Visible infrared dual-band refraction and reflection optical system based on free-form surface shared beam shrinking lens

Abstract

The invention relates to an optical imaging system, in particular to a visible and infrared dual-band refraction and reflection optical system based on a free-form surface shared beam shrinking lens, and solves the technical problems that an existing total reflection type earth remote sensing system and an existing refraction and reflection type earth remote sensing optical system are difficult to meet the overall requirements of compactness, stray light, convenient adjustment and large view field. The system comprises a beam shrinking unit, a dichroic mirror, a visible TDI imaging lens group, a reflecting mirror, an infrared TDI imaging lens group, a visible switching reflecting mirror and a visible area array imaging lens group, wherein the beam shrinking unit and the dichroic mirror are sequentially arranged along a light path; the visible TDI imaging lens group, the reflecting mirror and the infrared TDI imaging lens group are arranged on a reflecting light path of the dichroic mirror; the visible area array imaging lens group is arranged on a reflecting light path of the visible switching reflecting mirror; the beam shrinking unit comprises a primary mirror, a secondary mirror, an axis folding mirror and a third mirror which are sequentially arranged along a light path; the primary mirror and the secondary mirror are coaxially arranged; the included angle between the normal of the folding-axis mirror and the optical axis of the system is greater than 45 degrees; the third mirror is a free-form surface reflecting mirror, and emergent central view field light of the third mirror is perpendicular to primary and secondary mirror axes; and the dichroic mirror is arranged on an emergent light path of the third mirror.

Description

Technical Field

[0001] The invention relates to an optical imaging system, in particular to a visible infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer. Background Art

[0002] With the development of space optical payload technology and remote sensing inversion technology, the demand for wide-band detection is increasing in order to obtain more abundant information about detection targets. The visible light band in space optical imaging devices is mainly used for detection of land, ocean and specific targets during the day; the medium-wave infrared band is mainly used for nighttime detection, and the optical imaging device covering dual bands can achieve all-weather uninterrupted monitoring of the target area. Due to the limited space and weight of the aircraft carrying the space remote sensing optical system, strict requirements are placed on the compactness of the optical system. Free-form surfaces have super aberration balancing capabilities and can be effectively used in the design of compact optical systems. Therefore, they have attracted many scholars to carry out design and research.

[0003] There are mainly two types of compact space-based earth remote sensing imaging optical systems: total reflection earth remote sensing systems and catadioptric earth remote sensing optical systems. Among them, total reflection earth remote sensing systems are divided into off-axis reflection and coaxial reflection. The overall structure of the coaxial reflection is relatively compact. Not only does the secondary mirror block the primary mirror, but there are also factors such as openings that continue to block the incident light of the three mirrors, affecting the energy utilization and signal-to-noise ratio of the system. The off-axis reflection system has no central obstruction, but the vertical axis size of the system is easy to exceed the overall envelope of the system. Since the focal plane of the space remote sensing optical system usually has optical splicing or mechanical splicing, there is a link that requires adjusting the lens to achieve focusing, and the accuracy of adjusting the reflector is required to be higher, so it is more difficult to achieve.

[0004] The catadioptric ground remote sensing optical system usually adds a transmission lens to the Cassegrain system or RC system to correct the aberration and expand the field of view. However, due to the increasing requirements of the system's stray light and the increasing requirements of the system's field of view, the free-form surface can effectively increase the field of view and reduce the number of lenses due to its many controllable variables. By changing the optical path layout, it can effectively suppress stray light. Therefore, it is necessary to develop a new type of visible-infrared dual-band compact catadioptric optical system based on a free-form surface shared beam reducer, which can meet the overall requirements of the system's compactness, stray light, convenient adjustment and large field of view through a reasonable layout. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem that the existing fully reflective earth remote sensing systems and catadioptric earth remote sensing optical systems are difficult to meet the overall requirements of compactness, stray light, convenient adjustment and large field of view, and provide a visible infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A visible infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer, which is special in that it comprises a beam reducer unit and a color splitter arranged in sequence along an optical path, a visible TDI imaging lens group arranged on the reflection optical path of the color splitter, an infrared TDI imaging lens group arranged on the transmission optical path of the color splitter, a visible switching reflector and a visible array imaging lens group arranged on the reflection optical path of the visible switching reflector; the visible switching reflector is used to cut in or out of the visible TDI imaging lens group; the infrared TDI imaging lens group is provided with a reflector;

[0008] The beam reduction unit includes a primary mirror, a secondary mirror, a folding mirror and a third mirror arranged in sequence along the optical path; the primary mirror and the secondary mirror are arranged coaxially, and the axis is the primary and secondary mirror axis; the folding mirror is located on the side of the primary mirror away from the secondary mirror, and the angle between its normal and the system optical axis is greater than 45°; the third mirror is a free-form surface reflector, and its outgoing central field light is perpendicular to the primary and secondary mirror axes; the dichroic mirror is arranged on the outgoing light path of the third mirror;

[0009] The dichroic mirror is used to transmit the output light of the three mirrors along the optical path to the reflector and the infrared TDI imaging lens group, and at the same time reflect the output light of the three mirrors to the visible TDI imaging lens group, or reflect the light to the visible array imaging lens group when the visible switching reflector cuts into the visible TDI imaging lens group;

[0010] A visible TDI detection device is arranged on the outgoing light path of the visible TDI imaging lens group, so that the outgoing light of the visible TDI imaging lens group is imaged on the visible TDI detection device;

[0011] A visible light array detector is arranged on the outgoing light path of the visible light array imaging lens group, so that the outgoing light of the visible light array imaging lens group is imaged on the visible light array detector;

[0012] An infrared TDI detection device is arranged on the outgoing light path of the infrared TDI imaging lens group. By translating the infrared TDI imaging lens group, the outgoing light of the infrared TDI imaging lens group is imaged on the infrared TDI detection device.

