Dual-band off-axis common-aperture zoom optical system and design method thereof

Abstract

The invention discloses a dual-band off-axis common-aperture zoom optical system and a design method thereof, and solves the problem that the requirements of large aperture, double spectrum, long focal length and large zoom ratio cannot be considered in the prior art. The system is formed by butt joint of an off-axis three-mirror system, a field lens system and a two-gear zoom system, during butt joint, the requirements that calibers are equal and the two systems meet good image quality before butt joint are met, more importantly, the requirements that the directions of light beams of different view fields of the two systems are consistent are met, and otherwise butt joint of the two systems fails. The advantages of an off-axis three-mirror system and a two-gear zoom system are fully utilized, and the designed zoom optical system has the advantages of being large in aperture, long in focal length, double in spectrum band and large in zoom ratio. During application, more target information can be obtained by increasing the aperture of the optical system, application in a complex environment is improved, and meanwhile, the observation and aiming operating distance of the system can be increased by lengthening the focal length of the optical system.

Description

Technical Field

[0001] The present invention relates to the design of an optical imaging system, and particularly to a dual-band off-axis common-aperture zoom optical system and a design method thereof. Background Art

[0002] With the continuous improvement of the status of aerial reconnaissance technology in controlling the dominance of ground-air information, in order to ensure the acquisition of reliable, correct, diverse, and real-time intelligence information, the requirements for night-time, long-distance high-altitude detection technology are getting higher and higher. Therefore, the integration of multi-band, large-aperture, long-focal-length, and large-magnification-ratio optical imaging technologies has become a forefront hotspot in current scientific research tasks.

[0003] Due to the limitations of infrared materials and the influence of chromatic aberration, it is very difficult for a transmissive infrared system to achieve large-aperture imaging. Therefore, a reflective imaging system has become the research direction. Reflective imaging systems can be divided into coaxial reflective and off-axis reflective types. The coaxial reflective structure has a central obstruction, low energy transmittance, and a small magnification ratio. The off-axis reflective structure not only has no central obstruction and high transmittance, but also can achieve large-magnification-ratio optical imaging, which has certain advantages for optoelectronic detection imaging systems. However, for an off-axis reflective zoom imaging system, there are problems such as complex optical paths, compact structure design, difficult alignment, and difficult processing, and general imaging systems rarely involve it.

[0004] Patent CN 109188666 B introduces an off-axis three-mirror optical system with a 350 mm aperture and a focal length of 1778.9 mm, which has the advantages of a large aperture and a long focal length. However, this system is a fixed-focus system with only a single spectral band, and it cannot well meet the observation and aiming multi-function of integrating target search and target aiming, has no zoom ability, and is limited in use. Patent CN 110221420 introduces a dual-field-of-view common-aperture off-axis three-mirror optical system, which realizes the switching of large and small fields of view by means of inserting and removing a correction mirror and achieves the zoom function. Although the primary mirror, secondary mirror, and tertiary mirror all adopt aspherical surfaces, which reduces the processing and alignment difficulties, its aperture is 180 mm, the focal length changes from 700 mm to 233 mm, and it has only a single spectral band and cannot work properly in a complex night vision environment. In summary, the existing technologies cannot meet the requirements of large aperture, dual spectral band zoom, and long focal length at the same time, and there are deficiencies in information acquisition and the operating distance of the optical system. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that the existing technologies cannot take into account the requirements of large aperture, dual spectral band, long focal length, and large magnification ratio, and to provide a dual-band off-axis common-aperture zoom optical system and a design method thereof.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A dual-band off-axis common-aperture zoom optical system, characterized in that it includes an off-axis three-reflection system, a field lens system, and a two-stage zoom system;

[0008] The off-axis three-reflection system includes a primary mirror, a secondary mirror, a folding mirror, a tertiary mirror, and a beam splitter sequentially arranged on the optical path of the dual-band beam incident in parallel. After being reflected by the tertiary mirror, the beam exits parallel, and after passing through the beam splitter, a medium-wave beam and a long-wave beam are output; the reflecting surfaces of the secondary mirror and the tertiary mirror are even aspherical surfaces; the primary image plane is located between the folding mirror and the tertiary mirror;

