Wide-spectrum athermalization refrigeration lens suitable for 1.5-5um dual-color detection system

Abstract

The application discloses a wide-spectrum athermalization refrigeration lens suitable for a 1.5-5um dual-color detection system, which comprises a first lens, a second lens, a third lens and a fourth lens arranged in sequence from an object side to an image side; wherein the first lens is a concave-convex lens with negative refractive power; the second lens is a convex-convex lens with positive refractive power; the third lens is a convex-concave lens with positive refractive power; the fourth lens is a convex-concave lens with positive refractive power; a first image side is an aspheric surface; a third object side is a diffractive surface; a first object side, a second object side, a second image side, a third image side, a fourth object side and a fourth image side are all spherical lenses. The lens is suitable for a short-wave and medium-wave dual-color detector, and a diagonal field of view angle can reach 27.6 degrees, is suitable for related fields such as safety monitoring, air pollution, target characteristic detection, high-speed target detection and tracking and mechanical equipment state monitoring, and has high reliability.

Description

Technical Field

[0001] This invention relates to a broadband athermalized cooling lens suitable for a 1.5-5µm dual-color detection system, belonging to the technical field of broadband athermalized cooling lenses. Background Technology

[0002] High frame rate cooled mid-wave infrared sensors with a range of 1.5µm to 5.0µm are used in scientific research and industrial fields such as security monitoring, air pollution detection, target characteristic detection, high-speed target detection and tracking, and mechanical equipment condition monitoring. They feature high sensitivity, wide temperature range, high temperature accuracy, and fast measurement speed.

[0003] Wideband optical systems present design challenges such as difficulty in correcting system aberrations and chromatic aberration. Currently, cooled mid-wave lenses are generally nominally suitable for the 3.0µm–5.0µm band, but in reality, most are designed to eliminate chromatic aberration in the 3.7µm–4.8µm band. Using such lenses in 1.5µm–5.0µm camera modules results in energy loss and information loss in the 1.5µm–3.0µm band. CN106019534B discloses a 1.3–5µm wideband infrared imaging lens, which suffers from problems such as a large number of lenses, large size, small image plane, non-thermalization, and inconvenient overall processing and assembly. Summary of the Invention

[0004] This invention provides a wide-format spectral lens suitable for a 640*512 infrared core of a short-wave and mid-wave dual-color detector, applicable to fields such as security monitoring, air pollution detection, target characteristic detection, high-speed target detection and tracking, and mechanical equipment condition monitoring.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A broadband athermalized cooling lens suitable for a 1.5-5µm dual-color detection system includes a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the object side to the image side. The first lens is a concave-convex lens with negative refractive index; the second lens is a convex-convex lens with positive refractive index; the third lens is a convex-concave lens with positive refractive index; and the fourth lens is a convex-concave lens with positive refractive index. From the object side to the image side, the two sides of the first lens are, in sequence, a first object-side surface and a first image-side surface; the two sides of the second lens are, in sequence, a second object-side surface and a second image-side surface; the two sides of the third lens are, in sequence, a third object-side surface and a third image-side surface; and the two sides of the fourth lens are, in sequence, a fourth object-side surface and a fourth image-side surface. The first image-side surface is aspherical; the third object-side surface is a diffraction surface; and the first, second, second, third, fourth, and fourth object-side surfaces are all spherical lenses.

[0007] The aforementioned lens is a high-frequency cooled lens suitable for a 640*512-15um dual-color detector module for both short-wave and mid-wave wavelengths. This application presents a solution for a thermalized lens suitable for dual-color detectors from short-wave to mid-wave wavelengths, filling a gap in domestically produced thermalized imaging objectives for the short-wave to mid-wave bands.

[0008] The aforementioned lens uses a diffraction surface to optimize chromatic aberration and thermal aberration.

[0009] The aforementioned wide-spectrum athermalized cooling lens, applicable to dual-color detection systems of 1.5-5µm, has a combined focal length f' of 25mm, a system F number of 2.5, a diagonal imaging plane of 12.3mm, and a diagonal field of view of 27.6°.

[0010] The first to fourth lenses mentioned above are made of crystal materials and chalcogenide glass. Preferably, to ensure overall transmittance, reduce the number of lenses, and eliminate the adverse effects of temperature changes on image quality, the lenses are made of crystal materials with high refractive index and chalcogenide glass with a small coefficient of refractive index change with temperature, dn / dT. More preferably, the first and fourth lenses are made of zinc selenide and use aspherical surfaces to correct image quality; the second lens is made of calcium fluoride crystal, which has high transmittance in the 1.5-5µm range, achieving 90% transmittance even without coating; the third lens is made of chalcogenide glass, preferably domestically produced IRG206, which uses diffraction surfaces to help eliminate chromatic aberration and thermal aberration in the optical system.

