A dual-band infrared common aperture and common zoom optical system

Abstract

The present invention discloses a dual-band infrared common-aperture co-zoom optical system. The system comprises, in order from the object plane to the image plane, a dual-band front fixed lens group, a dual-band variable magnification lens group, a dual-band compensation lens group, and a beam splitter prism capable of reflecting long-wave infrared and transmitting medium-wave infrared. A medium-wave rear fixed lens group and a long-wave rear fixed lens group are respectively arranged in the transmission light path after the beam splitter prism. Refrigerated medium-wave and long-wave infrared detectors are respectively placed thereafter for final imaging. The system of the present invention is simple in design, uses a small number of lenses, and does not employ diffraction elements. It addresses the problems of existing infrared dual-band zoom optical systems, which are either uncooled or have split apertures, or, although achieving a cooled common aperture, suffer from high system complexity, excessive number of lens elements, or the use of binary diffraction surfaces under wide-band conditions, significantly reducing diffraction efficiency and affecting optical system transmittance.

Description

Technical Field

[0001] The invention belongs to the field of infrared thermal imaging and relates to a dual-band infrared common aperture common zoom optical system. Background Art

[0002] In the field of infrared imaging, as application scenarios continue to expand, the requirements for infrared optical systems are also increasing, expanding from traditional single-band systems to multi-band systems, and from traditional fixed-focus systems to zoom systems. Because different objects have different infrared radiation characteristics in different bands, multi-band detection capabilities can obtain more dimensional spectral characteristics of the target, significantly enhancing the system's detection and recognition capabilities and improving system performance.

[0003] However, existing infrared dual-band zoom optical systems, limited by system complexity, are often designed and assembled separately, and then assembled and fixed together to form a split-aperture infrared dual-band zoom optical system. This type of system is relatively complex, large, and heavy, and there are focal length errors and optical axis aiming errors in the observation area in different bands. To address this problem, some experts and scholars have carried out research on common-aperture infrared dual-band zoom optical systems. However, existing research literature either uses an off-axis reflective optical path type, which requires extremely high assembly and adjustment processes; the few results that use a transmissive optical path type generally introduce multiple binary diffraction elements into the dual-band system. Binary diffraction elements have obvious diffraction efficiency issues in wide-band systems, which can significantly reduce the transmittance of the optical system and affect system performance.

[0004] Among the patent documents currently published in China, visible light / infrared dual-band systems are the main ones, with a small number of medium and long-wave infrared dual-band systems. These systems generally have problems such as a large number of lens pieces, the use of binary diffraction surfaces, which leads to low energy conversion efficiency, and the use of a refractive index system, which requires high assembly and adjustment accuracy.

[0005] In view of the problems of existing infrared dual-band zoom optical systems, which are either uncooled or divided into apertures, or although cooled common aperture is achieved, the system complexity is high, the number of lens pieces is too large, or the use of binary diffraction surfaces under wide-band conditions significantly reduces the diffraction efficiency and affects the transmittance of the optical system, the development of a cooled dual-band infrared common aperture co-zoom optical system with good optical transmittance has become an urgent problem to be solved in the current field of infrared technology.

[0006] For example, the Chinese invention patent with the announcement number CN105372796B discloses a cooled common-aperture medium / long-wave infrared dual-band dual-field-of-view two-speed zoom optical system. The system uses a beam splitter prism to split the light, but it requires 12 and 10 lens pieces in the medium-wave optical path and the long-wave optical path, respectively, which is a large number of lenses; and four binary diffraction elements are used in the common front fixed group, the common compensation group, the medium-wave infrared light rear fixed group, and the long-wave infrared light rear fixed group (the common optical path contains two), which will significantly reduce the diffraction efficiency and have an adverse effect on the optical transmittance of the system.

[0007] For example, the Chinese invention patent with announcement number CN106950684B discloses an integrated infrared dual-band 20X zoom optical system. This system is an uncooled infrared system and cannot obtain the advantages of high sensitivity and high performance levels of cooled infrared systems. In addition, the system uses three binary diffraction elements (one in the common optical path) in the common front fixed group, the medium-wave infrared light rear fixed group, and the long-wave infrared light rear fixed group. This also has the same energy conversion efficiency problem caused by low diffraction efficiency.

[0008] For example, the Chinese invention patent with announcement number CN112180571B discloses a common-aperture infrared dual-band dual-field-of-view optical system. The system uses a stacked two-color infrared detector, which is expensive, rare, has a high application threshold, and its current response performance cannot be compared with that of a single-band infrared detector. In addition, the system uses 12 infrared lens pieces, which will also lead to a decrease in optical transmittance, affecting the system's long-distance detection capability.

