Large field of view, large relative aperture of the cooling type mid-wave infrared lens and optical system

Abstract

The application discloses a large-view-field and large-relative-aperture refrigeration type middle-wave infrared lens and optical system, relates to the field of optical lenses, and aims to solve the problems of small view field, small relative aperture and poor thermal stability of optical performance of the refrigeration type infrared detector optical lens. The lens comprises a negative focal length front group and a positive focal length rear group in the light advancing direction; the negative focal length front group comprises a positive focal length lens A, a negative focal length lens B and a negative focal length lens C in sequence; the positive focal length rear group comprises a positive focal length lens D, a negative focal length lens E, a positive focal length lens F, a negative focal length lens G and a positive focal length lens H in sequence; and all the surfaces of the lenses are spherical surfaces except that the object surface of the positive focal length lens F is a non-spherical surface. The lens has the characteristics of large view field, large relative aperture, small optical distortion, good thermal stability, low manufacturing difficulty, light weight, easy modification and the like.

Description

Technical Field

[0001] The present invention relates to the field of optical lenses, in particular to a refrigerated medium-wave infrared lens and an optical system with a large field of view and a large relative aperture. Background Art

[0002] Infrared optical systems are used in a wide range of fields because they can passively detect infrared radiation emitted by objects. Commonly used large-area detectors that can receive infrared radiation are primarily categorized as cooled and uncooled. Cooled infrared detectors offer high sensitivity, high resolution, and a wide temperature range, making them more suitable for applications requiring higher performance from infrared systems.

[0003] The structural characteristics of cooled infrared detectors make the design of infrared optical lenses for them difficult. For example, the distance between the cold stop and the detector surface is fixed, meaning the back working distance used in cooled medium-wave infrared systems is fixed. This makes the design of optical systems with large fields of view and large relative apertures difficult to apply to cooled infrared detectors. Currently, common optical systems using cooled infrared detectors often employ a secondary imaging approach, resulting in a small field of view and a long overall length.

[0004] The optical system using a cooled infrared detector usually has an aperture set on the cold aperture of the cooled infrared detector. Its severe asymmetry leads to a decrease in the optical performance of the optical system. If the optical performance of the system is to be improved, the structure of the optical system will be more complicated and the system volume will be larger. The performance of the optical system will be more susceptible to temperature and the thermal stability of the optical performance will be poor.

[0005] In addition, large-field-of-view infrared cooling optical systems often have a short distance between the front and rear groups, making it difficult to add other optical components between the two, thus limiting their scope of application. Summary of the Invention

[0006] The object of the present invention is to provide a cooled medium-wave infrared lens and optical system with a large field of view and a large relative aperture to address all or part of the above-mentioned problems, so as to solve the problems of small field of view, small relative aperture and poor thermal stability of optical performance of cooled infrared detector optical lenses.

[0007] The technical solution adopted in the present invention is as follows:

[0008] A cooled medium-wave infrared lens with a large field of view and a large relative aperture, wherein the lens comprises a front group with negative optical power and a rear group with positive optical power along the direction of light travel;

[0009] The negative power front group includes a positive power lens A, a negative power lens B and a negative power lens C in sequence along the direction of light travel;

[0010] The positive power rear group includes, in order along the direction of light travel, a positive power lens D, a negative power lens E, a positive power lens F, a negative power lens G and a positive power lens H;

[0011] The object surface of the positive power lens F is aspherical, and the image surface is spherical; the object surface and image surface of the positive power lens A, negative power lens B, negative power lens C, positive power lens D, negative power lens E, negative power lens G and positive power lens H are all spherical.

[0012] The present invention also provides an infrared optical system, which includes the above-mentioned lens and a refrigerated medium-wave infrared detector; the detector protection window of the refrigerated medium-wave infrared detector is located on the output light path of the positive optical power lens H, and the detection surface of the refrigerated medium-wave infrared detector is located at the focal plane of the lens.

[0013] In summary, due to the adoption of the above technical solution, the beneficial technical effects of the present invention are:

[0014] The present application provides a athermalized infrared lens with a large field of view, large relative aperture, and low optical distortion for a cooled medium-wave infrared detector. The lens of the present application has good athermal performance and strong thermal stability of optical performance. The lens of the present application uses spherical mirrors as much as possible, which reduces the difficulty of manufacturing the optical lens. The lens of the present application is designed with a large modification space between the front group and the rear group to increase optical components, and is suitable for systems with compact internal structures such as reflector scanning multi-eye infrared panoramic infrared optical systems. The present application also focuses on optimizing the aperture and thickness of the lens to minimize the size and weight of the lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be described by way of example with reference to the accompanying drawings, in which:

[0016] Figure 1 It is a structural diagram of the infrared optical system implemented in this application.

