A lightweight mid-wave infrared panoramic imaging system

Abstract

The present invention discloses a lightweight mid-wave infrared panoramic imaging system, which includes a second mirror, a first mirror, a metalens, an aspheric lens, and an infrared detector arranged in sequence from the object side to the image side; a central opening is provided in the first mirror, and the concave surfaces of the first mirror and the second mirror are close to the image side; the first mirror and the second mirror are used to collect mid-infrared light in a super-large field of view range and compress the incident angle of the mid-infrared light on the metalens; both the front and rear surfaces of the metalens are metasurfaces capable of introducing phase mutations, which are used to correct the high-order aberrations of the optical system; both the front and rear surfaces of the aspheric lens are even aspheres, which are used to correct the primary aberrations of the optical system and transmit the mid-infrared light to the infrared detector. The present invention integrates reflective optical elements, transmissive optical elements, and planar optical elements, realizes a lightweight architecture design on the premise of ensuring a large field of view angle, and can achieve low distortion and near diffraction-limited imaging in the temperature range of -30°C to +70°C.

Description

Technical Field

[0001] The present invention relates to the field of mid-wave infrared panoramic imaging, and particularly to a lightweight mid-wave infrared panoramic imaging system. Background Art

[0002] Mid-wave infrared optical imaging technology is a thermal imaging technology that can record the thermal radiation distribution information of target objects and has strong penetration and day-night operation capabilities. Therefore, it can be widely applied to important fields such as night reconnaissance, gas detection, thermal temperature measurement, and substance composition detection.

[0003] Ordinary infrared optical systems have a small field of view angle, which will lead to limited detection field of view and inability to detect more target information. With the continuous development of artificial intelligence and information processing technology, there is a greater demand for a larger field of view angle in infrared optical systems. For an infrared optical system with a larger field of view angle, a combination of multiple infrared lenses made of different materials is usually used to correct the aberration brought by the large field of view optical system. Since infrared lens materials are expensive and have low transmittance, this makes the optical system heavy and the processing cost high. The patent with the publication number CN222280941U discloses a large field of view infrared camera lens with a semi-field of view angle of 60°, and the entire optical system is composed of 8 lenses, making the structure relatively complex and bulky.

[0004] Compared with a fully transmissive infrared optical system, an infrared panoramic imaging system has a larger field of view angle and fewer optical element numbers, but its special head unit still has not completely solved the pain point of heavy structure. The patent with the publication number CN211348844U discloses an infrared panoramic periscope device, whose head unit can collect infrared light with an ultra-large field of view and effectively compress the light incident angle, but the architecture is complex and poses high requirements for processing and alignment. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a lightweight mid-wave infrared panoramic imaging system, which integrates reflective optical elements, transmissive optical elements, and planar optical elements, and adopts two reflectors, one metalens, and one aspherical lens to achieve a lightweight architecture design, solves the pain point of the heaviness of ordinary mid-wave infrared ultra-wide-angle optical systems, and can achieve low distortion and near diffraction-limited imaging in the temperature range of - 30°C to +70°C.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A lightweight mid-wave infrared panoramic imaging system includes a second reflector, a first reflector, a metalens, an aspherical lens, and an infrared detector arranged in sequence from the object side to the image side;

[0008] The center of the first reflector is provided with an opening, and the concave surfaces of the first reflector and the second reflector are close to the image side;

[0009] The first mirror and the second mirror are used to collect mid-infrared light in an ultra-wide field of view and compress the incident angle of the mid-infrared light onto the metalens.

[0010] Both the front and rear surfaces of the metalens are metasurfaces capable of introducing phase mutations, which are used to correct the high-order aberrations of the optical system.

[0011] Both the front and rear surfaces of the aspherical lens are even aspheres, which are used to correct the primary aberrations of the optical system and transmit the mid-infrared light to the infrared detector.

[0012] The infrared detector is used to sense mid-infrared light in the range of 3-5 μm and convert it into an infrared image.

[0013] In order to collect mid-infrared light in an ultra-wide field of view and improve the control ability thereof, and at the same time ensure the processability and convenient alignment of the mirrors, the surface profiles of the first mirror and the second mirror are both fourth-order even aspheres.