[0009] The field lens system includes a medium-wave field lens and a long-wave field lens;

[0010] The two-stage zoom system includes a first front fixed component, a first zoom component, a first rear fixed component, a first cold stop component, and a first photodetector arranged in sequence, and also includes a second front fixed component, a second zoom component, a second rear fixed component, a second cold stop component, and a second photodetector arranged in sequence;

[0011] The medium-wave field lens, the first front fixed component, the first zoom component, the first rear fixed component, and the first cold stop component are sequentially arranged on the optical path of the medium-wave beam, and the long-wave field lens, the second front fixed component, the second zoom component, the second rear fixed component, and the second cold stop component are sequentially arranged on the optical path of the long-wave beam. <{

[0012] Further, the secondary mirror and the tertiary mirror are both even high-order aspherical mirrors and satisfy the following formula:

[0013]

[0014] In the formula: z is the sag of the aspherical surface, c is the paraxial curvature radius, r is the semi-aperture of the mirror, k is the conic coefficient, and α1, α2, α3, α4, α5 are aspherical coefficients.

[0015] Further, the wavelength range of the medium-wave beam is 3.7 μm to 4.8 μm; the wavelength range of the long-wave beam is 7.7 μm to 10.5 μm.

[0016] Further, the lens surfaces of the first zoom component and the second zoom component are both even aspherical surfaces.

[0017] A design method for a dual-band off-axis common-aperture zoom optical system, characterized in that it includes the following steps:

[0018] Step 1, build the initial structure of the off-axis three-reflection system

[0019] A primary mirror, a secondary mirror, a folding mirror, a tertiary mirror, and a beam splitter are sequentially arranged on the optical path of the incident dual-band beam. The position of the primary image plane between the folding mirror and the tertiary mirror is controlled by an evaluation function, and the reflecting surfaces of the secondary mirror and the tertiary mirror are set as even aspherical surfaces, so that the beam is parallelly emitted after being reflected by the tertiary mirror. At the same time, the entrance pupil diameter is determined according to the set focal length and F-number, the zoom ratio of the off-axis three-mirror system is controlled, and the beam aperture size of the beam splitter is determined in combination with the entrance pupil diameter;

[0020] Step 2: Build the initial structure of the field lens system

[0021] A mid-wave field lens and a long-wave field lens are respectively built on the two optical paths split by the beam splitter, and the evaluation function is used to control the incident beam trajectories of the two outgoing rays of the beam splitter to be consistent with those of the mid-wave field lens and the long-wave field lens respectively. The evaluation function is set again to control the parallel emission of the beams of the mid-wave field lens and the long-wave field lens;

[0022] Step 3: Build the initial structure of the two-stage zoom system

[0023] The evaluation function is used to control the outgoing beam trajectories of the mid-wave field lens and the long-wave field lens to be consistent with the incident beam trajectories of the first front fixed component and the second front fixed component respectively. A first variable magnification component, a first rear fixed component, a first cold stop component, and a first photodetector are sequentially arranged on the outgoing optical path of the first front fixed component, and a second variable magnification component, a second rear fixed component, a second cold stop component, and a second photodetector are sequentially arranged on the outgoing optical path of the second front fixed component. The image heights of the first photodetector and the second photodetector are adjusted to be consistent with the aperture heights of the first cold stop component and the second cold stop component respectively;

[0024] Step 4: Optimize and adjust the above structure

[0025] The initial structure of the off-axis three-mirror system, the initial structure of the field lens system, and the initial structure of the two-stage zoom system form the initial structure of the zoom optical system. By changing the structural parameters in the initial structure of the zoom optical system, setting the maximum aperture and aperture eccentricity of the zoom optical system, and adjusting the distances between the lenses, a dual-band off-axis common-aperture zoom optical system with the minimum distance size is obtained.

[0026] Further, the formula for determining the entrance pupil diameter according to the set focal length and F-number in step 1 is:

[0027]

[0028] In the formula, D represents the entrance pupil diameter, f′ represents the set focal length, and F represents the f-number.

[0029] Further, in step 3, the beam distortion in the mid-wave two-stage zoom system formed by the first front fixed component, the first variable magnification component, the first rear fixed component, and the first cold stop component is less than 0.5%;

[0030] In the long-wave two-stage zoom system formed by the second front fixing component, the second variable magnification component, the second rear fixing component, and the second cold stop component, the beam distortion is less than 0.5%.