[0013] Furthermore, the primary mirror is an even-order aspheric reflector with a central opening or an eccentric opening, the surface of which is coated with a silver film or a gold film, and the cone coefficient K is less than 0; the material is quartz or K9 or microcrystal or silicon carbide, and the mirror F number is 0.5-1.5.

[0014] Furthermore, the secondary mirror is an even-order aspheric reflector, the surface of which is coated with a silver film or a gold film, and the cone coefficient K is less than 0; the material is quartz or K9 or microcrystal or silicon carbide, and the mirror F number is 0.5-1.5.

[0015] Furthermore, the folding mirror is a plane reflecting mirror, the surface of which is coated with a silver film or a gold film, and the material is quartz or K9 or microcrystal or silicon carbide.

[0016] Furthermore, an aperture is arranged on the primary mirror; the cone coefficient K of the three mirrors is less than 0, and is expressed by an XY polynomial, and the material is quartz or K9 or microcrystalline or silicon carbide; the dichroic mirror is a parallel flat plate coated with a dichroic film, and the material of the dichroic mirror is Silicon, Germanium or ZNSE or CLEARTRAN, and the reflectivity and transmittance are both greater than 90%; it can be seen that the switching reflector is a plane reflector, and the material is quartz or K9 or microcrystalline or SiC.

[0017] Further, the visible TDI imaging lens group includes a visible common lens front group and a visible imaging discrete rear group which are coaxially arranged in sequence along the optical path;

[0018] It can be seen that the front group of the common lens includes 6 lenses coaxially arranged in sequence along the optical path, wherein the first lens is a plano-convex lens, whose convex surface is a free-form surface, and the cone coefficient K is less than 0, which is expressed by an XY polynomial, the third lens is a negative lens, and the remaining lenses are all spherical lenses;

[0019] It can be seen that the imaging discrete rear group includes three lenses coaxially arranged in sequence along the optical path, among which one surface of the second lens is aspherical, the cone coefficient K is greater than 0 and less than 1, and there is no high-order term; the remaining lenses are all spherical mirrors;

[0020] The visible switching reflector is used to cut in or out between the visible common lens front group and the visible imaging discrete rear group. When the visible switching reflector is cut in, the reflected light of the dichroic mirror is transmitted through the visible common lens front group to the visible switching reflector, and then reflected to the visible array imaging lens group. When the visible switching reflector is cut out, the reflected light of the dichroic mirror is reflected to the visible TDI imaging lens group.

[0021] The visible array imaging lens group has the same structure as the visible imaging discrete rear group;

[0022] The visible TDI imaging lens group adjusts the image quality and air pressure by adjusting the interval of the third lens in the visible common lens front group.

[0023] Further, the infrared TDI imaging lens group includes two positive lens groups; there is a primary image plane between the two positive lens groups, one positive lens group includes three lenses, and the optical powers thereof are arranged in positive, negative and positive order respectively; the other positive lens group includes three lenses, and the optical powers thereof are arranged in negative, positive and positive order respectively; the materials of the two positive lens groups are Silicon and / or Germanium;

[0024] The infrared TDI imaging lens group adjusts the gas pressure by adjusting the position of the positive lens group located in front of the primary image.

[0025] Furthermore, the translation amount T of the infrared TDI imaging lens group is calculated according to the following formula:

[0026]

[0027] Where d is the thickness of the dichroic mirror, θ is the angle between the dichroic mirror and the horizontal plane, and n is the refractive index of the dichroic mirror.

[0028] Furthermore, the visible TDI detection device comprises an optical splicing device and N visible TDI detectors; the optical splicing device comprises a plurality of plane reflectors that are spliced ​​and fixedly connected, the plurality of plane reflectors have the same size and interval, and the materials are all quartz or K9 or microcrystal or SiC; each visible TDI detector is arranged on the reflection light path or the transmission light path of the plane reflector;

[0029] Alternatively, the visible TDI detection device includes N visible TDI detectors located in the same detection plane, the N visible TDI detectors are mechanically spliced ​​and placed parallel to each other, and there are no less than 10 overlapping pixels along the splicing direction, and N≥2.

[0030] Furthermore, the infrared TDI detection device comprises M infrared TDI detectors located in the same detection plane, the M infrared TDI detectors are mechanically spliced ​​and placed parallel to each other, and there are no less than 10 overlapping pixels along the splicing direction, M≥2; each infrared TDI detector is provided with a cold aperture;

[0031] The angle θ between the dichroic mirror and the horizontal plane is 45°.

[0032] Beneficial effects of the present invention:

[0033] 1. The present invention is a visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reduction mirror, which utilizes a primary mirror, a secondary mirror, a folding axis mirror and three mirrors to form a beam reduction unit with good image quality. By adjusting sensitive items such as the interval between the primary mirror and the secondary mirror and the eccentricity of the secondary mirror, it can be ensured that the image quality remains basically unchanged after adjustment. The primary mirror and the secondary mirror are coaxially installed, and the image quality of the central field of view of the combination of the two is good, which is convenient for processing, detection and adjustment.

