A large field of view afocal optical system based on an off-axis two-mirror plus corrector lens group

Abstract

The application discloses a large-view-field afocal optical system based on an off-axis two-reflection correction lens group, which is composed of a scanning plane mirror, a correction spherical lens group, a free-form surface secondary mirror and a parabolic primary mirror. The application has the following characteristics: in view of the characteristics of strong laser in the laser radar transmitting light path, the design of containing an intermediate real focus in the traditional large-view-field afocal optical system is avoided; the aperture stop of the system is arranged on the scanning plane mirror, which is beneficial to the miniaturization of the moving mechanism scanning mirror; the large design freedom of the free-form surface secondary mirror is used to correct the aberration and distortion of the large view field; and the imaging quality of the system is close to the diffraction limit in the large view field. The embodiment of the application realizes a high zoom ratio (five times) and an imaging quality close to the diffraction limit in a 10-degree scanning view field.

Description

TECHNICAL FIELD

[0001] The application discloses a large-view-field afocal optical system based on an off-axis two-reflection correction lens group, mainly used for a large-view-field laser radar beam expansion emission system with scanning, and relates to the optical lens and optical design fields, in particular to a large-view-field afocal optical system. BACKGROUND

[0002] The laser ranging radar mainly realizes target ranging according to the time of flight, has the characteristics of high ranging precision, long action distance and fast ranging rate, and is widely applied in fields such as long-distance ranging, three-dimensional imaging, topographic mapping, wind field detection and aerosol detection. In recent years, with the development of unmanned aerial vehicle technology, the identification and ranging of long-distance small targets have become one of the important needs of defense, and for the ranging scene of long-distance small targets, the laser radar system often needs higher laser pulse energy, smaller laser divergence angle, larger scanning field of view and larger optical aperture, which puts forward new requirements for the optical system of laser emission. In the image scanning type laser radar system, higher pulse energy requires the laser beam expansion emission system to avoid the original design with an intermediate real focus, to realize the expansion emission of no real focus, large field of view and large expansion ratio. SUMMARY

[0003] The application aims to provide a large-view-field laser radar emission beam expansion optical system with scanning, which can realize a high zoom ratio of five times or more in a 10-degree or more scanning field of view and imaging quality close to the diffraction limit.

[0004] The application provides a large-view-field afocal optical system based on an off-axis two-reflection correction lens group, the system comprising a scanning plane mirror, a correction lens group, a free-form surface secondary mirror and a parabolic primary mirror. The correction lens group comprises a concave object-side and convex image-side lens, a convex object-side and concave image-side lens and a convex object-side and concave image-side lens. Incident laser light passes through the above optical structures in sequence, and a large zoom ratio of five times or more and imaging quality close to the diffraction limit can be realized.

[0005] The afocal optical system sequentially comprises the scanning plane mirror 1, the correction spherical lens group 2, the free-form surface secondary mirror 3 and the parabolic primary mirror 4 in the order of the laser beam emitted by a laser device. The laser beam emitted by the laser device is reflected by the scanning plane mirror 1, refracted by the correction spherical lens group 2, reflected by the free-form surface secondary mirror 3 and reflected again by the parabolic primary mirror 4, and then emitted to a detection target at an angle of 1.1345 degrees with respect to the normal line of the parabolic primary mirror 4. The aperture stop of the system is arranged on the scanning plane mirror (1).

[0006] The correction spherical lens group 2) is in the order of laser exit beam passing through in sequence, and is a concave image side convex first lens 201, a convex image side concave second lens 202, and a convex image side concave third lens 203, and the surface type precision RMS value of each lens optical surface is better than 1 / 30 lambda, lambda=0.6328um.

[0007] The surface type precision RMS value of the optical surface of the scanning plane mirror 1 is better than 1 / 30 lambda, lambda=0.6328um.

[0008] The surface of the free surface secondary mirror 3 is a nine-order xy polynomial, and the surface type precision RMS value is better than 1 / 50 lambda, lambda=0.6328um.

[0009] The beneficial effects of the present application are:

[0010] 1) The system adopts an afocal design, and avoids the safety hazards caused by the design containing an intermediate real focal point in the traditional large field of view system in view of the strong laser characteristics of the laser radar emission light path;

[0011] 2) The aperture stop of the system is arranged on the scanning mirror, which is beneficial to the lightweight of the scanning mirror;

[0012] 3) The reflecting secondary mirror adopts a nine-order xy polynomial free surface design, which has great freedom and can correct the aberration and distortion of the large field of view;

[0013] 4) The afocal system of the present application has an angle of 1.1345 degrees with the normal line of the parabolic primary mirror (4) instead of being parallel to the normal line. The embodiment of the present application realizes a high zoom ratio (five times) and an imaging quality close to the diffraction limit under a 10-degree scanning field of view. The field of view and the zoom ratio are not limited to the above values in actual use. The present application can be applied to the field of scanning laser radar with a larger field of view. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is the optical structure diagram of the embodiment of the large field of view afocal optical system based on off-axis two reflections plus correction lens group provided by the present application.