[0014] In order to enable the mid-infrared light reflected by the second mirror R2 to pass through the center of the first mirror R1 and avoid excessive zero-order stray light from entering the system and causing negative effects, the obscuration ratio of the first mirror satisfies the following relationship: .

[0015] In order to achieve polarization-insensitive design of the metalens and satisfy the circularly symmetric phase distribution, the phase mutations introduced on both the front and rear surfaces of the metalens satisfy the following expression:

[0016]

[0017] where r is the radial distance of the surface of the metalens, R is the normalized radius of the surface of the metalens, and is the even diffraction coefficient of the surface of the metalens.

[0018] In order to facilitate the fabrication of the metalens and be able to cover all phase mutation ranges, the phase mutations on both the front and rear surfaces of the metalens are introduced by arranging cylindrical micro-nano units on a substrate, and the parameter ranges of the cylindrical micro-nano units are selected to satisfy that the introduced phase mutation range covers 0 to 2π.

[0019] In order to avoid excessive chromatic aberration introduced by the metalens, it should bear a small optical power in the optical system. The focal length f of the metalens M and the focal length f of the entire optical system satisfy: f M ≥200f.

[0020] To improve the correction ability of the transmissive optical element for the primary aberrations in the optical system, the surface profiles of the front and rear surfaces of the aspherical lens are tenth-order even aspheres.

[0021] To reduce the material and processing costs of the optical system, the shape of the aspherical lens is a meniscus lens, with the front surface being convex and the rear surface being concave.

[0022] Furthermore, the material of the aspherical lens is silicon or chalcogenide glass, and the material of the metalens is silicon.

[0023] To ensure that the optical system can detect a sufficiently large field of view and reduce the size of the central blind area of the detector, the maximum half field of view angle θ max and the minimum half field of view angle θ min of the entire imaging system satisfy the following relationship: θ max ≥100°, θ min ≤30°.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1. The mid-wave infrared panoramic imaging system of the present invention includes a reflective optical element, a transmissive optical element, and a planar optical element, and only uses two reflectors, one metalens, and one even aspherical lens to achieve lightweight while ensuring a large field of view angle, solving the pain points of the large number of elements in the large field of view transmissive infrared optical system and the top-heavy problem caused by the heavy shape of the head unit in the ordinary infrared panoramic imaging system.

[0026] 2. The present invention uses two reflectors, which greatly avoids the negative impact of chromatic aberration on the lightweight mid-wave infrared panoramic imaging system, enabling the optical system to achieve an ultra-large field of view angle, low distortion, athermalization, and near diffraction-limited imaging.

[0027] 3. Compared with the large number of elements required in the large field of view transmissive infrared optical system and the strict processing requirements brought by the head unit in the ordinary infrared panoramic imaging system, the lightweight mid-wave infrared panoramic imaging system of the present invention uses fewer optical elements and has a simple structure, with high processability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention.

[0029] Figure 2 It is a phase mutation distribution diagram of the front surface of the metalens in the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention.

[0030] Figure 3 It is a phase mutation distribution diagram of the rear surface of the metalens in the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention.

[0031] Figure 4 This is a graph showing the diameter and introduced phase of the micro-nano units on the front and back surfaces of the metalens of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention when the period is 1400 nm and the height is 6000 nm.

[0032] Figure 5 This is a ray tracing diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under normal temperature working conditions.

[0033] Figure 6 This is a spot diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under normal temperature working conditions.

[0034] Figure 7 This is an MTF curve diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under normal temperature working conditions.

[0035] Figure 8 This is a field curvature and distortion diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under normal temperature working conditions.

[0036] Figure 9 This is a spot diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under low temperature working conditions.

[0037] Figure 10 This is an MTF curve diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under low temperature working conditions.

[0038] Figure 11 This is a field curvature and distortion diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under low temperature working conditions.

[0039] Figure 12 This is a spot diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under high temperature working conditions.

[0040] Figure 13 This is an MTF curve diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under high temperature working conditions.

[0041] Figure 14 This is a field curvature and distortion diagram of the lightweight mid-wave infrared panoramic imaging system in the embodiment of the present invention under high temperature working conditions.