[0034] 2. The present invention is a visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer. The angle between the normal of the folding mirror and the optical axis of the system is greater than 45°, so as to ensure that the light path of the offset field of view incident through the primary mirror, secondary mirror, folding mirror, and the central field of view light emitted after the three mirrors is perpendicular to the optical axes of the primary mirror and the secondary mirror, making the system as a whole compact and insensitive to tolerances.

[0035] 3. The present invention is a visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer. Both the primary mirror and the secondary mirror are even-order aspheric reflectors, and the mirror F numbers are both 0.5-1.5, which further ensures the compactness of the system.

[0036] 4. The present invention is a visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer. In the visible light path, the lens for adjusting image quality and air pressure is set as the third lens in the front group of the visible shared lens, and the third lens is selected to be a negative lens; in the infrared light path, the lens for adjusting air pressure is set as the lens group in front of the primary image surface. Compared with the existing optical system in which the adjustment link is set on the secondary mirror, the accuracy requirement of the adjustment link is relatively low, and it is easier to implement and the cost is relatively low.

[0037] 5. The visible infrared dual-band catadioptric optical system of the present invention is based on a free-form surface shared beam reducer, and has visible infrared dual-band detection function, visible light array and surface array switching function (i.e., visible switching reflector cutting out and cutting in) and the function of optically splicing N visible line array TDI detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of an embodiment of the visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer of the present invention;

[0039] Figure 2 This is a light path diagram of an embodiment of a visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to the present invention;

[0040] FIG3( a ) is a YOZ plane optical path diagram of a beam reduction unit and a dichroic mirror in an embodiment of the present invention;

[0041] FIG3( b ) is a light path diagram of the beam reduction unit and the dichroic mirror in the XOY plane in an embodiment of the present invention;

[0042] FIG3( c ) is a diagram showing the visible light transfer function between the beam reduction unit and the dichroic mirror in an embodiment of the present invention;

[0043] FIG3( d ) is a diagram showing the infrared light transmission function between the beam reduction unit and the dichroic mirror in an embodiment of the present invention;

[0044] FIG4( a ) is a YOZ plane optical path diagram of the visible TDI detection optical path in an embodiment of the present invention;

[0045] FIG4( b ) is a XOY plane optical path diagram of the visible TDI detection optical path in an embodiment of the present invention;

[0046] FIG4( c ) is a diagram showing the visible light transfer function of the visible TDI detection optical path in an embodiment of the present invention;

[0047] FIG4( d ) is a point diagram of different fields of view of the visible TDI detection optical path in an embodiment of the present invention;

[0048] FIG4(e) is a transfer function diagram of the multi-spectral B1 segment visible TDI detection optical path in an embodiment of the present invention (spatial frequency is 71.43 lp / mm);

[0049] FIG4( f ) is a transfer function diagram of the multi-spectral B2 segment visible TDI detection optical path in an embodiment of the present invention (spatial frequency is 71.43 lp / mm);

[0050] FIG4( g ) is a transfer function diagram of the multi-spectral B3 segment visible TDI detection optical path in an embodiment of the present invention (spatial frequency is 71.43 lp / mm);

[0051] FIG4(h) is a transfer function diagram of the multi-spectral B4 segment visible TDI detection optical path in an embodiment of the present invention (spatial frequency is 71.43 lp / mm);

[0052] FIG5( a ) is a YOZ plane optical path diagram of the visible light array detection optical path in an embodiment of the present invention;

[0053] FIG5( b ) is a diagram of the XOY plane optical path of the visible light array detection optical path in an embodiment of the present invention;

[0054] FIG5( c ) is a diagram of the visible light transmission function of the visible light array detection light path in an embodiment of the present invention;

[0055] FIG5(d) is a point diagram of different fields of view of the visible light array detection light path in an embodiment of the present invention;

[0056] FIG6( a ) is a YOZ plane optical path diagram of the infrared TDI detection optical path in an embodiment of the present invention;

[0057] FIG6( b ) is a XOY plane optical path diagram of the infrared TDI detection optical path in an embodiment of the present invention;

[0058] FIG6( c ) is an infrared light transmission function diagram of the infrared TDI detection light path in an embodiment of the present invention;

[0059] FIG6( d ) is a point diagram of different fields of view of the infrared TDI detection optical path in an embodiment of the present invention.

[0060] Description of the reference numerals of the accompanying drawings:

[0061] 1-primary mirror, 2-secondary mirror, 3-folding mirror, 4-triple mirror, 5-color separation mirror, 6-visible TDI imaging lens group, 7-visible switching reflector, 8-visible array imaging lens group, 9-infrared TDI imaging lens group, 10-reflector. DETAILED DESCRIPTION