[0011] To further ensure imaging quality, the radius of curvature of the first object-side surface is -16.280±0.005mm, and the radius of curvature of the first image-side surface is -24.868±0.005mm; the radius of curvature of the second object-side surface is 63.376±0.005mm, and the radius of curvature of the second image-side surface is -65.842±0.005mm; the radius of curvature of the third object-side surface is 118.371±0.005mm, and the radius of curvature of the third image-side surface is 159.804±0.005mm; the radius of curvature of the fourth object-side surface is 43.214±0.005mm, and the radius of curvature of the fourth image-side surface is 110.284±0.005mm.

[0012] To further ensure image quality, the center-to-center distance between the first and second lenses is 11.073±0.005mm, the center-to-center distance between the second and third lenses is 0.300±0.005mm, and the center-to-center distance between the third and fourth lenses is 0.626±0.005mm.

[0013] To further ensure imaging stability and quality, the center thickness of the first lens is 7.000±0.05mm, the center thickness of the second lens is 6.200±0.05mm, the center thickness of the third lens is 2.700±0.05mm, and the center thickness of the fourth lens is 2.700±0.05mm.

[0014] To balance image quality and lens size, the outer diameter of the first lens is 21.2–28.3 mm, the outer diameter of the second lens is 27.5 ± 0.1 mm, the outer diameter of the third lens is 23.5–26.1 mm, and the outer diameter of the fourth lens is 21.8–24.7 mm.

[0015] The aforementioned lens achieves 100% cold aperture efficiency.

[0016] Any techniques not mentioned in this invention are based on existing technologies.

[0017] This invention provides a broadband, thermally cooled lens suitable for 1.5-5µm dual-color detection systems, offering the following advantages:

[0018] 1. Suitable for shortwave and medium-wave dual-color detectors, with a diagonal field of view of up to 27.6°. It is applicable to fields such as security monitoring, air pollution detection, target characteristic detection, high-speed target detection and tracking, and mechanical equipment condition monitoring, and has high reliability.

[0019] 2. Large imaging area, suitable for 640 camera module, with pixel size up to 15µm;

[0020] 3. The system has an F-number of 2.5, and the overall optical lens diameter is small, which can save costs to the greatest extent.

[0021] 4. The third object's side surface uses a diffraction surface, which can effectively correct for chromatic and thermal differences generated over a wide wavelength range;

[0022] 5. It adopts a straight-tube single-imaging system configuration. The optical system consists of four mirrors, and all components are arranged on the same optical axis. It features a wide operating wavelength, compact structure, good adaptability, good imaging quality, and a transfer function that reaches or approaches the diffraction limit. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the optical path of the broadband athermal cooling lens of the dual-color detection system described in this invention;

[0024] Figure 2 The image shows the optical transfer function curves of a specific embodiment at room temperature (20°C) for 1.5-5 μm.

[0025] Figure 3 This is a graph showing the optical transfer function of a specific embodiment at a low temperature of 1.5-5 μm and a temperature of -40°C.

[0026] Figure 4 This is a graph showing the optical transfer function of a specific embodiment at a high temperature of 80°C (1.5-5µm).

[0027] Figure 5 The images show the field curvature and distortion at 1.5-5µm in specific embodiments;

[0028] Figure 6 This is a specific embodiment with a light spot size of 1.5-5µm;

[0029] Figure 7 This is a chromatic aberration diagram of a specific embodiment at 1.5-5µm. Detailed Implementation

[0030] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0031] like Figure 1 The broadband athermalized cooling lens shown is suitable for a 1.5-5µm dual-color detection system and includes the following components arranged sequentially along the optical axis from the object side to the image side: a first lens L1 with negative optical power, a second lens L2 with positive optical power, a third lens L3 with positive optical power, a fourth lens L4 with positive optical power, a protective window L5, a system cold stop S11, and an imaging surface S12.

[0032] From the object side to the image side, the two sides of the first lens L1 are the first object side S1 and the first image side S2, the two sides of the second lens L2 are the second object side S3 and the second image side S4, the two sides of the third lens L3 are the third object side S5 and the third image side S6, the two sides of the fourth lens L4 are the fourth object side S7 and the fourth image side S8, and the two sides of the protective window L6 are the sixth object side S9 and the sixth image side S10. The first image side S2 is aspherical; the third object side S5 is a diffraction surface; the first object side S1, the second object side S3, the second image side S4, the third image side S6, the fourth object side S7, and the fourth image side S8 are all spherical lenses.

[0033] The first lens L1 is made of zinc selenide and uses an aspherical surface to correct image quality.

[0034] The second lens L2 uses calcium fluoride crystal. Fluoride crystal has high transmittance in the range of 1.5-5µm, and the transmittance can reach 90% even without coating.

[0035] The third lens L3 uses chalcogenide glass IRG206 and incorporates a diffraction surface, which helps to eliminate chromatic and thermal differences in the optical system.

[0036] The fourth lens, L4, is made of zinc selenide to mitigate aberrations.

[0037] Table 1. Technical parameters of the optical system in this embodiment of the invention.