[0042] Figure 15 This is a ray tracing diagram of the traditional mid-wave infrared panoramic annular lens in the comparative example of the present invention. Detailed implementation manners

[0043] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The objectives and effects of the present invention will become more apparent. It should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0044] As Figure 1 shown, the lightweight mid-wave infrared panoramic imaging system proposed by the present invention includes a second mirror R2, a first mirror R1, a metasurface lens M, an aspheric lens A, and an infrared detector D arranged in sequence from the object side to the image side.

[0045] Among them, the center of the first mirror R1 has an opening, and the concave surfaces of the first mirror R1 and the second mirror R2 are close to the image side. The first mirror R1 and the second mirror R2 are used to collect mid-infrared light in a large field of view range and compress the incident angle of the light onto the metasurface lens M; both the front and rear surfaces of the metasurface lens M are metasurfaces that can introduce phase mutations, which are used to correct the high-order aberrations of the optical system; both the front and rear surfaces of the aspheric lens A are even aspheres, which are used to correct the primary aberrations of the optical system and transmit the mid-infrared light to the infrared detector D; the infrared detector D is used to sense mid-infrared light in the range of 3-5 μm and convert it into an infrared image.

[0046] In this embodiment, in order to obtain a large target surface and adapt to the lightweight mid-wave infrared panoramic imaging system, the resolution of the infrared sensor D is selected as 640×512, and the pixel size is 15um.

[0047] In this embodiment, in order to sense mid-infrared light in a large field of view range and minimize the size of the central blind area of the infrared detector D as much as possible, the half field of view angle of the lightweight mid-wave infrared panoramic imaging system is 360°×(30°~100°). In order to obtain a panoramic annular image, the half image height of the maximum field of view on the infrared sensor D cannot exceed half of the short side of the infrared sensor D.

[0048] In this embodiment, in order to ensure that the light in the minimum field of view can be incident on the first mirror R1 and will not block the light reflected by the second mirror R2, the outer diameter size of the first mirror is 55mm, the central opening size is 9mm, and the obstruction ratio of the first mirror R1 .

[0049] In this embodiment, the focal length f of the metasurface lens M M and the focal length f of the entire optical system satisfy: f M =242f.

[0050] In this embodiment, the shape of the aspheric lens A is a meniscus lens, the front surface is convex, the rear surface is concave, and the material is selected as chalcogenide glass.

[0051] In this embodiment, the surface profiles of the first mirror R1 and the second mirror R2 are both fourth-order even aspheres, and their surface contours satisfy the following expression:

[0052]

[0053] where c is the curvature of the surface vertex, k is the conic coefficient, r is the radial distance, and are the fourth-order even aspheric coefficients.

[0054] In this embodiment, the front and rear surfaces of the metalens M introduce phase mutations by arranging cylindrical micro-nano units on a silicon substrate, and the introduced phase mutations satisfy the following expression:

[0055]

[0056] where r is the radial distance of the surface of the metalens, R is the normalized radius of the surface of the metalens, and are the even diffraction coefficients of the surface of the metalens.

[0057] In this embodiment, the surface profiles of the front and rear surfaces of the aspheric lens A are both tenth-order even aspheres, and their surface contours satisfy the following expression:

[0058]

[0059] where r is the radial distance, R is the normalized radius, and are the even aspheric coefficients.

[0060] In this embodiment, in order to improve the working stability of the lightweight mid-wave infrared panoramic imaging system at different ambient temperatures, an athermal design is carried out in the temperature range of -30°C to +70°C. According to the different ambient working temperatures, the working states of the system are divided into a normal-temperature working state (the ambient working temperature is +20°C), a low-temperature working state (the ambient working temperature is -30°C), and a high-temperature working state (the ambient working temperature is +70°C).

[0061] In this embodiment, the system parameters are optimized by the ray tracing method. Table 1 below gives the system structure parameters in this embodiment under the normal-temperature working state, and Tables 2, 3, and 4 respectively give the even aspheric parameters of the mirrors, the even diffraction parameters of the metalens, and the even aspheric parameters of the aspheric lens in this embodiment under the normal-temperature working state.