[0031] Further, in step 4, the structural parameters in the initial structure of the zoom optical system are the aperture types of the lenses in the initial structure of the off-axis three-reflection system, the initial structure of the field lens system, and the initial structure of the two-stage zoom system.

[0032] Further, in steps 1-3, the evaluation function is the modulation transfer function.

[0033] Further, steps 1-5 are all completed in optical design software.

[0034] Advantages of the present invention:

[0035] (1) A dual-band off-axis common-aperture zoom optical system provided by the present invention is formed by docking an off-axis three-reflection system, a field lens system, and a two-stage zoom system. When docking, not only the aperture sizes need to be equal, but also the image quality of the two systems should be good before docking. More importantly, the beam directions of each different field of view of the two systems need to be consistent, otherwise the docking will fail. The present invention makes full use of the advantages of the off-axis three-reflection system and the two-stage zoom system, and has more application prospects in the direction of on-vehicle or on-aircraft night reconnaissance missions.

[0036] (2) A dual-band off-axis common-aperture zoom optical system and its design method provided by the present invention integrate large aperture, long focal length, dual spectral bands, and large magnification ratio, and combine the three characteristics of large aperture, multi-spectral bands, and long focal length. Increasing the aperture of the optical system can obtain more target information and improve the application in complex environments. At the same time, lengthening the focal length of the optical system can increase the viewing and aiming distance of the system.

[0037] (3) A dual-band off-axis common-aperture zoom optical system and its design method provided by the present invention. The focal length of the off-axis three-reflection system can reach 1000 mm, and the relative aperture reaches 1 / 4. The system aperture can reach 250 mm. Compared with the known two-stage zoom optical system, the difference is that it has an 8-fold magnification ratio. The relative aperture of the mid-wave infrared reaches 1 / 4, and the relative aperture of the long-wave infrared reaches 1 / 2. The two-spectral-band two-stage zoom optical system can be docked with the front-end system to achieve an 8-fold magnification of the overall system. The system of the present invention has both a large aperture of 250 mm and an 8-fold change in system focal length of 1000 mm / 125 mm, and the imaging quality of both spectral bands is good. The modulation transfer function value in the mid-wave infrared spectral band reaches above 0.3 at a spatial frequency of 33 lp / mm, and the modulation transfer function value in the long-wave infrared spectral band approaches the diffraction limit at a spatial frequency of 20 lp / mm. Description of the Drawings

[0038] Figure 1 This is a schematic structural diagram of an embodiment of a dual-band off-axis common-aperture zoom optical system of the present invention;

[0039] Figure 2 This is a MTF curve graph of the long focal length system of the mid-wave infrared optical path in an embodiment of a dual-band off-axis common-aperture zoom optical system of the present invention;

[0040] Figure 3 This is a MTF curve graph of the short focal length system of the mid-wave infrared optical path in an embodiment of a dual-band off-axis common-aperture zoom optical system of the present invention;

[0041] Figure 4 This is a MTF curve graph of the long focal length system of the long-wave infrared optical path in an embodiment of a dual-band off-axis common-aperture zoom optical system of the present invention;

[0042] Figure 5 This is a MTF curve graph of the short focal length system of the long-wave infrared optical path in an embodiment of a dual-band off-axis common-aperture zoom optical system of the present invention.

[0043] In the figure, 1 - primary mirror; 2 - secondary mirror; 3 - folding mirror; 4 - tertiary mirror; 5 - beam splitter; 6 - mid-wave field lens; 7 - first front fixed component; 8 - first variable magnification component; 9 - first rear fixed component; 10 - first cold stop component; 11 - long-wave field lens; 12 - second front fixed component; 13 - second variable magnification component; 14 - second rear fixed component; 15 - second cold stop component. Specific embodiments

[0044] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] A dual-band off-axis common-aperture zoom optical system, as Figure 1 shown, includes an off-axis three-mirror system, a field lens system, and a two-stage zoom system.