[0062] like Figure 1 , Figure 2As shown, a visible infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer comprises a beam reducer unit and a color separation mirror 5 which are sequentially arranged along an optical path, a visible TDI (Time Delay Integration) imaging lens group 6 which is arranged on the reflected optical path of the color separation mirror 5, an infrared TDI imaging lens group 9 which is arranged on the transmitted optical path of the color separation mirror 5, a visible switching reflector 7 and a visible array imaging lens group 8 which is arranged on the reflected optical path of the visible switching reflector 7; the visible switching reflector 7 is used to cut in or out of the visible TDI imaging lens group 6; a reflector 10 is arranged in the infrared TDI imaging lens group 9; the visible TDI imaging lens group 6 and the visible array imaging lens group 8 complete the visible array or TDI imaging in time. DI optical system imaging; the beam reduction unit includes a primary mirror 1, a secondary mirror 2, a folding mirror 3 and a third mirror 4 arranged in sequence along the optical path; the primary mirror 1 and the secondary mirror 2 are arranged coaxially, and the axis is the primary and secondary mirror axis, so that a central field of view with good image quality can be obtained, which is convenient for the implementation of related technologies such as processing, detection, and adjustment; the folding mirror 3 is located on the side of the primary mirror 1 away from the secondary mirror 2, and the angle between its normal and the system optical axis is greater than 45°, which ensures that the central field of view light of the incident light of the biased field of view after passing through the primary mirror 1, the secondary mirror 2, the folding mirror 3, and the third mirror 4 is perpendicular to the primary and secondary mirror axes. The third mirror 4 is a free-form surface reflector, and the central field of view light after it is emitted is perpendicular to the primary and secondary mirror axes, with both aperture off-axis and field of view off-axis; the beam reduction unit formed by the primary mirror 1, the secondary mirror 2, the folding mirror 3, and the third mirror 4 has good image quality. By adjusting the interval between the primary mirror 1 and the secondary mirror 2, and sensitive items such as the eccentricity of the secondary mirror 2, the image quality of the beam reduction unit can be basically kept unchanged after adjustment. The dichroic mirror 5 is arranged on the output light path of the three mirrors 4, and the included angle with the horizontal plane is 45°. It splits the dual-band color light emitted by the beam reduction unit, transmits infrared light, and reflects visible light. It has a transmittance of ≥95% in the infrared band and a reflectivity of ≥95% in the visible light band.

[0063] The dichroic mirror 5 is used to transmit the output light of the three mirrors 4 along the optical path to the infrared TDI imaging lens group 9 and the reflector 10 in sequence, and at the same time reflect the output light of the three mirrors 4 to the visible TDI imaging lens group 6, or reflect the light to the visible array imaging lens group 8 when the visible switching reflector 7 cuts into the visible TDI imaging lens group 6; a visible TDI detection device is arranged on the output light path of the visible TDI imaging lens group 6, so that the output light of the visible TDI imaging lens group 6 is imaged on the visible TDI detection device; a visible light array detector is arranged on the output light path of the visible array imaging lens group 8, so that the output light of the visible array imaging lens group 8 is imaged on the visible light array detector; an infrared TDI detection device is arranged on the output light path of the infrared TDI imaging lens group 9, and the output light of the infrared TDI imaging lens group 9 is imaged on the infrared TDI detection device by translating the infrared TDI imaging lens group 9.

[0064] In order to ensure the compactness of the system, the primary mirror 1 is an even-order aspheric reflector with a central or eccentric opening, with a silver film or a gold film on its surface, a cone coefficient K less than 0, and three high-order aspheric items of the 4th, 6th, and 8th; the material is quartz or K9 or microcrystalline or silicon carbide, and the mirror F number is 0.5-1.5. The secondary mirror 2 is an even-order aspheric reflector, with a silver film or a gold film on its surface, a cone coefficient K less than 0, and three high-order aspheric items of the 4th, 6th, and 8th; the material is quartz or K9 or microcrystalline or silicon carbide, and the mirror F number is 0.5-1.5. The folding mirror 3 is a plane reflector, with a silver film or a gold film on its surface, an off-axis aperture layout to reduce the size, and a chamfered shape to avoid interference with the dichroic mirror 5; the material is quartz or K9 or microcrystalline or silicon carbide.

[0065] The three-mirror 4 is a free-form surface reflector with an off-axis aperture and a certain tilt angle on the mirror surface, which reduces the size and weight. Its cone coefficient K is less than 0 and is represented by an XY polynomial. There are 36 terms in total, and only 20 terms of even powers of X and arbitrary powers of Y are non-zero. The number of terms in the XY polynomial can be adjusted according to the aberration correction requirements. The material of the three-mirror 4 is quartz or K9 or microcrystalline or SiC.

[0066] The dichroic mirror 5 is a parallel flat plate with a dichroic film coated thereon, and is placed at an angle θ of 45° in general, which can be adjusted according to the system layout requirements; the dichroic mirror 5 has a certain thickness d to ensure the stability of the system during processing, coating, assembly and use of the lens. The material of the dichroic mirror 5 is Silicon, Germanium or ZNSE or CLEARTRAN, and the reflectivity and transmittance are both greater than 90%. It can be seen that the switching reflector 7 is a plane reflector, and the material is quartz or K9 or microcrystalline or SiC.

