An optical system for a lidar transmitting lens

Abstract

This invention provides an optical system for a lidar transmitting lens. The optical system includes a first lens, a second lens, an aperture stop, a third lens, a fourth lens, a fifth 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, this invention increases the field of view of the optical system to 150 degrees and the relative illumination to greater than 90%. This results in a wider and clearer radar detection field, with F-theta distortion less than 1% and CRA less than 1 degree, improving detection range and accuracy. It provides more accurate ranging data and a longer detection distance. With a TTL of 29mm, its small size facilitates miniaturization and in-vehicle installation. Furthermore, the combination of 2G3P glass and plastic optimizes high and low temperature drift compensation, ensuring the lens remains focused even at high and low temperatures. It also offers cost advantages and higher performance-to-price ratio.

Description

Technical Field

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

[0002] In recent years, intelligent identification technology has received increasing attention, and lidar technology, as an intelligent detection technology, has emerged. LiDAR, short for laser detection and ranging system, typically consists of two parts: a laser transmitter and a laser receiver. LiDAR emits a detection signal towards the target through a transmitting lens. The reflected light is then focused onto the detector by a receiving lens group positioned in front of the lidar detector. By comparing the signal reflected from the target with the emitted signal and performing appropriate processing, information such as the magnitude of the reflected energy, the amplitude, frequency, and phase of the reflected spectrum can be obtained. This allows for the determination of parameters such as the target's distance, altitude, and speed, enabling the detection, tracking, and identification of the target.

[0003] However, current lidar transmitting lenses generally suffer from insufficient field of view, resulting in a narrow field of view. In addition, these lenses mostly adopt a 4G2P structure, which includes four glass lenses. This not only increases manufacturing costs and mass production costs, but also results in an excessively long vertical dimension of the optical system, occupying a large space and making it unsuitable for installation inside vehicles. Summary of the Invention

[0004] This invention proposes an optical system for a lidar transmitting lens that combines the advantages of a large field of view, high illumination, low distortion, low cost, small CRA, and high and low temperature drift compensation capability.

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

[0006] The optical system has five lenses with optical power, which are arranged along the optical axis from the object plane to the image plane as follows: first lens, second lens, aperture stop, third lens, fourth lens, fifth lens, filter, protective glass, and image plane.

[0007] The first lens is a meniscus lens with negative optical power; the second lens is an M-type lens with negative optical power; the third lens is a biconvex lens with positive optical power; the fourth lens is a concave-convex lens with positive optical power; and the fifth lens is a biconvex lens with positive optical power.

[0008] The ratio of the focal length of the first to fifth lenses to the focal length of the lens satisfies the following set relationship:

[0009] 3.7 < |f1 / f| < 4.1, 3.0 < |f2 / f| < 3.5, 3.0 < |f3 / f| < 3.4, 13.3 < |f4 / f| < 14.2, 6.0 < |f5 / f| < 6.5, 2.0 < f4 / f5 < 2.4; where f1 represents the effective focal length of the first lens, f2 represents the effective focal length of the second lens, f3 represents the effective focal length of the third lens, f4 represents the effective focal length of the fourth lens, f5 represents the effective focal length of the fifth lens, and f represents the effective focal length of the optical system.

[0010] Further, the refractive indices of the third lens, the fourth lens, and the fifth lens are all greater than 1.4 and less than 1.65; the Abbe numbers of the second lens, the third lens, the fourth lens, and the fifth lens are all greater than 50 and less than 59.

[0011] Further, the maximum field of view angle FOV of the optical system: 150° ≤ FOV ≤ 155°.

[0012] Further, the relative illumination of the optical system at the maximum field of view angle: RI ≥ 90%.

[0013] Further, the chief ray angle of incidence CRA of the optical system: CRA < 1°.

[0014] Further, the optical system satisfies the following conditional formula: 0.2 < (h / 2) / (f × tan(FOV / 2)) < 0.6.

[0015] Where: f represents the effective focal length of the optical system, FOV represents the maximum field of view angle of the optical system, and h represents the maximum full image height of the optical system.