[0062] Table 1 System structure parameters in this embodiment under the normal-temperature working state

[0063]

[0064] Table 2 Even aspheric parameters of the mirrors in this embodiment under the normal-temperature working state

[0065]

[0066] Table 3 Diffraction parameters of the metalens in this embodiment under normal temperature working conditions

[0067]

[0068] Table 4 Even aspheric parameters of the aspheric lens in this embodiment under normal temperature working conditions

[0069]

[0070] Under the parameters in Table 3, the phase mutation distributions introduced by the front surface and the back surface of the metalens M are respectively as Figure 2 、 Figure 3 shown. The phase mutation distributions on its front and back surfaces change relatively smoothly, allowing for a relatively large manufacturing tolerance, which is beneficial to the processing and preparation of the metalens.

[0071] In this embodiment, as Figure 4 shown, the front and back surfaces of the metalens M are formed by arranging silicon cylinder micro-nano units with a period of 1400 nm, a height of 6000 nm, and a diameter range of 800 nm to 1020 nm on a silicon substrate to ensure that the phase mutation range of can be covered, so that the front and back surfaces of the metalens M can effectively introduce the phase distributions as Figure 2 、 Figure 3 shown.

[0072] Under the parameters in Table 1, Table 2, Table 3, and Table 4, the ray tracing diagrams of the system under normal temperature working conditions are as Figure 5 shown. The ray focusing of the system is good, the lens structure distribution is reasonable, and the overall architecture is simple and lightweight.

[0073] Under normal temperature working conditions, the spot diagram, MTF curve diagram, and field curvature distortion diagram of the system are respectively as Figure 6 、 Figure 7 、 Figure 8 shown; under low temperature working conditions, the spot diagram, MTF curve diagram, and field curvature distortion diagram of the system are respectively as Figure 9 、 Figure 10 、 Figure 11 shown; under high temperature working conditions, the spot diagram, MTF curve diagram, and field curvature distortion diagram of the system are respectively as Figure 12 、 Figure 13 、 Figure 14 shown.

[0074] Under normal temperature working conditions, low temperature working conditions, and high temperature working conditions, the maximum RMS radii of the system at five fields of view are respectively 。The spot size of the point spread function is approximately the same as and smaller than the pixel size of the infrared detector D, allowing for a certain range of manufacturing tolerances and adapting to the highest performance of the detector.

[0075] In the normal temperature operating state, low temperature operating state, and high temperature operating state, the MTF value of the system at a spatial frequency of 33 lp / mm is higher than 0.4, close to the diffraction limit, demonstrating its high imaging performance in a lightweight architecture design.

[0076] In the normal temperature operating state, low temperature operating state, and high temperature operating state, the maximum F-theta distortion of the system is 5.1072%, 5.1069%, and 5.1075% respectively. In different temperature operating states and when receiving mid-infrared light with an ultra-large field of view, the maximum F-theta distortion of the system is only close to 5%, proving the superior performance of the embodiments of the present invention.

[0077] In the embodiments of the present invention, in different temperature operating states, the focal length is close to -2 mm, the image space F-number is 3.2, the half field of view angle is 360°×(30°~100°), the total system length is close to 60 mm, and it has high temperature stability. Table 5 below gives the specific key performance parameters of the embodiments of the present invention in three operating states.

[0078] Table 5 Key performance parameters in three operating states of this embodiment

[0079]

[0080] Comparative example

[0081] A traditional mid-wave infrared panoramic annular lens, whose field of view range, focal length, imaging height, and imaging quality in the temperature range of -30°C to +70°C are all close to those of the embodiments of the present invention. Its system structure and ray tracing results are as Figure 15 shown, consisting of a panoramic head unit PHU, an aspherical lens L1, and a binary diffractive lens L2 arranged in sequence from the object side to the image side.

[0082] Different from the embodiments of the present invention, in the comparative example, a catadioptric hybrid panoramic head unit PHU was adopted to collect mid-infrared light in a large field of view and compress the light incident angle. Although the optical system of this architecture can significantly reduce the number of lenses and reduce distortion compared with the traditional athermalized refractive optical system, the thickness of its panoramic head unit PHU reaches more than 20 mm, which makes the whole system heavy and top-heavy. Since the price of infrared materials is relatively expensive, manufacturing such a heavy panoramic head unit PHU will cause a sharp increase in material costs. In addition, this type of head unit usually needs to be manufactured by gluing two lenses together and accurately coated with an annular reflective film on the rear surface, increasing the risk of ghost image interference and posing strict requirements on processing accuracy.

