A catadioptric Golay3 sparse aperture optical system

Abstract

The present invention belongs to the field of optical instruments. In order to solve the technical problems of small field angle and small filling factor of the existing coaxial sparse aperture optical system, a refractive-reflective Golay3 sparse aperture optical system is proposed. The optical system comprises: a Golay3 array primary reflector with a hyperbolic surface, a secondary reflector with a hyperbolic surface, and a correction lens group with a spherical surface. The sparse aperture optical system has a full field angle of 1°×1°, an F number of 5, an entrance pupil diameter of 300 mm, a compact structure, and an applicable band of visible light. The primary reflector adopts a Golay3 array structure with a filling factor of 40.3%, the secondary reflector has a smaller aperture than the sub-mirror, and the correction lens group adopts a positive-negative-positive structure using H‑ZK11 glass (Chengdu Guangming), and all three lenses are meniscus lenses. The present invention is suitable for imaging distant dim objects.

Description

Technical Field

[0001] The invention belongs to the field of optical instruments and relates to a catadioptric optical system. Background Art

[0002] The present invention aims to provide a refractive Golay3 sparse aperture optical imaging system. The sparse aperture imaging system is composed of multiple sub-apertures arranged and combined according to a certain rule to replace a large aperture area. Since the aperture of each sub-aperture is much smaller than the entire large aperture, the sparse aperture can not only overcome a series of difficulties caused by the large aperture of the optical system, but also obtain a spatial resolution equivalent to that of a large aperture optical system. For example, the civilian astronomical telescopes used by astronomy enthusiasts, the astronomical telescopes on the market are generally bounded by a 200mm aperture, and the price of astronomical telescopes with an aperture greater than 200mm is a hundred times that of astronomical telescopes with an aperture less than 200mm. The sparse aperture is used to replace the full aperture, thereby achieving a hundred times the economic benefit at a cost of more than ten times or even several times, which fully demonstrates that the research on sparse aperture is of great significance. In practical applications, the sparse aperture imaging system is mostly a two-reflection telescope structure (composed of a main reflector and a secondary reflector), and the main reflector is composed of a combination of small sub-mirrors. In terms of the specific structural selection of the sparse aperture, the Golay3 sparse aperture is the most widely used due to its simple structure.

[0003] Usually, the main reflector of a sparse aperture telescope is spherical, that is, the conic coefficient of the main reflector is 0, so that the curvature radius of each sub-mirror is the same as that of the main reflector, which makes it easy to mass-produce the sub-mirrors and also makes the testing and adjustment of each sub-mirror more convenient. However, the spherical surface shape will also bring relatively serious spherical aberration to the entire system. Therefore, the secondary reflector must increase its deformation to offset the spherical aberration introduced by the main reflector. At the same time, the entire system is also subject to off-axis aberrations such as coma and astigmatism. These off-axis aberrations seriously limit the field of view of the entire system. The document "Design, Processing and Inspection of Optical Aspheric Surfaces" ([M] Pan Junhua, Suzhou University Press, 2004) points out that even if both the primary and secondary reflectors are quadratic surfaces, for a two-reflector telescope system, all primary aberrations cannot be eliminated. In order to improve the image quality of the system and increase the field of view, two methods are generally used. First, use a more complex surface shape, such as a Zernike surface. Second, add a corrective lens.

[0004] The document “Study on the Structural Design and Assembly Method of Sub-aperture Stitching Imaging System” ([D] Gao Tianyuan, 2009, doctoral dissertation) discloses a physical device of a sparse aperture optical imaging system. The primary reflector of the sparse aperture optical imaging system is a spherical reflector, and the secondary reflector is an oblate ellipsoidal reflector. After adding four corrective mirrors, the field of view angle is only ±0.063°. The document “Design of Golay3 Telescope System” ([J] Optics Precision Engineering, 2011, 19(12): 2877-2883) discloses a design method of a Golay3 sparse aperture telescope. The method designs a full-aperture two-reflector telescope based on the theory of paraxial optics and third-order aberration, and then directly uses the Golay3 sparse aperture to replace the primary reflector. The selection of the sub-mirror parameters does not take into account the actual pixel size and detection capability of the CCD. In addition, the field of view of the sparse aperture telescope is small. After adding the spherical corrective mirror, the field of view is ±0.15°, and the maximum fill factor is 22.2%. The document “Research on a Three-mirror Sparse Aperture Two-mirror Telescope System” ([D] Hu Mengmeng, 2015, master’s thesis) also discloses the design of a Golay3 sparse aperture telescope. The primary and secondary reflectors of the telescope are both hyperbolic surfaces. After adding a spherical correction mirror, the field of view is ±0.5°. However, the telescope does not consider the obstruction of the primary reflector by the secondary reflector, and introduces a lens correction mirror without considering chromatic aberration. Both correction mirrors use unconventional glass, which is expensive. Summary of the invention

[0005] In order to solve the problems of small field angle and small filling factor of coaxial sparse aperture optical system in the prior art, a catadioptric Golay3 sparse aperture optical system is proposed.

