A hybrid refractive-diffraction long-wavelength infrared optical system with large relative aperture

Abstract

A hybrid refractive-diffraction long-wave infrared optical system with a large relative aperture is disclosed, relating to the field of infrared optical system technology. To address the problem that existing long-wave infrared systems cannot meet the requirements for detecting larger targets over longer distances, this system includes a meniscus negative lens, a meniscus positive lens, an aperture stop, a meniscus positive lens, a meniscus negative lens, a hybrid refractive-diffraction meniscus positive lens, and an image plane, arranged sequentially along the optical axis from object to image. The front surface of the second meniscus negative lens and the surface of the hybrid refractive-diffraction meniscus positive lens are spherical. The surface of the hybrid refractive-diffraction meniscus positive lens near the image plane has a diffraction surface, and the surfaces of the other lenses are even-order aspherical surfaces. This invention significantly improves the system's field of view and relative aperture by incorporating even-order aspherical surfaces and diffraction surfaces, while reducing the overall system length and weight, thus significantly enhancing the system's detection capability in the long-wave infrared band. Furthermore, the total distortion of this long-wave infrared optical system is ≤10%, improving the system's detection accuracy.

Description

Technical Field

[0001] This invention relates to the field of infrared optical system technology, and in particular to a large relative aperture long-wave infrared optical system with refractive-diffraction hybrid technology. Background Technology

[0002] Infrared optical systems can detect the thermal radiation energy of targets and their surrounding environment. These systems can perform real-time target detection in various harsh environments, making them widely used in both military and civilian fields. Furthermore, uncooled infrared detectors do not require cooling devices and can operate at room temperature. They offer advantages such as small size, light weight, low power consumption, long lifespan, low cost, and fast start-up, making them widely applicable in various detection applications.

[0003] Currently, there are two main factors affecting the detection capability of long-wave infrared lenses: First, the field of view of the long-wave infrared optical system directly affects the detection range of the optical system; second, the relative aperture size of the optical system affects the energy entering the optical system.

[0004] The Chinese patent publication number is "CN209297022U," and the patent title is "A Long-Wave Infrared System with a Large Field of View and Large Relative Aperture." This system consists of a first lens with positive optical power, a second lens with negative optical power, a third lens with positive optical power, a focal plane protective glass, and a focal plane, with the addition of even-order aspherical surfaces and diffraction surfaces. However, this long-wave infrared optical system has a focal length range of 9–21 mm and a field of view range of 37.5°–74.1°. Not only is the overall field of view smaller, but when the focal length range is 12–21 mm, the maximum field of view is only 60.3°, which is about 20° smaller than the field of view corresponding to the same focal length f′. This cannot meet the detection requirements for a larger field of view at a fixed focal length. Summary of the Invention

[0005] To address the problem that existing long-wave infrared systems cannot meet the requirements for detection of larger target ranges and longer distances, this invention proposes a hybrid refractive-diffraction long-wave infrared optical system with a large relative aperture. This system has a compact structure and is a long-wave infrared optical system with a relative aperture of 1, a focal length range f′ that can cover 12–25 mm, and a full field of view 2ω that can cover 43°–78.7°.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A large relative aperture long-wave infrared optical system with refractive-diffraction hybrid technology is characterized in that the system includes a meniscus negative lens I, a meniscus positive lens I, an aperture stop, a meniscus positive lens II, a meniscus negative lens II, a refractive-diffraction hybrid meniscus positive lens, and an image plane arranged sequentially along the optical axis from the object side to the image side; wherein, the front surface of the meniscus negative lens II and the surface of the refractive-diffraction hybrid meniscus positive lens are spherical, the surface of the refractive-diffraction hybrid meniscus positive lens near the image plane is provided with a diffraction surface, and the surfaces of the other lenses are even-order aspherical surfaces.

[0008] The concave surfaces of both the first and second meniscus negative lenses face the image plane.

[0009] The ratio of the total system length TTL to the system focal length f′ is 2≤TTL / f′≤2.5.

[0010] In this system: 12mm≤f′≤25mm, full field of view 43°≤2ω≤78.7°, and the focal length f′ and field of view ω satisfy the following relationship. Where y is the image height of the half field of view of the image plane (7).

[0011] The focal lengths of the meniscus negative lens 1 are: -133.5mm≤f1≤-38mm; the focal lengths of the meniscus positive lens 1 are: 24mm≤f2≤66.3mm; the focal lengths of the meniscus positive lens 2 are: 16.9mm≤f3≤45.5mm; the focal lengths of the meniscus negative lens 2 are: -1057mm≤f4≤-508mm; and the focal lengths of the refractive-diffractive hybrid meniscus positive lens are: 46.9mm≤f5≤58.2mm.

[0012] The even-order aspherical surface shape satisfies the following relationship:

[0013]

[0014] Where Z(r) is the distance vector from the vertex of the aspherical surface along the optical axis at a height of r; c is the surface curvature of the aspherical surface, where c = 1 / R, and R is the radius of curvature of the aspherical surface; k is the conic coefficient; and A, B, C, and D are aspherical coefficients.