[0016] Further, 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 concave, and the surface facing the image side is concave; the surface of the third lens facing the object side is convex, and the surface facing the image side is convex; the surface of the fourth lens facing the object side is concave, and the surface facing the image side is convex; the surface of the fifth lens facing the object side is convex, and the surface facing the image side is convex.

[0017] Further, the total optical length TTL of the optical system and the maximum full image height h corresponding to the maximum field of view angle satisfy: 4.8 < TTL / h < 5.3.

[0018] Further, the maximum full image height h corresponding to the maximum field of view angle of the optical system and the aperture FNO of the optical system satisfy: 3.2 mm < h / FNO < 3.8 mm.

[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 field of view of the optical system is increased to 150 degrees and the relative illumination is greater than 90%. The radar detection field of view is wider and clearer, the F-theta distortion is less than 1%, and the CRA is less than 1 degree, which improves its detection distance and accuracy. It can provide more accurate ranging data and a longer detection distance. The TTL is 29mm, and the size is small, which is conducive to miniaturization and easy to install in the vehicle. At the same time, the combination of 2G3P glass and plastic optimizes the high and low temperature drift compensation of the entire optical system, ensuring that the lens does not become out of focus at high and low temperatures. It is also more cost-effective and has a higher cost performance, ensuring the reliability and cost-effectiveness of the system. 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 embodiment of the present invention provides an MTF analysis diagram of the optical system corresponding to an incident infrared wavelength of 940nm at 20°C;

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

[0023] Figure 4 The embodiment of the present invention provides a defocusing curve of the optical system at 85°C when the incident light is an infrared wavelength of 940nm.

[0024] Figure 5 The embodiment of the present invention provides a defocusing curve of the optical system corresponding to the incident light of infrared 940nm wavelength at -40℃;

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

[0026] Figure 7 The embodiment of the present invention provides an F-THETA distortion diagram of the optical system corresponding to an incident light wavelength of infrared 940nm;

[0027] Figure 8 The embodiment of the present invention provides an illuminance diagram of the optical system corresponding to the incident light wavelength of infrared 940nm. Detailed Implementation

[0028] The following describes embodiments of the present invention in detail, 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 are not to 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 this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0032] like Figure 1 As shown, the present invention provides an optical system for a lidar transmitting lens, which includes, along the optical axis from the object plane to the image plane, the following components in sequence: a first lens E1, a second lens E2, an aperture stop STO, a third lens E3, a fourth lens E4, a fifth lens E5, a filter IR, a protective glass CG, and an image plane IMA; the optical system has a 2G3P structure, with the glass lenses being the first lens E1 and the third lens E3, and the plastic lenses being the second lens E2, the fourth lens E4, and the fifth lens E5, all of which are aspherical lenses.

[0033] The first lens E1 is a meniscus lens with a negative optical power; the second lens E2 is an M-shaped lens with a negative optical power; the third lens E3 is a biconvex lens with a positive optical power; the fourth lens E4 is a concave-convex lens with a positive optical power; the fifth lens E5 is a biconvex lens with a positive optical power;

[0034] Among them, the ratio of the focal lengths of the first lens E1 to the fifth lens E5 to the focal length of the optical system satisfies the following set relationship:

[0035] 3.7 < |f1 / f| < 4.1, 3.0 < |f2 / f| < 3.5, 3.0 < |f3 / f| < 3.4, 13.3 < |f4 / f| < 14.2, 6.0 < |f5 / f| < 6.5; where f1 represents the effective focal length of the first lens E1, f2 represents the effective focal length of the second lens E2, f3 represents the effective focal length of the third lens E3, f4 represents the effective focal length of the fourth lens E4, f5 represents the effective focal length of the fifth lens E5, and f represents the effective focal length of the optical system.

