Refrigeration type infrared medium-long wave optical system

Abstract

The invention provides a refrigeration type infrared medium-long wave optical system. The optical system comprises a first positive-focal-power biconvex lens, a negative-focal-power plano-concave lens, a negative-focal-power meniscus lens, a second positive-focal-power biconvex lens, a positive-focal-power meniscus lens, a negative-focal-power biconcave lens and a third positive-focal-power biconvex lens which are sequentially arranged from the object side to the image side of an optical axis. The optical system provided by the invention can well correct chromatic aberration in two wave band ranges of infrared medium wave and long wave, realizes correction of a secondary spectrum, and has excellent image quality in different working environments; the lens is simple in surface type and free of a diffraction surface, the lens is made of common processing materials such as germanium, the processing difficulty is reduced, and the processing cost is saved; and suitable medium-wave and long-wave image plane distortion directions are consistent, the phase difference is small, and good image plane consistency is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of optical systems, and in particular to a refrigerated infrared medium- and long-wave optical system. Background Art

[0002] Infrared imaging technology has been widely used in military reconnaissance, security monitoring, industrial detection and other fields due to its advantages of passive detection, strong resistance to electromagnetic interference, and all-weather working ability. With the complexity of application scenarios, the limitations of single-band infrared systems have gradually emerged: medium-wave infrared (MWIR) performs well in high-temperature target detection and humid environments, while long-wave infrared (LWIR) has more advantages in normal temperature / low temperature object contour imaging and stray radiation suppression. In order to adapt to the needs of multiple environments, medium- and long-wave dual-band composite detection systems have become a research hotspot. By fusing dual-band information, they can significantly improve detection accuracy and reliability in complex environments.

[0003] At present, the infrared dual-band imaging system mainly adopts three structures: split aperture type, common aperture type and common optical path type. The common optical path structure shares the same system and obtains the same detection image. The system is smaller and easier to achieve lightweight and miniaturization. However, its wide-band characteristics bring serious chromatic aberration problems. Therefore, the difficulty in designing the system is to correct the wide-band chromatic aberration and other monochromatic aberrations.

[0004] For the transmission common optical path dual-band infrared system, the system chromatic aberration affects the imaging quality of the system. The same structure has different material combinations and the system image quality also changes greatly. Although there are relatively few materials to choose from for infrared compared to the types of materials for visible light, there are many possibilities for which materials to choose for a system and how to combine them. Especially for the dual-band system, it is necessary to meet the requirements of simultaneous achromatic aberration in medium and long waves. In traditional designs, the fuzzy results of material combinations obtained through achromatic aberration formulas or design experience cannot obtain the best combination for achromatic aberration, and need to rely on subsequent optimization processes for adjustment; and often due to poor matching of material dispersion characteristics or unreasonable structural layout, the image plane consistency is difficult to meet the needs of high-precision detection. Summary of the invention

[0005] The present invention provides a refrigerated infrared medium- and long-wave optical system, which solves the problem of how to efficiently correct chromatic aberration in medium- and long-wave dual bands and meet the image surface consistency.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions: A refrigerated infrared medium and long wave optical system is provided, comprising: A first positive power biconvex lens, a negative power plano-concave lens, a negative power meniscus lens, a second positive power biconvex lens, a positive power meniscus lens, a negative power biconcave lens and a third positive power biconvex lens are arranged in sequence from the object side to the image side of the optical axis.

[0007] Further, the material of the first positive power biconvex lens is zinc selenide; The material of the negative focal power plano-concave lens is zinc sulfide; The material of the negative focal meniscus lens is germanium single crystal; The material of the second positive power biconvex lens is germanium single crystal; The material of the positive power meniscus lens is germanium single crystal; The material of the negative power biconcave lens is a chalcogenide material; The third positive power biconvex lens is made of germanium single crystal.

[0008] Furthermore, the refrigerated infrared medium and long wave optical system further includes an aperture and an image plane; The first positive power biconvex lens, the negative power plano-concave lens, the negative power meniscus lens, the second positive power biconvex lens, the positive power meniscus lens, the negative power biconcave lens, the third positive power biconvex lens, the aperture and the image plane are arranged in sequence from the object side to the image side of the optical axis.

[0009] Furthermore, the lens surfaces used in the refrigerated infrared medium and long wave optical system are spherical and aspherical.