[0009] The above analysis demonstrates that existing cooled dual-band infrared co-aperture and co-zoom optical systems face numerous challenges, including the large number of lens elements, diffraction efficiency issues across a wide wavelength range due to the use of diffraction elements, and high system complexity. Addressing these challenges and developing a dual-band infrared co-aperture and co-zoom optical system with excellent optical transmittance compatible with cooled detectors has significant value and potential for application. Summary of the Invention

[0010] The purpose of the present invention is to provide a dual-band infrared common-aperture co-zoom optical system to solve the problems of existing infrared dual-band zoom optical systems, such as uncooled or divided-aperture systems, or systems with high system complexity and excessive number of lens pieces despite achieving cooled common aperture, or the use of binary diffraction surfaces under wide-band conditions, which significantly reduces diffraction efficiency and affects the transmittance of the optical system.

[0011] To achieve the above object, the technical solution of the present invention is:

[0012] A dual-band infrared common-aperture co-zoom optical system is provided, which comprises a dual-band front fixed lens group, a dual-band variable magnification lens group, a dual-band compensation lens group, and a beam splitter prism capable of reflecting long-wave infrared and transmitting medium-wave infrared, in sequence along the optical axis from the object side to the image side. A medium-wave rear fixed lens group is provided on the medium-wave infrared transmission optical path of the beam splitter prism, and a long-wave rear fixed lens group is provided on the long-wave infrared reflection optical path of the beam splitter prism.

[0013] The dual-band front fixed lens group consists of a meniscus-shaped wide-spectrum zinc sulfide lens with negative optical power curved toward the image side and a chalcogenide glass lens with positive optical power curved toward the image side; the dual-band zoom lens group is a meniscus-shaped zinc selenide lens with negative optical power curved toward the object side; the dual-band compensation lens group is a meniscus-shaped germanium lens with positive optical power curved toward the image side;

[0014] A refrigerated medium-wave infrared detector is arranged behind the medium-wave rear fixed lens group, and a refrigerated long-wave infrared detector is arranged behind the long-wave rear fixed lens group.

[0015] The dual-band zoom lens group and the dual-band compensation lens group can be independently moved forward and backward along the optical axis and are movably arranged between the dual-band front fixed lens group and the beam splitter prism.

[0016] The optical power of the dual-band zoom lens group is The optical power of the dual-band compensation lens group is

[0017] The medium-wave rear fixed lens group consists of 4 lenses or less than 4 lenses, and the long-wave rear fixed lens group consists of 3 lenses or less than 3 lenses.

[0018] The fixed lens group after the medium wave has positive optical power, and is composed of a negative optical power meniscus germanium lens bending toward the object side, a positive optical power meniscus sapphire lens bending toward the image side, a negative optical power meniscus wide-spectrum zinc sulfide lens bending toward the object side, and a biconvex positive optical power silicon lens.

[0019] The long-wave rear fixed lens group has positive optical power, and is composed of a meniscus-type germanium lens with positive optical power bending toward the image side, a chalcogenide glass lens with negative optical power bending toward the object side, and a meniscus-type germanium lens with positive optical power bending toward the image side.

[0020] The beam splitter is made of ZnSe material.

[0021] The lens pieces constituting the dual-band front fixed lens group, the dual-band zoom lens group, the dual-band compensation lens group, the medium-wave rear fixed lens group and the long-wave rear fixed lens group are spherical or aspherical lenses without diffraction surfaces.

[0022] The surfaces of the lens pieces constituting the dual-band front fixed lens group, the dual-band zoom lens group, the dual-band compensation lens group, the medium-wave rear fixed lens group and the long-wave rear fixed lens group are all coated with anti-reflection films.