[0015] Figure 2 is Figure 1 the center field of view wavefront function (Wavefront Function) of the large field of view afocal optical system based on off-axis two reflections plus correction lens group of the embodiment shown. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0017] Please refer to Figure 1 The present application provides a large field of view afocal optical system based on off-axis two-reflection correction lens group, the incident light and the outgoing light are parallel light beams, and the light paths are in the following order:

[0018] The scanning plane mirror, the correction lens group, the curved surface secondary mirror and the parabolic primary mirror. The correction lens group is in turn: the object side concave image side convex first lens, the object side convex image side concave second lens and the object side convex image side concave third lens.

[0019] Further, the aperture stop in the optical system is arranged on the scanning plane mirror, so that the scanning mirror can be lightened.

[0020] Further, the curved surface secondary mirror in the optical system is a free curved surface, which can correct the aberration and distortion of the large field of view.

[0021] Embodiment

[0022] Please refer to Figure 1 In the embodiment shown in Figure 1 The correction lens group 2 is composed of the first lens, the second lens and the third lens from the object side to the image side, the object side concave surface of the first lens 201 is 201L, and the image side convex surface is 201R; the object side convex surface of the second lens 202 is 202L, and the image side concave surface is 202R; the object side convex surface of the third lens 203 is 203L, and the image side concave surface is 203R.

[0023] As shown in Table 1 and Table 2, the actual design cases of the above embodiments are as follows:

[0024] Table 1, curvature radius and thickness data of each surface

[0025] Surface No. Type Curvature radius / mm Thickness / mm Aperture / mm 1 Plane 22 201L Sphere 84.84 -19.5 19 201R Sphere 102.35 -0.2 22 202L Sphere -58.56 -5.0 22 202R Sphere -60.78 -6.5 22 203L Sphere -149.66 -5.0 22 203R Sphere -98.79 -262.35 22 3 Freeform secondary mirror -247.99 - 25 4 Parabolic primary mirror -732.14 - 130

[0026] Table 2, each order coefficient of the free curved surface secondary mirror

[0027] Order x1y0 x0y1 x2y0 x1y1 x0y2 x3y0 x2y1 x1y2 x0y3 Numerical 0 3.78e-4 -6.607e-7 0 1.03e-6 0 -5.55e-9 0 0

[0028] Please refer to Figure 2 , for Figure 1The wavefront function design result diagram of the large field of view afocal optical system based on the off-axis two-reflection correction lens group of the embodiment can show that the present application has the following technical effects: 1) the afocal design can avoid focusing of the strong laser in the system; 2) the present application has good imaging quality, and the design result of the embodiment can achieve ideal imaging quality in a wide waveband and a large field of view range. The embodiment of the present application realizes a high zoom ratio (5 times) and an imaging quality close to the diffraction limit in a 10-degree scanning field of view, and the field of view and the zoom ratio in actual use are not limited to the above values.

[0029] The above-described embodiments only express one or several embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, multiple modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A large field-of-view afocal optical system based on an off-axis dual-reflector correction lens group, comprising a scanning plane mirror (1), a correction spherical lens group (2), a freeform secondary mirror (3), and a parabolic primary mirror (4), characterized in that: The aforementioned afocal optical system consists of a scanning plane mirror (1), a correcting spherical lens group (2), a freeform secondary mirror (3), and a parabolic primary mirror (4) in that order. The laser beam is reflected by the scanning plane mirror (1), refracted by the correcting spherical lens group (2), reflected by the freeform secondary mirror (3), and reflected again by the parabolic primary mirror (4) before exiting at an angle of 1.1345 degrees to the normal of the parabolic primary mirror (4) to the target. The aperture stop of the system is set on the scanning plane mirror (1).

2. The large field-of-view afocal optical system based on an off-axis dual-reflector correction lens group according to claim 1, characterized in that: The corrected spherical lens group (2) consists of a first lens (201) with an object-side concave surface and an image-side convex surface, a second lens (202) with an object-side convex surface and an image-side concave surface, and a third lens (203) with an object-side convex surface and an image-side concave surface, in the order in which the laser beam passes through. The surface accuracy RMS value of each lens optical surface is better than 1 / 30λ, where λ = 0.6328 μm.

3. The large field-of-view afocal optical system based on an off-axis dual-reflector correction lens group according to claim 1, characterized in that: The surface accuracy RMS value of the optical surface of the scanning plane mirror (1) is better than 1 / 30λ, λ=0.6328um.

4. The large field-of-view afocal optical system based on an off-axis dual-reflector correction lens group according to claim 1, characterized in that: The surface of the freeform secondary mirror (3) is a ninth-order xy polynomial, and the surface accuracy RMS value is better than 1 / 50λ, λ=0.6328um.

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