Short-wave-medium-wave infrared dual-band common-aperture athermalization fisheye optical system

Abstract

The invention discloses a short wave-medium wave infrared dual-band common-aperture athermalization fisheye optical system, and relates to the technical field of infrared optical systems. Comprising a medium-wave infrared branch optical system, a short-wave infrared branch optical system and an object plane, wherein the medium-wave infrared branch optical system comprises a front fixing group, a dichroic mirror, a medium-wave aberration correction group and a detector which are sequentially, coaxially and fixedly connected and arranged from the object plane to a focal plane I; the short-wave infrared branch optical system comprises a front fixing group, a dichroic mirror, a short-wave aberration correction group, a cubic dichroic mirror, a focal plane II and a focal plane III which are coaxially and fixedly connected and arranged in sequence from an object plane to the focal plane II; the medium-wave infrared branch optical system and the short-wave infrared branch optical system share the front fixing group; according to the short wave-medium wave two-waveband infrared common-aperture athermalization fisheye optical system, excellent imaging of short wave and medium wave infrared wavebands is achieved by using the well-designed lens set, and meanwhile the system has the advantages of being small, exquisite, compact, athermalization, high in imaging quality and the like.

Description

Technical Field

[0001] The invention relates to the technical field of infrared optical systems, and in particular to a short-wave and medium-wave infrared dual-band common aperture athermalized fisheye optical system. Background Art

[0002] Fisheye optical system is an optical system with a field of view of 180° or more; among them, medium-wave infrared fisheye optical system occupies an important and irreplaceable position in forest fire prevention, public security border defense, intelligent driving, situational awareness, etc., but the single medium-wave infrared band can only be used to perceive the thermal radiation information of the target area. Under complex environmental conditions, it is easily interfered by background radiation and false alarms occur. Different from the medium-wave infrared band, the short-wave infrared band is usually used to detect the reflected radiation of the target or background. Since the latter has a longer wavelength than the visible light band, it is less affected by atmospheric scattering, the working distance can be farther, and it also has better smoke penetration ability and better environmental adaptability. Therefore, the fisheye optical system with short-wave infrared and medium-wave infrared dual bands is combined. The short-wave infrared is used to detect the background and the medium-wave infrared is used to detect the target. More information about the target and the background can be obtained, which can effectively improve the environmental adaptability of the entire imaging system, improve the contrast of the target background imaging, and enhance the system's ability to resist infrared interference and stealth, which puts forward an urgent demand for the design of the corresponding optical system.

[0003] However, a large field of view will inevitably make it difficult to correct the off-axis aberrations of the optical system. Furthermore, in order to ensure the cold aperture efficiency of the entire system, the fisheye optical system adapted to the cooled infrared detector must also be matched with the detector cold aperture to achieve excellent stray light suppression. On the other hand, the large temperature refractive index coefficient of the infrared optical material makes the performance of the infrared optical system extremely susceptible to changes in ambient temperature, resulting in defocusing and reduced imaging quality. The infrared fisheye optical system is required to have an optical athermalization function. Therefore, it is difficult to design a shortwave-mediumwave dual-band infrared common-aperture fisheye optical system with athermalization function.

[0004] There are some existing literature documents that disclose infrared fisheye optical systems. For example, U.S. Patent US5502592 discloses an infrared fisheye optical system with a super-hemispherical field of view. For different bands of mid-wave infrared and long-wave infrared, the field of view angle can reach 270°, but it cannot be applied to the short-wave infrared band and does not have the athermalization function. In addition, U.S. Patents US6989537 B2 and US2009 / 0212219 A1 also provide similar fisheye optical systems, but athermalization is not achieved.

[0005] In 2014, a document entitled "Design of Dual-Band Athermalized Infrared Fisheye Optical System" published in the Chinese journal "Infrared and Laser Engineering" Volume 43, Issue 10 also disclosed an optical system with a full field of view of ±98° and an operating band of 4.4μm~5.4μm and 7.8~8.8μm, achieving optical passive athermalization in a wide temperature range of -40℃ to +60℃; the medium-wave infrared fisheye lens disclosed in Chinese patent CN110161663B uses 5 lenses to achieve a field of view of ±102° and optical passive athermalization, which cannot be applied to the short-wave infrared band. In 2022, a document entitled "Design of Long-wave Infrared Fisheye Staring Optical System" published in the Chinese journal "Infrared and Laser Engineering" Volume 51, Issue 11 disclosed an optical system with a full field of view of ±100° and a working band of 8μm to 12μm; in 2022, a document entitled "Panoramic Fisheye Optical System Based on Free-form Surface Design" published in the Chinese journal "Applied Optics" Volume 43, Issue 3 disclosed an optical system with a full field of view of ±100° and a working band of the visible light band. Both cannot be used in the short-wave and medium-wave infrared bands. The fisheye lens with a full field of view of not less than ±92.5° and used in the visible and short-wave infrared bands disclosed in Chinese patent CN 118068528A and a wide-angle lens with a full field of view of not less than ±80° and used in the short-wave infrared band disclosed in Chinese patent CN 220553030U cannot be used in the medium-wave infrared band. Summary of the invention

