A laser radar receiving lens optical system

Abstract

This invention discloses an optical system for a lidar receiving lens, comprising a first lens, a second lens, a third lens, an aperture stop, a fourth lens, a fifth lens, a sixth lens, a seventh lens, a filter, a protective glass, and an image plane arranged along the object-side to the image-side. By rationally utilizing lenses with specific shapes and structures and limiting the optical power of each lens, the field of view of the optical system is increased to 153 degrees while possessing a large aperture of F1.0, resulting in a wider radar receiving field of view, providing high-definition imaging effects and recognition accuracy. Furthermore, the maximum target area is ≥10mm, F-theta distortion is less than 1%, and CRA is less than 1 degree, improving the imaging quality and accuracy for distant targets and providing more accurate receiving and ranging data. With a TTL of 32mm and a small size, it facilitates miniaturization. Simultaneously, the high and low temperature drift compensation of the optical system is optimized to ensure the stability of the lens's imaging effect during high and low temperature operation. The entire optical system has a cost advantage and higher cost-effectiveness.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, specifically to an optical system for a lidar receiving lens. Background Technology

[0002] In recent years, with the rapid development of intelligent technology, intelligent recognition technology has become the focus of attention. Against this backdrop, LiDAR technology, as a rising star in the field of intelligent detection, is gradually demonstrating its indispensable importance. LiDAR is like a detective with superhuman vision and keen analytical capabilities. It consists of two main components: a laser emitter, responsible for sending out thin beams of light in all directions; and a laser receiver, which waits patiently to capture the light signals reflected back from the target. When these reflected lights are converged onto the detector by a sophisticated array of receiving mirrors, a "dialogue" about light begins. By comparing the emitted laser light with the received reflected light, LiDAR can, like a decoding expert, decipher many secrets about the target: such as its distance, its altitude, and even whether it is moving or stationary, and its speed. This crucial information is like piecing together a puzzle. Figure 1 Generally, it helps us accurately locate, track, and identify each target in complex environments.

[0003] However, current lidar receiving lenses often suffer from problems such as excessively small target size and insufficient field of view, which to some extent limit their detection range and accuracy. In addition, existing lenses mostly adopt a structure of 7 spherical glass lenses and 1 aspherical lens. The high cost of 7 glass lenses directly leads to high overall costs during mass production. Summary of the Invention

[0004] This invention proposes an optical system for a lidar receiving lens that combines the characteristics of ultra-large target surface, large field of view, small distortion, small CRA, low cost, and stable thermal drift.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: an optical system for a laser radar receiving lens:

[0006] Along the optical axis from the object plane to the image plane, the following components are included in sequence: first lens, second lens, third lens, aperture stop, fourth lens, fifth lens, sixth lens, seventh lens, filter, protective glass, and image plane;

[0007] The first lens is a negative meniscus lens; the second lens is a negative meniscus lens; the third lens is a negative meniscus-convex lens; the fourth lens is a positive biconvex lens; the fifth lens is a positive biconvex lens; the sixth lens is a negative biconcave lens; the seventh lens is a positive biconvex lens;

[0008] Among them, the refractive indices of the first lens to the seventh lens satisfy the following conditions:

[0009] 1.7 < n1 < 2.3; 1.3 < n2 < 1.8; 1.5 < n3 < 1.9; 1.7 < n4 < 2.3; 1.4 < n5 < 1.8; 1.5 < n6 < 1.8; 1.4 < n7 < 1.7; where, n1 is the refractive index of the first meniscus lens, n2 is the refractive index of the second meniscus lens, n3 is the refractive index of the third meniscus-convex lens, n4 is the refractive index of the fourth biconvex lens, n5 is the refractive index of the fifth biconvex lens, n6 is the refractive index of the sixth biconcave lens, and n7 is the refractive index of the seventh biconvex lens.

[0010] A further solution is that the Abbe numbers of the second lens, the fifth lens, and the seventh lens are all greater than 53 and less than 59; the Abbe numbers of the third lens and the sixth lens are all greater than 17 and less than 22.

[0011] A further solution is that the maximum full-image height IHmax of the optical system satisfies the following condition: IHmax ≥ 10 mm.