[0015] The formula for the phase distribution of the diffraction surface shape of the hybrid meniscus lens is:

[0016] Φ=M(B1ρ 2 +B2ρ 4 )

[0017] Where M is the diffraction order, B1 and B2 are the diffraction surface coefficients, and ρ is the radial coordinate of the diffraction surface.

[0018] The optical materials of the meniscus negative lens one, meniscus positive lens one, meniscus positive lens two, meniscus negative lens two, and the refractive-diffraction hybrid meniscus positive lens are all germanium.

[0019] The system exhibits distortion ≤10% across the entire focal length range of 12–25 mm.

[0020] The system operates in the 8-14 μm band.

[0021] The beneficial technical effects of the present invention are as follows:

[0022] The system of this invention operates in the 8-14μm band, with a field of view of 43°≤2ω≤78.7°, an F-number of 1, and a total length to focal length ratio of 2≤L / f′≤2.5. By setting even-order aspherical surfaces and diffraction surfaces, the system's field of view and relative aperture are greatly improved, while the total length and weight of the system are reduced, significantly enhancing the system's detection capability in the long-wave infrared band. In addition, the total distortion of this long-wave infrared optical system is ≤10%, improving the system's detection accuracy. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a large relative aperture long-wave infrared optical system with refractive index and diffraction hybrid technology according to the present invention.

[0024] Figure 2 This is the MTF curve of the present invention at a spatial frequency of 20 lp / mm when the focal length f′=12mm;

[0025] Figure 3 This is the MTF curve of the present invention at a spatial frequency of 20 lp / mm when the focal length f′=25mm;

[0026] Figure 4 This is a distortion diagram of the system of the present invention at a focal length f′=12mm;

[0027] Figure 5 This is a distortion diagram of the system of the present invention at a focal length f′=25mm. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown, a large relative aperture long-wave infrared optical system with refractive-diffraction hybrid technology includes a meniscus negative lens 1, a meniscus positive lens 2, an aperture stop 3, a meniscus positive lens 4, a meniscus negative lens 5, a refractive-diffraction hybrid meniscus positive lens 6, and an image plane 7 arranged sequentially along the optical axis. The side of the meniscus negative lens 5 near the object plane and the side of the refractive-diffraction hybrid meniscus positive lens 6 near the object plane are both spherical. The side of the refractive-diffraction hybrid meniscus positive lens 6 near the image plane is provided with a diffraction surface. The surface types of the remaining lenses are all even-order aspherical. The concave surfaces of the meniscus negative lens 1 and the meniscus negative lens 5 both face the image side.

[0030] The even-order aspherical surface shape satisfies the following relationship:

[0031]

[0032] Where Z(r) is the distance vector from the vertex of the aspherical surface along the optical axis at a height of r; c is the surface curvature of the aspherical surface, where c = 1 / R, and R is the radius of curvature of the aspherical surface; k is the conic coefficient; and A, B, C, and D are aspherical coefficients.

[0033] The phase distribution of the diffraction surface profile of the hybrid meniscus lens 6 satisfies the following relationship:

[0034] Φ=M(B1ρ 2 +B2ρ 4 )

[0035] Where M is the diffraction order, B1 and B2 are the diffraction surface coefficients, and ρ is the radial coordinate of the diffraction surface.

[0036] The ratio of the total length TTL of the lens group to the system focal length f′ is 2≤TTL / f′≤2.5.

[0037] The system's focal length satisfies 12mm ≤ f′ ≤ 25mm, and its full field of view is 43° ≤ 2ω ≤ 78.7°. The focal length f′ and the field of view ω have a one-to-one correspondence, and they satisfy the following relationship: Where y is the half-field-of-view image height of the detector; f′=12mm corresponds to a full field-of-view angle 2ω=78.7°, and f′=25mm corresponds to a full field-of-view angle 2ω=43°.

[0038] The focal lengths f1 of the negative meniscus lens 1, f2 of the positive meniscus lens 2, f3 of the positive meniscus lens 4, f4 of the negative meniscus lens 5, and f5 of the refractive-diffraction hybrid positive meniscus lens 6 satisfy the following relationships:

[0039] -133.5mm≤f1≤-38mm

[0040] 24mm≤f2≤66.3mm

[0041] 16.9mm≤f3≤45.5mm

[0042] -1057mm≤f4≤-508mm

[0043] 46.9mm≤f5≤58.2mm.

[0044] All lenses in this system are made of germanium.

[0045] The system exhibits distortion ≤10% across the entire focal length range of 12–25 mm.

[0046] Example:

[0047] A hybrid refractive index and diffraction large relative aperture long-wave infrared optical system is disclosed, operating in the 8μm–14μm band. The image plane size is 15.36mm × 12.288mm, suitable for uncooled long-wave infrared detectors with a pixel size of 12μm and a detector resolution of 1280 × 1024. The system focal length is 12mm ≤ f′ ≤ 25mm, the ratio of the total optical system length to the focal length always satisfies 2 ≤ TTL / f′ ≤ 2.5, the full field of view satisfies 43° ≤ 2ω ≤ 78.7°, the system F-number is 1, and the distortion is less than 10%.

