A wide-band infrared optical system

Abstract

The present invention relates to a wide-band infrared optical system. Along the optical axis of this optical system, a positive-power meniscus lens L1, a negative-power meniscus lens L2, a positive-power meniscus lens L3, a filter, a detector protection window, a diaphragm and an image plane are sequentially arranged from the object side to the image side; the front surface of the positive-power meniscus lens L1 is an aspherical surface, the front surface of the negative-power meniscus lens L2 is a diffractive surface, and the surfaces of other lenses are spherical surfaces; the negative-power meniscus lens L2 is made of a chalcogenide glass material, and other optical elements are made of zinc sulfide. The structure of the present invention is simple and easy to assemble and align, the imaging quality is excellent, chromatic aberration and other monochromatic aberrations can be corrected well, the distortion is small, and 100% cold stop efficiency can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of imaging optical system design, and in particular relates to a wide-band infrared optical system. Background Art

[0002] The design of wide-band infrared optical systems at home and abroad mainly covers the medium- and long-wave spectrum range of 3 to 12 μm, and rarely involves the medium- and short-wave spectrum region of 1 to 5 μm. In the short-wave infrared, 1 to 1.3 μm, 1.5 to 1.8 μm, and 2.0 to 2.4 μm are all spectral transmission regions of the atmosphere. Indium antimonide (InSb) infrared focal plane detectors can have a good response in the 1 to 5 μm spectral region. InSb has good stability, and its performance does not change with working time and storage time. InSb is also easy to make large-scale arrays, and good array uniformity is also one of its advantages. Medium- and short-wave infrared optical systems are often used in multi-spectral / wide-spectrum imaging, laser detection, astronomical observation, medical testing and other fields.

[0003] For optical systems working in the 1-5 μm band, chromatic aberration correction is very difficult, and the commonly used optional materials are only Amtir1, CaF 2 , CsI, MgO, Sapphire and ZnS. Among them, CaF 2 The physical and chemical properties of CsI are unstable. Although MgO has good physical and chemical properties, it is expensive. In order to correct chromatic aberration and other monochromatic aberrations, the medium and short-wave infrared optical systems reported at home and abroad often use more than three optical materials at the same time, with a large number of lenses and a complex structure. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a wide-band infrared optical system, the working band of which covers the infrared short-wave and medium-wave spectral regions, and can correct chromatic aberration within the wide band with only two materials. It has a simple structure, is easy to assemble and adjust, and has excellent imaging quality.

[0005] In order to solve the above technical problems, the wide-band infrared optical system of the present invention is provided with a positive focal meniscus lens L1, a negative focal meniscus lens L2, a positive focal meniscus lens L3, a filter, a detector protection window, an aperture and an image plane in sequence along the optical axis from the object side to the image side; the front surface of the positive focal meniscus lens L1 is aspherical, and the rear surface is spherical; the front surface of the negative focal meniscus lens L2 is a diffraction surface, and the rear surface is a spherical surface; the front and rear surfaces of the positive focal meniscus lens L3 are both spherical; the aperture is arranged at the cold aperture of the detector; the positive focal meniscus lens L1, the positive focal meniscus lens L3, the filter, and the detector protection window are all made of zinc sulfide material, and the negative focal meniscus lens L2 is made of chalcogenide glass material.

[0006] Furthermore, the front and rear surface curvature radii of the positive focal power meniscus lens L1 are 76.97-79.04 mm and 221.65-241.59 mm respectively; the front and rear surface curvature radii of the negative focal power meniscus lens L2 are 108.06-110.16 mm and 55.63-58.36 mm respectively; the front and rear surface curvature radii of the positive focal power meniscus lens L3 are -117.05--105.10 mm and -63.89--61.12 mm respectively.

[0007] Furthermore, the center thickness of the positive power meniscus lens L1 is 9.0-9.1 mm; the center thickness of the negative power meniscus lens L2 is 18.15-18.25 mm; and the center thickness of the positive power meniscus lens L3 is 5.45-5.52 mm.

[0008] The center thickness of the filter and the detector protection window is 2.95-3.05 mm.

[0009] Furthermore, the central air interval between the positive power meniscus lens L1 and the negative power meniscus lens L2 is 2.35-2.45 mm; the central air interval between the negative power meniscus lens L2 and the positive power meniscus lens L3 is 23.85-23.95 mm.

[0010] The central air gap between the positive focal meniscus lens L3 and the filter is 5.05-5.15 mm; the central air gap between the filter and the detector protection window is 17.45-17.64 mm; the central air gap between the detector protection window and the aperture is 13.25-13.32 mm; and the central air gap between the aperture and the image plane is 26.0 mm.

