instruments for acquiring target information and are currently widely used in various remote sensing observation fields, including aerospace remote sensing, resource surveys, medical testing and diagnosis, environmental monitoring, and military reconnaissance and camouflage identification. With the continuous deepening of research and the expansion of applications in imaging spectroscopy technology, higher demands are being placed on the endurance and imaging quality of airborne imaging spectrometers. Traditional structural forms and design methods of imaging spectrometers can no longer meet these requirements. An imaging spectrometer mainly consists of two components: a telescope head and a beam splitting system. The telescope head images the target, while the beam splitting system separates the slit images of different wavelengths. The telescope head determines the quality of the spectral imaging; therefore, its design is crucial.

[0003] Since the telescope head primarily determines the imaging quality of an imaging spectrometer, it needs to be designed as a separate optical system, correcting for all types of aberrations to achieve good image quality. Simultaneously, to ensure good matching between the telescope head and the beam splitter system, the telescope system must have a telecentric optical path structure, meaning the principal rays of each field of view are perpendicular to the image plane. A larger field of view results in a wider detectable range, making increasing the field of view of the telescope system crucial. Achieving these goals presents significant challenges in designing the telescope system for an imaging spectrometer.

[0004] To overcome the above problems, a new imaging spectrometer telescope system based on freeform surfaces was designed. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide an imaging spectrometer telescope system based on freeform surfaces. This system can be used as an imaging lens alone or as a telescope head for an imaging spectrometer. The lens is designed with an image-side telecentric optical path structure, meeting the technical requirements for an imaging spectrometer telescope head. Furthermore, the system employs freeform surface technology based on Zernike polynomial representation to correct aberrations, while simplifying the optical path structure, resulting in a lens with advantages such as excellent image quality, large relative aperture, large field of view, and image-side telecentricity.

[0006] This invention provides an imaging spectrometer telescope system based on a freeform surface. Its lens includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged coaxially along the incident light direction, which are respectively a concave lens, a concave lens, a convex lens, a convex lens, a convex lens, and a concave lens. The first lens is made of NFK5_SCHOTT material, with a aperture diameter of 22.0 mm < 22.5 mm and a thickness of 3.5 mm < 4.0 mm. The second lens is made of SF4_SCHOTT material, with an aperture diameter of 11.5 mm < 12.0 mm and a thickness of 7.5 mm < 8.5 mm. The third lens... The materials for the first lens are KPBK60_SUMITA, with a diameter of 10.0mm < aperture diameter < 10.5mm and a thickness of 2.5mm < 3.0mm; the materials for the second lens are NFK5_SCHOTT, with a diameter of 13.5mm < aperture diameter < 14.0mm and a thickness of 4.0mm < 4.5mm; the materials for the third lens are KPBK60_SUMITA, with a diameter of 13.0mm < aperture diameter < 13.5mm and a thickness of 4.5mm < 5.0mm; and the materials for the fourth lens are SF4_SCHOTT, with a diameter of 12.5mm < aperture diameter < 13.0mm and a thickness of 1.0mm < 2.0mm. The aforementioned six lenses achieve good chromatic aberration and aberration correction effects through material combination.

[0007] Optionally, the first lens has a light-transmitting aperture of 22.20 mm and a thickness of 3.95 mm; the second lens has a light-transmitting aperture of 11.67 mm and a thickness of 8.00 mm; the third lens has a light-transmitting aperture of 10.29 mm and a thickness of 2.73 mm; the fourth lens has a light-transmitting aperture of 13.91 mm and a thickness of 4.36 mm; the fifth lens has a light-transmitting aperture of 13.42 mm and a thickness of 4.84 mm; and the sixth lens has a light-transmitting aperture of 12.62 mm and a thickness of 1.50 mm.

[0008] Optionally, the fifth lens and the sixth lens form a cemented lens.

[0009] Optionally, the distance between the center of the light exit surface of the sixth lens and the image plane is 15.0 mm.

[0010] Optionally, the external dimensions of the imaging spectrometer telescope system based on freeform surfaces are φ22.2×100mm.

[0011] Optionally, the optical system of the imaging spectrometer telescope based on freeform surfaces has a focal length of 7.6 mm and an F number of 2.0.

[0012] Optionally, the spectral range of the imaging spectrometer telescope system based on freeform surfaces is 400 nm to 700 nm.

[0013] Optionally, the full field of view of the imaging spectrometer telescope system based on freeform surfaces is 47.5°.

[0014] As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages:

[0015] 1. The imaging spectrometer telescope system based on freeform surfaces has a working spectral range of 400nm~700nm, has an image-side telecentric optical path structure, matches the technical requirements of the imaging spectrometer for the telescope head, can be perfectly integrated with the beam splitting system, the telescope head has a focal length of 7.6mm, an F number of 2.0, and the lens has a strong light-gathering capability.

