A short-wave infrared wide-band athermal image-space telecentric telescope objective

Abstract

The invention discloses a short-wave infrared wide-band athermal image-space telecentric telescope objective. It is a coaxial transmission optical system with a working band of 1.0μm to 2.5μm, including a plane window glass and eight spherical lenses. Along the incident direction of light, there are, in order, a first plane window piece, a second negative meniscus lens, a third positive meniscus lens, a fourth positive meniscus lens, an aperture stop, a fifth positive biconvex lens, a sixth negative meniscus lens, a seventh positive biconvex lens, an eighth negative biconcave lens, and a ninth positive biconvex lens. The invention has a wide applicable band; compact structure, small spherical aberration and distortion, uniform illumination on the image plane, and image-space telecentricity; within the range of ‑40℃ to 60℃, the diffuse spot is much smaller than one pixel, and the imaging quality is close to the diffraction limit; low processing and manufacturing costs; high energy utilization, strong light-gathering ability, good thermal adaptability, and easy installation and detection, and can be applied to military and civilian fields such as space remote sensing, machine vision, and agricultural and forestry detection.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and the present invention relates to a short-wave infrared wide-band athermal image space telecentric telescope objective lens, which can be applied to non-destructive testing, industrial multi-spectral imaging analysis, resource remote sensing, infrared astronomy, transportation, medical treatment, public security and other fields. Background Art

[0002] Short-wave infrared refers to the infrared band between 1μm and 2.5μm. It can provide information that visible light, low-light night vision, medium-wave and long-wave infrared cannot carry, making the details more prominent. In order to eliminate chromatic aberration and increase thermal stability, traditional short-wave infrared objective lenses are often reflective structures, such as Cassegrain structures. Its disadvantages are that the field of view is small, the off-axis structure increases the difficulty of installation and adjustment, and aspheric surfaces are often used to balance the image quality, which has a high processing cost; while the transmission structure is generally coaxial, which is conducive to processing and adjustment, and the processing cost is low. Compared with the reflective structure, it has the advantages of short total length, small volume and compact structure. At the same time, reasonable matching of materials and athermal design ideas can make the image quality of the transmission structure stable and close to the diffraction limit within a certain temperature range. In addition, in order to increase the detectable target range and the received light flux, it is necessary to increase the field of view angle and relative aperture of the objective lens so as to collect more target signal energy and increase the imaging range at one time. In order to ensure uniform illumination on the image plane, the objective lens needs to have an image telecentric structure. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a wide-band athermal image-space telecentric system which has a compact structure, high imaging quality, good thermal stability, is easy to process and assemble, and works in the short-wave infrared band.

[0004] In order to achieve the purpose, the present invention provides a short-wave infrared wide-band athermal image-side telecentric telescope objective lens, which, along the incident direction of light, comprises a first plane window, a second negative meniscus lens, a third positive meniscus lens, a fourth positive meniscus lens, an aperture stop, a fifth positive biconvex lens, a sixth negative meniscus lens, a seventh positive biconvex lens, an eighth negative biconcave lens, and a ninth positive biconvex lens; the image-side principal ray is parallel to the optical axis and vertically incident on the image plane; along the incident direction of light, the focal lengths of the lenses correspond in sequence to , , , , , which are relative to the focal length of the telescope objective The normalized values ​​of 0, -3.0 -2.0,8 9, 13 14, 0.7 1.0, -2.0 -1.0, 0.5 0.8, -0.5 -0.2, 0.6 0.9.

[0005] Furthermore, the telescope objective lens is a transmission optical system, and the structure of the optical system is a coaxial structure; all lenses of the telescope objective lens are spherical.

[0006] Furthermore, the lens material of the telescope objective lens is selected from any three of chalcogenide glass, fused quartz, and calcium fluoride.

[0007] Furthermore, along the incident direction of the light, the refractive index of each lens corresponds to , , , , The corresponding value ranges are , , 2.0 , , .

[0008] Furthermore, the telescope objective lens has an operating wavelength band of 1.0 to 2.5 μm and an operating temperature range of -40°C to 60°C.

[0009] Furthermore, the maximum field angle of the telephoto objective lens is 28.72°.

[0010] Furthermore, the maximum relative aperture of the telephoto objective lens is F / 3.0.

[0011] Furthermore, the maximum diameter of the lens in the telescope objective lens is less than 20 mm, and the maximum diameter of the window glass is less than 23 mm.

[0012] Furthermore, it is characterized in that: the maximum focal length of the lens in the telescope objective is 30 mm.

[0013] Furthermore, the telescope can be suitable for a detector resolution of 640×512 and a pixel size of 30 μm.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. The working band of the telephoto objective is 1μm ~2.5μm, which is a wide band. In the full band and at a temperature of -40℃~60℃, the image quality design results are: the diffuse spot radius is less than 3.5μm, the distortion is less than 1%, and the MTF is greater than 0.875@16.7lp / mm.

