Laser radar receiving lens optical system

Abstract

The invention discloses an optical system of a laser radar receiving lens. The optical system comprises a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an optical filter, protective glass and an image surface which are arranged in a direction from an object side to an image side. By reasonably using the lenses with specific shapes and structures and limiting the focal power of each lens, the field angle of the optical system is increased to 153 degrees, meanwhile, the optical system has an ultra-large aperture F1.0, the radar receiving field of view is wider, the high-definition imaging effect and the recognition accuracy are provided, the maximum target surface is larger than or equal to 10 mm, the F-theta distortion is smaller than 1%, the CRA is smaller than 1 degree, and the optical system can be widely applied to the field of view imaging. The imaging quality and precision of a long-distance target are improved, more accurate receiving ranging data can be provided, TTL is 32 mm, the size is small, and miniaturization is facilitated; meanwhile, high and low temperature drift compensation of the optical system is optimized, and the stability of the imaging effect of the lens during high and low temperature work is ensured; the whole optical system is more advantageous in cost and higher in cost performance.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a laser radar receiving lens optical system. Background Art

[0002] In recent years, with the rapid development of intelligent technology, intelligent recognition technology has become the focus of everyone's attention. Against this background, LiDAR technology, as a bright new star in the field of intelligent detection, is gradually showing its indispensable importance. LiDAR is like a detective with super long-range vision and keen analytical ability. It is divided into two main characters: the laser transmitting end, which is responsible for sending thin beams of light to the surroundings; and the laser receiving end, which waits quietly to capture the light signals that bounce back from the target. When these reflected lights are converged onto the detector through a precise receiving mirror group, a "dialogue" about light begins. By comparing the emitted laser and the received reflected light, the LiDAR can decipher many secrets about the target like a decoding master: such as how far away it is from us, how high it is, and even whether it is moving or still, and how fast it is. These key information, like puzzle pieces, are like a piece of paper. Figure 1 Generally, it helps us accurately locate, track and identify each target in a complex environment.

[0003] However, the current laser radar receiving lenses often have problems such as too small target size and insufficient field of view, which to some extent limits their detection range and accuracy. In addition, the existing lenses mostly use a structure of 7 spherical glass lenses and 1 aspherical lens. The 7 glass lenses are expensive, which directly leads to high overall costs during mass production. Summary of the invention

[0004] The present invention proposes a laser radar receiving lens optical system, which takes into account the characteristics of ultra-large target area, large field of view, small distortion, small CRA, low cost and stable thermal drift.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions: a laser radar receiving lens optical system: The optical axis includes, from the object plane to the image plane, 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 plane; The first lens is a meniscus lens with negative focal power; the second lens is a meniscus lens with negative focal power; the third lens is a concave-convex lens with negative focal power; the fourth lens is a biconvex lens with positive focal power; the fifth lens is a biconvex lens with positive focal power; the sixth lens is a biconcave lens with negative focal power; and the seventh lens is a biconvex lens with positive focal power; 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 meniscus lens, n2 is the refractive index of the second meniscus lens, n3 is the refractive index of the third convex-concave 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.

[0006] 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.

[0007] A further solution is that the maximum holographic height IHmax of the optical system satisfies the following condition: IHmax ≥ 10 mm.

[0008] A further solution is that the maximum field of view FOV of the optical system satisfies the following condition: 150° ≤ FOV ≤ 155°.

[0009] A further solution is that the chief ray angle of incidence CRA of the optical system: CRA < 1°. A further solution is that the effective focal length f of the optical system satisfies the following condition: 3.5 mm ≤ f ≤ 4 mm.

[0010] A further solution is that 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.

[0011] A further 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: 0.8 < |(n5 - n6) / (n6 - n7)| < 1.2.

[0012] A further solution is that the effective focal length f of the optical system satisfies 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。

[0013] A further solution is 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.

