Large-caliber all-time catadioptric visible light near-infrared optical system

Abstract

The invention relates to the field of optical imaging, in particular to a large-aperture all-time catadioptric visible light near-infrared optical system. The visible light near-infrared optical system comprises a main reflector (1), a secondary reflector (2), a compensation lens I (3), a compensation lens II (4), a compensation lens III (5), a compensation lens IV (6) and an optical filter (7). The large-caliber all-day refraction and reflection type visible light near-infrared optical system has the advantages of being large in caliber and suitable for all-day wide-temperature work. The primary mirror, the secondary mirror and the supporting structure are made of silicon carbide, high-low temperature deformation is reduced, focal length setting of the primary mirror and the secondary mirror is matched, and influences of temperature changes on reflector surface shape precision and position precision are reduced. And the compensation lens group selects a high-low chromatic aberration glass combination according to focal power distribution to carry out athermalization and aberration elimination design. The imaging quality of the large-aperture optical system is close to the diffraction limit within the temperature range of-30 DEG C to + 60 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catadioptric optical systems, in particular to a large-aperture all-weather catadioptric visible and near-infrared optical system. BACKGROUND

[0002] A star sensor acquires the attitude information of a space vehicle by detecting stars at different positions in space. Due to its high-precision detection and strong anti-interference capability, the star sensor is widely used in space vehicles. At present, new star sensors are developing towards large aperture and wide temperature range. The star sensor is affected by sunlight and changes in spatial position, and the working temperature range of the all-weather star sensor is large, and the working high and low temperature environment is harsh. The optical system is an important component of the star sensor. Therefore, the star sensor optical system needs to maintain good imaging quality in the high and low temperature environment of-30℃~+60℃. However, a large temperature difference will cause a certain thermal effect of the optical glass material and the structural material of the element, that is, the parameters of the optical element glass and the structural element change, and the light propagation path along the axis deviates, causing the optical system to have problems such as image plane drift and focal length change, resulting in serious degradation of the imaging quality of the optical system. The catadioptric optical system is a combination of reflective and transmissive structures, has the advantages of being easier to design for large aperture, easier to correct edge field aberration, and having smaller chromatic aberration. The traditional long-focus catadioptric optical system design cannot meet the imaging quality of large aperture in a wide temperature range. Therefore, the present application proposes a large-aperture all-weather catadioptric visible and near-infrared optical system. SUMMARY

[0003] The present application discloses a large-aperture all-weather catadioptric visible and near-infrared optical system. The optical system adopts a structure form of a front group coaxial two-mirror primary and secondary mirror system and a four-piece spherical compensation lens group. According to the coaxial two-mirror structure characteristics and the athermalization principle, the primary and secondary mirrors and their support structure materials are made of silicon carbide material, and the compensation lens group is used for aberration correction and system structure stability. Through the focal power, refractive index and distance of the four lenses, the aberration is eliminated, so that the large-aperture all-weather catadioptric visible and near-infrared optical system of the present application realizes athermalization design for good imaging in the temperature range of-30℃~+60℃.

[0004] TECHNICAL SCHEME

[0005] The present application designs a large-aperture all-weather catadioptric visible and near-infrared optical system, which has the advantages of large aperture and can adapt to all-weather wide temperature range work, and can be applied to the field of star sensors.

[0006] The present application adopts the following scheme to realize: A large aperture all-day catadioptric visible near-infrared optical system, the visible near-infrared optical system comprising: a primary mirror, a secondary mirror, a compensation lens one, a compensation lens two, a compensation lens three, a compensation lens four and a filter, the primary mirror and the secondary mirror are opposite to each other, the primary mirror is a parabolic mirror, the secondary mirror is a hyperboloidal mirror, the light emitting direction of the secondary mirror is sequentially provided with the compensation lens one, the compensation lens two, the compensation lens three and the compensation lens four, the compensation lens one, the compensation lens two, the compensation lens three and the compensation lens four are meniscus lenses, the focal length of the compensation lens one is 146.76 mm, the focal length of the compensation lens two is-25.53 mm, the focal length of the compensation lens three is-173.47 mm, and the focal length of the compensation lens four is 64.02 mm.