[0006] The present invention provides a shortwave-medium-wave infrared dual-band common aperture athermalized fisheye optical system to solve the problems in the background technology.

[0007] To achieve the above-mentioned object, the present invention provides the following technical solutions: a short-wave-medium-wave infrared dual-band common aperture athermalized fisheye optical system, comprising a medium-wave infrared branch optical system and a short-wave infrared branch optical system, wherein the medium-wave infrared branch optical system comprises a front fixing group, a dichroic mirror, a medium-wave aberration correction group and a detector which are coaxially fixedly arranged in sequence from the object plane to the focal plane one; the short-wave infrared branch optical system comprises a front fixing group, a dichroic mirror, a short-wave aberration correction group, a cubic dichroic mirror, a focal plane two and a focal plane three which are coaxially fixedly arranged in sequence from the object plane to the focal plane two;

[0008] The medium-wave infrared branch optical system and the short-wave infrared branch optical system together constitute the short-wave-medium-wave dual-band infrared common aperture athermalized fisheye optical system, the medium-wave infrared branch optical system and the short-wave infrared branch optical system share a front fixed group, and separation between the two bands is achieved through a dichroic mirror;

[0009] The medium-wave aberration correction group is coaxially configured with a second negative lens, a first positive lens, a third negative lens and a second positive lens in sequence along the optical axis from the object plane to the focal plane.

[0010] The detector comprises a detector protection window and a detector cold stop which are arranged in sequence from the object plane to the focal plane in the direction of the optical axis, and the aperture stop of the medium-wave infrared branch optical system coincides with the position of the detector cold stop;

[0011] The short-wave aberration correction group consists of a third positive lens, a fourth negative lens, a first reflecting mirror, a fourth positive lens, a short-wave aperture stop, a fifth positive lens, a fourth negative lens and a sixth positive lens, and has positive focal power.

[0012] Further, the front fixed group is composed of a first negative lens, and the front fixed group is a single lens structure with negative optical power;

[0013] Assume that the focal length of the front fixed group is f400, and the focal length of the wavelength band in the infrared fisheye optical system is fL MWIR , f400 and fL MWIR Requirements:

[0014] |f400 / fL MWIR |<3.6.

[0015] Further, the medium-wave aberration correction group is a four-separated lens group with positive optical power;

[0016] Assuming that the magnification of the medium wave aberration correction group is m200, then m200 satisfies the following conditional formula:

[0017] 0.2≤|m200|≤0.6.

[0018] Furthermore, the cubic dichroic mirror is used to achieve separation between different short-wave infrared bands, or to achieve separation of different energy ratios within the same short-wave infrared band; at this time, the same or different types of short-wave infrared detectors can be configured at focal plane one and focal plane two.

[0019] Furthermore, the shortwave aperture diaphragm is either a fixed aperture diaphragm or a variable aperture diaphragm, which further expands the dynamic range of imaging of the shortwave-medium wave dual-band infrared common aperture athermal fisheye optical system of the present invention.

[0020] Furthermore, the central axes of the front fixing group, the medium-wave aberration correction group, the detector and the aperture stop of the optical system are coaxial.

[0021] Furthermore, it also includes a dichroic mirror arranged between the front fixed group and the medium-wave aberration correction group; the front fixed group is located on the incident light axis of the dichroic mirror, and the medium-wave aberration correction group, the detector and the optical system aperture stop are sequentially located on the transmission light axis of the dichroic mirror.

[0022] Furthermore, the front fixed group is located on the incident light axis of the dichroic mirror, and the short-wave aberration correction group, the cubic dichroic mirror, the second focal plane and the third focal plane are respectively located on the transmission and reflection light axes of the dichroic mirror.