[0046] Among them, the off-axis three-mirror system includes a primary mirror 1, a secondary mirror 2, a folding mirror 3, a tertiary mirror 4, and a beam splitter 5 that are sequentially arranged on the optical path of the dual-band beam. After passing through the beam splitter 5, a mid-wave beam and a long-wave beam are output; the field lens system includes a mid-wave field lens 6 and a long-wave field lens 11; the two-stage zoom system includes a first front fixed component 7, a first variable magnification component 8, a first rear fixed component 9, a first cold stop component 10, and a first photodetector that are sequentially arranged, and also includes a second front fixed component 12, a second variable magnification component 13, a second rear fixed component 14, a second cold stop component 15, and a second photodetector that are sequentially arranged; the mid-wave field lens 6, the first front fixed component 7, the first variable magnification component 8, the first rear fixed component 9, the first cold stop component 10, and the first photodetector are sequentially arranged on the optical path of the mid-wave beam, and the long-wave field lens 11, the second front fixed component 12, the second variable magnification component 13, the second rear fixed component 14, the second cold stop component 15, and the second photodetector are sequentially arranged on the optical path of the long-wave beam.

[0047] The dual-band beam passes through the primary mirror 1, the secondary mirror 2, the folding mirror 3, and the tertiary mirror 4 in sequence, is reduced to a small-aperture beam, and is incident on the beam splitter 5. The beam splitter 5 splits the beam to obtain a mid-wave beam with a wavelength range of 3.7 μm to 4.8 μm and a long-wave beam with a wavelength range of 7.7 μm to 10.5 μm.

[0048] The mid-wave beam is reduced by the mid-wave field lens 6 and is sequentially incident on the first front fixed component 7, the first variable magnification component 8, the first rear fixed component 9, and the first cold stop component 10 to obtain a converging mid-wave beam. The converging mid-wave beam is finally incident on the first photodetector for mid-wave beam detection.

[0049] The long-wave beam is reduced by the long-wave field lens 11 and is sequentially incident on the second front fixed component 12, the second variable magnification component 13, the second rear fixed component 14, and the second cold stop component 15 to obtain a converging long-wave beam. The converging long-wave beam is finally incident on the second photodetector for long-wave beam detection.

[0050] In the present invention, the off-axis common-aperture zoom optical system uses an off-axis three-mirror optics as a telescopic system. After being split by a beam splitter at the rear end, the reflected path is for the mid-wave and the transmitted path is for the long-wave. The entire optical system is formed by two converging zoom optical paths respectively. This system can achieve dual-band and large magnification ratio imaging, and is easy to process and align.

[0051] In this embodiment, the secondary mirror 2 and the tertiary mirror 4 are both even-order high-order aspherical mirrors and satisfy the following formula:

[0052]

[0053] Where: z is the sag height of the aspheric surface, c is the paraxial curvature radius, r is the semi-aperture of the mirror, k is the conic coefficient, and α1, α2, α3, α4, α5 are the aspheric coefficients.

[0054] In this embodiment, the lens surfaces of the first variable magnification component 8 and the second variable magnification component 13 are both even aspheric surfaces.

[0055] This embodiment also provides a design method for a dual-band off-axis common-aperture zoom optical system, including the following steps:

[0056] Step 1, construct the initial structure of the off-axis three-mirror system

[0057] 1) In the optical design software, determine the off-axis three-mirror system constructed by the primary mirror 1, the secondary mirror 2, the folding mirror 3, the tertiary mirror 4, and the beam splitter 5. Control the position of the first image plane between the folding mirror 3 and the tertiary mirror 4 through the modulation transfer function. Set the secondary mirror 2 and the tertiary mirror 4 as even aspheric surfaces to make the light beam emerge parallel after passing through the tertiary mirror 4.

[0058] Among them, set the secondary mirror 2 and the tertiary mirror 4 as even high-order aspheric mirrors and satisfy the following formula:

[0059]

[0060] Where: z is the sag height of the aspheric surface, c is the paraxial curvature radius, r is the semi-aperture of the even high-order aspheric mirror, k is the conic coefficient, and α1, α2, α3, α4, α5 are the aspheric coefficients.

[0061] 2) Determine the entrance pupil diameter according to the set focal length and F-number. The formula is:

[0062] Where D represents the entrance pupil diameter, f′ represents the set focal length, and F represents the f-number.