[0016] 2. The imaging spectrometer telescope system based on freeform surfaces corrects aberrations through freeform surface technology, giving the system a larger field of view, simplifying the optical path structure, and improving imaging quality. Attached Figure Description

[0017] Figure 1 This is a diagram of the optical path structure of an imaging spectrometer telescope system based on a freeform surface according to the present invention.

[0018] Figure 2 This invention relates to an optical modulation transfer function for an imaging spectrometer telescope system based on a freeform surface.

[0019] Figure 3 This is a full-field spot diameter diagram of an imaging spectrometer telescope system based on a freeform surface according to the present invention;

[0020] Reference numerals in the attached diagram: 1-First lens; 2-Second lens; 3-Third lens; 4-Fourth lens; 5-Fifth lens; 6-Sixth lens. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0022] Please refer to Figure 1The diagram shows the optical system structure of this invention. This freeform surface-based imaging spectrometer telescope system includes six lenses arranged in a concave-convex-convex-convex-convex-convex-convex pattern. One lens employs an aspherical surface based on a Zernike polynomial, which facilitates aberration correction and simplifies the optical path structure, ensuring the lens's miniaturization and lightweight design. The six lenses are arranged coaxially along the light incident direction: a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, and a sixth lens 6. The first lens is made of NFK5_SCHOTT material, with a aperture of 22.0 mm < aperture diameter < 22.5 mm and a thickness of 3.5 mm < thickness < 4.0 mm. The second lens is made of SF4_SCHOTT material, with an aperture of 11.5 mm < aperture diameter < 12.0 mm and a thickness of 7.5 mm < thickness < 8.5 mm. The third lens is made of KPBK60_SUMITA material, with a diameter of 10.0 mm < aperture diameter < 12.0 mm and a thickness of 7.5 mm < thickness < 8.5 mm. The fourth lens is made of NFK5_SCHOTT, with a light-transmitting aperture of 13.5mm and a thickness of 4.0mm, and a light-transmitting aperture of 14.0mm. The fifth lens is made of KPBK60_SUMITA, with a light-transmitting aperture of 13.0mm and a thickness of 4.5mm. The sixth lens is made of SF4_SCHOTT, with a light-transmitting aperture of 12.5mm and a thickness of 1.0mm, and a light-transmitting aperture of 13.0mm.

[0023] In one embodiment, the first lens 1 has a light-transmitting aperture of 22.20 mm and a thickness of 3.95 mm; the second lens 2 has a light-transmitting aperture of 11.67 mm and a thickness of 8.00 mm; the third lens 3 has a light-transmitting aperture of 10.29 mm and a thickness of 2.73 mm; the fourth lens 4 has a light-transmitting aperture of 13.91 mm and a thickness of 4.36 mm; the fifth lens 5 has a light-transmitting aperture of 13.42 mm and a thickness of 4.84 mm; and the sixth lens 6 has a light-transmitting aperture of 12.62 mm and a thickness of 1.50 mm. This results in a freeform surface-based imaging spectrometer telescope system with a focal length of 7.6 mm, an F-number of 2.0, a full field of view of 47.5°, and external dimensions of φ22.2 × 100 mm. The lens ultimately possesses advantages such as excellent image quality, large relative aperture, large field of view, and telecentric image.

[0024] In one embodiment, the fifth lens and the sixth lens form a cemented lens, and the combination of optical materials of the two lenses ensures that the chromatic aberration of the optical system is well corrected.

[0025] In one embodiment, the spectral range of the imaging spectrometer telescope system based on freeform surfaces is 400 nm to 700 nm.

[0026] Please refer to Figure 2 The figure shows the optical modulation transfer function (MTF) of the imaging spectrometer telescope system based on freeform surfaces of the present invention. As can be seen from the figure, the MTF of each field of view is basically higher than 0.2 within the spatial frequency range of 80 cycles / mm, which meets the design requirements of the optical lens.

[0027] Please refer to Figure 3 The figure shows the full field-of-view spot diameter of the imaging spectrometer telescope system based on freeform surfaces of the present invention. It can be seen from the figure that the imaging quality is good in the full field of view, the maximum RMS of the spot does not exceed 8.5 μm, and the spot in the center field of view is the smallest, about 5.1 μm.

[0028] The following shows the lens data for this freeform surface-based imaging spectrometer telescope system. Table 1 shows the surface type and related optical parameters of each lens in the optical lens.