[0048] In this embodiment, the relevant parameters of the meniscus negative lens 1, meniscus positive lens 2, aperture 3, meniscus positive lens 4, meniscus negative lens 5, refractive-diffraction hybrid meniscus positive lens 6, and image plane 7 are shown in Table 1 below:

[0049]

[0050] The aspherical coefficients of each lens in this example are shown in Table 2:

[0051] surface A B C S1 -3.9E-5 to -8.3E-6 -8.5E-7 to -3.02E-8 -1.76E-9 to -4.05E-11 S2 -2.1E-5 to -3.16E-6 -1.2E-6 to -5.71E-8 S3 4.1E-5~2.95E-5 -1.07E-7 to -1.6E-8 3.99E-9~3.37E-11 S4 -4.8E-5 to -4.14E-6 1.4E-7~1.07E-8 S6 1.2E-5~2.07E-6 S7 2.9E-5~2.71E-6 -3.6E-8 to -4.85E-9 6.3E-10~9.8E-12 S9 3.2E-6 to -4.02E-6 -2.33E-8~3.57E-9 2.7E-9 to -4.19E-11 S11 4.99E-5~4.19E-6 1.56E-7~1.61E-008

[0052] In this example, the diffraction coefficients of the diffraction surface S11 in the mixed diffraction-refraction meniscus lens 6 are B1 = 11.53 and B2 = -15.37.

[0053] When the focal length f′=12mm, the total system length TTL is 30mm; when the focal length f′=25mm, the total system length TTL is 50mm; both satisfy the condition that the total length 2≤TTL / f′≤2.5.

[0054] like Figure 2-3 As shown, at a spatial frequency of 20 lp / mm, the transfer function of each field of view in this embodiment is greater than 0.5, indicating good image quality.

[0055] like Figure 4-5 As shown, the distortion curve results of the system indicate that the distortion of the system is less than 10% at focal lengths of 12mm and 25mm.

Claims

1. A hybrid catadioptric large relative aperture long wave infrared optical system, characterized in that, The system comprises, along the optical axis, in order from the object side to the image side, a meniscus negative lens (1), a meniscus positive lens (2), a diaphragm (3), a meniscus positive lens (4), a meniscus negative lens (5), a catadioptric meniscus positive lens (6) and an image plane (7); wherein the front surface of the meniscus negative lens (5) and the front surface of the catadioptric meniscus positive lens (6) are spherical surfaces, the catadioptric meniscus positive lens (6) is provided with a diffraction surface on the surface close to the image plane (7), and the other lens surfaces are even aspheric surfaces; the optical material of the meniscus negative lens (1), the meniscus positive lens (2), the meniscus positive lens (4), the meniscus negative lens (5) and the catadioptric meniscus positive lens (6) is germanium; the working waveband of the system is 8-14 μm, the F number of the system is 1, and the distortion is ≤10% in the full focal length range; in the system: 12 mm ≤ f' ≤ 25 mm, the full field angle 43° ≤ 2ω ≤ 78.7°, and the focal length f' and the field angle ω satisfy the relationship wherein y is the half-field image height of the image plane (7).

2. The hybrid catadioptric large-relative-aperture long-wave infrared optical system of claim 1, wherein, The concave surface of the meniscus negative lens one (1) and the meniscus negative lens two (5) are both towards the image surface (7) side.

3. The hybrid catadioptric large-relative-aperture long-wave infrared optical system of claim 1, wherein: The ratio of the total length TTL of the system to the focal length f' of the system is 2≤TTL / f'≤2.

5.

4. The hybrid catadioptric large-relative-aperture long-wave infrared optical system of claim 1, wherein: The focal length of the meniscus negative lens one (1) is -133.5mm≤f1≤-38mm, the focal length of the meniscus positive lens one (2) is 24mm≤f2≤66.3mm, the focal length of the meniscus positive lens two (4) is 16.9mm≤f3≤45.5mm, the focal length of the meniscus negative lens two (5) is -1057mm≤f4≤-508mm, and the focal length of the catadioptric meniscus positive lens (6) is 46.9mm≤f5≤58.2mm.

5. The hybrid catadioptric large-relative-aperture long-wave infrared optical system of claim 1, wherein, The even aspheric surface satisfies the following relationship: Wherein, Z(r) is the distance between the vertex of the aspheric surface and the aspheric surface at the height r along the optical axis; c is the aspheric surface curvature, here c=1 / R, R is the curvature radius of the aspheric surface; k is the conic coefficient; A, B, C, D are aspheric coefficients.

6. The hybrid catadioptric large-relative-aperture long-wave infrared optical system of claim 1, wherein, The phase distribution formula of the diffractive surface of the catadioptric meniscus positive lens (6) is: Φ = M(B1ρ 2 +B2ρ 4 ) Wherein, M is the diffraction order, B1, B2 are the diffractive surface coefficients, and p is the catadioptric surface radial coordinate.

Images