Wide-band long-wave cooled infrared 20x refractive-diffractive hybrid continuous zoom optical system

Abstract

A wide-band, long-wavelength, cooled infrared 20x refractive-diffractive hybrid continuous zoom optical system belongs to the field of optical system technology. To address the narrow operating band and large F-number issues of existing technologies, the system comprises a front fixed group, arranged in sequence from object to image, comprising a single-crystal germanium meniscus positive lens with a convex surface facing the object; a zoom group, comprising a single-crystal germanium negative lens with a convex surface facing the object, a chalcogenide glass positive lens with a convex surface facing the image, and a biconcave chalcogenide glass negative lens; a compensation group, comprising a single-crystal germanium biconvex positive lens; a rear fixed group, comprising a single-crystal germanium meniscus negative lens with a convex surface facing the image; a secondary imaging group, comprising a single-crystal germanium meniscus negative lens with a convex surface facing the image, a single-crystal germanium meniscus positive lens with a convex surface facing the object, and a single-crystal germanium meniscus positive lens; and a detector. The system achieves a 20x zoom ratio, operates in the 6μm to 13μm wavelength range, and has an F-number of 2.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical systems, and in particular relates to a wide-band long-wave refrigerated infrared 20x refractive-diffractive hybrid continuous zoom optical system. Background Art

[0002] With the rapid development of modern optical technology, infrared technology has gradually matured and has been widely used in national security and social life. Generally speaking, long-focal-length optical systems have higher spatial resolution but a narrower field of view, while short-focal-length optical systems have lower spatial resolution but a wider field of view. During the use of optical systems, a wide field of view is required for target search and aiming with high spatial resolution. Therefore, the optical system must frequently switch between different focal lengths. This has led to the emergence of continuous-zoom infrared optical systems, which select the appropriate focal length for different usage scenarios to achieve optimal performance. During operation, the detector of a cooled zoom optical system can reduce its own temperature, resulting in higher sensitivity, higher accuracy, smaller errors, and a wider detection temperature range when detecting other objects. Existing long-wave infrared zoom optical systems have a narrow applicable wavelength range and magnification ratio, resulting in weak detection capabilities for distant targets. Therefore, it is necessary to overcome the limitations of existing technologies and design a cooled long-wave infrared continuous-zoom optical system with a large magnification ratio, a small f-number, and a wide wavelength range.

[0003] See the paper "Design of a 20x Long-Wave Infrared Continuous Zoom Optical System" published by Chen Lüji et al. in Infrared Technology. This system uses mechanical compensation to maintain a constant relative aperture during zooming. By folding the optical path with a reflector and compressing the optical path, it achieves 20x zoom using six lenses. It is compatible with a 384×288@25μm cooled long-wavelength detector. However, the operating band is relatively narrow, at 8-9μm, and the F-number is relatively high, at 3. The above system has an excessively narrow band and a high F-number. Summary of the Invention

[0004] To address the narrow operating band and high F-number issues of existing technologies, this invention provides a wide-band, long-wavelength, cooled infrared 20x hybrid refractive-diffractive continuous zoom optical system. This system operates over a wide wavelength range of 6μm to 13μm, offers a 20x zoom ratio with a focal length range of 10mm to 200mm, and maintains an F-number of 2 throughout the zoom process.

[0005] The solution to the technical problem of the present invention is:

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

[0007] A wide-band, long-wavelength, cooled infrared 20x refractive-diffractive hybrid continuous zoom optical system comprising a front fixed group with positive optical power, a zoom group with negative optical power, a compensation group with positive optical power, a rear fixed group with negative optical power, a secondary imaging group with positive optical power, and a detector, arranged in sequence from the object side to the image side;

[0008] The front fixed group includes a meniscus-shaped germanium single crystal positive lens L1 with its convex surface facing the object, and its front surface S1 and rear surface S2 are both spherical;

[0009] The zoom group consists of a single-crystal germanium negative lens L2 with a convex surface facing the object, and a spherical front surface S3 and rear surface S4; a chalcogenide glass positive lens L3 with a convex surface facing the image, and a spherical front surface S5 and rear surface S6; and a biconcave chalcogenide glass negative lens L4, with an even-order aspheric front surface S7 and rear surface S8.

[0010] The compensation group includes a refractive-diffractive hybrid biconvex ZnSe positive lens L5, whose front surface S9 facing the object side is a diffractive surface and the rear surface S10 facing the image side is an even-order aspheric surface;

[0011] The rear fixed group includes a meniscus-shaped germanium single crystal negative lens L6 with its convex surface facing the image side, and its front surface S11 and rear surface S12 are both even-order aspherical surfaces;

[0012] The secondary imaging group includes, in sequence, a meniscus-shaped chalcogenide glass negative lens L7 with its convex surface facing the image side, a meniscus-shaped germanium single crystal positive lens L8 with its convex surface facing the object side, and a meniscus-shaped germanium single crystal positive lens L9 with its convex surface facing the object side. Surfaces S13, S14, S15, S16, S17, and S18 are all even-order aspherical surfaces.