[0023] The advantages of the present invention are: 1. The system is simple in type. Only four infrared lenses are used in the optical path of the common aperture and common zoom part, which realizes that the zoom light of the medium wavelength dual band is converged onto the intermediate image plane; 2. A dual-band magnification lens group and a dual-band compensation lens group that can move independently forward and backward along the optical axis are provided between the dual-band front fixed lens group and the beam splitter prism to obtain the change of the system focal length and field of view, thereby realizing zoom imaging; 3. No diffraction element is used, especially no diffraction element is used in the dual-band common optical path part, thereby avoiding the significant decrease in diffraction efficiency caused by the wide band range, which affects the transmittance of the optical system; 4. Common aperture and common zoom imaging is realized, which avoids the focal length error and optical axis difference of the observation area in different bands. Aiming error, convenient for pixel-level registration of medium-wave and long-wave dual-band images, and improved system performance; 5. In the optical path after the beam splitter prism, the medium-wave rear fixed lens group contains only 4 lenses, and the long-wave rear fixed lens group contains only 3 lenses, which can respectively image the image of the intermediate image plane onto the focal plane of the cooled infrared detector of their respective bands, and achieve 100% cold aperture matching for each; 6. The use of the beam splitter prism avoids the expensive cost and response degradation problems brought by the long-wave dual-band stacked detector in current applications, and can use the performance advantages of the monochromatic detector to improve the performance of the common-aperture dual-band imaging detection system; it is particularly suitable for application scenarios that require common-aperture dual-band high-performance imaging detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the optical path of the present invention at the telephoto end.

[0025] Figure 2 Schematic diagram of the optical path of the present invention at the short focal length.

[0026] Figure 3 This is the medium-wavelength MTF curve of the present invention at the telephoto end @33lp / mm.

[0027] Figure 4 This is the long-wave MTF curve of the present invention at the telephoto end @33lp / mm.

[0028] Figure 5 This is the medium-wave MTF curve of the present invention at the short focal length end @33lp / mm.

[0029] Figure 6 This is the long-wave MTF curve of the present invention at the short focal length @33lp / mm.

[0030] In the figure: 100—dual-band front fixed lens group; 101—broad-spectrum zinc sulfide lens; 102—chalcogenide glass lens; 200—dual-band zoom lens group; 300—dual-band compensation lens group; 400—beam splitter prism; 500—medium-wave rear fixed lens group; 501—germanium lens; 502—sapphire lens; 503—broad-spectrum zinc sulfide lens; 504—silicon lens; 600—long-wave rear fixed lens group; 601—germanium lens; 602—chalcogenide glass lens; 603—germanium lens. DETAILED DESCRIPTION

[0031] To more concisely illustrate this embodiment, some components well known to those skilled in the art but not relevant to the main content of this invention may be omitted from the drawings or descriptions. In addition, for ease of description, some components may be omitted, enlarged, or reduced in size in the drawings, but they do not represent the dimensions or entire structure of the actual product.

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0033] The present invention will be further described below with reference to the accompanying drawings, which are for illustrative purposes only and are not to be construed as limiting the present invention.

[0034] The present invention will now be further described with reference to the embodiments and accompanying drawings:

[0035] The present invention relates to a dual-band infrared common aperture common zoom optical system, such as Figure 1 、 Figure 2 As shown, along the optical axis direction from the object side to the image side, it includes a dual-band front fixed lens group 100, a dual-band zoom lens group 200, a dual-band compensation lens group 300, and a spectroscopic prism 400 that can reflect long-wave infrared and transmit medium-wave infrared. A medium-wave rear fixed lens group 500 is arranged on the transmitted medium-wave infrared light path of the spectroscopic prism 400, and a long-wave rear fixed lens group 600 is arranged on the reflected long-wave infrared light path of the spectroscopic prism 400; a cooled medium-wave infrared detector is arranged behind the medium-wave rear fixed lens group 500, and a cooled long-wave infrared detector is arranged behind the long-wave rear fixed lens group 600 for final imaging.

[0036] The present invention does not use any diffraction elements, thus avoiding a significant drop in diffraction efficiency due to a wide wavelength range, which affects the transmittance of the optical system; it realizes common-aperture and common-zoom imaging, which facilitates pixel-to-pixel registration of medium-wavelength and long-wavelength dual-band images and improves system performance; the system adopts a spectroscopic prism method, which avoids the expensive cost and response degradation problems brought by long-wavelength and long-wavelength dual-band stacked detectors in current applications, and can utilize the performance advantages of monochromatic detectors to improve the performance of the common-aperture dual-band imaging detection system; it is particularly suitable for application scenarios that require common-aperture dual-band high-performance imaging detection.

[0037] An embodiment with a field of view ranging from 6°×5° to 12°×10° is used for illustration. The operating wavelengths are 3.7-4.8μm for medium wave and 7.7-11.0μm for long wave. The infrared system has an F-number of 2 and has the advantages of a wide wavelength band and a large relative aperture. It is equipped with a cooled infrared detector with a 100% cold aperture efficiency. Both the medium wave and long wave detector arrays are 640×512, with a pixel size of 15μm, facilitating subsequent pixel-level registration and image fusion.