[0067] The primary mirror 1 and the secondary mirror 2 are used coaxially. After the two are combined, the image quality of the central field of view is perfect. When the two are combined and adjusted, there is no need to process the compensation mirror group or CGH used for adjustment, which is conducive to the implementation of the adjustment technology. The beam reduction unit composed of the primary mirror 1, the secondary mirror 2, the folding axis mirror 3, and the third mirror 4 is a visible and infrared dual-band beam reduction system with perfect image quality, which is conducive to the implementation of the combined adjustment of the beam reduction unit. First, the combined adjustment of the primary mirror 1 and the secondary mirror 2 must be completed, and then the adjustment of the folding axis mirror 3 is completed in combination with the theodolite, and then the adjustment of the third mirror 4 is performed. Since the beam reduction unit has perfect image quality, there is no need to process the compensation mirror group or CGH used for adjustment, and the image quality of the emitted parallel light can be controlled. Finally, if the image quality of the emitted parallel light still does not meet the overall image quality requirements of the beam reduction unit, the image quality of the entire beam reduction unit after adjustment is ensured to meet the requirements by fine-tuning the interval between the primary mirror 1 and the secondary mirror 2 and the eccentricity of the secondary mirror 2 and other sensitive items.

[0068] It can be seen that the TDI imaging lens group 6 includes a visible common lens front group and a visible imaging discrete rear group coaxially arranged in sequence along the optical path; the visible common lens front group includes 6 lenses coaxially arranged in sequence along the optical path, wherein the first lens is a plano-convex lens, the convex surface is a free-form surface, the cone coefficient K of the surface is less than 0, and is represented by an XY polynomial, with a total of 36 terms, and only 20 terms of even powers of X and arbitrary powers of Y are non-zero; the number of terms in its XY polynomial can be adjusted according to the aberration correction requirements, only keeping the even powers of X and arbitrary powers of Y non-zero, so that the lens surface has an axially symmetrical transmission mirror surface, and the remaining lenses are spherical mirrors; the visible imaging discrete rear group includes 3 lenses coaxially arranged in sequence along the optical path, wherein one surface of the second lens is an aspherical surface, the cone coefficient K is greater than 0 and less than 1, and there are no high-order terms; the remaining lenses are spherical mirrors.

[0069] If you want to fully adapt to the changes in temperature and air pressure, you can fine-tune the position of the third lens in the front group of the visible common lens to compensate for the changes. To meet the image quality requirements, the third lens is a negative lens. Compared with the existing system in which the adjustment link is set on the secondary lens 2, the adjustment link has relatively low precision requirements, is easier to implement, and has a low cost, which improves the economy of the system implementation.

[0070] The visible common lens front group and the visible imaging discrete rear group are placed coaxially, and there is a large air gap between the two. The space gap can allow the switching reflector 7 to be cut in and out. When the visible switching reflector 7 is cut into between the visible common lens front group and the visible imaging discrete rear group, the reflected light of the color dichroic mirror 5 is transmitted through the visible common lens front group to the visible switching reflector, and then reflected to the visible array imaging lens group 8. When the visible switching reflector 7 is cut out of the visible common lens front group and the visible imaging discrete rear group, the reflected light of the color dichroic mirror 5 is reflected to the visible TDI imaging lens group 6. The visible array imaging lens group 8 has the same structure as the visible imaging discrete rear group.

[0071] The infrared TDI imaging lens group 9 has a secondary imaging function, which ensures the pupil matching of the system without increasing the size of the system's main mirror 1; it includes two positive lens groups; there is a primary image plane between the two positive lens groups, one positive lens group includes 3 lenses, whose optical powers are arranged in positive, negative and positive order respectively; the other positive lens group includes 3 lenses, whose optical powers are arranged in negative, positive and positive order respectively; the materials of the two positive lens groups are Silicon and / or Germanium. In order to achieve 100% matching with the cold screen, there are 4 aspherical surfaces in the 6 lenses, the cone coefficient K value is 0, and there are 4th, 6th and 8th high-order aspherical items. The lens material, the number of aspherical surfaces and the location of the aspherical surfaces can be adjusted according to the overall needs of the system.

[0072] The visible TDI detection equipment includes an optical splicing device and a plurality of visible TDI detectors; the optical splicing device includes a plurality of plane reflectors that are spliced ​​and fixed, the plurality of plane reflectors have the same size and spacing, and the materials are all quartz or K9 or microcrystals or SiC; each visible TDI detector is arranged on the reflection light path or the transmission light path of the plane reflector; the optical splicing device can solve the problem of large field of view requirements and detector size limitations. The optical splicing device has the function of optically splicing N visible TDI detectors, N ≥ 2. The band of the plane reflector can be adjusted according to demand, so the optical splicing device can be expanded to detectors of different bands and different numbers. In other embodiments, the visible TDI detection equipment can also use 4 visible TDI detectors located on the same detection plane, and the 4 visible TDI detectors are mechanically spliced ​​and staggered in a triangular shape. In order to meet the needs of compact and miniaturized system, the pixel size of the selected single visible TDI detector is relatively small, and the number of pixels is close to tens of thousands, which still cannot directly cover the image size. It adopts an optical splicing method, 2×2 visible TDI detectors, and a 10-spaced array of transmission and reflector mirrors to complete large-field visible multi-spectral TDI push-scan imaging.

[0073] The infrared TDI detection equipment includes M infrared TDI detectors located in the same detection plane; the M infrared TDI detectors are mechanically spliced, placed in parallel when M=2, and placed in a herringbone shape when M=3; each infrared TDI detector is provided with a cold aperture; the lens for adjusting the air pressure in the infrared optical path of the infrared TDI imaging lens group 9 is a lens group located in front of the primary image plane. Compared with the system in which the adjustment link is set on the secondary mirror 2, the adjustment link has relatively lower precision requirements, is easier to implement, and is less costly, thereby improving the economy of the system implementation.