[0006] The catadioptric Golay3 sparse aperture optical system has a working band of visible light, and comprises a primary reflector with a hyperbolic surface, a secondary reflector with a hyperbolic surface, and a corrective lens group; approximately parallel light rays from a distant place sequentially pass through the primary reflector, the secondary reflector, and the corrective lens group, and are focused on an image plane; the primary reflector with a hyperbolic surface is composed of a Golay3 array, the aperture of the secondary reflector is smaller than the aperture of the sub-mirror, and the corrective lens group sequentially comprises a positive, negative, and positive first meniscus lens, a second meniscus lens, and a third meniscus lens along the positive direction of the optical axis.

[0007] Preferably, the main reflector adopts a Golay3 array structure with a filling factor of 40.4%. Due to the increase in the filling factor, the modulation transfer function (MTF) has a large value in a large spatial frequency range (MTF is above 0.4 at the Nyquist frequency (50lp / mm)), and compared with a small filling factor, direct imaging can be achieved in a higher spatial frequency range.

[0008] Preferred: The length of the catadioptric Golay3 sparse aperture optical system is equivalent to the aperture of the primary reflector. The entire optical system has a compact structure and a small volume. If applied to a space-based system, it can reduce transportation costs.

[0009] Preferably: the full field of view of the optical system is 1°×1°, the F number is 5, the entrance pupil diameter is 300mm, and the applicable band is visible light (F, d, C). Compared with the existing coaxial sparse aperture optical system, the field of view has been significantly improved, and a wider spatial range can be seen. Compared with the existing coaxial sparse aperture optical system, the F number has been significantly reduced, and dim objects can be imaged.

[0010] Preferably, the aperture of the secondary reflector of the optical system is smaller than that of the sub-mirror. The purpose of the sparse aperture is to use a small sub-mirror to replace a large primary mirror, thereby reducing costs. If the aperture of the secondary reflector is large, the manufacturing cost of the system cannot be effectively reduced.

[0011] Preferred: The correction lens group is a positive-negative-positive structure using H-ZK11 glass (Chengdu Guangming), and all three lenses are meniscus lenses. Glass H-ZK11 is the recommended brand of Chengdu Guangming Company: it has excellent comprehensive performance, is in stock for many years, has a relative cost of 1, and the price of the correction lens group is low. The positive-negative-positive structure similar to the three-piece camera lens is used, which is conducive to increasing the field of view of the system.

[0012] Beneficial Effects

[0013] The invention has the characteristics of large field of view, large relative aperture and large filling factor, and is suitable for imaging distant dim objects in the visible light range. In addition, the entire system is compact, and the total length of the system is only 308mm. The correction lens group structure of the same material is used to effectively balance the aberration of the entire system and has good imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0015] Figure 1 It is a schematic diagram of the structure of the catadioptric Golay3 sparse aperture optical system of the present invention;

[0016] Figure 2 It is a structural diagram of the main reflector of the catadioptric Golay3 sparse aperture optical system of the present invention;

[0017] Figure 3 It is a schematic diagram of the structure of the correction lens group of the catadioptric Golay3 sparse aperture optical system of the present invention;

[0018] Figure 4 It is a schematic diagram of field curvature and distortion of the catadioptric Golay3 sparse aperture optical system of the present invention;

[0019] Figure 5 It is a modulation transfer function diagram of the catadioptric Golay3 sparse aperture optical system of the present invention.

[0020] Reference numerals

[0021] 1-primary reflector, 2-secondary reflector, 3-correction lens group, 4-image plane, 5-first meniscus lens, 6-second meniscus lens, 7-third meniscus lens. DETAILED DESCRIPTION

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] A catadioptric Golay3 sparse aperture optical imaging system, such as Figure 1 As shown, the working band is visible light, and the optical system includes a primary reflector 1 with a hyperbolic surface, a secondary reflector 2 with a hyperbolic surface, and a corrective lens group 3; the light passes through the primary reflector, the secondary reflector, and the corrective lens group in sequence and is focused on the image plane 4; the primary reflector with a hyperbolic surface is composed of a Golay3 array, the secondary reflector has a smaller aperture than the sub-mirror, and the system length and aperture are equivalent; the corrective lens group includes a positive, negative, and positive first meniscus lens 5, a second meniscus lens 6, and a third meniscus lens 7 in sequence along the positive direction of the optical axis.

[0024] A refractive-reflective Golay3 sparse aperture optical imaging system, which consists of a primary reflector, a secondary reflector, and a correction lens group. The primary reflector is a concave hyperboloid, the secondary reflector is a convex hyperboloid, the correction lens group is a positive-negative-positive structure using H-ZK11 glass (Chengdu Guangming), and all three lenses are meniscus lenses. Since the surface shape of each sub-mirror has no non-rotational symmetry, the optical system belongs to the category of free-form surface optical system. The light first enters the primary reflector using the Golay3 sparse aperture array, the primary reflector reflects the light to the secondary reflector, the secondary reflector reflects the light through three correction lenses in sequence, and finally converges on the image plane. The full field of view angle of the optical system is 1°×1°, the F number is 5, the entrance pupil diameter is 300mm, the applicable band is visible light (F, d, C), the total length of the system is 308mm (compact structure, small system volume), and the image detector pixel size is 10μm.