[0017] Figure 2 This is the spot diagram of the cooled medium-wave infrared lens with medium to large field of view and large relative aperture that has been realized in this application.

[0018] Figure 3 This is the MTF curve of the cooled medium-wave infrared lens with medium to large field of view and large relative aperture that has been implemented in this application.

[0019] Figure 4 This is a distortion curve diagram of the cooled medium-wave infrared lens with medium to large field of view and large relative aperture that has been implemented in this application. DETAILED DESCRIPTION

[0020] All features disclosed in this specification, or all steps in the methods or processes disclosed, except for mutually exclusive features or steps, can be combined in any manner.

[0021] Any feature disclosed in this specification (including all appended claims and abstract), unless otherwise stated, may be replaced by other equivalent or similar features. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0022] In view of the problems that the design of optical systems with large field of view and large relative aperture is difficult to apply to cooled infrared detectors, and the optical performance and thermal stability of the optical systems of cooled infrared detectors are poor, while the application range of large-field-of-view infrared cooled optical systems is limited, the embodiments of the present application provide a cooled medium-wave infrared lens and optical system with a large field of view and large relative aperture, which aims to solve the problems of small field of view, small relative aperture and poor thermal stability of optical performance of cooled infrared detector optical lenses, as well as the problem of limited application range of large-field-of-view infrared cooled optical systems.

[0023] In some embodiments, as Figure 1 As shown, the cooled medium-wave infrared lens with large field of view and large relative aperture includes a negative optical power front group and a positive optical power rear group along the direction of light travel; wherein,

[0024] The negative power front group includes, along the direction of light travel, a positive power lens A, a negative power lens B, and a negative power lens C;

[0025] The positive power rear group includes, along the direction of light travel, a positive power lens D, a negative power lens E, a positive power lens F, a negative power lens G, and a positive power lens H;

[0026] The object surface S11 of the positive power lens F is aspherical, and the image surface S12 is spherical; the object surface and image surface of the positive power lens A, the negative power lens B, the negative power lens C, the positive power lens D, the negative power lens E, the negative power lens G, and the positive power lens H are all spherical. In this application, the object surface refers to the side facing the object, the image surface refers to the side facing the detector, the object side refers to the side facing the object, and the image side refers to the side facing the detector. The light emitted by the object enters the optical system through lenses A, B, C, D, E, F, G, and H in sequence; imaging is performed after the positive power lens A, the negative power lens B, the negative power lens C, the positive power lens D, the negative power lens E, the positive power lens F, the negative power lens G, and the positive power lens H.

[0027] The lens combination provides a large field of view, large relative aperture, and optical athermal infrared lens for a refrigeration type middle wave infrared detector. In the eight lenses of the lens, there are 15 spherical surfaces and only one aspherical surface, and the lens has low manufacturing difficulty.

[0028] As an optional embodiment, the positive lens A is a double-crescent lens with convex surface towards the object side, the negative lens B is a double-crescent negative lens with convex surface towards the object side, the negative lens C is a double-crescent negative lens with convex surface towards the object side, the positive lens D is a double-crescent positive lens with convex surface towards the object side, the negative lens E is a double-crescent negative lens with convex surface towards the object side, the positive lens F is a double-crescent positive lens with convex surface towards the object side, the negative lens G is a double-crescent positive lens with convex surface towards the object side, and the positive lens H is a double-crescent positive lens with convex surface towards the image side. The lenses of the structure are convenient to process.

[0029] As an optional embodiment, the ratio of the interval between the negative front group and the positive rear group to the focal length of the lens is not less than 9.06, the ratio of the aperture of the negative lens C to the focal length of the lens is not less than 2.427, and the ratio of the aperture of the positive lens D to the focal length of the lens is not less than 2.907. In this way, the lens has a wide modification space between the front group and the rear group while realizing a large field of view and a large relative aperture, and it is convenient to increase optical components to modify the optical path, and it is especially suitable for a reflective mirror scanning type infrared panoramic optical system.

