Low-cost wide-band large relative aperture infrared imaging optical system

Abstract

The application relates to a low-cost wide-band large-relative-aperture infrared imaging optical system, which is a transmission optical system and adopts a coaxial structure. Four lenses made of chalcogenide glass and zinc selenide are arranged, and the optical system is sequentially provided with a first positive lens, a first negative lens, a second negative lens and a second positive lens along the light incidence direction; the refractive indexes of the lenses of the optical system correspond to n1, n2, n3 and n4 along the light incidence direction, and the corresponding value ranges are 2.4<=n1<=3.2, 2.4<=n2<=2.8, 2.3<=n3<=2.7 and 2.4<=n4<=2.8; the light is converged through the lenses, and then is incident on a detector focal plane after passing through a detector protection window. The application provides an optical system which is small in size, compact in structure, suitable for a 3-14-micron mid-long-wave wide-band, and has a mid-long-wave wide-band confocal plane imaging capability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of infrared imaging optical systems, and particularly relates to a low-cost wide-band large relative aperture infrared imaging optical system. BACKGROUND

[0002] A 3-14 mu m spectral imaging system is disclosed in Chinese Patent CN102980657B, which has a focal length of 60 mm and an F number of 1.0. The system compensates for imaging defocus in each narrow waveband by replacing band-pass filters with different thicknesses, and the optical lens itself does not achieve a 3-14 mu m full-waveband confocal surface design. Chinese Patent Application CN120065481A also has the same problem.

[0003] A dual-band infrared system disclosed in Chinese Patent CN105319669B shares six lenses, and has a working waveband of 3.7-4.8 mu m and 8-12 mu m, which does not cover 3-14 mu m. A non-cooled dual-band optical system disclosed in US Patent US7369303B2 has a working waveband of 3-5 mu m and 8-12 mu m, which also fails to cover a 3-14 mu m wide waveband range.

[0004] Chinese Patent CN104297908B, CN202794679U and US Patent US6423969B1 are all refrigeration type mid-long wave infrared systems, and have a small relative aperture, which is difficult to match the demand of a non-cooled detector for a large relative aperture. US Patent US4871219A is designed for a non-cooled detector, but has a large F number, and cannot be used in a large relative aperture optical system.

[0005] An off-axis three-mirror optical system disclosed in Optical Engineering, Vol. 56, No. 6, 061308-1-11, 2013 and an off-axis four-mirror optical system disclosed in Chinese Patent Application CN112213847A both adopt a reflective optical structure, and have high requirements for processing, assembly and testing of the optical system.

[0006] Chinese Patent CN112882210B discloses a non-cooled mid-long wave wide-band confocal infrared optical system with a working waveband of 3-14 mu m, a focal length of 50 mm and an F number of 1.1, which realizes a wide-band range confocal surface with a common aperture, but the optical system adopts five lenses, has a large number of lenses, and contains expensive germanium materials, which further increases the production cost of the entire lens.

[0007] In the prior art, the mid-wave to long-wave infrared detection equipment working in the 3-14 mu m wave band range is mainly a transmission type split-aperture system and a reflection type common-aperture system. Among them, the former has very limited optical material selection in the 3-14 mu m wide wave band range, and the price of the traditional material such as germanium which has high applicability is very high, resulting in great design difficulty and high lens cost; and the latter has the characteristics of achromatism and athermalization, but the processing and adjustment are difficult, and the engineering implementation is difficult. SUMMARY

[0008] The present application provides a low-cost wide-band large relative aperture infrared imaging optical system, and the technical problem to be solved is how to reduce the cost of the mid-long wave wide-band transmission type optical system working in the 3-14 mu m wave band.

[0009] The technical solution adopted by the present application to solve the technical problem is: a low-cost wide-band large relative aperture infrared imaging optical system is provided, the optical system is a transmission type optical system, the optical structure is a coaxial structure, and the optical system is sequentially provided with a first positive lens, a first negative lens, a second negative lens and a second positive lens along the light incident direction. The refractive indexes of the lenses of the optical system correspond to n1, n2, n3 and n4 along the light incident direction, and the corresponding value ranges are 2.5<=n1<=3.2, 2.4<=n2<=2.8, 2.3<=n3<=2.7 and 2.4<=n4<=2.8. The light is converged through each lens, and then enters the detector focal plane after passing through the detector protection window. The focal lengths of the lenses correspond to f1, f2, f3 and f4 along the light incident direction, and the normalized values of the focal lengths relative to the focal length f of the optical system correspond to 0.48<=|f1 / f|<=0.85, 0.94<=|f2 / f|<=1.45, 0.45<=|f3 / f|<=0.92 and 0.36<=|f4 / f|<=0.87.

[0010] Preferably, the working wave band of the optical system is 3-14 mu m.

[0011] Preferably, the maximum relative aperture of the optical system is F / 1.0.

[0012] Preferably, the optical system can adapt to the focal plane diameter size of 14 mm.