[0011] Furthermore, the cone coefficient k of the front surface of the positive power meniscus lens L1 is -0.467 to -0.449, the aspheric coefficient A is 1.292E-7 to 1.345E-7, B is -9.401E-11 to -9.210E-11, C is 2.212E-14 to 2.242E-14, and D is -1.086E-16 to -1.055E-16.

[0012] The cone coefficient k of the front surface of the negative power meniscus lens L2 is -17.751 to -17.663, the aspheric coefficient A is 1.283E-6 to 1.285E-6, B is -9.758E-10 to -9.756E-10, C is 6.098E-13 to 6.145E-13, and D is -4.418E-17 to -4.083E-17; the diffraction order HOR is 1, the normalized radius Norm Radius is 100 mm, and the diffraction surface coefficient C 1-1.993E+3~-1.956E+3, C 2 0.77E+3~0.81E+3, C 3 It is 2.572E+3~3.094E+3.

[0013] The beneficial effects of the present invention are: the optical system has a wide working band range, only uses three lenses, has a simple structure and is easy to assemble and adjust, and the lens material is only zinc sulfide and chalcogenide glass material, avoiding the use of expensive optical materials with poor physical and chemical properties. The optical system has excellent imaging quality, can better correct chromatic aberration and other monochromatic aberrations, has small distortion, and the optical system can achieve 100% cold aperture efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of the wide-band infrared optical system of the present invention;

[0015] Figure 2 It is a modulation transfer function curve diagram of Example 1 of the wide-band infrared optical system of the present invention when imaging in the 1-1.8 μm band;

[0016] Figure 3 It is a modulation transfer function curve diagram of Example 1 of the wide-band infrared optical system of the present invention when imaging in the 2-2.4 μm band;

[0017] Figure 4 It is a modulation transfer function curve diagram of Example 1 of the wide-band infrared optical system of the present invention when imaging in the 3-5 μm band;

[0018] Figure 5 It is a distortion curve diagram of Example 1 of the wide-band infrared optical system of the present invention when imaging in the 1-1.8 μm band;

[0019] Figure 6 It is a distortion curve diagram of Example 1 of the wide-band infrared optical system of the present invention when imaging in the 2-2.4 μm band;

[0020] Figure 7 It is a distortion curve diagram of the wide-band infrared optical system embodiment 1 of the present invention when imaging in the 3-5 μm band;

[0021] Figure 8 It is a graph showing the phase and period variation of the diffraction surface of Example 1 of the wide-band infrared optical system of the present invention.

[0022] Figure 1 In the middle, L1: positive power meniscus lens; L2: negative power meniscus lens; L3: positive power meniscus lens; 1: filter; 2: detector protection window; 3: aperture; 4: image plane. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0024] like Figure 1 As shown, the wide-band infrared optical system of the present invention is provided with a positive focal meniscus lens L1, a negative focal meniscus lens L2, a positive focal meniscus lens L3, a filter 1, a detector protection window 2, an aperture 3 and an image plane 4 in sequence along the optical axis from the object side to the image side; the convex surface of the positive focal meniscus lens L1 faces the object side, the front surface is an aspherical surface, and the rear surface is a spherical surface; the convex surface of the negative focal meniscus lens L2 faces the object side, the front surface is a diffraction surface, and the rear surface is a spherical surface; the convex surface of the positive focal meniscus lens L3 faces the image side, and the front and rear surfaces are both spherical surfaces.

[0025] The aspheric surface of the positive power meniscus lens L1 satisfies the following relationship:

[0026]

[0027] Among them, Z(r) is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of r along the optical axis; c is the surface curvature of the aspherical surface, where c = 1 / R, R is the radius of curvature of the aspherical surface; k is the cone coefficient; A, B, C, and D are aspherical coefficients.

[0028] The diffraction surface of the negative power meniscus lens L2 satisfies the following relationship:

[0029]

[0030] Where 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 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, C, D are the aspheric coefficients; HOR is the diffraction order, C 1 , C 2 , C 3 is the diffraction surface coefficient, λ 0 is the design center wavelength, n is the refractive index of the negative focal meniscus lens L2, n 0 is the refractive index of air.

[0031] The positive power meniscus lens L1, the positive power meniscus lens L3, the filter, and the detector protection window are all made of zinc sulfide material; when the negative power meniscus lens L2 is made of chalcogenide glass materials such as IRG201 or IRG207, the optical system can obtain better imaging effects in the infrared wide band, and the modulation transfer function values ​​of the full field of view are better than 0.28, meeting the resolution requirements of the optical system.