[0007] Further, the diameter of the primary mirror is greater than the diameter of the secondary mirror, the center of the primary mirror has a through hole, and the light emitting direction of the secondary mirror is opposite to the through hole.

[0008] Further, the primary mirror and the secondary mirror constitute a front group primary-secondary mirror combination, the focal length of which is 846.83 mm, the radius of curvature of the primary mirror is-320.72, and the radius of curvature of the secondary mirror is-70.24.

[0009] Further, the focal length of the compensation lens one is 146.76 mm, the focal length of the compensation lens two is-25.53 mm, the focal length of the compensation lens three is-173.47 mm, and the focal length of the compensation lens four is 64.02 mm, the air gap between the compensation lens one and the compensation lens two is 5.65 mm, the air gap between the compensation lens two and the compensation lens three is 6.00 mm, and the air gap between the compensation lens three and the compensation lens four is 1.00 mm.

[0010] Further, the compensation lens one, the compensation lens two, the compensation lens three and the compensation lens four constitute a rear group compensation lens group, the radii of curvature of the front and rear surfaces of the compensation lens one are respectively: 12≤R 11 ≤15, 14≤R 12 ≤16, and the lens thickness is 3.8 mm; the radii of curvature of the front and rear surfaces of the compensation lens two are respectively: 140≤R 21 ≤145, 14≤R 22 ≤16, and the lens thickness is 2.0 mm; the radii of curvature of the front and rear surfaces of the compensation lens three are respectively: -12≤R 31 ≤-15, -15≤R 32 ≤-19, and the lens thickness is 2.5 mm; and the radii of curvature of the front and rear surfaces of the compensation lens four are respectively: -75≤R31 ≤-70, -27≤R 32 ≤-20, lens thickness 2.5mm, at least two of the refractive indices of the four compensating lenses are different from each other.

[0011] Further, the primary mirror, the secondary mirror and the support structures of both are made of silicon carbide material, and the compensating lens one, the compensating lens two, the compensating lens three and the compensating lens four are made of glass material.

[0012] Advantages

[0013] Compared with the prior art, the present application has the following advantages: The large-aperture all-day catadioptric visible and near-infrared optical system has the advantages of large aperture and wide temperature adaptation. The primary mirror, the secondary mirror and the support structures of both are made of silicon carbide, which reduces the deformation at high and low temperatures and reduces the influence of temperature change on the surface shape precision and position precision of the mirrors. The compensating lens group is designed for athermalization and aberration correction by matching the focal power, refractive index and distance of the four lenses. While eliminating chromatic aberration, the focal power is distributed to maintain the required total positive focal power of the combined lens. The large-aperture optical system of the present application has an imaging quality close to the diffraction limit within a temperature range of -30℃ to +60℃. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The figure is the optical path principle diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the present application; Figure 2 The figure is the imaging spot diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the present application; Figure 3 The figure is the energy concentration diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the present application; Figure 4 The figure is the MTF diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the present application; Figure 5 The figure is the imaging spot diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the present application at low temperature -30℃; Figure 6 The figure is the imaging spot diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the present application at high temperature +60℃; Figure 7 The figure is the MTF diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the present application at low temperature -30℃; Figure 8The MTF diagram of a large-aperture all-day catadioptric visible and near-infrared optical system in the high-temperature +60℃ state in the examples of the present application.