[0014] In summary, the present invention has the following beneficial effects: the present invention increases the field of view of the optical system to 153 degrees and has an ultra-large aperture F1.0 by reasonably using lenses of specific shapes and structures and limiting the optical focal length of each lens. The radar receiving field of view is wider, providing high-definition imaging effect and recognition accuracy, and the maximum target surface is ≥10mm, F-theta distortion is less than 1%, CRA is less than 1 degree, and the imaging quality and accuracy of targets at longer distances are improved. It can provide more accurate receiving ranging data, and the TTL is 32mm. The volume is small, which is conducive to miniaturization and placement in the car. At the same time, the combination of 2G5P glass and plastic optimizes the high and low temperature drift compensation of the optical system, ensures the stability of the imaging effect when the lens works at high and low temperatures, and also makes the cost of the entire optical system more advantageous and more cost-effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the structure of an optical system provided by an embodiment of the present invention; Figure 2 The MTF analysis diagram of the optical system provided in the embodiment of the present invention when the incident light is infrared 940nm wavelength at 20°C; Figure 3 A defocus curve diagram of the optical system provided in an embodiment of the present invention when the incident light is infrared 940nm wavelength at 20°C; Figure 4 A defocus curve diagram of the optical system provided in an embodiment of the present invention when the incident light is infrared 940nm wavelength at 85°C; Figure 5 A defocus curve diagram of the optical system provided in an embodiment of the present invention when the incident light is infrared 940nm wavelength at -40°C; Figure 6 Field curvature diagram of the optical system provided in the embodiment of the present invention corresponding to the incident light of infrared 940nm wavelength; Figure 7 F-THETA distortion diagram of the optical system provided in the embodiment of the present invention corresponding to the incident light of infrared wavelength of 940nm; Figure 8 The optical system provided in the embodiment of the present invention corresponds to a standard spot diagram when the incident light is infrared with a wavelength of 940 nm. DETAILED DESCRIPTION

[0016] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0017] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0018] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0019] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0020] like Figure 1 As shown, the present invention provides a laser radar receiving lens optical system, which includes: 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 plane IMA in sequence along the optical axis from the object plane to the image plane; wherein 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 matching glass lenses and plastic lenses, the high and low temperature drift of the entire optical system can be made more stable, and purple fringing can also be optimized.

[0021] 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; Among them, the refractive indices of the first lens E1 to the seventh lens E7 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 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.

[0022] It should be noted that for the refractive index n1 of the first lens E1, 1.7 < n1 < 2.3 is satisfied, and for the refractive index n4 of the fourth lens, 1.7 < n4 < 2.3 is satisfied. The first lens E1 and the fourth lens E4 adopt high-refractive-index glass. The high-refractive-index material can make the light focus more precisely, improve the spatial resolution of infrared imaging, and enhance the imaging quality of the lens.

[0023] 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, through reasonable selection of optical materials, ensuring that the refractive indices of adjacent lens materials match each other, the change in the refraction angle of light at the lens interface can be reduced, thereby reducing the CRA of the lens, which is beneficial to the matching of the lens and the chip.

[0024] 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 range, 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 then increase the field of view angle of the optical lens.

[0025] 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; satisfying the above range can expand the width of the light beam when large-angle light passes through the fourth lens E4 and the fifth lens E5. In this process, the light can be transmitted to the imaging surface fully and efficiently, thereby expanding the field of view range of the optical lens, which is beneficial for the optical lens to achieve high-pixel and large-image-plane imaging.

[0026] 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. Satisfying the above range can reasonably allocate the focal lengths of each lens and improve the imaging quality. As an improvement, the overall optical length TTL of the optical lens and the maximum holographic height IHmax corresponding to the maximum field of view angle satisfy: 3.0 < TTL / IHmax < 3.5. Satisfying the above range can balance the relationship between the image height and the overall optical length of the optical lens and reduce the lens volume.

[0027] 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.

[0028] As an improvement, the maximum holographic height IHmax of the optical system satisfies the following condition: IHmax ≥ 10 mm.

[0029] As an improvement, the maximum field of view angle FOV of the optical system satisfies the following condition: 150° ≤ FOV ≤ 155°.

[0030] As an improvement, the chief ray angle of incidence CRA of the optical system: CRA < 1°. As an improvement, the effective focal length f of the optical system satisfies the following condition: 3.5 mm ≤ f ≤ 4 mm.

[0031] As an improvement, a surface S1 of the first lens E1 facing the object side is convex, and a surface S2 facing the image side is concave; a surface S3 of the second lens E2 facing the object side is convex, and a surface S4 facing the image side is concave; a surface S5 of the third lens E3 facing the object side is concave, and a surface S6 facing the image side is convex; a surface S8 of the fourth lens E4 facing the object side is a small convex surface, and a surface S9 facing the image side is also a large convex surface; a surface S10 of the fifth lens E5 facing the object side is a large convex surface, and a surface S11 facing the image side is also a convex surface; a surface S12 of the sixth lens E6 facing the object side is a large concave surface, and a surface S13 facing the image side is also a concave surface; a surface S14 of the seventh lens E7 facing the object side is a large convex surface, and a surface S15 facing the image side is also a convex surface.

[0032] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0033] The parameters of the lenses of this embodiment are listed in Table 1 below, and the aspheric coefficients of the lenses are listed in Table 2 below.

[0034] Table 1 Physical parameters of each lens

[0035] Table 2 Lens aspheric coefficients

[0036]

[0037]

[0038] The aspheric coefficients satisfy the following equation:

[0039] Among them, z is the aspheric surface sag, c is the aspheric surface paraxial curvature, y is the lens aperture, k is the cone coefficient, a4 is the 4th aspheric surface coefficient, a6 is the 6th aspheric surface coefficient, a8 is the 8th aspheric surface coefficient, and a10 is the 10th aspheric surface coefficient.