[0074] The primary mirror 1, the secondary mirror 2, the folding mirror 3, the third mirror 4, the dichroic mirror 5, the infrared TDI imaging lens group 9 and the reflector 10 form an infrared subsystem; the exit pupil of the infrared subsystem is the infrared subsystem aperture, which is set on the cold screen of the infrared TDI detector, and can achieve 100% cold aperture matching. By controlling the entrance pupil position of the infrared light, it is ensured that its imaging beam is within the reflection area of ​​the primary mirror 1; the infrared TDI detector is a finished mechanically spliced ​​infrared detector. The primary mirror 1, the secondary mirror 2, the folding mirror 3, the third mirror 4, the dichroic mirror 5, the visible TDI imaging lens group 6, the visible switching reflector 7 and the visible array imaging lens group 8 form a visible subsystem, and the aperture of the visible subsystem is set on the primary mirror 1.

[0075] After the infrared light beam passes through the parallel plate (dichroic mirror 5) of a certain thickness and tilt angle, it enters the infrared TDI imaging lens group 9 and the infrared TDI detector for imaging. In order to ensure the image quality of the system and eliminate the influence of the system optical axis, the infrared TDI imaging lens group 9 needs to be translated as a whole, and the translation direction is consistent with the translation direction of the transmission light axis of the dichroic mirror 5. The translation amount T can be obtained according to the refractive index n, thickness d and tilt angle θ of the dichroic mirror 5, i.e. the parallel plate, by the following formula:

[0076]

[0077] The invention discloses a visible infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer, which is combined with a visible TDI detector, an infrared TDI detector and a visible array detector to realize space-to-earth remote sensing imaging and can perform all-day observation. The system has an entrance pupil diameter D=Φ650.0 mm, a biased field angle of -1°, an aperture Φ1 of a primary mirror 1=650 mm, a reflection diameter Φ2 of a secondary mirror 2=195.0 mm, and an obstruction ratio of 0.3. The visible focal length f′ of the visible TDI detector is 3600 mm, and the field angle is ±0.86°×±0.15°. The visible TDI detector is a multi-spectral linear array detector, having a full-color spectrum and five multi-spectral bands B1 to B4, wherein: The full-color spectral range is 0.45μm~0.8μm, the spectral range of multi-spectrum B1 is 0.45μm~0.52μm, the spectral range of multi-spectrum B2 is 0.52μm~0.59μm, the spectral range of multi-spectrum B3 is 0.63μm~0.69μm, and the spectral range of multi-spectrum B4 is 0.77μm~0.89μm; the field angle of the visible light array detector is ±0.31°×±0.22°, the spectral range is 0.45μm~0.89μm, and the back working distance is 68.977mm; the infrared focal length of the infrared TDI detector is f′=2010mm, the field angle is ±0.86°×±0.1°, and the spectral range is 2.9μm~5.4μm.

[0078] In this embodiment, the infinite light beam first passes through the coaxially arranged primary mirror 1 and secondary mirror 2, and then enters the off-axis three-mirror 4 through the off-axis folding mirror 3, and is converted into a small-aperture beam reduction optical path. After passing through the dichroic mirror 5, the transmitted infrared light passes through the secondary imaging infrared TDI imaging lens group 9 and is imaged on the focal plane of the infrared array TDI detector; the reflected visible light passes through the visible common lens front group, the visible imaging discrete rear group and the second visible imaging discrete rear group to reach the image plane of the large-field visible TDI detector; after the visible switching reflector 7 is cut in, the visible light passes through the visible array imaging lens group 8 to reach the image plane of the visible array detector. The optical parameters of the primary mirror 1, the secondary mirror 2, the folding mirror 3, the three-mirror 4 and the dichroic mirror 5 are detailed in Table 1.1:

[0079] Table 1.1

[0080] Surface type radius thickness Glass Refraction Mode Remark Physical surface Spherical unlimited unlimited 1(Aperture) even aspherical surface -1328.273 -502.609 reflection Primary mirror 1 2 even aspherical surface -241.066 803.88 reflection Secondary mirror 2 3 Spherical unlimited 332.21 reflection Folding mirror 3 4 Free-form surface 588.056000 374.40 reflection Three Mirrors 4 5 Spherical unlimited reflection Exit pupil

[0081] The optical parameters of the visible TDI imaging lens group 6 are shown in Table 1.2:

[0082] Table 1.2

[0083]

[0084]

[0085] The optical parameters of the infrared TDI imaging lens group 9 and the infrared TDI detector are shown in Table 1.3:

[0086] Table 1.3

[0087]

[0088] Figure 3(a) , 3(b) They are respectively the optical path diagrams in the YOZ plane and the XOY plane of the beam reduction unit and the dichroic mirror 5 in the embodiment of the present invention when light is incident on the beam reduction unit; FIG3(c) is the visible light transfer function diagram of the beam reduction unit and the dichroic mirror 5 in the embodiment of the present invention, wherein various colors represent the visible light transfer functions of different fields of view, the horizontal axis is the spatial frequency, the unit is cycles / mrad, and the vertical axis is the transfer function value, which is dimensionless; FIG3(d) is the infrared light transfer function diagram of the beam reduction unit and the dichroic mirror 5 in the embodiment of the present invention, wherein various colors represent the infrared transfer functions of different fields of view, the horizontal axis is the spatial frequency, the unit is cycles / mrad, and the vertical axis is the transfer function value, which is dimensionless.