[0016] 2. The refractive index of infrared glass is easily affected by temperature. In order to solve this problem in infrared systems, thermal control technology is used to control the temperature difference of the system. Because the reflector has good thermal stability, the system is also designed to be reflective. This paper uses the principle of athermal design and balances the thermal difference by using chalcogenide glass, quartz, and fluoride glass to keep the image quality stable within -40℃~60℃.

[0017] 3. The telephoto objective lens of the present invention has the characteristic of image telecentricity, which ensures uniform illumination of the image plane, a maximum relative aperture of 1 / 3.0, and a field of view of up to 28.72°, thereby improving the light-gathering ability of the objective lens, increasing the imaging range, and collecting more target information at one time.

[0018] 4. In addition to being used for independent imaging, image-side telecentric telescope objectives can also be used in other different scenarios, such as spectrometers. Due to their telecentric structure, the size and position of the exit pupil are easy to determine, and they are easy to be spliced ​​with the spectrometer system to form a new spectrometer system.

[0019] 5. All spherical mirrors are used and the optical system is concentric and coaxial, which reduces the difficulty of processing and installation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 An optical path diagram of a short-wave infrared wide-band athermal image-space telecentric telescope objective provided by an embodiment of the present invention;

[0021] Figure 2 A modulation transfer function curve diagram of the telephoto objective lens provided in an embodiment of the present invention at -40°C (cut-off frequency 16.7lp / mm);

[0022] Figure 3 A modulation transfer function curve diagram of the telephoto objective lens provided in an embodiment of the present invention at 20°C (cut-off frequency 16.7lp / mm);

[0023] Figure 4 A modulation transfer function curve diagram of the telephoto objective lens provided in an embodiment of the present invention at 60°C (cut-off frequency 16.7lp / mm);

[0024] Figure 5 A spot diagram of a telephoto objective lens provided by an embodiment of the present invention at -40°C;

[0025] Figure 6 A spot diagram of a telephoto objective lens provided by an embodiment of the present invention at 20°C;

[0026] Figure 7 The spot diagram of the telescope provided by the embodiment of the present invention at 60°C;

[0027] Figure 8 A field curvature distortion diagram of a telephoto objective lens provided by an embodiment of the present invention;

[0028] Fig. 9 A relative illumination diagram of a telephoto objective lens provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below through specific embodiments according to the accompanying drawings.

[0030] Example 1

[0031] The present embodiment provides a short-wave infrared wide-band athermal image-space telecentric telescope objective lens, which is a transmission optical system, and the structure of the optical system is a coaxial structure. The objective lens operates in the short-wave infrared band of 1.0μm~2.5μm, the operating temperature range is -40℃~60℃, the focal length is 30mm, the F / # is 3.0, the full field of view is 28.72°, and is suitable for a detector resolution of 640×512 and a pixel size of 30μm.

[0032] See attached Figure 1 , which is the optical path diagram of the optical lens provided in this embodiment, along the incident direction of the light, there are the first plane window 1, the second negative meniscus lens 2, the third positive meniscus lens 3, the fourth positive meniscus lens 4, the aperture stop 5, the fifth positive biconvex lens 6, the sixth negative meniscus lens 7, the seventh positive biconvex lens 8, the eighth negative biconcave lens 9, the ninth positive biconvex lens 10, and the image plane 11. The image side principal ray is parallel to the optical axis and vertically incident on the image plane; along the incident direction of the light, the focal lengths of the lenses correspond to , , , , , which are relative to the focal length of the telescope objective The normalized values ​​of 0, -3.0 -2.0,8 9, 13 14, 0.7 1.0, -2.0 -1.0, 0.5 0.8, -0.5 -0.2, 0.6 0.9. The refractive index of each lens corresponds to , , , , The corresponding value ranges are , , 2.0 , , Preferably, all lenses of the telescope objective are spherical. The maximum aperture of the lens is less than 20 mm, the maximum aperture of the window glass is less than 23 mm, and the maximum focal length of the lens is 30 mm. More preferably, the lens material of the telescope objective is selected from any three of chalcogenide glass, quartz, and fluoride glass.

[0033] By using the theory of athermalization and aberration elimination, four infrared optical glass materials with high transmittance are selected to ensure high imaging quality within a certain temperature range. The aperture is placed on the front focal plane of the rear lens group, so that the telephoto objective has the characteristic of image telecentricity, that is, the image light is incident vertically on the image plane, which can ensure uniform illumination of the image plane. There is enough space between the rear surface of the last lens of the telephoto objective and the image plane for placing the detector. All lenses are spherical, and the system is concentric and coaxial, which reduces the processing and manufacturing costs, the difficulty of detection, and is easy to install and adjust.

[0034] For the lenses of the short-wave infrared wide-band athermal image-space telecentric telescope objective lens, this embodiment provides a preferred solution. See Table 1 for specific data and materials used.