[0012] A further solution is that the maximum field angle FOV of the optical system satisfies the following condition: 150° ≤ FOV ≤ 155°.

[0013] A further solution is that the chief ray angle of incidence CRA of the optical system: CRA < 1°.

[0014] A further solution is that the effective focal length f of the optical system satisfies the following condition: 3.5 mm ≤ f ≤ 4 mm.

[0015] A further embodiment is that the first lens has a convex surface facing the object side and a concave surface facing the image side; the second lens has a convex surface facing the object side and a concave surface facing the image side; the third lens has a concave surface facing the object side and a convex surface facing the image side; the fourth lens has a convex surface facing the object side and a convex surface facing the image side; the fifth lens has a convex surface facing the object side and a convex surface facing the image side; the sixth lens has a concave surface facing the object side and a concave surface facing the image side; and the seventh lens has a convex surface facing the object side and a convex surface facing the image side.

[0016] A further proposed solution is that the refractive index n5 of the fifth lens, the refractive index n6 of the sixth lens, and the refractive index n7 of the seventh lens satisfy the following condition: 0.8 < |(n5-n6) / (n6-n7)| < 1.2.

[0017] A further approach is to ensure that the effective focal length f of the optical system satisfies the same conditions as the focal length f1 of the first lens and the focal length f2 of the second lens: -3.1 <f1 / f<-2.6;-4.9<f2 / f<-4.3。

[0018] A further proposed solution is that the focal length f4 of the fourth lens and the focal length f5 of the fifth lens in the optical system satisfy: 6.5 < |(f4+f5) / (f4-f5)| < 7.0.

[0019] In summary, the present invention has the following beneficial effects: By rationally using lenses with specific shapes and structures and limiting the optical power of each lens, the present invention increases the field of view of the optical system to 153 degrees while possessing a super-large aperture of F1.0, resulting in a wider radar receiving field of view, providing high-definition imaging effects and recognition accuracy. Furthermore, the maximum target area is ≥10mm, F-theta distortion is less than 1%, and CRA is less than 1 degree, improving the imaging quality and accuracy for distant targets and providing more accurate receiving and ranging data. With a TTL of 32mm, the small size facilitates miniaturization and installation in vehicles. Simultaneously, the combination of 2G5P glass and plastic optimizes the high and low temperature drift compensation of the optical system, ensuring the stability of the imaging effect when the lens operates at high and low temperatures, and also making the entire optical system more cost-effective and cost-efficient. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of an optical system provided in an embodiment of the present invention;

[0021] Figure 2 The MTF analysis diagram of the optical system provided in this embodiment of the invention when the incident light is an infrared 940nm wavelength at 20°C;

[0022] Figure 3The defocusing curve of the optical system provided in the embodiment of the present invention when the incident light is an infrared wavelength of 940nm at 20°C;

[0023] Figure 4 The defocusing curve of the optical system provided in this embodiment of the invention when the incident light is an infrared wavelength of 940nm at 85°C;

[0024] Figure 5 The defocusing curve of the optical system provided in this embodiment of the invention when the incident light is an infrared 940nm wavelength at -40℃;

[0025] Figure 6 The field curve diagram of the optical system provided in the embodiment of the present invention corresponding to the incident light wavelength of infrared 940nm;

[0026] Figure 7 The F-THETA distortion diagram of the optical system provided in the embodiments of the present invention for incident light with an infrared wavelength of 940nm;

[0027] Figure 8 The optical system provided in this embodiment of the invention corresponds to a standard dot plot of incident light at an infrared wavelength of 940nm. Detailed Implementation

[0028] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0031] In the present invention, unless otherwise clearly specified and defined, terms such as "installation", "connection", "linkage", "fixation", etc. shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] As Figure 1 shown, the present invention provides a lidar receiving lens optical system, which sequentially includes, along the optical axis from the object surface to the image surface: a first lens E1, a second lens E2, a third lens E3, an aperture STO, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, a filter IR, a protective glass CG, and an image surface IMA; among them, the first lens and the fourth lens are two spherical glass lenses, and the remaining five lenses are aspherical plastic lenses. It should be noted that by the combination of glass lenses and plastic lenses, the temperature drift of the entire optical system at high and low temperatures can be made more stable, and the purple fringing can also be optimized.