[0063] 3) Control the zoom ratio of the off-axis three-mirror system and determine the size of the beam diameter emerging from the beam splitter 5 in combination with the entrance pupil diameter.

[0064] In this embodiment, an ideal paraxial plane is set behind the beam splitter 5, and the focal length of the ideal paraxial plane is the focal length of the two-stage zoom system.

[0065] Step 2, construct the initial structure of the field lens system

[0066] In the design of the field lens system, it is necessary to satisfy that the entrance pupil diameter is the same as the exit beam diameter of the initial structure of the off-axis three-mirror system, and the field of view is set as the actual image height, which is the same as the entrance pupil diameter; to meet the above requirements, a mid-wave field lens 6 and a long-wave field lens 11 are respectively built on the two optical paths split by the beam splitter 5, and the modulation transfer function is used to control the trajectories of the two exit rays of the beam splitter 5 to be the same as the incident ray trajectories of the mid-wave field lens 6 and the long-wave field lens 11 respectively. The modulation transfer function is set again to control the parallel exit of the beams of the mid-wave field lens 6 and the long-wave field lens 11.

[0067] Step 3. Build the initial structure of the two-stage zoom system

[0068] The modulation transfer function is used to control the exit ray trajectories of the mid-wave field lens 6 and the long-wave field lens 11 to be the same as the incident ray trajectories of the first front fixing component 7 and the second front fixing component 12 respectively. A first zoom component 8, a first rear fixing component 9, a first cold stop component 10, and a first photodetector are sequentially arranged on the exit surface of the front fixing component 7, and a second zoom component 13, a second rear fixing component 14, a second cold stop component 15, and a second photodetector are sequentially arranged on the exit surface of the second front fixing component 12; and the image heights of the first photodetector and the second photodetector are adjusted to be the same as the aperture heights of the first cold stop component 10 and the second cold stop component 15 respectively, and the field of view is the detector image height.

[0069] Among them, the beam distortion in the mid-wave two-stage zoom unit formed by the front fixing component 7, the first zoom component 8, the first rear fixing component 9, and the first cold stop component 10 is less than 0.5%.

[0070] The beam distortion in the long-wave two-stage zoom unit formed by the second front fixing component 12, the second zoom component 13, the second rear fixing component 14, and the second cold stop component 15 is less than 0.5%.

[0071] In this embodiment, the distances between the first rear fixing component 9 and the first cold stop component 10 and between the second rear fixing component 14 and the second cold stop component 15 can be reserved, so that the distances between the first cold stop component 10, the second cold stop component 15 and the image plane cannot be changed during the adjustment process.

[0072] Step 4. Optimize and adjust the above structure

[0073] The initial structure of the off-axis three-mirror system, the initial structure of the field lens system, and the initial structure of the two-stage zoom system form the initial structure of the zoom optical system. By changing the aperture types of the lenses in the initial structure of the zoom optical system, setting the maximum aperture of the zoom optical system and the aperture eccentricity, and adjusting the distances between the lenses, a dual-band off-axis common-aperture zoom optical system with the minimum distance dimension is obtained.

[0074] Based on the above design method, a dual-band off-axis common-aperture zoom optical system is obtained in this embodiment, with the following parameters: the off-axis amount of the off-axis three-mirror system is 250 mm. The system focal length is 1000 mm, the system aperture is 250 mm, the light beam exits parallel from the beam splitter 5, and the MTF curve of the off-axis three-mirror system approaches the diffraction limit. The specific parameters are as follows:

[0075] The radius of curvature of the reflecting surface of the primary mirror 1 is -1026.08 mm, the distance from the secondary mirror 2 is 400 mm, the aperture type of the primary mirror 1 is a circular aperture, the aperture value is 260 mm, and the aperture eccentricity is -250 mm.

[0076] The radius of curvature of the reflecting surface of the secondary mirror 2 is -351.24 mm, the distance from the folding mirror 3 is 165 mm, the aperture type is a circular aperture, the aperture value is 90 mm, and the aperture eccentricity is -50 mm.

[0077] The distance between the folded-axis mirror 3 and the tertiary mirror 4 is 400 mm, the aperture type is a circular aperture, the aperture value is 90 mm, and the aperture eccentricity is -40 mm.