[0036] It should be noted that for the effective focal length f of the optical lens, the focal length f1 of the first lens E1, and the focal length f2 of the second lens E2, they satisfy: -4.1 < f1 / f < -3.7; -3.5 < f2 / f < -3.0. Meeting the above range can make the first lens E1 and the second lens E2 have appropriate negative optical powers, which is beneficial to large-angle light entering the optical lens, and then increasing the field angle of the optical lens. And for the effective focal length f of the optical lens and the focal length f4 of the fourth lens E4, they satisfy: 13.3 < f4 / f < 14.2; the focal length f4 of the fourth lens E4 and the focal length f5 of the fifth lens E5 satisfy: 2.0 < f4 / f5 < 2.4. Meeting the above range is beneficial to expanding the width of the light beam. After the light is refracted by the fourth lens E4 and the fifth lens E5, the width of the light beam entering the optical lens is larger, and then it can be fully transmitted to the high-pixel imaging surface, enabling the optical lens to obtain a wider field range, and at the same time, it is also beneficial for the optical lens to achieve high-pixel and large-image-plane imaging.[[ID=...]] [[ID=...]]

[0037] As an improvement, the refractive indices of the third lens E3, the fourth lens E4, and the fifth lens E5 are all greater than 1.4 and less than 1.65; the Abbe numbers of the second lens E2, the third lens E3, the fourth lens E4, and the fifth lens E5 are all greater than 50 and less than 59. It should be noted that meeting the above range, by reasonably selecting optical materials and ensuring that the refractive indices of adjacent lens materials match each other, the light exit angle can be reduced, thereby reducing the CRA of the lens; it is beneficial for the chip to match the lens.

[0038] As an improvement, the maximum field angle FOV of the optical system: 150° ≤ FOV ≤ 155°.

[0039] As an improvement, the relative illumination of the optical system at the maximum field angle: RI ≥ 90%.

[0040] As an improvement, the chief ray angle of incidence CRA of the optical system: CRA < 1°.

[0041] As an improvement, the effective focal length f of the optical system, the maximum field angle, and the maximum holographic height h corresponding to the maximum field angle satisfy: 0.2 < (h / 2) / (f × tan(FOV / 2)) < 0.6. Meeting the above range can further reduce the F-THETA distortion of the optical system and improve the imaging picture accuracy.

[0042] As an improvement, the total optical length TTL of the optical lens and the maximum holographic height h corresponding to the maximum field angle satisfy: 4.8 < TTL / h < 5.3. Meeting the above range can balance the relationship between the image height and the total optical length of the optical lens, reduce the lens volume, and is beneficial to miniaturization.

[0043] As an improvement, the maximum holographic height h corresponding to the maximum field angle of the optical lens and the aperture FNO of the optical system satisfy: 3.2 mm < h / FNO < 3.8 mm. Meeting the above range can improve the edge brightness of the lens picture, enhance the relative illumination of the entire optical system, and optimize the imaging quality.

[0044] Where: f represents the effective focal length of the optical system, FOV represents the maximum field angle of the optical system, and h represents the maximum holographic height of the optical system.

[0045] As an improvement, the object side S1 of the first lens E1 is convex, and the image side S2 of the first lens E1 is concave; the object side S3 of the second lens E2 is concave, and the image side S4 of the second lens E2 is concave; the object side S6 of the third lens E3 is convex, and the image side S7 of the third lens E3 is convex; the object side S8 of the fourth lens E4 is concave, and the image side S9 of the fourth lens E4 is convex; the object side S10 of the fifth lens E5 is convex, and the image side S11 of the fifth lens E5 is convex.

[0046] This specific embodiment is only an interpretation of the present invention, and it is not a limitation of the present invention. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

[0047] Among them, the parameters of each lens in this embodiment are listed in Table 1 below, and the aspherical coefficients of the lens are shown in Table 2 below.

[0048] Table 1 Physical parameters of each lens

[0049]

[0050] Table 2 Aspherical coefficients of lenses

[0051]

[0052]

[0053] The aspherical coefficients satisfy the following equation:

[0054]

[0055] 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.

[0056] Specifically, the R-values ​​and thicknesses of each lens surface in this embodiment are shown in Table 1, and the aspherical parameters are shown in Table 2. The R-values ​​(radius of curvature), thickness, refractive index, Abbe number (ABB), and optical focal length (EFL-E) of each lens surface in this embodiment are shown in Table 1, and the aspherical parameters are shown in Table 2. In Table 1, Surf represents the mirror surface 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.