[0013] Preferably, the surface of the first positive lens close to the object plane is the stop of the optical system.

[0014] Preferably, the materials of the first positive lens, the first negative lens and the second positive lens are chalcogenide glass, and the material of the second negative lens is zinc selenide.

[0015] The beneficial effect is that the optical system has small volume, compact structure, is suitable for a middle-long wave wide waveband of 3-14 mu m, and has a middle-long wave wide waveband confocal surface imaging capability.

[0016] Compared with the prior art, the lens is made of a combination of zinc selenide and a sulfide glass without using germanium material, both of which are common infrared optical materials, low in price and easy to obtain, ensuring the maturity and continuity of the technology, and being capable of correcting aberration caused by large aperture well, realizing confocal imaging in a middle-long wave infrared wide waveband range of 3-14 mu m and a relative aperture of not less than F / 1.0 through the design of the focal length of the lens, and the optical system is high in imaging quality and good in stability, and one lens is reduced compared with the prior art, and is easy to manufacture and low in price.

[0017] As Figures 2-5 , the imaging quality evaluation results of the optical system provided by the present application from MTF, point array, relative distortion, and relative illumination are given, and it can be seen that the full field of view MTF of the optical system is not less than 0.5@30lp / mm, the RMS dispersion spot is not more than 19 mu m, the relative distortion is better than 0.5%, and the relative illumination is better than 95%, indicating that the present application has excellent imaging performance.

[0018] In addition, the present application also has a long working distance, can place a filter switching mechanism in front of the focal plane to realize multi-waveband imaging, and can be applied to various industrial detection, aviation remote sensing, astronomical observation and other purposes.

[0019] In actual application, such as in a middle-long wave wide waveband uncooled infrared imager, the optical system is installed to cover the working waveband of 3-14 mu m, and the middle wave (3-5 mu m) and long wave (8-14 mu m) radiation can be captured at one time, and the advantages of both are combined and the shortcomings are complemented; in power inspection, the same image can find the middle wave hot spot in the wire joint and locate the long wave water leakage area of the insulator, reducing repeated flights; in the field of petroleum and petrochemical industry, the wide waveband can synchronously monitor the 3.3 mu m absorption peak of hydrocarbon gas and the background 8-10 mu m radiation, and the detection capacity is improved by one order of magnitude compared with single waveband; in medical treatment, the wide waveband takes into account the long wave radiation of the skin and the middle wave characteristics of respiratory gas, realizing non-invasive simultaneous measurement of body temperature and CO2 concentration. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a low-cost wide waveband large relative aperture infrared imaging optical system lens structure schematic diagram;

[0021] Figure 2 It is a MTF evaluation schematic diagram of a low-cost wide waveband large relative aperture infrared imaging optical system;

[0022] Figure 3 A point diagram evaluation schematic diagram for a low-cost wide-band large relative aperture infrared imaging optical system;

[0023] Figure 4 A field curvature and distortion evaluation schematic diagram for a low-cost wide-band large relative aperture infrared imaging optical system;

[0024] Figure 5 A relative illumination evaluation schematic diagram for a low-cost wide-band large relative aperture infrared imaging optical system;

[0025] Wherein, 1~the first positive lens, 2~the first negative lens, 3~the second negative lens, 4~the second positive lens, 5~the detector protection window, 6~the detector focal plane. DETAILED DESCRIPTION

[0026] The application will be further described below in connection with specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content taught by the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope of the appended claims.

[0027] As Figure 1 shown, the application provides a low-cost wide-band large relative aperture infrared imaging optical system, which is a transmission optical system and adopts a coaxial structure. The optical system is coaxially provided with a first positive lens 1, a first negative lens 2, a second negative lens 3 and a second positive lens 4 in sequence along the light incident direction; the light is converged by the lenses 1-4 and then enters the detector focal plane 6 through the detector protection window 5; along the light incident direction, the focal lengths of the lenses correspond to f1, f2, f3 and f4 in sequence, and the normalized values of the focal lengths relative to the focal length f of the optical system correspond to 0.48≤|f1 / f|≤0.85, 0.94≤|f2 / f|≤1.45, 0.45≤|f3 / f|≤0.92 and 0.36≤|f4 / f|≤0.87 respectively.

[0028] Along the light incident direction, the refractive indexes of the lenses of the optical system correspond to n1, n2, n3 and n4 in sequence, and the corresponding value ranges are 2.5≤n1≤3.2, 2.4≤n2≤2.8, 2.3≤n3≤2.7 and 2.4≤n4≤2.8 respectively.