[0010] Further, the front and rear surfaces of the first positive power biconvex lens are both spherical surfaces; The front surfaces of the negative power plano-concave lens, the negative power meniscus lens, and the third positive power biconvex lens are spherical surfaces; The rear surfaces of the second positive power biconvex lens, the positive power meniscus lens, and the negative power biconcave lens are spherical surfaces.

[0011] Further, the rear surfaces of the negative power meniscus lens and the third positive power biconvex lens are even-order aspherical surfaces; The front surfaces of the second positive power biconvex lens, the positive power meniscus lens, and the negative power biconcave lens are even-order aspherical surfaces.

[0012] Furthermore, the surface shape of the aspheric surface of the refrigerated infrared medium and long wave optical system satisfies the following equation: Among them, Z represents the distance of the surface from the vertex of the surface in the direction of the optical axis, c represents the curvature of the surface vertex, k represents the quadratic surface coefficient, rrepresents the distance from the optical axis to the surface, They represent the fourth-order, sixth-order, eighth-order, and tenth-order surface coefficients respectively.

[0013] Furthermore, the air gap between the first positive power biconvex lens and the negative power plano-concave lens is 6.54 mm, the air gap between the negative power plano-concave lens and the negative power meniscus lens is 152.96 mm, the air gap between the negative power meniscus lens and the second positive power biconvex lens is 75 mm, the air gap between the second positive power biconvex lens and the positive power meniscus lens is 180 mm, the air gap between the positive power meniscus lens and the negative power biconcave lens is 10.57 mm, and the air gap between the negative power biconcave lens and the third positive power biconvex lens is 12.54 mm.

[0014] Furthermore, the focal length of the optical system is 180 mm, the system F number is 1.63, the field of view angle is ±2.93°, the total length of the optical system is 589 mm, the working bands of the optical system are 3.7um to 4.8um and 7.5um to 9.5um, and the detector pixel size is 30um.

[0015] The refrigerated infrared medium and long wave optical system of the present invention has the following advantages: The optical system can well correct the chromatic aberration within the infrared medium wave and long wave bands, and realizes the correction of the secondary spectrum, and has excellent image quality at different working temperatures; the lens surface is simple, without diffraction surface, and the lens material is commonly used processing materials such as germanium, which reduces the processing difficulty and saves processing costs; the medium wave and long wave image distortion directions are consistent, and the phase difference is small, with good image consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of an optical path structure provided in an embodiment of the present application; Figure 2 A schematic diagram of a medium wave optical path modulation transfer function MTF provided in an embodiment of the present application; Figure 3 A schematic diagram of a modulation transfer function (MTF) of a long-wave optical path provided in an embodiment of the present application; Figure 4 Field curvature and distortion of a medium wave optical system provided in an embodiment of the present application; Figure 5 Field curvature and distortion of a long-wave optical system provided in an embodiment of the present application; Figure 6 A schematic diagram of chromatic aberration of a medium wave optical system provided in an embodiment of the present application; Figure 7 A schematic diagram of chromatic aberration of a long-wave optical system provided in an embodiment of the present application.

[0017] Reference numerals: Positive power biconvex lens A; negative power plano-concave lens B; negative power meniscus lens C; positive power biconvex lens D; positive power meniscus lens E; negative power biconcave lens F; and positive power biconvex lens G; aperture 1; image plane 2. DETAILED DESCRIPTION

[0018] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose, the technical solutions in the embodiments of the present application are clearly described. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present application.

[0019] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the terms used in this way are interchangeable where appropriate, so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0020] The description of the method flow in the specification of the present application and the steps of the flowchart in the drawings of the present specification do not have to be strictly executed according to the step numbers, and the method steps can be executed in a different order. Moreover, some steps can be omitted, multiple steps can be combined into one step, and / or one step can be decomposed into multiple steps.

[0021] The following is a detailed description of the refrigerated infrared medium and long wave optical system provided in the embodiments of the present application in conjunction with the accompanying drawings and preferred embodiments.

[0022] Related technologies: The split-aperture structure is designed for medium-wave / long-wave infrared separately. The detected target information is imaged onto two detectors through two systems. The two systems do not interfere with each other. The system design is relatively simple, but the system occupies a large volume and has a relatively high cost.

[0023] The common aperture structure generally shares a system objective lens, which is then split by a dichroic mirror and enters the medium-wave / long-wave system to be imaged on the detector. For the transmission branch, the dichroic mirror will introduce aberrations such as spherical aberration and astigmatism, which increases the difficulty of aberration correction. At the same time, the acquired imaging scene cannot be completely consistent.