[0035] Table 1 Optical structure parameters of the lens

[0036]

[0037] See attached Figures 2~4 , the modulation transfer function (MTF) curves of the optical system of this embodiment at -40℃, 20℃, and 60℃, the detector pixel size is 30μm×30μm, and at the Nyquist frequency of 16.7lp / mm, the MTF of the system is greater than 0.875, and the imaging quality is close to the diffraction limit.

[0038] See attached Figures 5 to 7 , the optical system of this embodiment obtains the spot diagram on the image plane by ray tracing at -40℃, 20℃, and 60℃. The circle in the figure represents the diffraction Airy disk of the system. The energy of the spot diagram of each field of view is concentrated within the range of the Airy disk, with good imaging quality.

[0039] See attached Figure 8 , the field curvature distortion diagram of the optical system of this embodiment, the distortion is less than 1%, and the image will not be distorted.

[0040] See attached Fig. 9 , the relative illumination curve of the optical system of this embodiment shows that the relative illumination of the image plane is uniform and the relative illumination value of the edge field of view is close to 1.

[0041] It can be seen from the above that the short-wave infrared wide-band athermal image-space telecentric objective provided by the present invention has good imaging quality at -40°C to 60°C.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the present invention, and are not intended to limit the technical solutions described in the present invention. Therefore, although this specification has described the present invention in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified; and all technical solutions and improvements that do not depart from the scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A short-wave infrared wide-band athermal image-space telecentric telescope objective lens, Features: Along the incident direction of light, the lens is composed of a first plane window (1), a second negative meniscus lens (2), a third positive meniscus lens (3), a fourth positive meniscus lens (4), an aperture stop (5), a fifth positive biconvex lens (6), a sixth negative meniscus lens (7), a seventh positive biconvex lens (8), an eighth negative biconcave lens (9), and a ninth positive biconvex lens (10), wherein the image side principal light is parallel to the optical axis and vertically incident on the image plane; along the incident direction of light, the focal lengths of the first plane window (1), the second negative meniscus lens (2), the third positive meniscus lens (3), the fourth positive meniscus lens (4), the fifth positive biconvex lens (6), the sixth negative meniscus lens (7), the seventh positive biconvex lens (8), the eighth negative biconcave lens (9), and the ninth positive biconvex lens (10) correspond to f in sequence. 1 、f 2 、f 3 、f 4 、f 6 、f 7 、f 8 、f 9 、f 10 , their normalized values ​​relative to the telephoto objective focal length f correspond to f' 1 =0, -3.0≤f' 2 ≤-2.0, 8≤f' 3 ≤9, 13≤f' 4 ≤14, 0.7≤f' 6 ≤1.0、-2.0≤f' 7 ≤-1.0, 0.5≤f' 8 ≤0.8、-0.5≤f' 9 ≤-0.2、0.6≤f' 10 ≤0.9; all lenses of the telescope objective are spherical; the lens material of the telescope objective is selected from any one of chalcogenide glass, quartz, and fluoride glass.

2. A short-wave infrared wide-band athermal image-space telecentric telescope objective lens according to claim 1, Features: Along the incident direction of the light, the refractive indices of the first plane window plate (1), the second negative meniscus lens (2), the third positive meniscus lens (3), the fourth positive meniscus lens (4), the fifth positive biconvex lens (6), the sixth negative meniscus lens (7), the seventh positive biconvex lens (8), the eighth negative biconcave lens (9), and the ninth positive biconvex lens (10) are n respectively. 1 、n 2 、n 3 、n 4 、n 6 、n 7 、n 8 、n 9 、n 10 , the corresponding value ranges are 1.5≤n 1 ≤2.0、2.2≤n 2 ≤2.7、2.0≤n 3 ≤2.5、2.0≤n 4 ≤2.5、1.2≤n 6 ≤1.7、1.2≤n 7 ≤1.7、2.2≤n 8 ≤2.5、2.2≤n 9 ≤2.7、2.0≤n 10 ≤2.

5.

3. The short-wave infrared wide-band athermal image-space telecentric telescope objective lens according to claim 1, Features: The telescope objective lens has an operating wavelength range of 1.0 μm to 2.5 μm and an operating temperature range of -40°C to 60°C.

4. The short-wave infrared wide-band athermal image-space telecentric telescope objective lens according to claim 1, Features: The maximum viewing angle of the telephoto objective lens is 28.72°.

5. The short-wave infrared wide-band athermal image-space telecentric telescope objective lens according to claim 1, Features: The maximum relative aperture of the telephoto objective lens is F / 3.

0.

6. The short-wave infrared wide-band athermal image-space telecentric telescope objective lens according to claim 1, Features: The maximum aperture of the lens in the telescope objective is less than 20 mm, and the maximum aperture of the first plane window piece (1) is less than 23 mm.

7. The short-wave infrared wide-band athermal image-space telecentric telescope objective lens according to claim 1, Features: The maximum focal length of the lens in the telescope objective is 30 mm.

8. The short-wave infrared wide-band athermal image-space telecentric telescope objective lens according to claim 1, Features: The telescope objective lens is suitable for a detector with a resolution of 640×512 and a pixel size of 30 μm.

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