[0029] Table 1

[0030]

[0031] The formula for representing aspherical surface shape used in the embodiments of this invention is as follows:

[0032]

[0033] Where z is the sag of the aspherical surface at a position with radius r along the optical axis from the vertex of the aspherical surface; c is the paraxial curvature of the aspherical surface; and k is the conic coefficient. A i is the correction coefficient of the i-th order for the aspherical surface.

[0034] Table 2 shows the coefficients of each aspherical higher-order term in this embodiment.

[0035] Table 2

[0036]

[0037] The Zernike polynomial used in this embodiment of the invention is expressed as follows:

[0038]

[0039] The first half of the formula is a spherical base. , where is the vertex curvature; k is the conic coefficient, and the latter part is a Zernike polynomial. These are the coefficients of the i-th polynomial. The Zernike polynomial used in this paper has N=9 terms. Normalized radial coordinates; For the normalized radius, These are angular coordinates.

[0040] Table 3 shows the Zernike coefficients of each order of the Zernike polynomial surface used in this embodiment.

[0041] Table 3

[0042]

[0043] The imaging spectrometer telescope system based on freeform surfaces described in this invention has a focal length of 7.6mm, an F-number of 2.0, operates in the visible light band with a wavelength range of 400nm~700nm, a field of view of 47.5°, and a total optical length of 100mm. The lens is designed with an image-side telecentric structure and can be used as a telescope head for an imaging spectrometer or as a standalone imaging spectroscopic lens. The lens design employs freeform surface technology based on Zernike polynomial representation to correct for all types of aberrations, resulting in a lens with advantages such as excellent image quality, large relative aperture, large field of view, and image-side telecentricity.

[0044] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An imaging spectrometer telescope system based on freeform surfaces, characterized in that: It includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged coaxially along the direction of light incidence; The first lens is made of NFK5_SCHOTT material, with a convex and aspherical object side and a concave and freeform image side. It has a light-transmitting aperture of 22.0 mm and a thickness of 3.5 mm, and a negative optical power. The second lens is made of SF4_SCHOTT, with a convex object side and a concave image side. It has a light-transmitting aperture of 11.5mm and a thickness of 7.5mm, which is 8.5mm. It is a negative optical power. The third lens is made of KPBK60_SUMITA, with a convex object-side surface and a convex image-side surface. It has a aperture diameter of 10.0 mm < 10.5 mm, a thickness of 2.5 mm < 3.0 mm, and is a positive optical power. The fourth lens is made of NFK5_SCHOTT material, with a convex object side and a convex image side. It has a aperture diameter of 13.5mm < 14.0mm and a thickness of 4.0mm < 4.5mm, and is a positive optical power. The fifth lens is made of KPBK60_SUMITA, with a convex object-side surface and a convex image-side surface. It has a light-transmitting aperture of 13.0 mm and a thickness of 4.5 mm, which is positive optical power. The sixth lens is made of SF4_SCHOTT, with a concave object side and a convex image side. It has a light-transmitting aperture of 12.5mm and a thickness of 1.0mm, and is a negative optical power.

2. The imaging spectrometer telescope system based on freeform surfaces as described in claim 1, characterized in that: The first lens has a light-transmitting aperture of 22.20 mm and a thickness of 3.95 mm; The second lens has a light-transmitting aperture of 11.67 mm and a thickness of 8.00 mm; The third lens has a light-transmitting aperture of 10.29 mm and a thickness of 2.73 mm. The fourth lens has a light-transmitting aperture of 13.91 mm and a thickness of 4.36 mm. The fifth lens has a light-transmitting aperture of 13.42 mm and a thickness of 4.84 mm. The sixth lens has a light-transmitting aperture of 12.62 mm and a thickness of 1.50 mm.

3. The imaging spectrometer telescope system based on freeform surfaces as described in claim 1, characterized in that: The fifth lens and the sixth lens together form a cemented lens.

4. The imaging spectrometer telescope system based on freeform surfaces as described in claim 1, characterized in that: The distance between the center of the light exit surface of the sixth lens and the image plane is 15.0 mm.

5. The imaging spectrometer telescope system based on freeform surfaces as described in claim 1, characterized in that: The telescope head of the imaging spectrometer based on freeform surfaces has external dimensions of φ22.2×100mm.

6. The imaging spectrometer telescope system based on freeform surfaces as described in claim 1, characterized in that: The optical system of the imaging spectrometer telescope head based on freeform surfaces has a focal length of 7.6 mm and an F number of 2.

0.

7. The imaging spectrometer telescope system based on freeform surfaces as described in claim 1, characterized in that: The full field of view of the imaging spectrometer telescope head based on freeform surfaces is 47.5°.

8. The imaging spectrometer telescope system based on freeform surfaces as described in claim 1, characterized in that: The spectral range of the imaging spectrometer telescope head based on freeform surfaces is 400nm~700nm.

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