Multi-rotation mirror coaxial composite long-wave infrared monitoring optical system

Abstract

The multi-rotating mirror coaxial composite long-wave infrared monitoring optical system belongs to the technical field of monitoring optics. The prior art is not suitable for long-wave infrared imaging and has a high processing cost. In the present application, a multi-rotating mirror coaxial composite mirror group and a subsequent meniscus lens are arranged along the system optical axis; the multi-rotating mirror coaxial composite mirror group is composed of six mirror surfaces, all of which are rotating around the system optical axis, and the six mirror surfaces along the light-in and light-out path are in turn a convex aspheric light-in refractive mirror surface, a plane primary reflecting mirror surface, a plane secondary reflecting mirror surface, a plane tertiary reflecting mirror surface, a convex aspheric fourth reflecting mirror surface and a convex aspheric light-out refractive mirror surface; the plane tertiary reflecting mirror surface is recessed by a distance d towards the inside of the mirror body relative to the plane primary reflecting mirror surface; the outer dimension of the subsequent meniscus lens matches the recessed distance d and the outer diameter D of the plane tertiary reflecting mirror surface; the subsequent meniscus lens is embedded in the middle of the rear end of the multi-rotating mirror coaxial composite mirror group; and the material of the present application is germanium crystal.

Description

TECHNICAL FIELD

[0001] The multi-rotation mirror coaxial composite long-wave infrared monitoring optical system belongs to the technical field of monitoring optics. BACKGROUND

[0002] The closest prior art to the present application is a Chinese invention patent with the name of "Annular aperture ultra-thin wide-band imaging system containing multi-layer diffraction structure" and the application publication number CN111880298A. The imaging system is characterized in that, as shown in the figure, Figure 1 the main mirror 1' and the secondary mirror 2' are arranged along the imaging system optical axis from the direction of light incidence to the direction of light emission; on the light incidence side of the main mirror 1', the annular band refractive mirror 3, the annular band secondary reflection mirror 4, and the circular fourth reflection mirror 5 are arranged from the periphery to the center; on the light emission side of the main mirror 1', the annular band primary reflection mirror 6, the annular band tertiary reflection mirror 7, and the circular fold-diffraction mirror 8 are arranged from the periphery to the center; the surface types of the annular band refractive mirror 3, the annular band secondary reflection mirror 4, the circular fourth reflection mirror 5, the annular band primary reflection mirror 6, and the annular band tertiary reflection mirror 7 are all high-order aspheric surfaces; the vertices of the respective high-order aspheric surfaces are all located on the imaging system optical axis; the circular fold-diffraction mirror 8 is sunken inside the main mirror 1' along the imaging system optical axis; the light incidence side of the secondary mirror 2' is a fold-diffraction mirror 9; the light emission side of the secondary mirror 2' is a refractive mirror 10 with a planar surface type; the surface types of the circular fold-diffraction mirror 8 and the fold-diffraction mirror 9 are both concave spherical surfaces.

[0003] Among the eight mirror surfaces of the imaging system, five have high-order aspheric surface types, two have spherical surface types, and only one has a planar surface type. Although the materials of the main mirror 1' and the secondary mirror 2' of the imaging system are optical glass, and the imaging system is manufactured using precision molding technology, the mold manufacturing (opening) is very difficult, and the diffraction optical structures on the circular fold-diffraction mirror 8 and the fold-diffraction mirror 9 are also formed in one step during the precision molding process, which requires a very high molding process. Therefore, this prior art has the disadvantages of high manufacturing difficulty and high cost.

[0004] In addition, the ratio of the axial size to the focal length of the imaging system is 0.3~0.4, reaching the level of ultra-thin, but the demand for ultra-thin is endless in reality. Therefore, this prior art needs to be further improved in terms of ultra-thin to improve the lightness and concealment of the imaging system, and the practical demand is, for example, the installation of an infrared imaging device on a gun, security in key passages and places, etc.

[0005] Moreover, the working waveband of the imaging system is visible-near infrared waveband of 0.45~1.1μm, which determines that the prior art is not applicable to infrared thermal imaging of mammals including human, because the infrared radiation emitted by mammals is located in long wave waveband of 6~14μm. Therefore, the prior art is not applicable to infrared monitoring of mammals including human. There is the same demand in the fields of environmental protection monitoring, urban security monitoring, forest fire warning, and prevention of enemy sneak attack.