[0032] The wide-band infrared optical system of the present invention has an operating band of 1 to 5 μm, an effective focal length of 100 mm, an F number of 2.8, a diagonal maximum half field angle of 4.7°, an adapted InSb infrared focal plane detector array of 640×512, and an image plane size of 20 μm×20 μm.

[0033] Embodiment 1:

[0034] The specific parameters of each lens in this embodiment are shown in Table 1-1.

[0035] Table 1-1

[0036]

[0037]

[0038] The optical parameters of the aspheric surface in this embodiment are shown in Table 1-2.

[0039] Table 1-2

[0040]

[0041] The optical parameters of the diffraction surface in this embodiment are shown in Table 1-3.

[0042] Table 1-3

[0043]

[0044] In this embodiment, the working band of the wide-band infrared optical system is 1 to 5 μm, the effective focal length is 100 mm, the F number is 2.8, the maximum diagonal half field angle is 4.7°, the adapted InSb infrared focal plane detector array is 640×512, and the image plane size is 20 μm×20 μm.

[0045] like Figure 2 The figure shows the modulation transfer function curve of the optical system of this embodiment when imaging in the 1-1.8 μm band. The modulation transfer function value of the central field of view at the cutoff frequency of 25 lp / mm is better than 0.43; the modulation transfer function value of the maximum field of view at the cutoff frequency of 25 lp / mm is better than 0.67, which meets the resolution requirement of the optical system.

[0046] like Figure 3 The figure shows the modulation transfer function curve of the optical system of this embodiment when imaging in the 2-2.4 μm band. The modulation transfer function value of the central field of view at the cutoff frequency of 25 lp / mm is better than 0.45; the modulation transfer function value of the maximum field of view at the cutoff frequency of 25 lp / mm is better than 0.55, which meets the resolution requirement of the optical system.

[0047] like Figure 4The figure shows the modulation transfer function curve of the optical system of this embodiment when imaging in the 3-5 μm band. The modulation transfer function value of the central field of view at the cutoff frequency of 25 lp / mm is better than 0.61; the modulation transfer function value of the maximum field of view at the cutoff frequency of 25 lp / mm is better than 0.28, which meets the resolution requirement of the optical system.

[0048] like Figure 5 The figure shows the distortion curve of the optical system of this embodiment when imaging in the 1-1.8 μm band. The maximum distortion of the full field of view at each wavelength is less than 0.44%, and the fidelity is good, which fully meets the distortion requirements of the optical system.

[0049] like Figure 6 The figure shows the distortion curve of the optical system of this embodiment when imaging in the 2-2.4 μm band. The maximum distortion of the full field of view at each wavelength is less than 0.43%, and the fidelity is good, which fully meets the distortion requirements of the optical system.

[0050] like Figure 7 The figure shows the distortion curve of the optical system of this embodiment when imaging in the 3-5 μm band. The maximum distortion of the full field of view at each wavelength is less than 0.33%, and the fidelity is good, which fully meets the distortion requirements of the optical system.

[0051] like Figure 8 The figure shows the phase and period variation curve of the diffraction surface of the optical system of this embodiment, wherein the horizontal axis represents the semi-aperture size of the diffraction surface (in mm), curve 1 represents the annular zone period corresponding to different gyration radii, and curve 2 represents the annular zone frequency under different gyration radii. It can be seen from the figure that the diffraction surface is easy to process.

[0052] Example 2

[0053] The specific parameters of each lens in this embodiment are shown in Table 2-1.

[0054] Table 2-1

[0055]

[0056] The optical parameters of the aspheric surface in this embodiment are shown in Table 2-2.

[0057] Table 2-2

[0058]

[0059] The optical parameters of the diffraction surface in this embodiment are shown in Table 2-3.

[0060] Table 2-3

[0061]

[0062] In this embodiment, the working band of the wide-band infrared optical system is 1 to 5 μm, the effective focal length is 100 mm, the F number is 2.8, the maximum diagonal half field angle is 4.7°, the adapted InSb infrared focal plane detector array is 640×512, and the image plane size is 20 μm×20 μm.

[0063] When the optical system of this embodiment forms images in the bands of 1 to 1.8 μm, 2 to 2.4 μm, and 3 to 5 μm, the modulation transfer function curve values ​​of each field of view are all better than 0.3, meeting the resolution requirements of the optical system; the maximum distortion of the entire field of view at each wavelength is less than 0.46%, with a good degree of fidelity, which fully meets the distortion requirements of the optical system.