[0023] Further, the normalized thermal differential coefficient of the first negative lens is assumed to be T401;

[0024] T is calculated by the following formula:

[0025]

[0026] T401 should meet the following conditions: T401<3.5×10 -5 ;

[0027] Where n is the refractive index of the lens material, dn / dt is the refractive index / temperature coefficient of the lens material; α g is the expansion coefficient of the lens material.

[0028] Furthermore, the focal lengths of the short-wave aberration correction group are f500, f500 and fL SWIR Requirements:

[0029] 5.3<|f500 / fL SWIR |.

[0030] As described above, the shortwave-mediumwave dual-band infrared common-aperture athermalized fisheye optical system of the present invention can achieve a small size, compact structure, passive athermalization, and shortwave and medium-wave infrared dual-band imaging capability by simultaneously satisfying or satisfying multiple of the above conditions.

[0031] Compared with the prior art, the present invention provides a shortwave-medium-wave infrared dual-band common aperture athermalized fisheye optical system, which has the following beneficial effects:

[0032] The present invention is a short-wave and medium-wave dual-band infrared common aperture athermalized fisheye optical system, which achieves excellent imaging in the short-wave and medium-wave infrared bands by using a carefully designed lens group, and has the advantages of being compact, athermalized and having high imaging quality;

[0033] The system adopts a special optical design. The two optical systems of different bands have the same incident light axis, so that the optical systems maintain a common aperture. The front fixed group is used to correct the aberrations associated with the large field of view, and the aberrations of different bands are corrected by the medium-wave aberration correction group and the short-wave aberration correction group through separation through a color dichroic mirror, thereby achieving dual-band imaging.

[0034] The key technologies in the system include the use of common infrared optical materials and glass materials. By matching the expansion coefficients of lens materials and structural materials, the defocus problem caused by temperature changes is effectively compensated. Users can also use variable aperture diaphragms in the short-wave optical path as needed to expand the dynamic range of imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 A schematic diagram of the lens structure of a short-wave and medium-wave dual-band infrared common aperture athermalized fisheye optical system of the present invention;

[0037] Figure 2 This is a light path diagram of a short-wave and medium-wave dual-band infrared common aperture athermalized fisheye optical system according to a first embodiment of the present invention;

[0038] Figure 3 This is an optical path diagram of Embodiment 2 of a shortwave-mediumwave dual-band infrared common aperture athermalized fisheye optical system of the present invention;

[0039] Figure 4 It is a schematic diagram of MTF evaluation in the medium-wave infrared band of an embodiment of a short-wave and medium-wave dual-band infrared common aperture athermalized fisheye optical system of the present invention;

[0040] Figure 5 It is a schematic diagram of MTF evaluation in the shortwave infrared band of an embodiment of a shortwave-mediumwave dual-band infrared common aperture athermalized fisheye optical system of the present invention.

[0041] In the figure: 100, detector; 101, focal plane 1; 102, detector cold stop; 103, detector protection window; 200, medium-wave aberration correction lens group; 201, second positive lens; 202, third negative lens; 203, first positive lens; 204, second negative lens; 300, dichroic mirror; 400, front fixing group; 401, first negative lens; 500, short-wave aberration correction group; 501, third positive lens; 502, fourth negative lens; 503, first reflecting mirror; 504, fourth positive lens; 505, short-wave aperture stop; 506, fifth positive lens; 507, fourth negative lens; 508, sixth positive lens; 600, cubic dichroic mirror; 700, focal plane 2; 800, focal plane 3. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0043] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0045] See also Figure 1 and Figure 2 As shown, the present invention discloses a short-wave-medium-wave infrared dual-band common aperture athermalized fisheye optical system, comprising a medium-wave infrared branch optical system, a short-wave infrared branch optical system and an object plane, wherein the medium-wave infrared branch optical system comprises a front fixing group 400, a dichroic mirror 300, a medium-wave aberration correction group 200 and a detector 100 which are coaxially fixedly arranged in sequence from the object plane to the focal plane 1 101; the short-wave infrared branch optical system comprises a front fixing group 400, a dichroic mirror 300, a short-wave aberration correction group 500, a cubic dichroic mirror 600, a focal plane 2 700 and a focal plane 3 800 which are coaxially fixedly arranged in sequence from the object plane to the focal plane 2 700;

[0046] like Figure 1 , Figure 2 and Figure 3 As shown, the cubic dichroic mirror 600 is used to achieve separation between different short-wave infrared bands, or to achieve separation of different energy ratios in the same short-wave infrared band; at this time, the same or different types of short-wave infrared detectors can be configured at the focal plane 1 700 and the focal plane 2 800.