[0025] The specific design method is as follows: Using the Cassegrain system as the initial structure, the curvature radius of the primary and secondary reflectors and the distance between them, as well as the distance between the secondary reflector and the image plane are calculated according to the paraxial imaging formula (Gaussian imaging formula). The initial structure is substituted into the commercial optical design software Zemax, and the Golay3 sparse aperture array is used to replace the primary reflector according to the primary and secondary reflectors. The cone coefficients of the primary and secondary reflectors are used to eliminate spherical aberration and coma, and a correction lens group with a focal length of 0 is added near the image plane. In order to ensure that the chromatic aberration of the system is small enough, three separation lenses of the same material are used to achromatize. Finally, while using the evaluation function to ensure the system structure, the point diagram radius is used as the optimization target, and all the curvature radii, thicknesses, and cone coefficients of the primary and secondary reflectors are set as variables to eliminate the residual aberration of the system. Along the optical axis, with the object side as the front and the image side as the back, the object side of the first meniscus lens is the front surface, and the image side is the back surface; the object side of the second meniscus lens is the front surface, and the image side is the back surface; the object side of the third meniscus lens is the front surface, and the image side is the back surface. The detailed parameters of the system are finally obtained as shown in Table 1.

[0026] Table 1

[0027]

[0028] The parameters of the optical system can also be scaled as needed based on Table 1.

[0029] like Figure 2 The array distribution of the main reflector is shown, the enclosing circle diameter (entrance pupil diameter) is 300mm, and the three sub-mirrors are distributed in a Golay3 array, and the diameter of each sub-mirror is 110mm. The filling factor is 40.3%, and the actual aperture is 190.5mm.

[0030] like Figure 3 The figure shows the structure of the correction lens group, which is positive, negative and positive in overall distribution. All three lenses are meniscus lenses made of Chengdu Guangming's H-ZK11 glass. This correction lens group reduces the primary monochromatic aberration of the system while having very small chromatic aberration in the visible light range. Glass H-ZK11 is the recommended brand of Chengdu Guangming Company: it has excellent comprehensive performance, is in stock for many years, and has a relative cost of 1.

[0031] like Figure 4 The field curvature and distortion of the entire optical system are shown in the figure. The maximum sagittal field curvature is 0.0567mm, the maximum meridian field curvature is 0.0446mm, and the maximum distortion is 0.0632%. Both the field curvature and distortion are very small and can be ignored, and the image is almost not deformed.

[0032] like Figure 5The figure shows the modulation transfer function (MTF) of the entire optical system. It can be seen that the MTF of each field of view is close to the diffraction limit, there is no zero point in the cutoff frequency range, and the MTF value at the Nyquist frequency (50lp / mm) is greater than 0.4, and the imaging quality is excellent. The equivalent aperture is defined as Where D max is the circular aperture diameter corresponding to the cutoff frequency in the meridian direction, D min The circular aperture diameter corresponding to the cut-off frequency in the sagittal direction can be calculated to be 234 mm. The present invention obtains a telescope system with an equivalent aperture of 234 mm with a through aperture of 190.5 mm, which has obvious benefits in reducing the mass of the system.

[0033] The above is only to illustrate the technical concept and features of the present invention, and its purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A catadioptric Golay3 sparse aperture optical system, operating in the visible light band, characterized in that: It comprises a primary reflector with a hyperbolic surface, a secondary reflector with a hyperbolic surface, and a correction lens group; light passes through the primary reflector, the secondary reflector, and the correction lens group in sequence and is focused on the image plane; the primary reflector with a hyperbolic surface is composed of a Golay3 array, and the aperture of the secondary reflector is smaller than that of the sub-mirror; the correction lens group comprises a positive, negative, and positive first meniscus lens, a second meniscus lens, and a third meniscus lens in sequence along the positive direction of the optical axis; The main reflector adopts a Golay3 array structure with a filling factor of 40.3%; Along the optical axis, with the object side as the front and the image side as the back, the object side of the first meniscus lens is the front surface and the image side is the back surface; the object side of the second meniscus lens is the front surface and the image side is the back surface; the object side of the third meniscus lens is the front surface and the image side is the back surface. The detailed parameters of the system are finally obtained in Table 1: Table 1 Table 1 is a parameter table of the optical system.

2. The catadioptric Golay 3 sparse aperture optical system according to claim 1, characterized in that: The full field of view of the optical system is 1°×1°.

3. The catadioptric Golay 3 sparse aperture optical system according to claim 1, characterized in that: The F number of the optical system is 5.

4. The catadioptric Golay 3 sparse aperture optical system according to claim 1, characterized in that: The entrance pupil diameter of the optical system is 300mm.

5. The catadioptric Golay 3 sparse aperture optical system according to claim 1, characterized in that: The parameters of the optical system are scaled proportionally based on Table 1.

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