[0024] The common optical path structure is to share the same system, image the detection target onto the dual-color detector, and obtain the same detection image. The system is small in size and easier to achieve lightweight and miniaturization. However, the common optical path system spans a wide band and the system chromatic aberration is large. Therefore, the design difficulty of the common aperture infrared dual-band optical system is to correct the chromatic aberration of the wide band and other monochromatic aberrations. In addition, the dual-band confocal plane system simultaneously images the medium wave and long wave onto the dual-color detector, so the consistency of the medium wave and long wave image planes in the system is required to be high.

[0025] In order to solve the above technical problems, this application uses the wide-band achromatic theory at the beginning of the design, combined with matrix optics to calculate the minimum theoretical chromatic aberration value that can be achieved by different combinations of infrared materials, and based on this, the types of glass materials of the system are determined to be ZNSE, ZNS, germanium and sulfur-based materials. In addition, the consistency of the medium-wave and long-wave image planes in the system is required to be high, and a reasonable structural layout is determined on the basis of ensuring better correction of the system chromatic aberration. For a cooled infrared system, in order to meet 100% cold aperture efficiency, it is necessary to ensure that the exit pupil of the optical system matches the cold aperture of the detector. The primary imaging system will cause the radial aperture of the front-end lens of the system to be too large, and the volume and cost of the system will increase. This embodiment adopts a secondary imaging structure, which can reduce the radial aperture of each lens of the system, reduce the weight of the lens, reduce the volume of the lens, and reduce the cost. On the basis of the secondary imaging structure, the lens layout is adjusted to make the dual-band distortion directions consistent, and the difference does not exceed three thousandths, which better ensures the consistency of the image plane. Based on the above technical route, a cooled infrared medium and long-wave optical system is provided, please refer to Figure 1 .like Figure 1 As shown, the refrigerated infrared medium and long wave optical system of the embodiment of the present application includes: A positive power biconvex lens A, a negative power plano-concave lens B, a negative power meniscus lens C, a positive power biconvex lens D, a positive power meniscus lens E, a negative power biconcave lens F and a positive power biconvex lens G are arranged in sequence from the object side to the image side of the optical axis.

[0026] The material of the positive power biconvex lens A is zinc selenide; The material of the negative focal power plano-concave lens B is zinc sulfide; The material of the negative focal power meniscus lens C is germanium single crystal; The material of the positive power biconvex lens D is germanium single crystal; The material of the positive power meniscus lens E is germanium single crystal; The material of the negative power biconcave lens F is a chalcogenide material; The positive power biconvex lens G is made of germanium single crystal.

[0027] Furthermore, the lenses used in the refrigerated infrared medium and long wave optical system are all made of domestic optical materials.

[0028] Furthermore, the refrigerated infrared medium and long wave optical system also includes an aperture 1 and an image plane 2; the positive focal power biconvex lens A, the negative focal power plano-concave lens B, the negative focal power meniscus lens C, the positive focal power biconvex lens D, the positive focal power meniscus lens E, the negative focal power biconcave lens F, the positive focal power biconvex lens G, the aperture 1 and the image plane 2 are arranged in sequence from the object side to the image side of the optical axis.

[0029] In some possible embodiments, in order to improve image quality, the refrigerated infrared medium and long wave optical system introduces an aspherical surface, and the lens surfaces used in the refrigerated infrared medium and long wave optical system are spherical and aspherical.

[0030] Furthermore, the front and rear surfaces of the positive power biconvex lens A are both spherical surfaces; The front surfaces of the negative power plano-concave lens B, the negative power meniscus lens C, and the positive power biconvex lens G are spherical surfaces; The rear surfaces of the positive power biconvex lens D, the positive power meniscus lens E, and the negative power biconcave lens F are spherical surfaces.

[0031] Furthermore, the rear surfaces of the negative power meniscus lens C and the positive power biconvex lens G are even-order aspherical surfaces; The front surfaces of the positive power biconvex lens D, the positive power meniscus lens E, and the negative power biconcave lens F are even-order aspherical surfaces.

[0032] Furthermore, the surface shapes of the aspheric surfaces of the refrigerated infrared medium and long wave optical systems all satisfy the following equations: Among them, Z represents the distance of the surface from the vertex of the surface in the direction of the optical axis, c represents the curvature of the surface vertex, k represents the quadratic surface coefficient, r represents the distance from the optical axis to the surface, They represent the fourth-order, sixth-order, eighth-order, and tenth-order surface coefficients respectively.