[0038] band 1.5-5um F# 2.5 Field of view (H)21.7°*(V)17.5°*(D)27.6° distortion ≤|4％| Detector specifications 640*512-15um Cold aperture size 8.37mm

[0039] Table 2 Specific parameters of the embodiments of the present invention

[0040]

[0041] The aspherical equations used in Table 2 are:

[0042]

[0043] The meanings of each quantity are as follows:

[0044] ZA: The lens sagitta along the optical axis of the aspherical surface;

[0045] R: Radius of curvature at the intersection of the surface and the optical axis;

[0046] Y: Half-aperture of the lens perpendicular to the optical axis;

[0047] k: Conic coefficient;

[0048] Coefficients for surfaces A, B, C, and D; see Table 3 for specific coefficients.

[0049] Table 3

[0050] S2 0 -4.58781E-06 -5.99653E-010 -6.88452E-011 1.06469E-013 S5 0 -1.91318E-06 1.61548E-09 -5.39029E-011 1.79397E-013

[0051] The diffraction surface equations used in Table 2 are as follows:

[0052] Φ=A1Y 2 +A2Y 4 +A3Y 6

[0053] in:

[0054] Φ: Phase of the diffraction plane;

[0055] Y: Half-aperture of the lens perpendicular to the optical axis;

[0056] Phase coefficients of diffraction planes A1, A2, and A3;

[0057] Table 2 shows the diffraction surface coefficients used in specific embodiments, and Table 4 shows the diffraction surface coefficients used in these embodiments.

[0058] Table 4

[0059] S5 +1 3um -7.2844E-04 -3.1355E-07 0

[0060] Figures 2 to 4The example shows optical transfer function curves at temperatures of -40°C, +20°C, and +80°C, requiring a resolution of 33 line pairs / mm with a 640x51215μm detector; Figures 2 to 4 It can be seen that as the temperature changes, the edge MTF values ​​are all above 0.28, indicating good image resolution and anechoic effects; Figure 6 It can be seen that the system has a small dispersion spot, indicating a strong ability to recognize objects; from Figure 7 It can be seen that the chromatic aberration along the vertical axis is basically controlled within the diffraction-limited Airy disk, and the chromatic aberration correction is good.

Claims

1. A broadband athermalized cooling lens suitable for a 1.5-5µm dual-color detection system, characterized in that: It consists of a first lens, a second lens, a third lens, and a fourth lens arranged sequentially from the object side to the image side; wherein, the first lens is a concave-convex lens with negative refractive index; the second lens is a convex-convex lens with positive refractive index; the third lens is a convex-concave lens with positive refractive index; and the fourth lens is a convex-concave lens with positive refractive index; from the object side to the image side, the two sides of the first lens are the first object-side surface and the first image-side surface, the two sides of the second lens are the second object-side surface and the second image-side surface, the two sides of the third lens are the third object-side surface and the third image-side surface, and the two sides of the fourth lens are the fourth object-side surface and the fourth image-side surface; the first image-side surface is aspherical; the third object-side surface is a diffraction surface; and the first object-side surface, the second object-side surface, the second image-side surface, the third image-side surface, the fourth object-side surface, and the fourth image-side surface are all spherical lenses; The first lens is made of zinc selenide; the second lens is made of calcium fluoride crystal; the third lens is made of chalcogenide glass; and the fourth lens is made of zinc selenide.

2. The broadband athermalized cooling lens for a 1.5-5µm dual-color detection system as described in claim 1, characterized in that: The system has a combined focal length f' of 25mm, a system F number of 2.5, a diagonal imaging plane of 12.3mm, and a diagonal field of view of 27.6°.

3. The broadband athermalized cooling lens for a 1.5-5µm dual-color detection system as described in claim 1 or 2, characterized in that: The radius of curvature of the first object side is -16.280±0.005mm, and the radius of curvature of the first image side is -24.868±0.005mm; the radius of curvature of the second object side is 63.376±0.005mm, and the radius of curvature of the second image side is -65.842±0.005mm; the radius of curvature of the third object side is 118.371±0.005mm, and the radius of curvature of the third image side is 159.804±0.005mm; the radius of curvature of the fourth object side is 43.214±0.005mm, and the radius of curvature of the fourth image side is 110.284±0.005mm.

4. The broadband athermalized cooling lens for a 1.5-5µm dual-color detection system as described in claim 1 or 2, characterized in that: The center-to-center distance between the first and second lenses is 11.073±0.005mm, the center-to-center distance between the second and third lenses is 0.300±0.005mm, and the center-to-center distance between the third and fourth lenses is 0.626±0.005mm.

5. The broadband athermalized cooling lens for a 1.5-5µm dual-color detection system as described in claim 1 or 2, characterized in that: The center thickness of the first lens is 7.000±0.05mm, the center thickness of the second lens is 6.200±0.05mm, the center thickness of the third lens is 2.700±0.05mm, and the center thickness of the fourth lens is 2.700±0.05mm.

6. The broadband athermalized cooling lens for a 1.5-5µm dual-color detection system as described in claim 1 or 2, characterized in that: The outer diameter of the first lens is 21.2~28.3mm, the outer diameter of the second lens is 27.5±0.1mm, the outer diameter of the third lens is 23.5~26.1mm, and the outer diameter of the fourth lens is 21.8~24.7mm.

Images