[0029] The lens material satisfying the refractive index requirement of the present application is low-cost chalcogenide glass and zinc selenide, and the refractive index of the lens made of germanium material is generally around 4.0. Specifically, in the present embodiment, the first positive lens 1 is made of chalcogenide glass IRG209, the first negative lens 2 is made of chalcogenide glass IRG207, the second negative lens 3 is made of zinc selenide material, and the material of the second positive lens 4 is chalcogenide glass IRG207. The chalcogenide material used can be replaced by glass or crystal material with similar performance, and at this time, only the curvature radius, thickness, lens spacing, etc. of each lens in the optical structure need to be modified to obtain similar or better optical performance of the present application.

[0030] The diaphragm of the present application is located on the surface of the first positive lens 1 close to the object plane, and is imaged far away from the image plane by the rear objective lens group and the imaging lens group, forming a quasi-image telecentric optical path, which can ensure uniform relative illumination distribution of the entire image plane.

[0031] The optical system adopts a four-piece structure, the working waveband is 3-14 μm, the focal length is 50 mm, the relative aperture is F / 1.0, and the adapted focal plane diameter is 14 mm.

[0032] The present application can realize an optical system with small size, compact structure, and mid-long wave wide waveband confocal surface imaging capability by simultaneously satisfying or satisfying multiple conditions.

[0033] The following Tables 1-3 show various numerical data related to a specific embodiment of a low-cost wide waveband large relative aperture infrared imaging optical system.

[0034]

[0035] Table 1: Specific parameters of each lens of the optical system of the present embodiment (unit: mm)

[0036]

[0037] Table 2: Aspheric surface parameter table of the optical system

[0038] The aspheric surface expression is as follows:

[0039] In the formula, z is the sag of the aspheric surface, c is the curvature of the aspheric surface, k is the quadratic surface coefficient, r is the radial height of the lens, A2i is the expansion term coefficient, N is the number of terms.

[0040]

[0041] Table 3: Parameter values of the optical system of the present embodiment

[0042] As Figures 2-5The imaging quality evaluation results of the optical system in the embodiment are given from the modulation transfer function (MTF), point spread diagram, relative distortion, relative illumination and the like. Figure 2 The modulation transfer function (MTF) of the optical system in the embodiment is not less than 0.5@30lp / mm; see Figure 3 The RMS spot of the optical system in the embodiment is not more than 19μm; see Figure 4 The relative distortion of the optical system in the embodiment is better than 0.5%; see Figure 5 The relative illumination of the optical system in the embodiment is better than 95%, which indicates that the optical system in the embodiment has excellent imaging performance.

[0043] In the embodiment, the total length from the surface close to the object plane of the first positive lens 1 to the focal plane 6 of the detector is not more than 75mm, the maximum light passing diameter of each lens is 50mm, and the focal length is 50mm. The aperture number F / 1.0 is used. The optical system has small volume, light weight and large relative aperture.

[0044] As can be seen from the above data, by using the optical structure of the present application, only four lenses of common infrared optical material are used, and the confocal imaging in the wide waveband range of 3μm~14μm and the relative aperture of not less than F / 1.0 can be realized. Since the number of lenses is reduced, the optical system provided by the present application is easy to manufacture, and has high imaging quality and good stability.

Claims

1. A low-cost, wide-band, large relative aperture infrared imaging optical system, characterized in that, The optical system is a transmission optical system with a coaxial optical structure. Along the direction of light incidence, the optical system consists of, in sequence, a first positive lens, a first negative lens, a second negative lens, and a second positive lens. Along the incident direction of the light, the refractive indices of each lens in the optical system are n1, n2, n3, and n4, respectively, with corresponding value ranges of 2.5 ≤ n1 ≤ 3.2, 2.4 ≤ n2 ≤ 2.8, 2.3 ≤ n3 ≤ 2.7, and 2.4 ≤ n4 ≤ 2.

8. The light rays converge through the lenses and, after passing through the detector's protective window, are incident on the detector's focal plane. Along the incident direction of light, let the focal lengths of each lens be f1, f2, f3, and f4 respectively. The normalized values ​​of their relative focal length f of the optical system are 0.48≤|f1 / f|≤0.85, 0.94≤|f2 / f|≤1.45, 0.45≤|f3 / f|≤0.92, and 0.36≤|f4 / f|≤0.87 respectively.

2. The low-cost, wide-band, large relative aperture infrared imaging optical system according to claim 1, characterized in that, The optical system operates in the wavelength range of 3μm to 14μm.

3. The low-cost, wide-band, large relative aperture infrared imaging optical system according to claim 1, characterized in that, The maximum relative aperture of the optical system is F / 1.

0.

4. The low-cost, wide-band, large relative aperture infrared imaging optical system according to claim 1, characterized in that, The optical system is compatible with a focal diameter of 14 mm.

5. The low-cost, wide-band, large relative aperture infrared imaging optical system according to claim 1, characterized in that, The first positive lens has its aperture stop on the side surface closest to the object plane.

6. The low-cost, wide-band, large relative aperture infrared imaging optical system according to claim 1, characterized in that, The first positive lens, the first negative lens, and the second positive lens are made of chalcogenide glass, and the second negative lens is made of zinc selenide.

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