[0033] Furthermore, detailed parameters of the technical solution are obtained, namely, the air spacing between the positive power biconvex lens A and the negative power plano-concave lens B is 6.54 mm, the air spacing between the negative power plano-concave lens B and the negative power meniscus lens C is 152.96 mm, the air spacing between the negative power meniscus lens C and the positive power biconvex lens D is 75 mm, the air spacing between the positive power biconvex lens D and the positive power meniscus lens E is 180 mm, the air spacing between the positive power meniscus lens E and the negative power biconcave lens F is 10.57 mm, and the air spacing between the negative power plano-concave lens F and the positive power biconvex lens G is 12.54 mm.

[0034] Finally, based on the above technical solution, the focal length of the cooled infrared medium and long wave system is 180mm, the system F number is 1.63, the field of view angle is ±2.93°, the total length of the optical system is 589mm, the working band of the optical system is 3.7um~4.8um and 7.5um~9.5um, and the detector pixel size is 30um.

[0035] Exemplarily, specific parameters of the optical element are shown in Table 1. Exemplarily, the parameters of the aspheric surface of each lens are shown in Table 2. The embodiments of the present application have the following advantages: 1. The optical system of the present invention has a wide band, covering from medium wave to long wave; 2. The optical system of the present invention can realize simultaneous imaging of medium and long waves; 3. The optical system of the present invention can better correct the chromatic aberration within the infrared medium wave and long wave bands, and realizes the correction of the secondary spectrum, and has excellent image quality under different working environments; 4. The present invention has a small number of detection optical path lenses, a compact system structure, and is easy to install and adjust; 5. The lens of the present invention has a simple surface shape and no diffraction surface. The lens material is commonly used processing materials such as germanium, which reduces the processing difficulty and saves processing costs; 6. The optical system of the present invention has good imaging quality and high resolution; 8. The optical system of the present invention performs secondary imaging and compresses the system aperture; 7. The present invention is applicable to medium-wave and long-wave image planes with consistent distortion directions and small phase difference, and has good image plane consistency.

[0036] The embodiment of the present application also provides a refrigerated medium-wave / long-wave dual-color infrared detector, including the refrigerated infrared medium- and long-wave optical system described in the above embodiment.

[0037] See also Figure 2-7 , the following experimental data is provided to further illustrate the effect of the refrigerated infrared medium and long wave optical system of the embodiment of the present application.

[0038] Figure 2 The diagram shows the modulation transfer function (MTF) of the medium wave optical path. The system pixel size is 30μm×30μm, and the cutoff frequency of the system is 17p / mm. Figure 2 The black dashed line in the middle is the diffraction limit of the system, and the other straight lines of different colors represent the variation of the modulation transfer function MTF of different fields of view with frequency. Figure 2 It can be seen that at the cutoff frequency, the MTF value of the medium wave system is greater than 0.7, close to the diffraction limit, the imaging quality is good, and meets the design requirements.

[0039] Figure 3 The diagram shows the modulation transfer function (MTF) of the long-wave optical path. The system pixel size is 30μm×30μm, and the cutoff frequency of the system is 17p / mm. Figure 3 The black dashed line in the middle is the diffraction limit of the system, and the other straight lines of different colors represent the variation of the modulation transfer function MTF of different fields of view with frequency. Figure 3 It can be seen that at the cutoff frequency, the MTF value of the long-wave system is greater than 0.5, close to the diffraction limit, and the imaging quality is good, meeting the design requirements.

[0040] Figure 4 The field curvature and distortion of the medium wave optical system are shown; the left side is the field curvature of the medium wave system, and the right side is the distortion of the medium wave system. It can be seen from the figure that the maximum field curvature of the whole field of view of the medium wave in the system is <0.2, and the maximum distortion of the whole field of view of the medium wave in the system is <2%. The imaging quality of the system is good.

[0041] Figure 5 The field curvature and distortion of the long-wave optical system are shown; the left side is the field curvature of the long-wave system, and the right side is the distortion of the long-wave system. It can be seen from the figure that the maximum field curvature of the system's long-wave full field of view is <0.2, and the maximum distortion of the system's long-wave full field of view is <1%. The imaging quality of the system is good.

[0042] Figure 6 The diagram shows the chromatic aberration of the medium wave optical system. The red curve in the figure shows the curve of the ideal image point of the medium wave optical system changing with the wavelength, and the green curve shows the curve of the actual image point of the medium wave optical system changing with the wavelength. The difference between the two is small. Figures 2 to 5 , which shows that the system chromatic aberration has been well corrected while ensuring the system imaging quality.