[0013] The detector is a long-wave cooling detector, which comprises a protection window, a filter and an imaging surface in sequence, and the rear surface of the filter serves as a cold stop.

[0014] The effective focal length EFL of the optical system is 10 to 200 mm, the F number is 2, the working band is 6 to 13 μm, and continuous zooming is achieved by axial movement of the variable magnification lens group and the compensation lens group, and the relative positions of all lenses remain constant during the zooming process.

[0015] The even aspheric surface shape of the lens of the system satisfies the following relationship:

[0016]

[0017] Wherein, Z(r) is the distance vector height from the vertex of the aspheric surface at a height of r along the optical axis; c is the surface curvature of the aspheric surface, where c = 1 / R, R is the radius of curvature of the aspheric surface; k is the cone coefficient; A, B, and C are the aspheric coefficients.

[0018] The diffraction phase equation of the refractive-diffractive hybrid biconvex ZnSe positive lens is determined by the following formula:

[0019] Φ=MB1ρ 2 ,

[0020] Where M is the diffraction order, B1 is the diffraction surface coefficient, and ρ is the radial coordinate of the diffraction surface.

[0021] The operating band of this system is 6 to 13 μm.

[0022] Continuous zooming is achieved by axially moving the zooming group and the compensation group, and the relative positions of all lenses remain constant during the zooming process.

[0023] Beneficial effects of the present invention:

[0024] The present invention uses a diffraction surface in the compensation lens group, and takes advantage of the negative dispersion characteristics and primary aberration characteristics of the diffraction surface to well correct chromatic aberration without increasing the number of lenses. It can also adjust the phase of the incident light beam according to the specific needs of the optical system, and realize the correction of various aberrations in the system during the zoom process, so as to ensure that the present invention still has good imaging quality while meeting the requirements of a small F number, a large zoom ratio and a wide band.

[0025] The wide-band long-wave infrared 20x cooled refractive-diffractive hybrid continuous zoom optical system provided by the present invention is a cooled zoom optical system. It is designed to address the difficulties of current long-wave infrared continuous zoom optical systems in meeting the requirements of large zoom ratio, wide band, small F number and high imaging quality. The system has a zoom ratio of 20x, a working band of 6μm to 13μm, and an F number of 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the composition of the wide-band long-wave refrigerated infrared 20x refractive-diffractive hybrid continuous zoom optical system of the present invention;

[0027] Figure 2 1 is an optical transfer function diagram of a wide-band long-wavelength cooled infrared 20x diffractive hybrid continuous zoom optical system with a focal length of 200 mm (cut-off frequency of 17 lp / mm);

[0028] Figure 3 1 is an optical transfer function diagram of a wide-band long-wavelength cooled infrared 20x diffractive hybrid continuous zoom optical system with a focal length of 150 mm (cut-off frequency of 17 lp / mm) according to an embodiment;

[0029] Figure 41 is an optical transfer function diagram of a wide-band long-wavelength cooled infrared 20x diffractive hybrid continuous zoom optical system with a focal length of 118 mm (cut-off frequency of 17 lp / mm) according to an embodiment;

[0030] Figure 5 1 is an optical transfer function diagram of a wide-band long-wave cooled infrared 20x diffractive hybrid continuous zoom optical system with a focal length of 55 mm (cut-off frequency of 17 lp / mm) according to an embodiment;

[0031] Figure 6 1 is an optical transfer function diagram of the wide-band long-wave cooled infrared 20x diffractive hybrid continuous zoom optical system involved in the embodiment when the focal length is 10 mm (the cut-off frequency is 17 lp / mm). DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the accompanying drawings.

[0033] like Figure 1 As shown, a wide-band long-wave cooled infrared 20x diffractive hybrid continuous zoom optical system includes a front fixed group with positive optical power, a zoom group with negative optical power, a compensation group with positive optical power, a rear fixed group with negative optical power, a secondary imaging group with positive optical power, and a detector, which are coaxially arranged from the object side to the image side.

[0034] The front fixed group includes a meniscus-shaped germanium single crystal positive lens L1 with a convex surface facing the object side, and its front surface S1 and rear surface S2 are both spherical surfaces.

[0035] The zoom group comprises, in order, a single-crystal germanium negative lens L2 with a convex surface facing the object side, whose front surface S3 and rear surface S4 are both spherical; a chalcogenide glass positive lens L3 with a convex surface facing the image side, whose front surface S5 and rear surface S6 are both spherical; and a biconcave chalcogenide glass negative lens L4, whose front surface S7 and rear surface S8 are both even-order aspherical.

