Large-view-field and large-relative-aperture refrigeration type medium-wave infrared lens and optical system

Abstract

The invention discloses a large-view-field and large-relative-aperture refrigeration type medium-wave infrared lens and an optical system, relates to the field of optical lenses, and is used for solving the problems that a refrigeration type infrared detector optical lens is small in view field, small in relative aperture and poor in optical performance and thermal stability. The lens comprises a negative-focal-power front group and a positive-focal-power rear group in the light advancing direction. The front negative-focal-power group sequentially comprises a positive-focal-power lens A, a negative-focal-power lens B and a negative-focal-power lens C; the positive focal power rear group sequentially comprises a positive focal power lens D, a negative focal power lens E, a positive focal power lens F, a negative focal power lens G and a positive focal power lens H; except that the object plane of the positive-focal-power lens F is an aspheric surface, the other surfaces of all the lenses are spherical surfaces. The lens has the advantages of being large in view field, large in relative aperture, small in optical distortion, good in thermal stability, low in manufacturing difficulty, light in weight, convenient to refit and the like.

Description

Technical Field

[0001] The 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 many fields because they can passively detect infrared radiation emitted by objects. Commonly used large-surface detectors that can receive infrared radiation are mainly divided into cooled infrared detectors and uncooled detectors. Among them, cooled infrared detectors have the characteristics of high sensitivity, high resolution, and wide detection temperature range, and are more suitable for occasions with higher requirements on infrared system performance.

[0003] The structural characteristics of cooled infrared detectors make it difficult to design infrared optical lenses for cooled infrared detectors. For example, the distance between the cold aperture of a cooled infrared detector and the detector surface is fixed, that is, the rear working distance used in a cooled medium-wave infrared system is fixed, making it difficult to design optical systems with large field of view and large relative aperture for cooled infrared detectors. Currently, common optical systems using cooled infrared detectors often use secondary imaging, which is a small field of view optical system with a long total system 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, 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, which limits their application range. Summary of the invention

[0006] The object of the present invention is to provide a cooled medium-wave infrared lens and an 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 the cooled infrared detector optical lens.

[0007] The technical solution adopted by 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 a negative optical power and a rear group with a positive optical power along the direction of light advance; wherein,

[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 light advancing direction;

[0010] The positive power rear group includes 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 in sequence along the light advancing direction;

[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 exit 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 refrigerated medium-wave infrared detector with a large field of view, large relative aperture, and low optical distortion. 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 optical lenses. 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 It is a spot diagram of a 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 a cooled medium-wave infrared lens with a medium to large field of view and a 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 mutually exclusive features or steps, can be combined in any way.

[0021] Any feature disclosed in this specification (including all attached claims and abstracts), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. 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 large-field-of-view and large-relative-aperture optical system designs are difficult to apply to cooled infrared detectors, and that the optical performance thermal stability of the optical system of the cooled infrared detector is poor, while the application range of the large-field-of-view infrared cooled optical system is limited, the embodiments of the present application provide a large-field-of-view and large-relative-aperture cooled medium-wave infrared lens and optical system, aiming to solve the problems of small field of view, small relative aperture and poor thermal stability of optical performance of the optical lens of the cooled infrared detector, as well as the limited application range of the large-field-of-view infrared cooled optical system.

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

[0024] 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;

[0025] The positive power rear group includes 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 in sequence along the light traveling direction;

[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 the present 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; 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 are imaged.

[0027] The above lens combination provides a large field of view, large relative aperture optical athermal infrared lens for the cooled medium-wave infrared detector. Among the eight lenses of the lens, there are 15 spherical surfaces and only one aspherical surface, and the manufacturing difficulty of the lens is low.

[0028] As an optional implementation, the positive power lens A is a double-curved moon lens with a convex surface facing the object, the negative power lens B is a double-curved moon negative lens with a convex surface facing the object, the negative power lens C is a double-curved moon negative lens with a convex surface facing the object, the positive power lens D is a double-curved moon positive lens with a convex surface facing the object, the negative power lens E is a double-curved moon negative lens with a convex surface facing the object, the positive power lens F is a double-curved moon positive lens with a convex surface facing the object, the negative power lens G is a double-curved moon positive lens with a convex surface facing the object, and the positive power lens H is a double-curved moon positive lens with a convex surface facing the image. Each lens of this structure is easy to process.