[0038] During the entire zooming process, the total optical length of the zoom optical system remains constant, and there is no need to adjust the detector. The dual-band magnification lens group 200 and the dual-band compensation lens group 300 move on the optical axis to obtain changes in the focal length and field of view of the system, thereby realizing zoom imaging. When the focal length of the infrared zoom optical system changes from long focus to short focus, the dual-band magnification lens group 200 moves along the optical axis toward the object side to change the focal length of the optical system, and the dual-band compensation lens group 300 moves along the optical axis toward the object side to compensate for changes in the image plane position during the zooming process.

[0039] The dual-band front fixed lens group 100 is composed of a meniscus-shaped wide-spectrum zinc sulfide lens 101 with negative optical power curved toward the image side and a chalcogenide glass lens 102 with positive optical power curved toward the image side. It can correct aberrations within the dual-band range, expand the field of view, and improve imaging quality.

[0040] Preferably, the dual-band zoom lens assembly 200 uses zinc selenide material to better correct off-axis aberrations within the entire zoom range; the dual-band zoom lens assembly 200 uses a meniscus zinc selenide lens with negative optical power curved toward the object side to change the focal length within the dual-band range.

[0041] Preferably, the dual-band compensation lens assembly 300 is made of germanium. This is because the dispersion characteristics of germanium differ significantly between the mid-wave infrared and long-wave infrared bands. Therefore, using a germanium lens element in the dual-band compensation lens assembly 300 can leverage this difference to better compensate for the aberrations and chromatic aberrations generated during dual-band zooming, maintaining the final image position unchanged. The dual-band compensation lens assembly 300 consists of a positive-power meniscus germanium lens curved toward the image side, used to compensate for image position shift during zooming within the dual-band range.

[0042] Furthermore, the optical power of the dual-band zoom lens assembly 200 is The optical power of the dual-band compensation lens group 300 is

[0043] The beam splitter prism 400 is made of ZnSe material.

[0044] like Figure 2 As shown, the medium-wave rear fixed lens group 500 has positive focal length and is composed of no more than four lens elements. In this embodiment, four lens elements are used, which are composed of a negative-power meniscus germanium lens 501 curved toward the object side, a positive-power meniscus sapphire lens 502 curved toward the image side, a negative-power meniscus wide-spectrum zinc sulfide lens 503 curved toward the object side, and a biconvex positive-power silicon lens 504.

[0045] The long-wave rear fixed lens group 600 has positive focal length and is composed of no more than three lens pieces. This embodiment uses three lens pieces, which are composed of a meniscus-shaped germanium lens 601 with positive focal length curved toward the image side, a chalcogenide glass lens 602 with negative focal length curved toward the object side, and a meniscus-shaped germanium lens 603 with positive focal length curved toward the image side.

[0046] Beam splitter prism 400 is used to reflect long-wave infrared light and transmit medium-wave infrared light, achieving the design goal of the second half of the optical path splitting into different wavelength bands. By placing a medium-wavelength rear fixed lens group 500 and a long-wavelength rear fixed lens group 600 in the optical path after beam splitter prism 400, the primary image formed by the dual-band front fixed lens group 100, the dual-band magnification lens group 200, and the dual-band compensation lens group 300 is re-imaged onto the focal plane of a cooled medium-wave infrared detector located behind the medium-wavelength rear fixed lens group 500 and the focal plane of a cooled long-wave infrared detector located behind the long-wavelength rear fixed lens group 600. This eliminates residual aberrations in the preceding lens groups while achieving 100% cold stop matching across the dual-band range, improving system performance.

[0047] All lens sheets only contain spherical and aspherical surfaces, and do not use any diffraction surfaces. In particular, no diffraction elements are used in the dual-band common optical path part, avoiding the problem of significant decrease in diffraction efficiency caused by the use of diffraction elements in a wide band range.

[0048] Furthermore, in order to improve energy utilization efficiency, the present invention coats the front and back surfaces of all lenses with high-quality anti-reflection films to improve system response sensitivity and detection distance.

[0049] For a more detailed explanation, the structural parameters of an embodiment are given below: Table 1 shows the structural parameters of the common optical path portion (lens curvature radius, thickness, spacing, material); Table 2 shows the structural parameters of the medium-wave rear fixed lens group (lens curvature radius, thickness, spacing, material); Table 3 shows the structural parameters of the long-wave rear fixed lens group (lens curvature radius, thickness, spacing, material).