[0089] like Figure 4(a) , 4(b) As shown in FIG. 4 , under the condition of conventional push-scanning imaging, the visible light enters the visible TDI imaging lens group 6 after being reflected by the dichroic mirror 5, and is finally imaged on the visible TDI detector; FIG. 4( c ) is a visible light transfer function diagram of the visible TDI detection optical path in the embodiment of the present invention, wherein various colors represent visible light transfer functions of different fields of view, the horizontal axis is the spatial frequency, the unit is cycles / mm, and the vertical axis is the transfer function value, which is dimensionless; FIG. 4( d ) is a visible point array diagram of different fields of view of the visible TDI detection optical path in the embodiment of the present invention; Figure 4(c) , 4(d)It can be seen that the visible transfer function is greater than 0.3 at a spatial frequency of 142.9lp / mm, the diffuse spot has good consistency in each field of view, and the image quality is close to the limit. From Figure 4(e), it can be seen that the visible multi-spectral B1 segment transfer function is greater than 0.45 at a spatial frequency of 71.43lp / mm, and the image quality is excellent; from Figure 4(f), it can be seen that the visible multi-spectral B2 segment transfer function is greater than 0.5 at a spatial frequency of 71.43lp / mm, and the image quality is excellent; from Figure 4(g), it can be seen that the visible multi-spectral B1 transfer function is greater than 0.47 at a spatial frequency of 71.43lp / mm, and the image quality is excellent; from Figure 4(h), it can be seen that the visible multi-spectral B4 transfer function is greater than 0.3 at a spatial frequency of 71.43lp / mm, and the image quality is excellent.

[0090] like Figure 5(a) , 5(b) As shown in FIG. 5 , under the imaging condition of the discrete target area of ​​interest, the visible switching reflector 7 is inserted between the dichroic mirror 5 and the visible array imaging lens group 8, and the visible light enters the visible array imaging lens group 8 after being reflected by the dichroic mirror 5, and is finally imaged on the visible light array detector; FIG. 5( c ) is a visible light transfer function diagram of the visible light array detection optical path in an embodiment of the present invention, wherein various colors represent visible light transfer functions of different fields of view, the horizontal axis is the spatial frequency, the unit is cycles / mm, and the vertical axis is the transfer function value, which is dimensionless; FIG. 5( d ) is a point diagram of different fields of view of the visible light array detection optical path in an embodiment of the present invention, from Figure 5(c) , 5(d) It can be seen that the visible transfer function is greater than 0.32 at a spatial frequency of 110lp / mm, the diffuse spot has good consistency in each field of view, and the image quality is close to the limit.

[0091] like Figure 6(a) , 6(b) As shown in FIG. 6 , under the condition of conventional push-scanning imaging, the visible light enters the infrared TDI imaging lens group 9 after being transmitted by the dichroic mirror 5, and is finally imaged on the infrared TDI detector; FIG. 6( c) is a visible light transfer function diagram of the infrared TDI detection optical path in an embodiment of the present invention, wherein various colors represent infrared light transfer functions of different fields of view, the horizontal axis is the spatial frequency, the unit is cycles / mm, and the vertical axis is the transfer function value, which is dimensionless; FIG. 6( d) is a point diagram of different fields of view of the infrared TDI detection optical path in an embodiment of the present invention, from Figure 6(c) , 6(d) It can be seen that the infrared transfer function is greater than 0.35 at a spatial frequency of 25lp / mm, the diffuse spot has good consistency in each field of view, and the image quality is close to the limit.

[0092] The invention discloses a visible infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer, which can achieve a good image quality level and is relatively simple to process and assemble. Its envelope size is 800 (X direction) × 750 (Y direction) × 870 (Z direction is the system optical axis direction), the effective aperture of the optical system is 650, the visible focal length is 3600, the focal length ratio is 4.137:1, and the system layout is compact.

Claims

1. A visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer, characterized in that: The invention comprises a beam reduction unit and a dichroic mirror (5) arranged in sequence along an optical path, a visible TDI imaging lens group (6) arranged on the reflection optical path of the dichroic mirror (5), an infrared TDI imaging lens group (9) arranged on the transmission optical path of the dichroic mirror (5), a visible switching reflector (7), and a visible array imaging lens group (8) arranged on the reflection optical path of the visible switching reflector (7); the visible switching reflector (7) is used to cut in or out of the visible TDI imaging lens group (6); the infrared TDI imaging lens group (9) is provided with a reflector (10); The beam reduction unit comprises a primary mirror (1), a secondary mirror (2), a folding mirror (3) and a third mirror (4) which are arranged in sequence along the optical path; the primary mirror (1) and the secondary mirror (2) are arranged coaxially, the axis being the primary and secondary mirror axis; the folding mirror (3) is located on the side of the primary mirror (1) away from the secondary mirror (2), and the angle between its normal and the system optical axis is greater than 45°; the third mirror (4) is a free-form surface reflector, and the emitting central field light rays are perpendicular to the primary and secondary mirror axes; the dichroic mirror (5) is arranged on the emitting optical path of the third mirror (4); The dichroic mirror (5) is used to transmit the output light of the three mirrors (4) along the optical path to the infrared TDI imaging lens group (9) and the reflector (10), and at the same time reflect the output light of the three mirrors (4) to the visible TDI imaging lens group (6), or reflect the light to the visible array imaging lens group (8) when the visible switching reflector (7) cuts into the visible TDI imaging lens group (6); A visible TDI detection device is arranged on the outgoing light path of the visible TDI imaging lens group (6), so that the outgoing light of the visible TDI imaging lens group (6) is imaged on the visible TDI detection device; A visible light array detector is arranged on the outgoing light path of the visible light array imaging lens group (8), so that the outgoing light of the visible light array imaging lens group (8) is imaged on the visible light array detector; An infrared TDI detection device is arranged on the output light path of the infrared TDI imaging lens group (9), and the output light of the infrared TDI imaging lens group (9) is imaged on the infrared TDI detection device by translating the infrared TDI imaging lens group (9).

2. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 1, characterized in that: The primary mirror (1) is an even-order aspheric reflector with a central opening or an eccentric opening, the surface of which is coated with a silver film or a gold film, and the cone coefficient K is less than 0; the material is quartz or K9 or microcrystal or silicon carbide, and the mirror surface F number is 0.5-1.

5.

3. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 2, characterized in that: The secondary mirror (2) is an even-order aspheric reflector, the surface of which is coated with a silver film or a gold film, and the cone coefficient K is less than 0; the material is quartz or K9 or microcrystal or silicon carbide, and the mirror surface F number is 0.5-1.

5.

4. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 3, characterized in that: The folding mirror (3) is a plane reflecting mirror, the surface of which is plated with a silver film or a gold film, and the material is quartz or K9 or microcrystal or silicon carbide.

5. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 4, characterized in that: The primary mirror (1) is provided with an aperture; The cone coefficient K of the three mirrors (4) is less than 0, and is represented by an XY polynomial, and the material is quartz or K9 or microcrystal or silicon carbide; The dichroic mirror (5) is a parallel plate on which a dichroic film is plated. The material of the dichroic mirror (5) is Silicon, Germanium, ZNSE or CLEARTRAN, and the reflectivity and transmittance are both greater than 90%. The visible switching reflector (7) is a plane reflector made of quartz, K9, microcrystal or SiC.

6. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to any one of claims 1 to 5, characterized in that: The visible TDI imaging lens group (6) comprises a visible common lens front group and a visible imaging discrete rear group which are coaxially arranged in sequence along the optical path; The visible common lens front group includes 6 lenses coaxially arranged in sequence along the optical path, wherein the first lens is a plano-convex lens, the convex surface of which is a free-form surface, the cone coefficient K is less than 0, and is represented by an XY polynomial, the third lens is a negative lens, and the remaining lenses are all spherical lenses; The visible imaging discrete rear group comprises three lenses coaxially arranged in sequence along the optical path, wherein one surface of the second lens is aspherical, the cone coefficient K is greater than 0 and less than 1, and there is no high-order term; the remaining lenses are spherical mirrors; The visible switchable reflector (7) is used to cut in or out between the visible common lens front group and the visible imaging discrete rear group. When the visible switchable reflector (7) is cut in, the reflected light of the dichroic mirror (5) is transmitted to the visible switchable reflector (7) through the visible common lens front group and then reflected to the visible array imaging lens group (8). When the visible switchable reflector (7) is cut out, the reflected light of the dichroic mirror (5) is reflected to the visible TDI imaging lens group (6); The visible array imaging lens group (8) has the same structure as the visible imaging discrete rear group; The visible TDI imaging lens group (6) adjusts the image quality and air pressure by adjusting the interval between the third lenses of the visible common lens front group.

7. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 6, characterized in that: The infrared TDI imaging lens group (9) comprises two positive lens groups; a primary image plane is provided between the two positive lens groups; one positive lens group comprises three lenses, whose optical powers are arranged in positive, negative and positive order respectively; the other positive lens group comprises three lenses, whose optical powers are arranged in negative, positive and positive order respectively; the materials of the two positive lens groups are Silicon and / or Germanium; The infrared TDI imaging lens group (9) adjusts the air pressure by adjusting the position of the positive lens group located in front of the primary image plane.

8. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 1, characterized in that: The translation amount T of the infrared TDI imaging lens group (9) is calculated according to the following formula: Wherein, d is the thickness of the dichroic mirror (5), θ is the angle between the dichroic mirror (5) and the horizontal plane, and n is the refractive index of the dichroic mirror (5).

9. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 8, characterized in that: The visible TDI detection device comprises an optical splicing device and N visible TDI detectors; the optical splicing device comprises a plurality of plane reflectors that are spliced ​​and fixedly connected, the plurality of plane reflectors have the same size and interval, and the materials are all quartz or K9 or microcrystal or SiC; each visible TDI detector is arranged on the reflection light path or the transmission light path of the plane reflector; Alternatively, the visible TDI detection device includes N visible TDI detectors located in the same detection plane, the N visible TDI detectors are mechanically spliced ​​and placed parallel to each other, and there are no less than 10 overlapping pixels along the splicing direction, and N≥2.

10. The visible-infrared dual-band catadioptric optical system based on a free-form surface shared beam reducer according to claim 9, characterized in that: The infrared TDI detection device comprises M infrared TDI detectors located in the same detection plane, the M infrared TDI detectors are mechanically spliced ​​and placed parallel to each other, and there are no less than 10 overlapping pixels along the splicing direction, M≥2; each infrared TDI detector is provided with a cold light stop; The included angle θ between the dichroic mirror (5) and the horizontal plane is 45°.

Images