[0006] Moreover, the imaging system has a full field of view of 7.66°, but under the premise of ensuring imaging quality, expanding the field of view is always the pursuit of the design of imaging optical system. Therefore, further increasing the field of view of infrared imaging can better meet the demand of infrared imaging monitoring.

[0007] Although the imaging system corrects monochromatic spherical aberration of the imaging system by high-order aspheric multiple reflection imaging and corrects wide waveband chromatic aberration of the imaging system by using separated multi-layer diffractive optical structure to improve imaging quality, the technical measures are effective for visible-near infrared waveband of 0.45~1.1μm, but if the imaging waveband is long wave infrared, the technical measures may not be as expected. Moreover, the patent only describes the correction of wide waveband chromatic aberration according to the modulation transfer function curve, and does not give a comprehensive characterization of the imaging quality. And long wave infrared high-quality imaging has an urgent demand in the accurate discrimination of monitoring targets. SUMMARY

[0008] In order to obtain a long wave infrared imaging system with larger field of view, higher imaging quality, thinner thickness, and lower manufacturing cost, we propose a technical scheme named “Multi-rotating mirror coaxial composite long wave infrared monitoring optical system”.

[0009] The multi-rotating mirror coaxial composite long wave infrared monitoring optical system of the present application is characterized in that, Figure 2As shown, the multi-rotation mirror surface coaxial composite mirror group 1 and the subsequent meniscus lens 2 are arranged along the system optical axis; the multi-rotation mirror surface coaxial composite mirror group 1 is composed of six mirror surfaces which are all rotated around the system optical axis, and the six mirror surfaces along the light-in and light-out path are in turn a convex aspheric light-in refractive mirror surface 1-1, a plane primary reflecting mirror surface 1-2, a plane secondary reflecting mirror surface 1-3, a plane tertiary reflecting mirror surface 1-4, a convex aspheric fourth reflecting mirror surface 1-5, and a convex aspheric light-out refractive mirror surface 1-6, wherein the convex aspheric light-in refractive mirror surface 1-1, the plane secondary reflecting mirror surface 1-3, and the convex aspheric fourth reflecting mirror surface 1-5 are distributed from the outer ring to the middle part of the front end of the mirror body of the multi-rotation mirror surface coaxial composite mirror group 1, the plane primary reflecting mirror surface 1-2, the plane tertiary reflecting mirror surface 1-4, and the convex aspheric light-out refractive mirror surface 1-6 are distributed from the outer ring to the middle part of the rear end of the mirror body of the multi-rotation mirror surface coaxial composite mirror group 1, and the plane tertiary reflecting mirror surface 1-4 is recessed by a distance d relative to the plane primary reflecting mirror surface 1-2 towards the inside of the mirror body; the subsequent meniscus lens 2 is composed of a concave aspheric light-in mirror surface 2-1 and a concave aspheric light-out mirror surface 2-2 along the light-in and light-out path; the outer dimension of the subsequent meniscus lens 2 matches the recessed distance d and the outer diameter D of the plane tertiary reflecting mirror surface 1-4; the subsequent meniscus lens 2 is embedded in the middle part of the rear end of the mirror body of the multi-rotation mirror surface coaxial composite mirror group 1; the materials of the multi-rotation mirror surface coaxial composite mirror group 1 and the subsequent meniscus lens 2 are both germanium crystals.