[0047] The medium-wave infrared branch optical system and the short-wave infrared branch optical system together constitute the short-wave-medium-wave dual-band infrared common aperture athermalized fisheye optical system. The medium-wave infrared branch optical system and the short-wave infrared branch optical system share a front fixed group 400, and separation between the two bands is achieved through a dichroic mirror 300; the front fixed group 400 is composed of a first negative lens 401, and the front fixed group 400 is a single lens structure with negative optical power;

[0048] The medium wave aberration correction group 200 is a four-separated lens group with positive optical power. The medium wave aberration correction group 200 is coaxially configured with a second negative lens 204, a first positive lens 203, a third negative lens 202 and a second positive lens 201 in sequence along the optical axis from the object plane to the focal plane 101;

[0049] The detector 100 comprises a detector protection window 103 and a detector cold stop 102 which are arranged in sequence from the object plane to the focal plane 101 along the optical axis, and the aperture stop of the medium-wave infrared branch optical system coincides with the position of the detector cold stop 102;

[0050] The short-wave aberration correction group 500 is composed of a third positive lens 501, a fourth negative lens 502, a first reflecting mirror 503, a fourth positive lens 504, a short-wave aperture diaphragm 505, a fifth positive lens 506, a fourth negative lens 507 and a sixth positive lens 508, and has positive optical power; the short-wave aperture diaphragm 505 is either a fixed aperture diaphragm or a variable aperture diaphragm, further expanding the dynamic range of imaging of the short-wave and medium-wave dual-band infrared common aperture athermal fisheye optical system of the present invention.

[0051] Front fixed group 400: a single lens structure, located at the front end of the entire system, with negative optical power, providing basic light collection function.

[0052] Dichroic mirror 300: used to separate incident light into medium-wave infrared and short-wave infrared.

[0053] The medium-wave aberration correction group 200 comprises four separate lenses, and is used to correct the aberration of the medium-wave infrared branch optical system.

[0054] Detector 100: located at the end of the medium-wave infrared imaging path, used for receiving image information.

[0055] Short-wave aberration correction group 500: includes a plurality of lenses and reflectors, and is used to correct the aberration of the short-wave infrared branch optical system.

[0056] Cube dichroic mirror 600: used to separate different bands or energies in the short-wave infrared imaging path.

[0057] Focus plane 2 700 and focus plane 3 800: receive short-wave infrared image information and can be configured with different types of detectors.

[0058] Specifically, the front fixing group 400, the medium-wave aberration correction group 200, the detector 100 and the central axis of the optical system aperture stop are coaxial.

[0059] Specifically, it also includes a dichroic mirror 300 arranged between the front fixed group 400 and the medium-wave aberration correction group 200; the front fixed group 400 is located on the incident light axis of the dichroic mirror 300, and the medium-wave aberration correction group 200, the detector 100 and the optical system aperture stop are sequentially located on the transmission light axis of the dichroic mirror.

[0060] Specifically, the front fixing group 400 is located on the incident optical axis of the dichroic mirror 300 , and the short-wave aberration correction group 500 , the cubic dichroic mirror 600 , the second focal plane 700 and the third focal plane 800 are respectively located on the transmission optical axis and the reflection optical axis of the dichroic mirror 300 .

[0061] Compared with the prior art, the advantages of the present invention are:

[0062] 1. The optical system of the present invention adopts common infrared optical materials and glass materials, can achieve excellent imaging in the short-wave and medium-wave infrared bands, can well correct the aberrations associated with the large field of view, especially can better correct the astigmatism and field curvature in the infrared fisheye optical system, and realizes the co-aperture and athermalization of the dual-band optical system. The optical system is easy to manufacture, has high imaging quality and good stability.

[0063] 2. The central axes of the front fixed group 400, the medium-wave aberration correction group 200, the detector 100, the short-wave aberration correction group 500, the detector 700 and the detector 800 of the optical system of the present invention are coaxial, and the total number of lenses is 11, which can achieve an imaging range of not less than ±92° field of view. The optical system has a compact structure and a small size.

[0064] 3. The shortwave aperture diaphragm of the present invention can be configured with a fixed aperture diaphragm or a variable aperture diaphragm, further expanding the dynamic range of imaging of the shortwave-mediumwave dual-band infrared common aperture athermal fisheye optical system of the present invention.