[0033] The first lens E1 is a meniscus lens with a negative optical power; the second lens E2 is a meniscus lens with a negative optical power; the third lens E3 is a concave-convex lens with a negative optical power; the fourth lens E4 is a biconvex lens with a positive optical power; the fifth lens E5 is a biconvex lens with a positive optical power; the sixth lens E6 is a biconcave lens with a negative optical power; the seventh lens E7 is a biconvex lens with a positive optical power;

[0034] Among them, the refractive indices of the first lens E1 to the seventh lens E7 satisfy the following conditions:

[0035] 1.7 < n1 < 2.3; 1.3 < n2 < 1.8; 1.5 < n3 < 1.9; 1.7 < n4 < 2.3; 1.4 < n5 < 1.8; 1.5 < n6 < 1.8; 1.4 < n7 < 1.7; where n1 is the refractive index of the first meniscus lens, n2 is the refractive index of the second meniscus lens, n3 is the refractive index of the third concave-convex lens, n4 is the refractive index of the fourth biconvex lens, n5 is the refractive index of the fifth biconvex lens, n6 is the refractive index of the sixth biconcave lens, and n7 is the refractive index of the seventh biconvex lens.

[0036] It should be noted that the refractive index n1 of the first lens E1 satisfies: 1.7 < n1 < 2.3, and the refractive index n4 of the fourth lens satisfies: 1.7 < n4 < 2.3. The first lens E1 and the fourth lens E4 are made of high-refractive-index glass. High-refractive-index materials can focus light more precisely, improve the spatial resolution of infrared imaging, and enhance the imaging quality of the lens.

[0037] As an improvement, the refractive index n5 of the fifth lens, the refractive index n6 of the sixth lens, and the refractive index n7 of the seventh lens satisfy: 0.8 < |(n5 - n6) / (n6 - n7)| < 1.2; by satisfying the above conditional formula and reasonably selecting optical materials, it is ensured that the refractive indices of adjacent lens materials match each other, which can reduce the change in the refraction angle of light at the lens interface, thereby reducing the CRA of the lens and being beneficial to the matching of the lens and the chip.

[0038] As an improvement, the effective focal length f of the optical lens, the focal length f1 of the first lens, and the focal length f2 of the second lens satisfy: -3.1 < f1 / f < -2.6; -4.9 < f2 / f < -4.3. By satisfying the above ranges, the first lens E1 and the second lens E2 can have appropriate negative optical powers, which is beneficial for large-angle light to enter the optical lens, and further increases the field angle of the optical lens.

[0039] As an improvement, the focal length f4 of the fourth lens E4 and the focal length f5 of the fifth lens E5 of the optical lens satisfy: 6.5 < |(f4 + f5) / (f4 - f5)| < 7.0; by satisfying the above ranges, the width of the light beam can be expanded when large-angle light passes through the fourth lens E4 and the fifth lens E5. In this process, light can be transmitted to the imaging surface fully and efficiently, thereby expanding the field range of the optical lens, which is beneficial for the optical lens to achieve high-pixel and large-image-plane imaging.

[0040] As an improvement, the focal length f1 of the first lens, the focal length f2 of the second lens, and the focal length f3 of the third lens of the optical lens satisfy: 0.8 < (f1 - f2) / (f1 - f3) < 1.1. By satisfying the above ranges, the focal lengths of each lens can be reasonably allocated to improve the imaging quality;

[0041] As an improvement, the overall optical length TTL of the optical lens and the maximum holographic height IHmax corresponding to the maximum field angle satisfy: 3.0 < TTL / IHmax < 3.5. By satisfying the above ranges, the relationship between the image height and the overall optical length of the optical lens can be balanced, and the volume of the lens can be reduced.

[0042] As an improvement, the Abbe numbers of the second lens E2, the fifth lens E5, and the seventh lens E7 are all greater than 53 and less than 59; the Abbe numbers of the third lens E3 and the sixth lens E6 are all greater than 17 and less than 22.