[0050] Table 1 Structural parameters of the common optical path part

[0051]

[0052] Table 2 Structural parameters of the fixed lens group after the medium wave

[0053]

[0054] Table 3 Structural parameters of the long-wavelength rear fixed lens group

[0055]

[0056] from Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 It can be seen that under the conditions of different wavelengths of medium wave and long wave and different focal lengths of long focus and short focus, the MTF curve of the present invention at a spatial frequency of 33lp / mm is close to the diffraction limit, and has good imaging quality, proving that the zoom image quality of the present invention in the dual-band range meets the usage requirements.

[0057] Technical features not described in the present invention can be implemented by existing technologies and will not be described in detail here. The above description is only a preferred embodiment of the present invention and does not limit the present invention. The present invention is not limited to the above example. Changes, modifications, additions, or substitutions made by a person skilled in the art within the scope of the present invention, such as replacing lens materials or increasing or decreasing the number of lenses in the same lens set, should also fall within the scope of protection of the present invention.

Claims

1. A dual-band infrared common aperture co-zoom optical system, comprising: a dual-band front fixed lens group (100), a dual-band magnification lens group (200), a dual-band compensation lens group (300), and a beam splitter prism (400) capable of reflecting long-wave infrared and transmitting medium-wave infrared, a medium-wave rear fixed lens group (500) being arranged on the medium-wave infrared transmission optical path of the beam splitter prism (400), and a long-wave rear fixed lens group (600) being arranged on the long-wave infrared reflection optical path of the beam splitter prism (400); Its characteristics are: The dual-band front fixed lens group (100) is composed of a meniscus-shaped wide-spectrum zinc sulfide lens (101) with negative optical power curved toward the image side and a chalcogenide glass lens (102) with positive optical power curved toward the image side; the dual-band variable magnification lens group (200) is a meniscus-shaped zinc selenide lens with negative optical power curved toward the object side; and the dual-band compensation lens group (300) is a meniscus-shaped germanium lens with positive optical power curved toward the image side. A refrigerated medium-wave infrared detector is arranged behind the medium-wave rear fixed lens group (500), and a refrigerated long-wave infrared detector is arranged behind the long-wave rear fixed lens group (600).

2. The dual-band infrared common-aperture common-zoom optical system according to claim 1, characterized in that: The dual-band variable magnification lens group (200) and the dual-band compensation lens group (300) are movably arranged between the dual-band front fixed lens group (100) and the beam splitting prism (400) so as to be relatively independently movable forward and backward along the optical axis.

3. The dual-band infrared common-aperture common-zoom optical system according to claim 1, characterized in that: The optical focal length of the dual-band variable magnification lens group (200) is -0.004<φ<-0.002, and the optical focal length of the dual-band compensation lens group (300) is 0.015<φ<0.

025.

4. The dual-band infrared common-aperture common-zoom optical system according to claim 1, characterized in that: The medium-wave rear fixed lens group (500) is composed of four lens pieces or less than four lens pieces, and the long-wave rear fixed lens group (600) is composed of three lens pieces or less than three lens pieces.

5. The dual-band infrared common-aperture common-zoom optical system according to claim 4, characterized in that: The medium-wave rear fixed lens group (500) has positive optical power and is composed of a negative optical power meniscus germanium lens (501) bent toward the object side, a positive optical power meniscus sapphire lens (502) bent toward the image side, a negative optical power meniscus wide-spectrum zinc sulfide lens (503) bent toward the object side, and a biconvex positive optical power silicon lens (504).

6. The dual-band infrared common-aperture common-zoom optical system according to claim 4, characterized in that: The long-wave rear fixed lens group (600) has positive focal power and is composed of a meniscus-shaped germanium lens (601) with positive focal power bent toward the image side, a chalcogenide glass lens (602) with negative focal power bent toward the object side, and a meniscus-shaped germanium lens (603) with positive focal power bent toward the image side.

7. The dual-band infrared common-aperture common-zoom optical system according to claim 1, characterized in that: The beam splitter prism (400) is made of ZnSe material.

8. The dual-band infrared common-aperture common-zoom optical system according to any one of claims 1 to 6, characterized in that: The lens pieces constituting the dual-band front fixed lens group (100), the dual-band variable magnification lens group (200), the dual-band compensation lens group (300), the medium-wave rear fixed lens group (500) and the long-wave rear fixed lens group (600) are spherical or aspherical lenses without a diffraction surface.

9. The dual-band infrared common-aperture common-zoom optical system according to any one of claims 1 to 6, characterized in that: The surfaces of the lens pieces constituting the dual-band front fixed lens group (100), the dual-band variable magnification lens group (200), the dual-band compensation lens group (300), the medium-wave rear fixed lens group (500) and the long-wave rear fixed lens group (600) are all coated with anti-reflection films.

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