[0065] 4. The lenses in the optical system of the present invention are all made of common infrared optical materials and glass materials, which have excellent processing characteristics, ensuring the maturity and continuity of the technology. When other infrared optical materials are used, it is only necessary to make corresponding adjustments to the focal length of each lens group under the technical conditions of the present invention to obtain equivalent or better imaging performance.

[0066] 5. A replaceable filter can be provided in the optical system of the present invention. When the optical system needs to work in a specific spectral band, the optical image of the corresponding spectral band can be obtained by simply inserting the filter of the corresponding spectral band.

[0067] 6. The optical system of the present invention has dual-band imaging capability, so that one optical system has detection capabilities of multiple bands, which can effectively realize the miniaturization, lightweight and integration of detection means, and also reduce the difficulty of optical debugging.

[0068] 7. The lens of the present invention adopts a material combination that matches the linear expansion coefficient of the lens barrel material, compensating for the defocus caused by thermal expansion and contraction due to temperature changes in the lens barrel material, and achieving optical passive athermalization within the temperature range of -45°C to +75°C.

[0069] 8. The present invention is applicable to various forest fire prevention, public security border defense, regional monitoring and other purposes.

[0070] 9. The present invention can set a reflector in the medium-wave aberration correction group to reduce the volume of the entire system.

[0071] Working principle: The separation and imaging of infrared light in different bands is achieved through a combination of specific optical elements, while specific materials and optical designs are used to compensate for changes in optical performance caused by temperature changes.

[0072] Working process: light from the object enters the negative lens (first negative lens 401) in the front fixed group 400, and then is divided into two beams of medium-wave infrared and short-wave infrared by the dichroic mirror 300; the medium-wave infrared light passes through the dichroic mirror, passes through the medium-wave aberration correction group 200 and is finally received by the detector 100; and the short-wave infrared light is reflected by the dichroic mirror, passes through the short-wave aberration correction group 500 and finally reaches the focal plane 101.

[0073] The preferred conditions of each lens group in the optical system of the present invention are as follows:

[0074] 1. Front fixed group 400

[0075] The front fixed group 400 is a single lens structure, which is composed of a first negative lens 401 made of chalcogenide material. On the side of the optical system closest to the object plane, the front fixed group 400 with negative focal length and negative refractive power can be configured, which is conducive to the large field of view of the optical system. Assume that the focal length of the front fixed group 400 is f400, and the focal length of the wavelength band in the infrared fisheye optical system is fL MWIR , f400 and fL MWIR Requirements:

[0076] |f400 / fL MWIR |<3.6; (1)

[0077] Conditional expression (1) is an expression for limiting the focal length range of the front fixed group 400. By satisfying conditional expression (1), a large field of view of the optical system can be ensured, and the miniaturization of the optical system can be achieved. If the upper limit of conditional expression (1) is exceeded, the focal length of the front fixed group 400 becomes small, and the beam width accompanying the large field of view cannot be compressed, and the large field of view of the optical system cannot be achieved.

[0078] In addition, assuming that the normalized thermal coefficient of the first negative lens 401 is T401, T401 should satisfy the following condition:

[0079] T401<3.5×10 -5 ; (2)

[0080] The T is calculated by the following formula:

[0081]

[0082] Where n is the refractive index of the lens material, dn / dt is the refractive index / temperature coefficient of the lens material; α g is the expansion coefficient of the lens material.

[0083] Conditional formula (2) is a formula for correcting the thermal difference generated by the front fixed group of the optical system. By satisfying conditional formula (2), the defocus amount of the entire front fixed group in a wide band can be maintained, and the environmental adaptability of the optical system under different use conditions can be guaranteed. If the conditional formula (2) is higher than its upper limit, the normalized thermal difference coefficient of the first negative lens 401 becomes larger, and the environmental defocus amount of the front fixed group becomes larger, so that the heat removal of the optical system becomes difficult, which becomes a problem.

[0084] In this way, the front fixing group 400 can ensure a large field of view of the optical system while maintaining good correction of thermal differences, and can effectively compress the outer diameter of subsequent optical elements to achieve miniaturization of the optical system.