[0043] As an improvement, the maximum holographic height IHmax of the optical system satisfies the following condition: IHmax ≥ 10 mm.

[0044] As an improvement, the maximum field of view (FOV) of the optical system satisfies the following condition: 150°≤FOV≤155°.

[0045] As an improvement, the principal ray incident angle CRA of the optical system is CRA < 1°.

[0046] As an improvement, the effective focal length f of the optical system satisfies the following condition: 3.5mm ≤ f ≤ 4mm.

[0047] As an improvement, the first lens E1 has a convex surface S1 facing the object side and a concave surface S2 facing the image side; the second lens E2 has a convex surface S3 facing the object side and a concave surface S4 facing the image side; the third lens E3 has a concave surface S5 facing the object side and a convex surface S6 facing the image side; the fourth lens E4 has a slightly convex surface S8 facing the object side and a large convex surface S9 facing the image side; the fifth lens E5 has a large convex surface S10 facing the object side and a convex surface S11 facing the image side; the sixth lens E6 has a large concave surface S12 facing the object side and a concave surface S13 facing the image side; and the seventh lens E7 has a large convex surface S14 facing the object side and a convex surface S15 facing the image side.

[0048] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0049] The parameters of each lens in this embodiment are listed in Table 1 below, and the aspherical coefficients of the lenses are shown in Table 2 below.

[0050] Table 1 Physical parameters of each lens

[0051]

[0052] Table 2 Aspherical coefficients of lenses

[0053]

[0054]

[0055]

[0056] The aspherical coefficients satisfy the following equation:

[0057]

[0058] Where z is the aspherical sagitta, c is the paraxial curvature of the aspherical surface, y is the lens aperture, k is the conic coefficient, a4 is the 4th order aspherical coefficient, a6 is the 6th order aspherical coefficient, a8 is the 8th order aspherical coefficient, and a10 is the 10th order aspherical coefficient.

[0059] Specifically, in this embodiment, the R-value (radius of curvature), thickness, refractive index, Abbe number (ABB), and focal length (EFL-E) of each lens surface are shown in Table 1, and the aspherical parameters are shown in Table 2. In Table 1, Surf represents the mirror number, and InFInITY represents infinity. In Table 2, R1 represents the radius of curvature of the corresponding lens surface facing the object side, and R2 represents the radius of curvature of the corresponding lens surface facing the image side. A positive radius of curvature indicates that the mirror is curved towards the object side, and a negative radius of curvature indicates that the mirror is curved towards the image side.

[0060] The optical system provided in Table 1 has an effective focal length of 3.69 mm, a total TTL optical length of 32 mm, a maximum holographic height of 10 mm, an F-theta distortion of less than 1%, a field of view of 153 degrees, and a CRA of less than 1 degree. In Table 1, mirror numbers 1 and 2 represent the two mirrors of lens 1 along the direction of light incidence, mirror numbers 3 and 4 represent the two mirrors of lens 2 along the direction of light incidence, mirror numbers 5 and 6 represent the two mirrors of lens 3 along the direction of light incidence, mirror numbers 8 and 9 represent the two mirrors of lens 4 along the direction of light incidence, mirror numbers 10 and 11 represent the two mirrors of lens 5 along the direction of light incidence, mirror numbers 12 and 13 represent the two mirrors of lens 6 along the direction of light incidence, and mirror numbers 14 and 15 represent the two mirrors of lens 7 along the direction of light incidence.

[0061] In an embodiment of the present invention, Figure 2 This is a modulation transfer function (MTF) curve for the infrared band, representing the overall resolving power of an optical system. The horizontal axis represents spatial frequency, in cycles per millimeter (mm), and the vertical axis represents the MTF value. The MTF value is used to evaluate the image quality of a lens, ranging from 0 to 1. It is worth noting that the optical transfer function is a relatively accurate, intuitive, and common way to evaluate the image quality of an optical system. The higher and smoother the curve, the better the image quality and the stronger the ability to reproduce the true image. Figure 2 It can be seen that the MTF in the imaging region near the center of the infrared band is >0.9, indicating good imaging quality. Figure 3 The defocus curve shows that the lens has good MTF concentration, making focusing easy. From... Figure 4and Figure 5 It can be seen that the defocus curves at both high and low temperatures meet the requirements of high resolution, with small changes in focus and stable thermal drift effect; Figure 6 Represented as a field curve diagram, by Figure 6 It can be seen that the field curvature value should be controlled between -20um and 20um. The smaller the field curvature value, the better the image quality of the lens. Figure 7 This is represented as an F-THETA distortion map. The smaller the F-THETA distortion, the less the compression at the edges of the image. Figure 8 This is a standard dot plot corresponding to the infrared 940nm wavelength in an embodiment of the invention.