[0030] As an optional embodiment, the curvature radius of the object surface S1 of the positive lens A is 125-129 mm, the curvature radius of the image surface S2 is 193-197 mm; the curvature radius of the object surface S3 of the negative lens B is 92-96 mm, the curvature radius of the image surface S4 is 45-51 mm; the curvature radius of the object surface S5 of the negative lens C is 131-135 mm, the curvature radius of the image surface S6 is 78-83 mm; the curvature radius of the object surface S7 of the positive lens D is 45-51 mm, the curvature radius of the image surface S8 is 54-58 mm; the curvature radius of the object surface S9 of the negative lens E is 128-134 mm, the curvature radius of the image surface S10 is 65-70 mm; the curvature radius of the object surface S11 of the positive lens F is 50-55 mm, the curvature radius of the image surface S12 is 216-220 mm; the curvature radius of the object surface S13 of the negative lens G is 110-113 mm, the curvature radius of the image surface S14 is 40-45 mm; and the curvature radius of the object surface S15 of the positive lens H is -788--785 mm, the curvature radius of the image surface S16 is -61--58 mm.

[0031] As an optional embodiment, the relationship between the focal length of each lens of the lens and the focal length of the lens is as follows:

[0032] 10.94≤f1 / f≤11.30,

[0033] -3.18≤f2 / f≤2.82,

[0034] -6.07≤f1 / f≤-5.71,

[0035] 7.78≤f4 / f≤8.14,

[0036] -3.59≤f5 / f≤-3.22,

[0037] 1.96≤f6 / f≤2.32,

[0038] -1.77≤f7f≤-1.41,

[0039] 1.78≤f8f≤2.14;

[0040] Among them, f1, f2, f3 are the focal lengths of positive power lens A, negative power lens B and negative power lens C respectively; f4, f5, f6, f7, f8 are the focal lengths of positive power lens D, negative power lens E, positive power lens F, negative power lens G and positive power lens H respectively; and f is the focal length of the lens.

[0041] As an optional embodiment, the center thickness of the positive power lens A is 4.57-5.05mm, the center thickness of the negative power lens B is 2.75-3.25mm, the center thickness of the negative power lens C is 2.75-3.25mm, the center thickness of the positive power lens D is 2.85-3.35mm, the center thickness of the negative power lens E is 2.95-3.45mm, the center thickness of the positive power lens F is 4.75-5.25mm, the center thickness of the negative power lens G is 2.75-3.25mm, and the center thickness of the positive power lens H is 2.75-3.25mm. By optimizing the lens aperture and thickness, the lens volume and weight are minimized.

[0042] As an optional embodiment, the center spacing between the positive power lens A and the negative power lens B is 0.75 to 1.25 mm, the center spacing between the negative power lens B and the negative power lens C is 6.00 to 6.50 mm, the center spacing between the negative power lens C and the positive power lens D is 124.75 to 125.25 mm, the center spacing between the positive power lens D and the negative power lens E is 2.95 to 3.45 mm, the center spacing between the negative power lens E and the positive power lens F is 0.75 to 1.25 mm, the center spacing between the positive power lens F and the negative power lens G is 1.95 to 2.45 mm, and the center spacing between the negative power lens G and the positive power lens H is 2.35 to 2.85 mm.

[0043] In a specific implementation, each lens in the lens is installed in the lens barrel through a pressure ring, and adjacent lenses are separated by spacers to ensure that the lenses maintain the correct installation position.

[0044] As an optional embodiment, the object surface and image surface of all lenses are coated with a medium-wave infrared anti-reflection film.

[0045] As an optional embodiment, positive power lens A, negative power lens B, negative power lens C, positive power lens F, and positive power lens H are all made of single crystal silicon, while positive power lens D, negative power lens E, and negative power lens G are all made of single crystal germanium. This material sequence is used to eliminate thermal differences in the mid-infrared lens and improve the thermal stability of optical performance.

[0046] As an optional embodiment, the object surface S11 of the positive power lens F is a standard quadratic surface or an even-order aspheric surface.

[0047] Taking an even-order aspheric surface as an example, the expression of the aspheric surface is:

[0048]

[0049] Among them, z is the sagittal height of the aspheric surface at a height of r along the optical axis, and c is the vertex curvature of the aspheric surface, which is the reciprocal of the vertex radius r0 of the aspheric surface, that is, k is the cone coefficient, k=0; α2, α3, α4, α5, α6 are high-order aspheric coefficients.

[0050] The embodiment of the present application also provides a specific large field of view, large relative aperture cooled medium-wave infrared lens to verify the design performance.