[0078] The radius of curvature of the reflecting surface of the tertiary mirror 4 is 575.80 mm, the distance from the beam splitter 5 is 470 mm, the aperture type is a circular aperture, the aperture value is 320 mm, and the aperture eccentricity is 40 mm.

[0079] In the two-stage zoom system, the focal lengths of the medium-wave two-stage zoom system are 160 mm / 20 mm, the relative aperture is 1 / 4, the entrance pupil diameter is 40 mm - 5 mm, the total length is 470 mm, the incident light is parallel light, the light trajectory between the last lens surface and the image surface is unified for the outgoing light, and the MTF curve of the medium-wave two-stage zoom system approaches the diffraction limit.

[0080] The focal lengths of the long-wave two-stage zoom system are 80 mm - 10 mm, the relative aperture is 1 / 2, the entrance pupil diameter is 40 mm - 5 mm, the total length is 420 mm, the incident light is parallel light, the light trajectory between the last lens surface and the image surface is unified for the outgoing light, and the MTF curve of the long-wave two-stage zoom system approaches the diffraction limit.

[0081] The resolution of the photodetector for detecting medium waves is 640×512, and the pixel size is 15μm×15μm.

[0082] The resolution of the photodetector for detecting long waves is 640×512, and the pixel size is 25μm×25μm.

[0083] The first zoom component 8 consists of four lenses on the same optical axis. The material of the first lens is zinc sulfide, and the lens thickness is 4 mm. The material of the second lens is silicon, and the lens thickness is 7 mm. The material of the third lens is germanium, and the lens thickness is 4.5 mm. The material of the fourth lens is silicon, and the lens thickness is 5 mm.

[0084] The first rear fixing component 9 consists of two lenses on the same optical axis. The material of the first lens is germanium, and the lens thickness is 4.2 mm. The material of the second lens is silicon, and the lens thickness is 4.2 mm.

[0085] The first cold stop component 10 consists of four lenses and a stop on the same optical axis. The material of the second lens is germanium, and the materials of the remaining lenses are all silicon. The thickness of the first lens is 2.950 mm, the thickness of the second lens is 3.978 mm, the thickness of the third lens is 3.012 mm, the thickness of the fourth lens is 3.988 mm. The distance between the fourth lens and the stop is 3.75 mm, the distance between the stop and the image plane is 19.1 mm, and the aperture of the stop is 4.84 mm.

[0086] At long focal lengths, the spacing between the first front fixing component 7 and the first lens of the first zoom component 8 is 84.366 mm, and the spacing between the first zoom component 8 and the first lens of the first rear fixing component 9 is 110.771 mm.

[0087] At short focal lengths, the spacing between the first front fixing component 7 and the first lens of the first zoom component 8 is 55.320 mm, and the spacing between the first zoom component 8 and the first lens of the first rear fixing component 9 is 16.566 mm.

[0088] The second zoom component 13 consists of three lenses on the same optical axis. The material of the first lens is zinc sulfide, and the lens thickness is 5 mm. The material of the second lens is germanium, and the lens thickness is 6.5 mm. The material of the third lens is germanium, and the lens thickness is 5.5 mm.

[0089] The second rear fixing component 14 consists of two lenses on the same optical axis. The material of the first lens is germanium, and the lens thickness is 5.5 mm. The material of the second lens is germanium, and the lens thickness is 5.2 mm.

[0090] The second cold stop component 15 consists of four lenses and a stop on the same optical axis. The material of the second lens is germanium, and the materials of the remaining lenses are all silicon. The thickness of the first lens is 2.552 mm, the thickness of the second lens is 4.233 mm, the thickness of the third lens is 3.500 mm, the thickness of the fourth lens is 4.500 mm. The distance between the fourth lens and the stop is 3.75 mm, the distance between the stop and the image plane is 19.1 mm, and the aperture of the stop is 4.84 mm.

[0091] At long focal length, the distance between the first lens of the second front fixed component 12 and the second variable magnification component 13 is 57.432 mm, and the distance between the first lens of the second variable magnification component 13 and the second rear fixed component 14 is 66.050 mm.