[0083] According to the results of the embodiments and comparative examples of the present invention, a comparison between the lightweight mid-wave infrared panoramic imaging system and the traditional mid-wave infrared panoramic annular lens is made, as shown in Table 6.

[0084] Table 6 Performance comparison between the lightweight mid-wave infrared panoramic imaging system and the traditional mid-wave infrared panoramic annular lens

[0085]

[0086] Compared with other large-field mid-wave infrared optical systems, the lightweight mid-wave infrared panoramic imaging system of this embodiment solves the pain points of a large number of components, high cost, and heavy system, and has the characteristics of compactness, light weight, and low distortion, and can achieve near-diffraction-limited imaging in the temperature range of -30°C to +70°C.

[0087] In the present invention, the terms "first", "second", "third", etc. are used to distinguish similar objects and cannot be understood as indicating or implying relative importance.

[0088] Those of ordinary skill in the art can understand that the above are only preferred examples of the invention and are not used to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, for those skilled in the art, they can still modify the technical solutions described in the foregoing examples, or perform equivalent replacements for some of the technical features. All modifications, equivalent replacements, etc. made within the spirit and principle of the invention shall be included within the protection scope of the invention.

Claims

1. A lightweight mid-wave infrared panoramic imaging system, characterized in that It includes a second reflector, a first reflector, a metalens, an aspherical lens, and an infrared detector arranged in sequence from the object side to the image side; The center of the first reflector is provided with an opening, and the concave surfaces of the first reflector and the second reflector are close to the image side; The first reflector and the second reflector are used to collect mid-infrared light in a super-large field of view range and compress the incident angle of the mid-infrared light onto the metalens; Both the front and rear surfaces of the metalens are metasurfaces capable of introducing phase mutations, which are used to correct the high-order aberrations of the optical system; Both the front and rear surfaces of the aspherical lens are even-order aspheres, which are used to correct the primary aberrations of the optical system and transmit the mid-infrared light to the infrared detector; The infrared detector is used to sense mid-infrared light of 3-5 μm and convert it into an infrared image.

2. The lightweight mid-wave infrared panoramic imaging system according to claim 1, characterized in that, The surface profiles of the first reflector and the second reflector are both fourth-order even-order aspheres.

3. The lightweight mid-wave infrared panoramic imaging system according to claim 1, wherein The obscuration ratio of the first reflector satisfies the following relationship: .

4. The lightweight mid-wave infrared panoramic imaging system according to claim 1, wherein The phase mutations introduced on both the front and rear surfaces of the metalens both satisfy the following expression: ； where r is the radial distance on the surface of the superlens, and R is the normalized radius of the surface of the superlens, is the even diffraction coefficient of the surface of the superlens.

5. The lightweight mid-wave infrared panoramic imaging system according to claim 4, wherein, The phase mutations on both the front and rear surfaces of the metalens are introduced by arranging cylindrical micro-nano units on a substrate, and the parameter range of the cylindrical micro-nano units is selected to satisfy that the introduced phase mutation range covers 0 to 2π.

6. The lightweight mid-wave infrared panoramic imaging system according to claim 1, wherein The focal length f of the metalens M and the focal length f of the entire optical system satisfy: f M ≥ 200f.

7. The lightweight mid-wave infrared panoramic imaging system according to claim 1, characterized in that, The surface profiles of both the front and rear surfaces of the aspherical lens are tenth-order even-order aspheres.

8. The lightweight mid-wave infrared panoramic imaging system according to claim 7, characterized in that, The shape of the aspherical lens is a meniscus lens, with the front surface being convex and the rear surface being concave.

9. The lightweight mid-wave infrared panoramic imaging system according to claim 8, characterized in that The material of the aspherical lens is silicon or chalcogenide glass, and the material of the metalens is silicon.

10. The lightweight mid-wave infrared panoramic imaging system according to claim 1, wherein The maximum half field of view angle θ of the entire imaging system max and the minimum half field of view angle θ min satisfy the following relationship: θ max ≥100°, θ min ≤30°.

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