Claims

1. A lidar receiving lens optical system, characterized in that: The optical system has seven lenses with optical power, and sequentially includes from the object surface to the image surface along the optical axis: a first lens, a second lens, a third lens, an aperture, a fourth lens, a fifth lens, a sixth lens, a seventh lens, a filter, a protective glass, and an image surface; The first lens is a meniscus lens with negative optical power; the second lens is a meniscus lens with negative optical power; the third lens is a concave-convex lens with negative optical power; the fourth lens is a biconvex lens with positive optical power; the fifth lens is a biconvex lens with positive optical power; the sixth lens is a biconcave lens with negative optical power; the seventh lens is a biconvex lens with positive optical power; The surface of the first lens facing the object side is convex, and the surface facing the image side is concave; the surface of the second lens facing the object side is convex, and the surface facing the image side is concave; the surface of the third lens facing the object side is concave, and the surface facing the image side is convex; the surface of the fourth lens facing the object side is convex, and the surface facing the image side is also convex; the surface of the fifth lens facing the object side is convex, and the surface facing the image side is also convex; the surface of the sixth lens facing the object side is concave, and the surface facing the image side is also concave; the surface of the seventh lens facing the object side is convex, and the surface facing the image side is also convex; Among them, the refractive indices of the first lens to the seventh lens satisfy the following conditions: 1.7 < n1 < 2.3; 1.3 < n2 < 1.8; 1.5 < n3 < 1.9; 1.7 < n4 < 2.3; 1.4 < n5 < 1.8; 1.5 < n6 < 1.8; 1.4 < n7 < 1.7; where, n1 is the refractive index of the first lens, n2 is the refractive index of the second lens, n3 is the refractive index of the third lens, n4 is the refractive index of the fourth lens, n5 is the refractive index of the fifth lens, n6 is the refractive index of the sixth lens, and n7 is the refractive index of the seventh lens; The Abbe numbers of the second lens, the fifth lens, and the seventh lens are all greater than 53 and less than 59; the Abbe numbers of the third lens and the sixth lens are all greater than 17 and less than 22.

2. The optical system for a lidar receiving lens according to claim 1, characterized in that: The maximum full image height IHmax of the optical system satisfies the following condition: IHmax ≥ 10 mm.

3. The optical system for a lidar receiving lens according to claim 1, characterized in that: The maximum field of view FOV of the optical system satisfies the following condition: 150° ≤ FOV ≤ 155°.

4. The optical system for a lidar receiving lens according to claim 1, characterized in that: The chief ray angle of incidence CRA of the optical system: CRA < 1°.

5. The optical system for a lidar receiving lens according to claim 1, characterized in that: The effective focal length f of the optical system satisfies the following condition: 3.5 mm ≤ f ≤ 4 mm.

6. The optical system for a lidar receiving lens according to claim 1, characterized in that: The refractive index n5 of the fifth lens, the refractive index n6 of the sixth lens, and the refractive index n7 of the seventh lens satisfy: 0.8 < |(n5 - n6) / (n6 - n7)| < 1.

2.

7. The optical system for a lidar receiving lens according to claim 1, characterized in that: The effective focal length f of the optical system, the focal length f1 of the first lens, and the focal length f2 of the second lens satisfy: -3.1 < f1 / f < -2.6; -4.9 < f2 / f < -4.

3.

8. A lidar receiving lens optical system according to claim 1, characterized in that: The focal length f4 of the fourth lens and the focal length f5 of the fifth lens of the optical system satisfy: 6.5 < |(f4+f5) / (f4-f5)| < 7.0.

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