[0092] At short focal length, the distance between the first lens of the second front fixed component 12 and the second variable magnification component 13 is 81.688 mm, and the distance between the first lens of the second variable magnification component 13 and the second rear fixed component 14 is 18.125 mm.

[0093] For the optical system obtained in this embodiment, through software design and simulation, the MTF curve graph of the long focal length system of the mid-wave infrared optical path is obtained, as Figure 2 shown. According to Figure 2 it can be known that the imaging quality of the long focal length system of the mid-wave infrared optical path designed by the optical structure proposed in the present invention reaches the diffraction limit, and further it can be known that the mid-wave infrared long focal length system designed by the design method of the present invention has excellent imaging quality.

[0094] For the optical system obtained in this embodiment, through software design and simulation, the MTF curve graph of the short focal length system of the mid-wave infrared optical path is obtained, as Figure 3 shown. According to Figure 3 it can be known that the imaging quality of the short focal length system of the mid-wave infrared optical path designed by the optical structure proposed in the present invention reaches the diffraction limit, and further it can be known that the mid-wave infrared short focal length system designed by the design method of the present invention has excellent imaging quality.

[0095] For the optical system obtained in this embodiment, through software design and simulation, the MTF curve graph of the long focal length system of the long-wave infrared optical path is obtained, as Figure 4 shown. According to Figure 4 it can be known that the imaging quality of the long focal length system of the long-wave infrared optical path designed by the optical structure proposed in the present invention reaches the diffraction limit, and further it can be known that the long-wave infrared long focal length system designed by the design method of the present invention has excellent imaging quality.

[0096] For the optical system obtained in this embodiment, through software design and simulation, the MTF curve graph of the short focal length system of the long-wave infrared optical path is obtained, as Figure 5 shown. According to Figure 5 it can be known that the imaging quality of the short focal length system of the long-wave infrared optical path designed by the optical structure proposed in the present invention reaches the diffraction limit, and further it can be known that the long-wave infrared short focal length system designed by the design method of the present invention has excellent imaging quality.

[0097] The above is only the specific implementation manner of the present invention, as well as the effect comparison with relevant specific implementation manners and related comparative examples. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claimed rights.

Claims

1. A dual-band off-axis common-aperture zoom optical system, characterized in that: It includes an off-axis three-mirror system, a field lens system and a two-step zoom system; The off-axis three-mirror system includes a primary mirror (1), a secondary mirror (2), a folding mirror (3), a tertiary mirror (4) and a beam splitter (5) that are sequentially arranged on the optical path of the parallel incident dual-band beam. After the beam is reflected by the tertiary mirror (4), it exits parallel, and after passing through the beam splitter (5), a mid-wave beam and a long-wave beam are output; the reflecting surfaces of the secondary mirror (2) and the tertiary mirror (4) are even aspheres; the primary image plane is located between the folding mirror (3) and the tertiary mirror (4); The field lens system includes a mid-wave field lens (6) and a long-wave field lens (11); The two-step zoom system includes a first front fixed component (7), a first zoom component (8), a first rear fixed component (9), a first cold stop component (10) and a first photodetector that are sequentially arranged, and also includes a second front fixed component (12), a second zoom component (13), a second rear fixed component (14), a second cold stop component (15) and a second photodetector that are sequentially arranged; The mid-wave field lens (6), the first front fixed component (7), the first zoom component (8), the first rear fixed component (9), the first cold stop component (10), and the first photodetector are sequentially arranged on the optical path of the mid-wave beam, and the long-wave field lens (11), the second front fixed component (12), the second zoom component (13), the second rear fixed component (14), the second cold stop component (15), and the first photodetector are sequentially arranged on the optical path of the long-wave beam.

2. The dual-band off-axis common-aperture zoom optical system according to claim 1, wherein The secondary mirror (2) and the tertiary mirror (4) are both even high-order aspherical mirrors and satisfy the following formula: In the formula: z is the sag height of the aspherical surface, c is the paraxial curvature radius, r is the semi-aperture of the mirror, k is the conic coefficient, and α1, α2, α3, α4, α5… are the aspherical coefficients.

3. The dual-band off-axis common-aperture zoom optical system according to claim 1, wherein: The wavelength range of the mid-wave beam is 3.7 μm to 4.8 μm; the wavelength range of the long-wave beam is 7.7 μm to 10.5 μm.