[0015] Figure 1 M: 1 - primary mirror, 2 - secondary mirror, 3 - compensation lens one, 4 - compensation lens two, 5 - compensation lens three, 6 - compensation lens four, 7 - filter. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0017] The present application will be further described in detail below in combination with the drawings: 1) As shown in the drawings, the large-aperture all-day catadioptric visible and near-infrared optical system of the embodiments of the present application adopts a structure form of "front group coaxial two-mirror system, rear group compensation", from the object side to the image side, along the light propagation direction, in order, primary mirror 1, secondary mirror 2, compensation lens one 3, compensation lens two 4, compensation lens three 5, compensation lens four 6, filter 7. Figure 1 2) The front group optical system is composed of the primary mirror 1 and the secondary mirror 2 and their support structures, the primary mirror 1, the secondary mirror 2 and their support structures all adopt silicon carbide material for high-low temperature athermalization design, to reduce the influence of temperature change on the mirror surface accuracy and position accuracy. Through material selection and focal length matching, the optical system becomes an "intelligent" whole, which can automatically adapt to temperature change or be insensitive to temperature change, maintaining stable focal point and clear image.

[0018] The front group optical system adopts coaxial structure and the same material silicon carbide to realize opto-mechanical material matching design, to offset high-low temperature deformation, reduce the influence of temperature change on the mirror surface accuracy and position accuracy, and ensure the imaging quality under high-low temperature.

[0019] The diameter of the primary mirror 1 is greater than the diameter of the secondary mirror 2, the reflecting surface of the primary mirror 1 faces the secondary mirror 2, the center of the primary mirror 1 has a through hole, and the light emitting direction of the secondary mirror 2 is opposite to the through hole.

[0020] 3) The primary mirror 1 is a parabolic surface, and the secondary mirror 2 is a hyperboloid, and the specific parameters are shown in Table 1. The front group focal length is 846.83mm.

[0021] Table 1 Primary and secondary mirror parameters

[0022]

[0023] ​4) The air gap between the primary mirror 1 and the secondary mirror 2 in the front lens group is 131.92 mm; the air gap between the lens one and the lens two in the rear lens group is 5.65 mm, the air gap between the lens two and the lens three is 6.00 mm, the air gap between the lens three and the lens four is 1.00 mm; the air gap between the front group and the rear group is 104.88 mm, and the air gap between the rear lens group and the filter is 7.31 mm.

[0024] 5) Continuing to refer to Figure 1 , the rear compensation lens group comprises a compensation lens one 3, a compensation lens two 4, a compensation lens three 5 and a compensation lens four 6, and the four compensation lenses are all meniscus lenses. The rear compensation lens group not only adopts reasonable power distribution, selects appropriate glass material (and the refractive indexes of different compensation lenses need to have a specific matching relationship), effectively compensates various aberrations of the system, but also adopts a lens material with low wavelength absorption, to ensure the energy utilization rate in the near-infrared band.

[0025] 6) The focal length of the compensation lens one is 146.76 mm, the focal length of the compensation lens two is -25.53 mm, the focal length of the compensation lens three is -173.47 mm, and the focal length of the compensation lens four is 64.02 mm.

[0026] 7) The optical parameters of each lens in the rear compensation lens group are shown in Table 2: Table 2 Optical parameters of each lens in the rear compensation lens group

[0027] The ZEMAX design results of the system are as follows: Figure 2 is the spot diagram of the optical system at room temperature in the embodiment, and the RMS diameter of the imaging spot in each field of view is less than 12 μm; Figure 3 is the energy concentration curve of the optical system at room temperature in the embodiment, and the 80% energy concentration of the full field of view is within 2 pixels; Figure 4 is the MTF curve of the optical system at room temperature in the embodiment, and the MTF is greater than 0.3 at a frequency of 100 lp / mm. Figure 5~Figure 6 、 Figure 7~Figure 8 are the optical performance (spot diagram and MTF) of the optical system at low temperature -30℃ and high temperature +60℃, respectively. The RMS diameter of the imaging spot diagram is less than 12 μm at low temperature and high temperature; and the transfer function MTF curve is greater than 0.3 at 100 lp / mm. Therefore, it can be seen that the visible and near-infrared optical system has excellent performance.

[0028] The working temperature of the optical system is -30 DEG C to +60 DEG C, and good imaging can be achieved in the temperature range. Technical indexes are as follows: working waveband is visible light near-infrared waveband, focal length is 1500mm, aperture is 250mm, image element size is 3.45mu m*3.45mu m, and total length is less than 180mm. The optical system has the advantages of large aperture, compact structure, good imaging quality at high and low temperatures and the like.