[0064] Example 3

[0065] The specific parameters of each lens in this embodiment are shown in Table 3-1.

[0066] Table 3-1

[0067]

[0068] The optical parameters of the aspheric surface in this embodiment are shown in Table 3-2.

[0069] Table 3-2

[0070]

[0071] The optical parameters of the diffraction surface in this embodiment are shown in Table 3-3.

[0072] Table 3-3

[0073]

[0074] In this embodiment, the working band of the wide-band infrared optical system is 1 to 5 μm, the effective focal length is 100 mm, the F number is 2.8, the maximum diagonal half field angle is 4.7°, the adapted InSb infrared focal plane detector array is 640×512, and the image plane size is 20 μm×20 μm.

[0075] When the optical system of this embodiment images in the bands of 1-1.8μm, 2-2.4μm, and 3-5μm, the modulation transfer function curve values ​​of each field of view are all better than 0.28, meeting the resolution requirements of the optical system; the maximum distortion of the full field of view at each wavelength is less than 0.43%, with a good degree of fidelity, which fully meets the distortion requirements of the optical system.

Claims

1. A wide-band infrared optical system, characterized in that along the optical axis, a positive meniscus lens L1, a negative meniscus lens L2, a positive meniscus lens L3, a filter, a detector protection window, a diaphragm and an image plane are sequentially arranged from the object side to the image side; the front surface of the positive meniscus lens L1 is an aspherical surface and the rear surface is a spherical surface; the front surface of the negative meniscus lens L2 is a diffractive surface and the rear surface is a spherical surface; the front and rear surfaces of the positive meniscus lens L3 are both spherical surfaces; the diaphragm is arranged at the cold diaphragm of the detector; the positive meniscus lens L1, the positive meniscus lens L3, the filter and the detector protection window are all made of zinc sulfide material, and the negative meniscus lens L2 is made of chalcogenide glass material; the front and rear surface curvature radii of the positive meniscus lens L1 are 76.97 - 79.04 mm and 221.65 - 241.59 mm respectively; the front and rear surface curvature radii of the negative meniscus lens L2 are 108.06 - 110.16 mm and 55.63 - 58.36 mm respectively; the front and rear surface curvature radii of the positive meniscus lens L3 are -117.05 - -105.10 mm and -63.89 - -61.12 mm respectively.

2. The wide-band infrared optical system according to claim 1, characterized in that the central thickness of the positive meniscus lens L1 is 9.0 - 9.1 mm; the central thickness of the negative meniscus lens L2 is 18.15 - 18.25 mm; the central thickness of the positive meniscus lens L3 is 5.45 - 5.52 mm.

3. The wide-band infrared optical system according to claim 1, characterized in that the central thicknesses of the filter and the detector protection window are both 2.95 - 3.05 mm.

4. The wide-band infrared optical system according to claim 1 or 2, characterized in that the central air gap between the positive meniscus lens L1 and the negative meniscus lens L2 is 2.35 - 2.45 mm; the central air gap between the negative meniscus lens L2 and the positive meniscus lens L3 is 23.85 - 23.95 mm.

5. The wide-band infrared optical system according to claim 1, characterized in that the central air gap between the positive meniscus lens L3 and the filter is 5.05 - 5.15 mm; the central air gap between the filter and the detector protection window is 17.45 - 17.64 mm; the central air gap between the detector protection window and the diaphragm is 13.25 - 13.32 mm; the central air gap between the diaphragm and the image plane is 26.0 mm.

6. The wide-band infrared optical system according to claim 1, characterized in that The conic constant k of the front surface of the positive meniscus lens L1 is -0.467 to -0.449, the aspheric coefficients A are 1.292E-7 to 1.345E-7, B are -9.401E-11 to -9.210E-11, C are 2.212E-14 to 2.242E-14, and D are -1.086E-16 to -1.055E-16.

7. The wide-band infrared optical system according to claim 1, characterized in that The conic coefficient k of the front surface of the negative meniscus lens L2 is -17.751 to -17.663, the aspheric coefficients A are 1.283E-6 to 1.285E-6, B are -9.758E-10 to -9.756E-10, C are 6.098E-13 to 6.145E-13, and D are -4.418E-17 to -4.083E-17; the diffraction order HOR is 1, the normalized radius Norm Radius is 100 mm, and the diffraction surface coefficient C 1 is -1.993E+3 to -1.956E+3, C 2 is 0.77E+3 to 0.81E+3, C 3 is 2.572E+3 to 3.094E+3.

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