[0036] The compensation group includes a refractive-diffractive hybrid biconvex zinc selenide positive lens L5, whose surface S9 facing the object side is a diffractive surface and the surface S10 facing the image side is an even-order aspheric surface;

[0037] The rear fixed group includes a meniscus-shaped germanium single crystal negative lens L6 with a convex surface facing the image side, and its front surface S11 and rear surface S12 are both even-order aspherical surfaces;

[0038] The secondary imaging group includes, in order, a meniscus chalcogenide glass negative lens L7 with a convex surface facing the image side, a front surface S13 and a rear surface S14; a meniscus germanium single crystal positive lens L8 with a convex surface facing the object side, a front surface S15 and a rear surface S16; a meniscus germanium single crystal positive lens L9 with a convex surface facing the object side, a front surface S17 and a rear surface S18; surfaces S13, S14, S15, S16, S17, and S18 are all even-order aspherical surfaces;

[0039] The detector is a long-wave refrigerated detector, which sequentially comprises a protective window 100, a filter 101 and an imaging surface 102. The rear surface of the filter 101 (the side close to the imaging surface 102) serves as a cold stop.

[0040] The optical system of the present invention has an effective focal length EFL of 10 to 200 mm, an F number of 2, and an operating band of 6 to 13 μm. Continuous zooming is achieved by axially moving the zoom group and the compensation group, and the relative positions of all lenses remain constant during the zooming process.

[0041] The even-order aspheric surface of the lens of the optical system of the present invention satisfies the following relationship:

[0042]

[0043] Wherein, Z(r) is the distance vector height from the vertex of the aspheric surface at a height of r along the optical axis; c is the surface curvature of the aspheric surface, where c = 1 / R, R is the radius of curvature of the aspheric surface; k is the cone coefficient; A, B, and C are the aspheric coefficients.

[0044] Table 1 shows the optical structure parameters of the optical system when the focal length is 200 mm.

[0045] Table 1

[0046]

[0047]

[0048] As shown in Table 2, the aspheric coefficients of surfaces S7, S8, S10, S11, S12, S13, S14, S15, S16, S17, and S18.

[0049] Table 2

[0050] Optical surface A B C S7 -1.024326E-5 2.976532E-8 -1.823376E-11 S8 -1.785175E-5 2.859771E-8 -1.413866E-11 S10 1.497705E-6 4.663139E-10 1.118189E-12 S11 -4.180084E-4 -5.496183E-6 -1.123494E-7 S12 -2.668619E-5 8.969590E-7 -3.345674E-9 S13 -1.139747E-4 -2.084927E-6 -6.382766E-9 S14 5.483568E-5 -2.319286E-6 -1.391453E-8 S15 -1.013460E-4 1.421687E-6 4.939339E-9 S16 -4.351194E-4 1.701254E-6 -6.071626E-9 S17 3.348878E-5 -2.642979E-7 1.312500E-9 S18 -5.473217E-5 -3.504965E-7 1.647959E-9

[0051] The diffraction phase equation of the diffraction surface of L5 under the refractive-diffractive hybrid biconvex ZnSe positive lens is determined by the following formula:

[0052] Φ=MB1ρ 2 ,

[0053] Where M is the diffraction order, B1 is the diffraction surface coefficient, and ρ is the radial coordinate of the diffraction surface.

[0054] Table 3

[0055] Optical surface B1 S9 1.160650E+002

[0056] like Figure 2 Figure 2 shows the aberration analysis of the optical system at a focal length of 200mm. At this focal length, the MTF of the system in all fields of view is greater than 0.398.

[0057] like Figure 3 Figure 2 shows the aberration analysis of the optical system at a focal length of 150mm. At this focal length, the MTF of the system in all fields of view is greater than 0.498.

[0058] like Figure 4 Figure 2 shows the aberration analysis of the optical system at a focal length of 118mm. At this focal length, the MTF of the system in all fields of view is greater than 0.508.

[0059] like Figure 5 Figure 2 shows the aberration analysis of the optical system at a focal length of 55mm. At this focal length, the MTF of the system in all fields of view is greater than 0.459.

[0060] like Figure 6 Figure 2 shows the aberration analysis of the optical system at a focal length of 10 mm. At this focal length, the MTF of the system in all fields of view is greater than 0.410.

[0061] As can be seen from the figure, various aberrations at different focal lengths are well corrected, with the MTF and energy concentration showing good results.