[0010] The technical effect of the present application is embodied in the imaging process of the multi-rotation mirror surface coaxial composite long-wave infrared monitoring optical system, as shown in the following figure: Figure 2 As shown, the infrared light from the infrared target in the monitoring range enters the optical system through the aperture stop, first enters the mirror body of the multi-rotation mirror surface coaxial composite mirror group 1 from the convex aspheric light-in refractive mirror surface 1-1, then is reflected four times by the plane primary reflecting mirror surface 1-2, the plane secondary reflecting mirror surface 1-3, the plane tertiary reflecting mirror surface 1-4, and the convex aspheric fourth reflecting mirror surface 1-5 in turn, and then is emitted from the convex aspheric light-out refractive mirror surface 1-6, passes through the thin layer of air medium, is transmitted by the subsequent meniscus lens 2, and finally forms an image on the image plane. In the imaging process, since the convex aspheric light-in refractive mirror surface 1-1 is arranged at the outer ring of the front end of the mirror body of the multi-rotation mirror surface coaxial composite mirror group 1, an edge aperture is formed, and the actual F number of the optical system can reach 1.708, which is not only beneficial to the expansion of the field of view of the optical system, but also can collect more light energy, the image brightness is large, and the image information is more. The plane primary reflecting mirror surface 1-2, the plane secondary reflecting mirror surface 1-3, and the plane tertiary reflecting mirror surface 1-4 reflect the imaging infrared light three times in turn to fold the large aperture into a small aperture, realizing the convergence of the infrared imaging light. The convex aspheric fourth reflecting mirror surface 1-5 plays a further converging role. The convex aspheric light-out refractive mirror surface 1-6 changes the emission angles of the imaging infrared light of each field of view to meet the image height requirement, and cooperates with the subsequent meniscus lens 2 to realize further convergence of the infrared imaging light, and finally converges to the image plane.

[0011] The technical effect of the present application is also reflected by the structural features of the multi-rotary mirror coaxial composite long-wave infrared monitoring optical system, such as: the combination of the multi-rotary mirror coaxial composite mirror group 1 and the subsequent meniscus lens 2, the five aspheric mirrors can effectively compensate and correct the off-axis aberration of the optical system, and fully guarantee the imaging performance of the optical system outside the axis. The six mirrors in the multi-rotary mirror coaxial composite mirror group 1 have three plane mirrors, which not only are easy to process and reduce manufacturing cost, but also avoid producing spherical aberration; the four times of reflection imaging is carried out inside the multi-rotary mirror coaxial composite mirror group 1, which avoids producing chromatic aberration; in addition, the setting of the subsequent meniscus lens 2 obviously improves the imaging quality of the optical system. The multi-rotary mirror coaxial composite mirror group 1 is integrated with six mirrors at the front and rear ends of the mirror body, and the subsequent meniscus lens 2 is embedded in the multi-rotary mirror coaxial composite mirror group 1, so that the structure of the optical system is particularly compact, and the axial size of the optical system is greatly shortened. Moreover, the outer contour size of the subsequent meniscus lens 2 matches the retracted distance d and the outer diameter D of the plane cubic mirror 1-4, so that the adjustment of the optical system becomes very simple, and the manufacturing cost is further reduced. The materials of the multi-rotary mirror coaxial composite mirror group 1 and the subsequent meniscus lens 2 are both germanium crystals. Since the transmission band of the germanium crystal is 2-23 µm, it meets the long-wave infrared imaging requirements of the present application, and the refractive index of the germanium crystal is approximately 4.0, which is conducive to aberration correction.

[0012] The technical effect of the present application is also reflected by the technical parameters of the multi-rotary mirror coaxial composite long-wave infrared monitoring optical system, for example, the working waveband of the multi-rotary mirror coaxial composite long-wave infrared monitoring optical system is 8-12 µm, the full field angle is 10.24° (the maximum axial symmetric rotation half field angle reaches 5.12°×5.12°), and the ratio of the axial size of the optical system to the focal length reaches 0.227 (the total length of the optical system is equal to the axial distance between the plane quadratic mirror 1-3 and the image plane, which is 4.66 mm, and the focal length is 20.4975 mm). BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a prior art structure and imaging light path cross-sectional view.

[0014] Figure 2 is a structure and imaging light path cross-sectional view of the present application, which also serves as an abstract drawing.

[0015] Figure 3 is an MTF curve diagram of the present application.

[0016] Figure 4 is a field curvature curve diagram of the present application.

[0017] Figure 5 is a distortion curve diagram of the present application.

[0018] Figure 6 This is the standard dot matrix diagram of the present invention. Detailed Implementation

[0019] The present invention needs to be further described as follows.

[0020] The convex aspherical light-incoming and refractive mirrors 1-1, 1-6, 2-1, and 2-2 are coated with long-wave infrared anti-reflection films. The planar primary reflection mirror 1-2, 1-3, 1-4, and 1-5 are coated with long-wave infrared reflective films.