[0057] The optical system provided in Table 1 has an effective focal length of 2.13 mm, a total TTL optical length of 29 mm, a maximum holographic height of 5.71 mm, an F-theta distortion of less than 1%, a relative illumination of 90%, a maximum field of view of 150 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 6 and 7 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, and mirror numbers 10 and 11 represent the two mirrors of lens 5 along the direction of light incidence.

[0058] In an embodiment of the present invention, Figure 2This 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 graph shows that the lens has good MTF concentration, making focusing easy. Figure 3 The vertical axis represents the MTF value, and the horizontal axis represents the offset in millimeters. From Figure 4 and 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 -40um and 40um. 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 represented as a relative illumination diagram. Higher relative illumination indicates a higher overall brightness in the captured image. Figure 8 The vertical axis represents "relative illumination", and the horizontal axis represents "field of view: angle".

Claims

1. A lidar emission lens optical system, characterized in that: The optical system has five lenses with optical power, and successively includes, along the optical axis from the object surface to the image surface: a first lens, a second lens, an aperture stop, a third lens, a fourth lens, a fifth lens, a filter, a protective glass, and an image surface; The first lens is a negative meniscus lens with optical power; the second lens is a negative M-shaped lens with optical power; the third lens is a positive biconvex lens with optical power; the fourth lens is a positive concave-convex lens with optical power; the fifth lens is a positive biconvex lens with optical power; Among them, the ratio of the focal lengths of the first lens to the fifth lens to the focal length of the lens satisfies the following set relationship: 3.7 < |f1 / f| < 4.1, 3.0 < |f2 / f| < 3.5, 3.0 < |f3 / f| < 3.4, 13.3 < |f4 / f| < 14.2, 6.0 < |f5 / f| < 6.5, 2.0 < f4 / f5 < 2.4; where f1 represents the effective focal length of the first lens, f2 represents the effective focal length of the second lens, f3 represents the effective focal length of the third lens, f4 represents the effective focal length of the fourth lens, f5 represents the effective focal length of the fifth lens, and f represents the effective focal length of the optical system.

2. The optical system for a lidar transmitting lens according to claim 1, characterized in that: The refractive indices of the third lens, the fourth lens, and the fifth lens are all greater than 1.4 and less than 1.65; the Abbe numbers of the second lens, the third lens, the fourth lens, and the fifth lens are all greater than 50 and less than 59.

3. The laser radar transmitting lens optical system according to any one of claims 1 or 2, characterized in that: The maximum field angle FOV of the optical system: 150° ≤ FOV ≤ 155°.

4. The laser radar transmitting lens optical system according to any one of claims 1 or 2, characterized in that: The relative illumination at the maximum field angle of the optical system: RI ≥ 90%.

5. The laser radar transmitting 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. The laser radar transmitting lens optical system according to any one of claims 1 or 2, characterized in that: The optical system satisfies the following conditional formula: 0.2 < (h / 2) / (f × tan(FOV / 2)) < 0.6, where: f represents the effective focal length of the optical system, FOV represents the maximum field angle of the optical system, and h represents the maximum full image height of the optical system.

7. The laser radar transmitting 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 concave, and the surface facing the image side is concave; the surface of the third lens facing the object side is convex, and the surface facing the image side is convex; the surface of the fourth lens facing the object side is concave, and the surface facing the image side is convex; the surface of the fifth lens facing the object side is convex, and the surface facing the image side is convex.

8. The optical system for a lidar transmitting lens according to claim 1, characterized in that: The total optical length TTL of the optical system and the maximum full image height h corresponding to the maximum field angle satisfy: 4.8 < TTL / h < 5.

3.

9. The optical system for a lidar transmitting lens according to claim 1, characterized in that: The maximum full image height h corresponding to the maximum field angle of the optical system and the aperture FNO of the optical system satisfy: 3.2 mm < h / FNO < 3.8 mm.

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