[0029] In conclusion, the large-aperture all-day catadioptric visible light near-infrared optical system is composed of a primary mirror, a secondary mirror, four compensation lenses and a filter. The optical system adopts an optical passive compensation method to realize athermalization lens design. The primary mirror, the secondary mirror and their support structures are all made of the same material, silicon carbide, to achieve lightweight and low cost. In the case of temperature -30 DEG C to +60 DEG C, the optical system does not produce defocus, and clear imaging can be ensured without focusing adjustment of the optical system.

[0030] It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A large aperture all-day catadioptric visible near-infrared optical system characterized in that, The visible light near-infrared optical system comprises a primary mirror (1), a secondary mirror (2), a compensation lens one (3), a compensation lens two (4), a compensation lens three (5), a compensation lens four (6) and a filter (7), the primary mirror (1) and the secondary mirror (2) are opposite to each other, the primary mirror (1) is a parabolic mirror, the secondary mirror (2) is a hyperboloidal mirror, the light emitting direction of the secondary mirror (2) is sequentially provided with the compensation lens one (3), the compensation lens two (4), the compensation lens three (5) and the compensation lens four (6), the compensation lens one (3), the compensation lens two (4), the compensation lens three (5) and the compensation lens four (6) are meniscus lenses, the focal length of the compensation lens one is 146.76 mm, the focal length of the compensation lens two is -25.53 mm, the focal length of the compensation lens three is -173.47 mm, and the focal length of the compensation lens four is 64.02 mm.

2. The large aperture all-day catadioptric visible near-infrared optical system according to claim 1, characterized in that, The diameter of the primary mirror (1) is larger than that of the secondary mirror (2), the center of the primary mirror has a through hole, and the light emitting direction of the secondary mirror (2) is opposite to the through hole.

3. The large aperture all-weather catadioptric visible near-infrared optical system according to claim 1, characterized in that, The primary mirror (1) and the secondary mirror (2) constitute a front group primary-secondary mirror combination, the focal length of which is 846.83 mm, the curvature radius of the primary mirror (1) is -320.72, and the curvature radius of the secondary mirror (2) is -70.

24.

4. The large aperture all-sky catadioptric visible near-infrared optical system according to claim 1, characterized in that, The focal length of the compensation lens one is 146.76 mm, the focal length of the compensation lens two is -25.53 mm, the focal length of the compensation lens three is -173.47 mm, and the focal length of the compensation lens four is 64.02 mm, the air gap between the compensation lens one and the compensation lens two is 5.65 mm, the air gap between the compensation lens two and the compensation lens three is 6.00 mm, and the air gap between the compensation lens three and the compensation lens four is 1.00 mm.

5. The large aperture all-sky catadioptric visible near-infrared optical system according to claim 4, characterized in that, The compensation lens one, the compensation lens two, the compensation lens three, the compensation lens four constitute a rear group compensation lens group, the radii of curvature of the front and back surfaces of the compensation lens one are respectively: 12≤R 11 ≤15, 14≤R 12 ≤16, the lens thickness is 3.8mm; the radii of curvature of the front and back surfaces of the compensation lens two are respectively: 140≤R 21 ≤145, 14≤R 22 ≤16, the lens thickness is 2.0mm; the radii of curvature of the front and back surfaces of the compensation lens three are respectively: -12≤R 31 ≤-15, -15≤R 32 ≤-19, the lens thickness is 2.5mm; the radii of curvature of the front and back surfaces of the compensation lens four are respectively: -75≤R 31 ≤-70, -27≤R 32 ≤-20, the lens thickness is 2.5mm, and at least two of the refractive indexes of the four compensation lenses are different from each other.

6. The large aperture all-weather catadioptric visible light near infrared optical system according to claim 1, characterized in that, The primary mirror (1), the secondary mirror (2) and the support structure of the two are made of silicon carbide material, and the compensation lens one, the compensation lens two, the compensation lens three and the compensation lens four are made of glass material.

Images