[0051] The focal length of the lens is 13.85mm, and the target size is 640*512 (@25 ), lens design wavelength 3 ~5 , suitable for object distance 1m~ The RMS radius within the field of view of -37.5°~37.5° is less than 14.5 , suitable for 25 Pixel size of cooled medium-wave infrared detector. Spacing between negative optical power front group and positive optical power rear group 125.481mm, that is, the ratio of this distance to the focal length of the lens (13.85mm) is not less than 9.06; the ratio of this distance to the aperture of the negative focal power lens C is not less than 2.427, and the ratio to the aperture of the positive focal power lens D is not less than 2.907.

[0052] The parameters of each lens are shown in Table 1.

[0053] Table 1 Lens parameters

[0054]

[0055]

[0056] The center thickness of the positive power lens A is 4.8 mm, the center thickness of the negative power lens B is 3 mm, the center thickness of the negative power lens C is 3 mm, the center thickness of the positive power lens D is 3.1 mm, the center thickness of the negative power lens E is 3.2 mm, the center thickness of the positive power lens F is 5 mm, the center thickness of the negative power lens G is 3 mm, and the center thickness of the positive power lens H is 3 mm.

[0057] The object and image surfaces of each lens are coated with medium-wave 3.7-4.8μm anti-reflection film with a transmittance of ≥97%.

[0058] The relationship between the focal length of each lens and the focal length of the lens is:

[0059] 10.94≤f1 / f≤11.30,

[0060] -3.18≤f2 / f≤2.82,

[0061] -6.07≤f1 / f≤-5.71,

[0062] 7.78≤f4 / f≤8.14,

[0063] -3.59≤f5 / f≤-3.22,

[0064] 1.96≤f6 / f≤2.32,

[0065] -1.77≤f7 / f≤-1.41,

[0066] 1.78≤f8 / f≤2.14.

[0067] The lens of the above structure has a focal length of 13.85mm, an F number of 2.0, an optical field of view of 75°×75° (the field of view of a traditional cooled infrared lens is usually 10°×10°), and an optical distortion of ≤5%. The lens has good athermal performance and good optical performance stability within the temperature range of -40℃ to 60℃.

[0068] The present application also provides an infrared optical system, comprising the lens of the above embodiment and a refrigerated medium-wave infrared detector (e.g., a staring type). The detector protection window I of the refrigerated medium-wave infrared detector is located on the exit light path of the positive power lens H of the lens, and the detection surface of the refrigerated medium-wave infrared detector is located at the focal plane K of the lens.

[0069] Taking the lens in the aforementioned specific embodiment as an example, the focal length of the lens is 13.85mm, the F number is 2.0, and the optical field of view is 75°×75°. The array size of the cooled medium-wave infrared detector is 640×512, the size of a single pixel is 25μm, the working band is 3.7~4.8μm; the F number is 2.0, and the imaging circle diameter is greater than Φ19.95mm. In addition, the total length TTL from the object plane of the positive focal power lens A to the detection surface of the cooled medium-wave infrared detector is ≤219.35mm, and the total length from the image plane of the positive focal power lens H to the detection surface of the cooled medium-wave infrared detector is ≥34mm. Figure 2 Shown is the spot diagram of the lens detected by the infrared optical system. Figure 3 The following is the MTF curve of the lens drawn based on the detection results. Figure 4 The figure shows the distortion curve of the lens drawn according to the detection structure. Figure 2-Figure 4 It can be seen that the cooled medium-wave infrared lens of the present application has the characteristics of large field of view, large relative aperture, good thermal stability and small optical distortion.

[0070] The present invention is not limited to the aforementioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A cooled medium-wave infrared lens with a large field of view and a large relative aperture, characterized in that: The lens comprises a front group with negative optical power and a rear group with positive optical power along the direction of light travel; wherein, The negative power front group includes a positive power lens A, a negative power lens B and a negative power lens C in sequence along the direction of light travel; The positive power rear group includes, in order along the direction of light travel, a positive power lens D, a negative power lens E, a positive power lens F, a negative power lens G and a positive power lens H; The object surface of the positive power lens F is aspherical, and the image surface is spherical; the object surface and image surface of the positive power lens A, negative power lens B, negative power lens C, positive power lens D, negative power lens E, negative power lens G and positive power lens H are all spherical.

2. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 1, characterized in that: The positive power lens A is a double-curved moon lens with the convex surface facing the object, the negative power lens B is a double-curved meniscus negative lens with the convex surface facing the object, the negative power lens C is a double-curved meniscus negative lens with the convex surface facing the object, the positive power lens D is a double-curved meniscus positive lens with the convex surface facing the object, the negative power lens E is a double-curved meniscus negative lens with the convex surface facing the object, the positive power lens F is a double-curved meniscus positive lens with the convex surface facing the object, the negative power lens G is a double-curved meniscus positive lens with the convex surface facing the object, and the positive power lens H is a double-curved meniscus positive lens with the convex surface facing the image side.

3. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 2, characterized in that: The ratio of the distance between the negative power front group and the positive power rear group to the focal length of the lens is not less than 9.06, the ratio to the aperture of the negative power lens C is not less than 2.427, and the ratio to the aperture of the positive power lens D is not less than 2.

907.

4. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 2 or 3, characterized in that: The object surface of the positive power lens A has a curvature radius of 125 to 129 mm, and the image surface has a curvature radius of 193 to 197 mm; the object surface of the negative power lens B has a curvature radius of 92 to 96 mm, and the image surface has a curvature radius of 45 to 51 mm; the object surface of the negative power lens C has a curvature radius of 131 to 135 mm, and the image surface has a curvature radius of 78 to 83 mm; the object surface of the positive power lens D has a curvature radius of 45 to 51 mm, and the image surface has a curvature radius of 54 to 58 mm; The object surface of the negative power lens E has a curvature radius of 128 to 134 mm, and the image surface has a curvature radius of 65 to 70 mm; the object surface of the positive power lens F has a curvature radius of 50 to 55 mm, and the image surface has a curvature radius of 216 to 220 mm; the object surface of the negative power lens G has a curvature radius of 110 to 113 mm, and the image surface has a curvature radius of 40 to 45 mm; the object surface of the positive power lens H has a curvature radius of -788 to -785 mm, and the image surface has a curvature radius of -61 to 58 mm.

5. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 4, characterized in that: The relationship between the focal length of each lens of the lens and the focal length of the lens is: 10.94≤f1 / f≤11.30, -3.18≤f2 / f≤2.82, -6.07≤f1 / f≤-5.71, 7.78≤f4 / f≤8.14, -3.59≤f5 / f≤-3.22, 1.96≤f6 / f≤2.32, -1.77≤f7 / f≤-1.41, 1.78≤f8 / f≤2.14; Among them, f1, f2, f3 are the focal lengths of the positive power lens A, negative power lens B and negative power lens C respectively, f4, f5, f6, f7, f8 are the focal lengths of the positive power lens D, negative power lens E, positive power lens F, negative power lens G and positive power lens H respectively, and f is the focal length of the lens.

6. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 5, characterized in that: The center thickness of the positive power lens A is 4.57-5.05 mm, the center thickness of the negative power lens B is 2.75-3.25 mm, the center thickness of the negative power lens C is 2.75-3.25 mm, the center thickness of the positive power lens D is 2.85-3.35 mm, the center thickness of the negative power lens E is 2.95-3.45 mm, the center thickness of the positive power lens F is 4.75-5.25 mm, the center thickness of the negative power lens G is 2.75-3.25 mm, and the center thickness of the positive power lens H is 2.75-3.25 mm.

7. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 6, characterized in that: The center spacing between the positive power lens A and the negative power lens B is 0.75-1.25 mm, the center spacing between the negative power lens B and the negative power lens C is 6.00-6.50 mm, the center spacing between the negative power lens C and the positive power lens D is 124.75-125.25 mm, the center spacing between the positive power lens D and the negative power lens E is 2.95-3.45 mm, the center spacing between the negative power lens E and the positive power lens F is 0.75-1.25 mm, the center spacing between the positive power lens F and the negative power lens G is 1.95-2.45 mm, and the center spacing between the negative power lens G and the positive power lens H is 2.35-2.85 mm.

8. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 1, wherein: The aspheric surface is a standard quadratic surface or an even-order aspheric surface.

9. The cooled medium-wave infrared lens with a large field of view and a large relative aperture according to claim 1, wherein: The positive power lens A, negative power lens B, negative power lens C, positive power lens F and positive power lens H are all made of single crystal silicon, and the positive power lens D, negative power lens E and negative power lens G are all made of single crystal germanium.

10. An infrared optical system, characterized in that: It comprises the lens as described in any one of claims 1 to 9, and a refrigerated medium-wave infrared detector; the detector protection window of the refrigerated medium-wave infrared detector is located on the output light path of the positive optical power lens H, and the detection surface of the refrigerated medium-wave infrared detector is located at the focal plane of the lens.

Images