4. The dual-band off-axis common-aperture zoom optical system according to claim 1, wherein: The lens surfaces of the first zoom component (8) and the second zoom component (13) are both even aspheres.

5. A design method of the dual-band off-axis common-aperture zoom optical system according to any one of claims 1-4, characterized in that, It includes the following steps: Step 1, build the initial structure of the off-axis three-mirror system Sequentially arrange the primary mirror (1), the secondary mirror (2), the folding mirror (3), the tertiary mirror (4) and the beam splitter (5) on the optical path of the incident dual-band beam. Control the position of the primary image plane between the folding mirror (3) and the tertiary mirror (4) through the evaluation function, and set the reflecting surfaces of the secondary mirror (2) and the tertiary mirror (4) as even aspheres, so that the beam exits parallel after being reflected by the tertiary mirror (4). At the same time, determine the entrance pupil diameter according to the set focal length and F-number, control the zoom ratio of the off-axis three-mirror system, and combine the entrance pupil diameter to determine the size of the beam diameter output by the beam splitter (5); Step 2, build the initial structure of the field lens system On two optical paths split by the spectroscope (5), a mid-wave field lens (6) and a long-wave field lens (11) are respectively set up, and the evaluation function is used to control the two outgoing light rays of the spectroscope (5) to be consistent with the incident beam trajectories of the mid-wave field lens (6) and the long-wave field lens (11) respectively. The evaluation function is set again to control the parallel outgoing of the beams of the mid-wave field lens (6) and the long-wave field lens (11); Step 3: Set up the initial structure of the two-stage zoom system The evaluation function is used to control the outgoing beams of the mid-wave field lens (6) and the long-wave field lens (11) to be consistent with the incident beam trajectories of the first front fixed component (7) and the second front fixed component (12) respectively. A first variable magnification component (8), a first rear fixed component (9), a first cold stop component (10), and a first photodetector are sequentially set on the outgoing optical path of the first front fixed component (7), and a second variable magnification component (13), a second rear fixed component (14), a second cold stop component (15), and a second photodetector are sequentially set on the outgoing optical path of the second front fixed component (12). The image heights of the first photodetector and the second photodetector are adjusted to be consistent with the aperture heights of the first cold stop component (10) and the second cold stop component (15) respectively; Step 4: Optimize and adjust the above structure The initial structure of the off-axis three-reflection system, the initial structure of the field lens system, and the initial structure of the two-stage zoom system form the initial structure of the zoom optical system. By changing the structural parameters in the initial structure of the zoom optical system, the maximum aperture and aperture eccentricity of the zoom optical system are set, and the distances between the lenses are adjusted to obtain a dual-band off-axis common-aperture zoom optical system with the minimum distance dimension.

6. The design method of a dual-band off-axis common-aperture zoom optical system according to claim 5, wherein The formula for determining the entrance pupil diameter according to the set focal length and F-number in Step 1 is: In the formula, D represents the entrance pupil diameter, f′ represents the set focal length, and F represents the f-number.

7. The design method of a dual-band off-axis common-aperture zoom optical system according to claim 5, characterized in that: In Step 3, the beam distortion in the mid-wave two-stage zoom system formed by the first front fixed component (7), the first variable magnification component (8), the first rear fixed component (9), and the first cold stop component (10) is less than 0.5%; The beam distortion in the long-wave two-stage zoom system formed by the second front fixed component (12), the second variable magnification component (13), the second rear fixed component (14), and the second cold stop component (15) is less than 0.5%.

8. The design method of a dual-band off-axis common-aperture zoom optical system according to claim 5, characterized in that: In Step 4, the structural parameters in the initial structure of the zoom optical system are the aperture types of the lenses in the initial structure of the off-axis three-reflection system, the initial structure of the field lens system, and the initial structure of the two-stage zoom system.

9. The design method of a dual-band off-axis common-aperture zoom optical system according to claim 5, characterized in that: In Steps 1-3, the evaluation function is the modulation transfer function.

10. The design method of a dual-band off-axis common-aperture zoom optical system according to claim 5, characterized in that: Steps 1-4 are all completed in the optical design software.

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