[0021] The convex aspherical light-reflecting mirror 1-1 has positive optical power; the planar primary reflection mirror 1-2, the planar secondary reflection mirror 1-3, and the planar tertiary reflection mirror 1-4 have zero optical power; the convex aspherical quaternary reflection mirror 1-5 has negative optical power; the convex aspherical light-exiting reflection mirror 1-6 has negative optical power; and the subsequent meniscus lens 2 has positive optical power.

[0022] The convex aspherical light-entering and refractive mirror 1-1, the convex aspherical fourth-order reflection mirror 1-5, the convex aspherical light-exiting and refractive mirror 1-6, the concave aspherical light-entering mirror 2-1, and the concave aspherical light-exiting mirror 2-2 are all even-order aspherical surfaces, and their surface shape is defined by the following formula for even-order aspherical surfaces:

[0023] ,

[0024] In the formula: z The vertical coordinates are in a cylindrical coordinate system (with the optical axis of the imaging system as the vertical axis of the cylindrical coordinate system). c Let be the radius of curvature of the aspherical surface near its axis. r Let be the distance from a point on the aspherical surface to the vertical axis. k For aspherical conic coefficients, Here are the polynomial coefficients, where: The coefficient of the quadratic term, The coefficient of the fourth term, The coefficient of the sixth term, The coefficient of the eighth term.

[0025] The present invention will be further illustrated by a specific example below.

[0026] The specific parameters of the optical system are given in Table 1. The radius of curvature is the radius of curvature at the paraxial position of the corresponding mirror surface. The units of the radius of curvature and the distance between the center of the mirror surface are both mm.

[0027] Table 1 Specific parameters of the optical system

[0028]

[0029] Table 2 gives the conic coefficients of each even aspherical surface in the optical system k and the polynomial coefficients .

[0030] Table 2 conic coefficients of each even aspherical surface k and the polynomial coefficients

[0031]

[0032] The imaging quality of this example is verified by the following test results.

[0033] As shown in FIG. 6, the graph is the MTF (Modulation Transfer Function) curve of this example, in which the abscissa represents the line pair per millimeter (lp / mm) represented, and the ordinate represents the MTF value size. When the cutoff frequency is 20 cycles / mm, the MTF modulation transfer function of each field of view is not less than 0.24, and the full field of view MTF value is not less than 0.16. It shows that the imaging quality of this example is good and the imaging quality of each field of view is very stable. Figure 3 lp / mm lp / mm

[0034] As shown in FIG. 7, the graph is the field curvature graph of this example under the reference wavelength of 8 μm, in which the abscissa represents the field curvature, unit: mm, and the ordinate represents the normalized field of view. Under the reference wavelength, the field curvature of this example is better than 0.4 mm, which shows that the field curvature of this example is well compensated. Figure 4

[0035] As shown in FIG. 8, the graph is the distortion graph of this example under the defined visible light wavelength, in which the abscissa represents the distortion size, and the ordinate represents the normalized field of view. Under the reference wavelength of 8 μm, the distortion of this example is better than 4.5%, which shows that the distortion of this example is well corrected. Figure 5

[0036] As shown in FIG. 9, the graph is the distortion graph of this example under the defined visible light wavelength, in which the abscissa represents the distortion size, and the ordinate represents the normalized field of view. Under the reference wavelength of 8 μm, the distortion of this example is better than 4.5%, which shows that the distortion of this example is well corrected. Figure 6 ​​​​​As shown in the figure, the figure is an image plane standard point column diagram of the example at a reference wavelength of 8 μm, wherein the abscissa represents a relative field of view, and the ordinate represents a root mean square radius size, in mm. At the reference wavelength, the root mean square radius size of the 0° field of view of the example is better than 13 μm, the root mean square radius size of the 0.7300° field of view is better than 15 μm, the root mean square radius size of the 1.4629° field of view is better than 19 μm, the root mean square radius size of the 2.1943° field of view is better than 24 μm, the root mean square radius size of the 2.9257° field of view is better than 29 μm, the root mean square radius size of the 3.5840° field of view is better than 27 μm, the root mean square radius size of the 4.3886° field of view is better than 22 μm, and the root mean square radius size of the 5.1200° field of view is better than 23 μm, which indicates that the spherical aberration of the example is better compensated.