Claims

1. Wide-band long-wave cooled infrared 20x refractive-diffractive hybrid continuous zoom optical system, characterized by: It includes a front fixed group with positive optical power, a varifocal group with negative optical power, a compensating group with positive optical power, a rear fixed group with negative optical power, a secondary imaging group with positive optical power and a detector, which are coaxially arranged in sequence from the object side to the image side; The front fixed group includes a meniscus germanium single crystal positive lens with its convex surface facing the object side. The surface facing the object side is a spherical surface with a curvature radius of 100 < R < 120, and the surface facing the image side is a spherical surface with a curvature radius of 170 < R < 190. The lens thickness is 9.16 mm; The varifocal group successively includes a germanium single crystal negative lens with its convex surface facing the object side. The surface facing the object side is a spherical surface with a curvature radius of 1300 < R < 1320, and the surface facing the image side is a spherical surface with a curvature radius of 900 < R < 920. The lens thickness is 5.50 mm, and the air gap between it and the next lens is 3.11 mm; a chalcogenide glass positive lens with its convex surface facing the image side. The surface facing the object side is a spherical surface with a curvature radius of -2280 < R < -2260, and the surface facing the image side is a spherical surface with a curvature radius of -600 < R < -580. The lens thickness is 4.73 mm, and the air gap between it and the next lens is 4.92 mm; a double concave chalcogenide glass negative lens. The surface facing the object side is an aspherical surface with a curvature radius of -120 < R < -100, and the surface facing the image side is an aspherical surface with a curvature radius of 30 < R < 50. The lens thickness is 3.33 mm; The compensating group includes a refractive-diffractive hybrid double convex zinc selenide positive lens. The surface facing the object side is a diffractive surface with a curvature radius of 50 < R < 70, and the surface facing the image side is an aspherical surface with a curvature radius of -120 < R < -100. The lens thickness is 9.69 mm; The rear fixed group includes a meniscus germanium single crystal negative lens with its convex surface facing the image side. The surface facing the object side is an aspherical surface with a curvature radius of -30 < R < -10, and the surface facing the image side is an aspherical surface with a curvature radius of -40 < R < -20. The lens thickness is 8.00 mm; the air gap between the rear fixed group and the secondary imaging group is 31.64 mm; The secondary imaging group sequentially includes a meniscus chalcogenide glass negative lens with its convex surface facing the image side. The surface facing the object side is an aspherical surface with a curvature radius of -860 < R < -840, and the surface facing the image side is an aspherical surface with a curvature radius of -330 < R < -310. The lens thickness is 7.50 mm, and the air gap between it and the next lens is 3.46 mm; a meniscus germanium single crystal positive lens with its convex surface facing the object side. The surface facing the object side is an aspherical surface with a curvature radius of 10 < R < 30, and the surface facing the image side is an aspherical surface with a curvature radius of 10 < R < 30. The lens thickness is 6.25 mm, and the air gap between it and the next lens is 36.36 mm; a meniscus germanium single crystal positive lens with its convex surface facing the object side. The surface facing the object side is an aspherical surface with a curvature radius of 30 < R < 50, and the surface facing the image side is an aspherical surface with a curvature radius of 70 < R < 90. The lens thickness is 7.23 mm; the air gap between the secondary imaging group and the detector protection window is 5.30 mm; In the long focal length state, the air gap between the front fixed group and the zoom group is 46.43 mm; the air gap between the zoom group and the compensation group is 3.00 mm; the air gap between the compensation group and the rear fixed group is 53.33 mm; The detector is a long-wave cooled detector, which sequentially includes a protection window, a filter, and an imaging surface. The rear surface of the filter serves as a cold stop.

2. The broadband long-wavelength refrigerated infrared 20x hybrid refractive-diffractive continuous zoom optical system according to claim 1, characterized in that: The effective focal length EFL of the system is 10 - 200 mm, and the F number is 2.

3. The broadband long-wavelength refrigerated infrared 20x hybrid refractive-diffractive continuous zoom optical system according to claim 1, characterized in that: The even aspherical surface types of the lenses in the system satisfy the following relationship: ， Where, Z(r) is the distance sag from the vertex of the aspherical surface along the optical axis at the position with a height of r; c is the curvature of the aspherical surface, where c = 1 / R and R is the curvature radius of the aspherical surface; k is the conic coefficient; A, B, C are the aspherical coefficients.

4. The broadband long-wavelength refrigerated infrared 20x hybrid refractive-diffractive continuous zoom optical system according to claim 1, characterized in that: The diffraction phase equation of the refractive-diffractive hybrid double convex zinc selenide positive lens is determined by the following formula: ， Where, M is the diffraction order, B1 is the diffraction surface coefficient, and ρ is the radial coordinate of the refractive-diffractive surface.

5. The broadband long-wavelength refrigerated infrared 20x hybrid refractive-diffractive continuous zoom optical system according to claim 1, characterized in that: The working wavelength range of the system is 6 - 13 μm.

6. The broadband long-wavelength refrigerated infrared 20x hybrid refractive-diffractive continuous zoom optical system according to claim 1, characterized in that: Continuous zooming is achieved by axially moving the zoom group and the compensation group, and the relative positions of all lenses remain constant during the zooming process.

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