[0043] Figure 7 The diagram shows the chromatic aberration of the long-wave optical system. The red curve in the figure shows the curve of the ideal image point of the long-wave optical system changing with the wavelength, and the green curve shows the curve of the actual image point of the long-wave optical system changing with the wavelength. The difference between the two is small. Figures 2 to 5 , which shows that the system chromatic aberration has been well corrected while ensuring the system imaging quality.

[0044] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0045] It can be understood that the embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific embodiments, which are merely illustrative and not restrictive, and those skilled in the art are aware that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, those of ordinary skill in the art can modify these features and embodiments to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention under the inspiration or teaching of the present application. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application belong to the scope protected by the present invention.

Claims

1. A refrigerated infrared medium and long wave optical system, characterized in that: include: A first positive power biconvex lens, a negative power plano-concave lens, a negative power meniscus lens, a second positive power biconvex lens, a positive power meniscus lens, a negative power biconcave lens and a third positive power biconvex lens are arranged in sequence from the object side to the image side of the optical axis.

2. The refrigerated infrared medium and long wave optical system according to claim 1, characterized in that: The material of the first positive power biconvex lens is zinc selenide; The material of the negative focal power plano-concave lens is zinc sulfide; The material of the negative focal meniscus lens is germanium single crystal; The material of the second positive power biconvex lens is germanium single crystal; The material of the positive power meniscus lens is germanium single crystal; The material of the negative power biconcave lens is a chalcogenide material; The third positive power biconvex lens is made of germanium single crystal.

3. The refrigerated infrared medium and long wave optical system according to any one of claims 1 to 2, characterized in that: The refrigerated infrared medium and long wave optical system also includes an aperture and an image plane; The first positive power biconvex lens, the negative power plano-concave lens, the negative power meniscus lens, the second positive power biconvex lens, the positive power meniscus lens, the negative power biconcave lens, the third positive power biconvex lens, the aperture and the image plane are arranged in sequence from the object side to the image side of the optical axis.

4. The refrigerated infrared medium and long wave optical system according to any one of claims 1 to 2, characterized in that: The lens surfaces used in the refrigeration type infrared medium and long wave optical system are spherical and aspherical.

5. The refrigerated infrared medium and long wave optical system according to claim 4, characterized in that: The front and rear surfaces of the first positive power biconvex lens are both spherical surfaces; The front surfaces of the negative power plano-concave lens, the negative power meniscus lens, and the third positive power biconvex lens are spherical surfaces; The rear surfaces of the second positive power biconvex lens, the positive power meniscus lens, and the negative power biconcave lens are spherical surfaces.

6. The refrigerated infrared medium and long wave optical system according to claim 4, characterized in that: The rear surfaces of the negative power meniscus lens and the third positive power biconvex lens are even-order aspherical surfaces; The front surfaces of the positive power biconvex lens, the positive power meniscus lens and the negative power biconcave lens are even-order aspherical surfaces.

7. The refrigerated infrared medium and long wave optical system according to claim 6, characterized in that: The surface shapes of the aspherical surfaces of the refrigerated infrared medium and long wave optical system all satisfy the following equations: Among them, Z represents the distance of the surface from the vertex of the surface in the direction of the optical axis, c represents the curvature of the surface vertex, k represents the quadratic surface coefficient, r represents the distance from the optical axis to the surface, They represent the fourth-order, sixth-order, eighth-order, and tenth-order surface coefficients respectively.

8. The refrigerated infrared medium and long wave optical system according to claim 7, characterized in that: The air gap between the first positive power biconvex lens and the negative power plano-concave lens is 6.54 mm, the air gap between the negative power plano-concave lens and the negative power meniscus lens is 152.96 mm, the air gap between the negative power meniscus lens and the second positive power biconvex lens is 75 mm, the air gap between the second positive power biconvex lens and the positive power meniscus lens is 180 mm, the air gap between the positive power meniscus lens and the negative power biconcave lens is 10.57 mm, and the air gap between the negative power biconcave lens and the third positive power biconvex lens is 12.54 mm.

9. The refrigerated infrared medium and long wave optical system according to claim 8, characterized in that: The focal length of the optical system is 180mm, the system F number is 1.63, the field of view angle is ±2.93°, the total length of the optical system is 589mm, the working band of the optical system is 3.7um~4.8um and 7.5um~9.5um, and the detector pixel size is 30um.

Images