Claims

1. A multi-rotating mirror coaxial composite long-wave infrared monitoring optical system, characterized in that, A multi-rotational mirror coaxial composite mirror group (1) and a subsequent meniscus lens (2) are arranged along the optical axis of the system. The multi-rotational mirror coaxial composite mirror group (1) consists of six mirrors, each with the optical axis of the system as its rotation axis. Along the light-incoming and light-outcoming paths, the six mirrors are, in order, a convex aspherical light-incoming refraction mirror (1-1), a plane primary reflection mirror (1-2), a plane secondary reflection mirror (1-3), a plane tertiary reflection mirror (1-4), a convex aspherical quaternary reflection mirror (1-5), and a convex aspherical light-outcoming refraction mirror (1-6). Among them, the convex aspherical light-incoming refraction mirror (1-1), the plane secondary reflection mirror (1-3), and the convex aspherical quaternary reflection mirror (1-5) are distributed from the outer ring to the middle at the front end of the multi-rotational mirror coaxial composite mirror group (1). The plane primary reflection mirror (1-6) is arranged from the outer ring to the middle at the front end of the mirror body. 2) The planar triple-reflection mirror (1-4) and the convex aspherical light-emitting refraction mirror (1-6) are distributed from the outer ring to the middle at the rear end of the multi-rotation mirror coaxial composite mirror group (1). The planar triple-reflection mirror (1-4) is recessed into the mirror body by a certain distance d relative to the planar primary-reflection mirror (1-2). The subsequent meniscus lens (2) is composed of a concave aspherical light-inducing mirror (2-1) and a concave aspherical light-emitting mirror (2-2) along the light-inducing and light-outducing paths. The outer dimensions of the subsequent meniscus lens (2) match the recessed distance d and outer diameter D of the planar triple-reflection mirror (1-4). The subsequent meniscus lens (2) is embedded in the middle of the rear end of the multi-rotation mirror coaxial composite mirror group (1). The materials of the multi-rotation mirror coaxial composite mirror group (1) and the subsequent meniscus lens (2) are both germanium crystals.

2. The multi-rotating mirror coaxial composite long-wave infrared monitoring optical system according to claim 1, characterized in that, The convex aspherical light-incoming refraction mirror (1-1), the convex aspherical light-outgoing refraction mirror (1-6), the concave aspherical light-incoming mirror (2-1), and the concave aspherical light-outgoing mirror (2-2) are coated with long-wave infrared anti-reflection films. The planar primary reflection mirror (1-2), the planar secondary reflection mirror (1-3), the planar tertiary reflection mirror (1-4), and the convex aspherical quaternary reflection mirror (1-5) are coated with long-wave infrared reflective films.

3. The multi-rotating mirror coaxial composite long-wave infrared monitoring optical system according to claim 1, characterized in that, The convex aspherical light-reflecting mirror (1-1) has positive optical power, the plane primary reflection mirror (1-2), the plane secondary reflection mirror (1-3), and the plane tertiary reflection mirror (1-4) have zero optical power, the convex aspherical quaternary reflection mirror (1-5) has negative optical power, the convex aspherical light-exiting reflection mirror (1-6) has negative optical power, and the subsequent meniscus lens (2) has positive optical power.

4. The multi-rotating mirror coaxial composite long-wave infrared monitoring optical system according to claim 1, characterized in that, The convex aspherical light-entering and refractive mirror (1-1), the convex aspherical fourth-order reflection mirror (1-5), the convex aspherical light-exiting and refractive mirror (1-6), the concave aspherical light-entering mirror (2-1), and the concave aspherical light-exiting mirror (2-2) are all even-order aspherical surfaces, and their surface shape is defined by the following even-order aspherical surface formula: ， In the formula: z The vertical coordinates are in a cylindrical coordinate system. c Let be the radius of curvature of the aspherical surface near its axis. r Let be the distance from a point on the aspherical surface to the vertical axis. k The conic coefficient for aspherical surfaces. Here are the polynomial coefficients, where: The coefficient of the quadratic term, The coefficient of the fourth term, The coefficient of the sixth term, The coefficient of the eighth term.

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