[0029] As an optional implementation, the ratio of the interval 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. In this way, the lens has a wide modification space between the front and rear groups while achieving a large field of view and a large relative aperture, which is convenient for adding optical components to modify the optical path, and is particularly suitable for a reflector scanning infrared panoramic optical system.

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

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

[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 the positive power lens A, the negative power lens B and the negative power lens C respectively, f4, f5, f6, f7, f8 are the focal lengths of 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 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 4.57-5.05 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. By optimizing the lens aperture and thickness, the minimization of the lens volume and weight is achieved.

[0042] As an optional embodiment, 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.

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

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

[0045] As an optional implementation, 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 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 the thermal difference of the mid-infrared lens and improve the thermal stability of the optical performance.

[0046] As an optional implementation, the object surface S11 of the positive power lens F is a standard quadratic surface or an even-order aspherical 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 vector height of the aspheric surface at a height of r along the optical axis, and c is the vertex curvature of the aspheric surface, and its value 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 Cooled MWIR detector with pixel size. Spacing between negative power front group and positive power rear group 125.481mm, that is, the ratio 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 4.8mm, the center thickness of the negative power lens B is 3mm, the center thickness of the negative power lens C is 3mm, the center thickness of the positive power lens D is 3.1mm, the center thickness of the negative power lens E is 3.2mm, the center thickness of the positive power lens F is 5mm, the center thickness of the negative power lens G is 3mm, and the center thickness of the positive power lens H is 3mm.

[0057] The object and image surfaces of each lens are coated with medium-wave 3.7-4.8μm anti-reflection films 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°C to 60°C.

[0068] The present application also provides an infrared optical system, which includes the lens of the above embodiment and a refrigerated medium-wave infrared detector (such as 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 focal 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 MTF curve of the lens is drawn according to 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 refrigerated 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 above-mentioned 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 light advancing direction; The positive power rear group includes 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 in sequence along the light advancing direction; 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 large field of view, large relative aperture refrigerated medium-wave infrared lens according to claim 1, characterized in that: The positive power lens A is a double-curved moon lens with a convex surface facing the object, the negative power lens B is a double-curved moon negative lens with a convex surface facing the object, the negative power lens C is a double-curved moon negative lens with a convex surface facing the object, the positive power lens D is a double-curved moon positive lens with a convex surface facing the object, the negative power lens E is a double-curved moon negative lens with a convex surface facing the object, the positive power lens F is a double-curved moon positive lens with a convex surface facing the object, the negative power lens G is a double-curved moon positive lens with a convex surface facing the object, and the positive power lens H is a double-curved moon positive lens with a convex surface facing the image.

3. The large field of view, large relative aperture refrigerated medium-wave infrared lens as claimed in claim 2, characterized in that: The ratio of the interval 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 large field of view and large relative aperture as claimed in 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 large field of view and large relative aperture as claimed in 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, the negative power lens B and the negative power lens C respectively, f4, f5, f6, f7, f8 are the focal lengths of 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 respectively, and f is the focal length of the lens.

6. The cooled medium-wave infrared lens with large field of view and large relative aperture as claimed in 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 large field of view and large relative aperture as claimed in claim 6, characterized in that: The center interval between the positive power lens A and the negative power lens B is 0.75-1.25 mm, the center interval between the negative power lens B and the negative power lens C is 6.00-6.50 mm, the center interval between the negative power lens C and the positive power lens D is 124.75-125.25 mm, the center interval between the positive power lens D and the negative power lens E is 2.95-3.45 mm, the center interval between the negative power lens E and the positive power lens F is 0.75-1.25 mm, the center interval between the positive power lens F and the negative power lens G is 1.95-2.45 mm, and the center interval 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 large field of view and large relative aperture as claimed in claim 1, characterized in that: The aspheric surface is a standard quadratic surface or an even-order aspheric surface.

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

10. An infrared optical system, characterized in that: It comprises a 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 exit 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