[0040] Specifically, the R value (Radius curvature radius), thickness (Thickness), refractive index (Index), Abbe coefficient (ABB), lens focal length (EFL-E) of each lens surface in this embodiment are shown in Table 1, and the aspheric parameters are shown in Table 2. In Table 1, Surf represents the mirror number, InFInITY represents infinity, and in Table 2, R1 represents the curvature radius of the corresponding lens facing the object side, and R2 represents the curvature radius of the corresponding lens facing the image side. A positive number for the curvature radius indicates that the mirror is curved toward the object side, and a negative number for the curvature radius indicates that the mirror is curved toward the image side.

[0041] Among them, the effective focal length of the optical system provided in Table 1 is 3.69mm, the total TTL optical length is 32mm, the maximum full image height is 10mm, the F-theta distortion is less than 1%, the field of view is 153 degrees, and the CRA is less than 1 degree. In Table 1, mirror numbers 1 and 2 represent the two mirrors of lens 1 along the light incident direction, mirror numbers 3 and 4 represent the two mirrors of lens 2 along the light incident direction, mirror numbers 5 and 6 represent the two mirrors of lens 3 along the light incident direction, mirror numbers 8 and 9 represent the two mirrors of lens 4 along the light incident direction, mirror numbers 10 and 11 represent the two mirrors of lens 5 along the light incident direction, mirror numbers 12 and 13 represent the two mirrors of lens 6 along the light incident direction, and mirror numbers 14 and 15 represent the two mirrors of lens 7 along the light incident direction.

[0042] In an embodiment of the present invention, Figure 2 The modulation transfer function (MTF) curve of the infrared light band represents the comprehensive resolution ability of the optical system. The horizontal axis of the figure represents the spatial frequency, the unit is cycles per millimeter (cycles / mm), and the vertical axis represents the value of the modulation transfer function (MTF). The value of MTF is used to evaluate the imaging quality of the lens, and the value range is 0-1. It is particularly pointed out that the optical transfer function is used to evaluate the imaging quality of an optical system. The more accurate, intuitive and common way, the higher and smoother the curve is, the better the imaging quality of the system is, and the stronger the ability to restore the real image is; from Figure 2 It can be seen that the MTF of the infrared light band in the imaging area near the center is greater than 0.9, and the imaging quality is good. Figure 3 From the defocus curve, we can see that the MTF concentration of this lens is good, which is convenient for focusing. Figure 4 and Figure 5 It can be seen that the defocus curves at both high and low temperatures meet high resolution, the focus change of the defocus curve is small, and the thermal drift effect is stable; Figure 6 Represented as a field curvature diagram, Figure 6 It can be seen that the field curvature value is controlled between -20um and 20um. The smaller the field curvature value, the better the imaging quality of the lens. Figure 7It is expressed as F-THETA distortion diagram. The smaller the F-THETA distortion, the smaller the compression of the edge of the imaging picture. Figure 8 It is the standard spot diagram corresponding to the infrared wavelength of 940nm of the embodiment of the invention.

Claims

1. A lidar receiving lens optical system, characterized in that: Along the optical axis from the object plane to the image plane, it successively includes: a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, a sixth lens, a seventh lens, a filter, a protective glass, and an image plane; The first lens is a meniscus lens with a negative optical power; the second lens is a meniscus lens with a negative optical power; the third lens is a concave-convex lens with a negative optical power; the fourth lens is a biconvex lens with a positive optical power; the fifth lens is a biconvex lens with a positive optical power; the sixth lens is a biconcave lens with a negative optical power; the seventh lens is a biconvex lens with a positive optical power; Wherein, 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; wherein, 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.

2. The laser radar receiving lens optical system according to claim 1, characterized in 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.

3. A laser radar receiving lens optical system according to any one of claims 1 or 2, characterized in that: The maximum full image height IHmax of the optical system satisfies the following condition: IHmax ≥ 10 mm.

4. A laser radar receiving lens optical system according to any one of claims 1 or 2, characterized in that: The maximum field of view FOV of the optical system satisfies the following condition: 150° ≤ FOV ≤ 155°.

5. A laser radar receiving lens optical system according to any one of claims 1 or 2, characterized in that: The chief ray angle of incidence CRA of the optical system: CRA < 1°.

6. A laser radar receiving lens optical system according to any one of claims 1 or 2, characterized in that: The effective focal length f of the optical system satisfies the following condition: 3.5 mm ≤ f ≤ 4 mm.

7. A laser radar receiving lens optical system according to any one of claims 1 or 2, characterized in that: 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.

8. The laser radar receiving lens optical system 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.

9. The laser radar receiving lens optical system 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.

10. The 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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