[0085] 2. Medium wave aberration correction group 200

[0086] The medium wave aberration correction group 200 has positive power and is a four-separated lens group. From the object plane to the focal plane 101, the second negative lens 204, the first positive lens 203, the third negative lens 202 and the second positive lens 201 are coaxially arranged in sequence along the optical axis. Assuming that the magnification of the medium wave aberration correction group 200 is m200, then m200 satisfies the following conditional formula:

[0087] 0.2≤|m200|≤0.6; (3)

[0088] Conditional formula (3) is a formula for limiting the magnification range of the medium-wave aberration correction group 200. By satisfying this conditional formula (3), it is possible to ensure that the aberrations associated with the wide field of view are well corrected, especially the astigmatism and field curvature in the medium-wave infrared wide-angle optical system can be better corrected. If the conditional formula (3) is lower than its lower limit, the optical power of the medium-wave aberration correction lens group 200 increases, which is beneficial to the miniaturization of the optical system, but in particular, the correction of astigmatism and field curvature in the optical system becomes difficult, the optical performance deteriorates, and the imaging quality is affected. On the other hand, if the conditional formula (3) exceeds its upper limit, it is beneficial to the aberration correction of the optical system, but the axial length of the aberration correction group 200 will become longer, making it difficult to miniaturize the optical system.

[0089] In this way, the medium-wave aberration correction group 200 can ensure that the astigmatism and field curvature of the optical system are well corrected while ensuring the miniaturization of the optical system.

[0090] 3. Short-wave aberration correction group 500:

[0091] The short-wave aberration correction group 500 has positive power, and is coaxially arranged in sequence along the optical axis from the object plane to the second focal plane 700 and the third focal plane 800, and is composed of a third positive lens 501, a fourth negative lens 502, a first reflecting mirror 503, a fourth positive lens 504, a short-wave aperture stop 505, a fifth positive lens 506, a fourth negative lens 507 and a sixth positive lens 508. Assume that the focal length of the short-wave aberration correction group 500 is f500, the Abbe number of the fourth positive lens 504 for the d-line is vd504, f500, fL SWIR And vd504 meets the conditions:

[0092] 5.3<|f500 / fL SWIR |; (4)

[0093] vd504>60; (5)

[0094] Conditional formula (4) is a formula for limiting the focal length range of the short-wave aberration correction group 500. By satisfying this conditional formula (4), it is possible to ensure that the aberrations associated with the wide field of view are well corrected, especially the astigmatism and field curvature in the short-wave infrared wide-angle optical system can be better corrected. If the conditional formula (4) is below its lower limit, the optical power of the short-wave aberration correction lens group 400 increases, which is beneficial to the miniaturization of the optical system, but in particular, the correction of astigmatism and field curvature in the optical system becomes difficult, the optical performance deteriorates, and the imaging quality is affected.

[0095] The conditional expression (5) is a conditional expression for correcting the chromatic aberration associated with the wide working band in the short-wave infrared band. By forming the fourth positive lens 504 in the short-wave aberration correction group 500 from a low-dispersion material that satisfies the conditional expression (6), the chromatic aberration associated with the wide working band can be well corrected. In addition, in the conditional expression (5), if it is below its lower limit, the chromatic aberration correction in the short-wave aberration correction group 500 becomes difficult, resulting in a complicated optical structure of the lens group.

[0096] In this way, the short-wave aberration correction group 500 can ensure that the astigmatism, field curvature and chromatic aberration of the optical system are well corrected while ensuring the miniaturization of the optical system.

[0097] In addition, the shortwave aperture diaphragm can be configured with a fixed aperture diaphragm or a variable aperture diaphragm, further expanding the dynamic range of imaging of the shortwave-mediumwave dual-band infrared common aperture athermal fisheye optical system of the present invention.

[0098] The optical system of this embodiment has three lens groups in total. The front fixed group 400 is located on the incident light axis of the dichroic mirror 300. The medium-wave aberration correction group 200, the detector 100 and the optical system aperture stop are sequentially located on the transmission light axis of the dichroic mirror 300. The short-wave aberration correction group 500, the cubic dichroic mirror 600, the focal plane 2 700 and the focal plane 3 800 are respectively located on the transmission and reflection light axes of the dichroic mirror 300, forming a complete short-wave and medium-wave dual-band infrared common aperture athermalized fisheye optical system.

[0099] As described above, the shortwave-mediumwave dual-band infrared common aperture athermalized fisheye optical system of this embodiment can achieve a small size, a compact structure, and achieve optical passive athermalization by satisfying the above conditions. By satisfying the above conditions at the same time or satisfying multiple of them, better optical performance can be obtained.

[0100] Embodiment 1:

[0101] Various numerical data related to the optical system of this embodiment are as follows:

[0102] Field of view: ±92°

[0103] Working F / #: 2 (MWIR) and 2 (SWIR);

[0104] Working spectrum range: 3.7~4.8μm and 0.9~1.7μm

[0105] Detector size: φ29.0mm (mid-wave infrared) and φ11.0mm (short-wave infrared)

[0106] Heat removal temperature range: -45℃~+75℃

[0107] Figure 2 Schematic diagram of the lens structure of the optical system of this embodiment.

[0108] The following Tables 1, 2, 3, 4, 5 and 6 give various numerical values ​​related to the optical system involved in this embodiment.

[0109] Table 1 Specific parameters of each lens of the wave branch optical system in this embodiment (unit: mm)

[0110]

[0111] Note: The * surface is aspherical, and the $ surface is diffraction surface.

[0112] The expression of aspheric surface is:

[0113]

[0114] Where: z is the aspheric surface height, c is the aspheric surface curvature, k is the quadratic surface coefficient, r is the radial height of the lens, A2i is the expansion term coefficient; N is the number of terms.

[0115] The expression of the diffraction surface $ is:

[0116]

[0117] The central wavelength of the diffraction surface is 4.2μm, and the diffraction order is +1, where C 1 and C 2 is the diffraction surface coefficient, and r is the radial height of the lens.

[0118] Table 2 Aspheric parameters of the wave branch optical system in this embodiment

[0119]

[0120] Table 3: Parameters of the diffraction surface of the wave branch optical system in this embodiment

[0121]

[0122] Table 4 Specific parameters of each lens of the short-wave branch optical system of this embodiment (unit: mm)

[0123]

[0124] Note: The * surface is aspherical, and the $ surface is diffraction surface.

[0125] Table 5 Aspheric parameters of the short-wave branch optical system of this embodiment

[0126]

[0127] Table 6 Parameters of the optical system of this embodiment

[0128] Serial number condition Parameter Value 1 <![CDATA[|f400 / fL MWIR| ]]> 2.71 2 T401 7.17×10-7 3 |m200| 0.37 4 <![CDATA[|f500 / fL SWIR| ]]> 7.79 5 vd504 63.4

[0129] In this embodiment, the aperture stop of the medium wave branch optical system is placed on the detector cold stop 102, ensuring 100% cold stop efficiency.

[0130] The invention uses a method of bending a key surface and coating an anti-reflection film to enable the optical system to have better cold reflection suppression characteristics under different viewing fields.

[0131] The lens of this embodiment adopts a material combination that matches the linear expansion coefficient of the lens barrel material and an athermalization method for optical passive compensation in the full temperature range of -45°C to +75°C, compensating for defocusing caused by thermal expansion and contraction due to temperature changes in the lens barrel material.

[0132] In this embodiment, the chalcogenide glass and chalcogenide material used can be replaced by other optical materials with similar normalized thermal differential coefficients. In this case, it is only necessary to modify the radius of curvature, thickness, lens spacing, etc. of each lens in the optical structure to obtain optical performance similar to or better than that of the present invention at high and low temperatures.

[0133] The total number of lenses in the optical system of this embodiment is small, and has good tolerance characteristics; the optical materials used in each lens group are all common infrared materials, and have good availability and processability.

[0134] like Figure 4 and Figure 5 The MTF evaluation curves of this embodiment in the medium-wave and short-wave infrared bands are respectively given, from which it can be seen that in the optical system of this embodiment, in each band and in the full field of view, at 30lp / mm, the MTF is not less than 0.4, which can ensure excellent imaging.

[0135] Embodiment 2

[0136] like Figure 3 As shown, the difference from the first embodiment is that it also includes a reflector 205 arranged in the medium-wave aberration correction lens group 200. Accordingly, for the medium-wave aberration correction group 200 and the detector 100, the front fixed group 400 is located on the incident light axis of the splitter 300, and the medium-wave aberration correction group 200 and the detector 100 are located on the transmission light axis of the dichroic mirror 300 in sequence. The reflector 205 changes the transmission direction of the light beam, which can change the outer envelope of the entire optical system, further meeting the application requirements in an environment with strict volume requirements.

[0137] In summary, the short-wave and medium-wave infrared dual-band common aperture athermalized fisheye optical system of the present invention has achieved a small size and compact structure through reasonable lens design, material selection and temperature compensation technology, and can perform dual-band imaging of short-wave and medium-wave infrared bands, and has good imaging quality and environmental adaptability. Each part in the design scheme, such as the front fixed group, the aberration correction group, the cubic dichroic mirror, the detector, etc., is allocated according to specific optical principles and temperature compensation technology, and works together to ensure that the volume of the system is greatly reduced and the optical system is kept stable, thereby achieving the above-mentioned technical effects. It should be noted that the above embodiments are only used to illustrate the technical scheme of the present invention and are not limited. Although the present invention is described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the technical scheme of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical scheme of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system, characterized in that: The invention comprises a medium-wave infrared branch optical system, a short-wave infrared branch optical system and an object plane, wherein the medium-wave infrared branch optical system comprises a front fixing group (400), a color separation mirror (300), a medium-wave aberration correction group (200) and a detector (100) which are coaxially fixedly arranged in sequence from the object plane to the first focal plane (101); the short-wave infrared branch optical system comprises a front fixing group (400), a color separation mirror (300), a short-wave aberration correction group (500), a cubic color separation mirror (600), a second focal plane (700) and a third focal plane (800) which are coaxially fixedly arranged in sequence from the object plane to the second focal plane (700); The medium-wave infrared branch optical system and the short-wave infrared branch optical system share a front fixed group (400), and separation between the two wavebands is achieved through a dichroic mirror (300); The medium-wave aberration correction group (200) is coaxially arranged in sequence along the optical axis direction from the object plane to the focal plane 1 (101) with a second negative lens (204), a first positive lens (203), a third negative lens (202) and a second positive lens (201); The detector (100) comprises a detector protection window (103) and a detector cold stop (102) which are arranged in sequence in the direction of the optical axis from the object plane to the focal plane 1 (101), and the aperture stop of the medium-wave infrared branch optical system coincides with the position of the detector cold stop (102); The short-wave aberration correction group (500) is composed of a third positive lens (501), a fourth negative lens (502), a first reflecting mirror (503), a fourth positive lens (504), a short-wave aperture stop (505), a fifth positive lens (506), a fourth negative lens (507) and a sixth positive lens (508), and has positive optical power.

2. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: The front fixed group (400) is composed of a first negative lens (401), and the front fixed group (400) is a single lens structure with negative optical power; Assume that the focal length of the front fixed group (400) is f400, and the focal length of the wavelength band in the infrared fisheye optical system is fL MWIR , f400 and fL MWIR Requirements: |f400 / fL MWIR |<3.6。 3. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: The medium-wave aberration correction group (200) is a four-separation lens group with positive optical power; Assuming that the magnification of the medium-wave aberration correction group (200) is m200, then m200 satisfies the following conditional expression: 0.2≤|m200|≤0.6。 4. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: The cubic dichroic mirror (600) is used to achieve separation between different short-wave infrared bands, or to achieve separation of different energy ratios within the same short-wave infrared band.

5. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: The short-wave aperture diaphragm (505) is any one of a fixed aperture diaphragm and a variable aperture diaphragm.

6. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: The front fixing group (400), the medium-wave aberration correction group (200), the detector (100) and the central axis of the optical system aperture stop are coaxial.

7. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: It also includes a dichroic mirror (300) arranged between a front fixed group (400) and a medium-wave aberration correction group (200); the front fixed group (400) is located on the incident light axis of the dichroic mirror (300), and the medium-wave aberration correction group (200), the detector (100) and the optical system aperture stop are sequentially located on the transmission light axis of the dichroic mirror.

8. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: The front fixed group (400) is located on the incident light axis of the dichroic mirror (300), and the short-wave aberration correction group (500), the cubic dichroic mirror (600), the second focal plane (700) and the third focal plane (800) are respectively located on the transmission and reflection light axes of the dichroic mirror (300).

9. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: Assume that the normalized thermal differential coefficient of the first negative lens 401 is T401; T is calculated by the following formula: T401 should meet the following conditions: T401<3.5×10 -5 ; Where n is the refractive index of the lens material, dn / dt is the refractive index / temperature coefficient of the lens material; α g is the expansion coefficient of the lens material.

10. The shortwave-medium wave infrared dual-band common aperture athermalized fisheye optical system according to claim 1, characterized in that: The focal length of the short-wave aberration correction group (500) is f500, f500 and fL SWIR Requirements: 5.3<|f500 / fL SWIR |。

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