Large target surface laser radar receiving lens and laser radar containing the same

Abstract

According to one aspect of the present application, a large target surface laser radar receiving lens is provided, comprising: first lens to Nth lens arranged in order from object side to image side, N being 3 or 4; wherein the first lens is a spherical convex-concave lens with positive focal power; the second lens is a lens with negative focal power; the Nth lens is an aspherical convex-concave lens with negative focal power; the focal power of the lens with positive focal power is in the range of 0<Φ<0.04, and the focal power of the lens with negative refractive focal power is in the range of-0.04<Φ<0. The present application has the advantages of large target surface high-fidelity imaging, super-high light collection efficiency, 32%-41% shorter than similar large target surface lenses, and meets the space constraints.

Description

Technical Field

[0001] This invention relates to photoelectric detection and lidar optical system technology, and more particularly to a large-area lidar receiving lens suitable for large array detectors of single-photon avalanche diodes (SPADs). Background Technology

[0002] SPAD (Single Photon Avalanche Diode) large array (also known as large target surface) detectors have the advantages of single photon level detection capability, nanosecond-level time resolution and easy chip integration. As its technology matures, it has been applied to the receiver end of the new generation of high-performance lidar.

[0003] Existing lidar receiving lenses are mainly compatible with CCD / CMOS detectors and have good performance. However, when they are adapted to SPAD large array detectors (typical target face diagonal size ≥15mm, pixel ≤10.08μm, and highly sensitive to dark count rate), they reveal non-negligible defects.

[0004] For example, existing wide field of view (±15°–±20°) and large aperture (f / 1.8–f / 2.0) large target surface lidar receiving lenses mostly adopt a structure of 5 or more elements. In order to correct off-axis aberrations, they often introduce long focal length positive lenses and far back intercept designs, resulting in a total track length (TTL) ≥60mm, which cannot meet the hard constraint of vehicle / airborne platforms for TTL ≤50mm, causing difficulties in system integration.

[0005] For example, existing large-area lidar receiving lens designs mostly follow the traditional photographic optics evaluation system (such as MTF@40lp / mm), and have not established a four-dimensional coupling constraint model of "target surface-relative aperture-field of view-total optical length" for SPAD large array detectors. This results in systematic performance redundancy or deficiency of large-area lidar receiving lenses in scenarios adapted to SPAD large array detectors.

[0006] Therefore, there is an urgent need to provide a large-area lidar receiving lens designed for SPAD large array detectors, which can simultaneously achieve large pixel coverage, high relative aperture, low aberration residue, and strong stray light suppression under the constraint of compact optical total length. Summary of the Invention

[0007] The present invention provides a large-target-area lidar receiving lens to solve at least one of the above-mentioned problems.

[0008] According to one aspect of the present invention, a large-area lidar receiving lens is provided, comprising: a first lens to an Nth lens arranged sequentially from the object side to the image side, where N is 3 or 4; wherein, The first lens is a spherical convex-concave lens with positive optical power; The second lens is a lens with negative optical power; The Nth lens is an aspherical concave-convex lens with negative optical power; The optical power of a lens with positive optical power ranges from 0 < Φ < 0.04, while the optical power of a lens with negative refractive power ranges from -0.04 < Φ < 0.

[0009] In this invention, the optical power Φ is compared to 0 to represent the positive focal length; it does not need to be infinitely close to 0, and according to the definition of optical power, this is impossible. The value of optical power is directly determined by the refractive index, surface curvature, and thickness, and is subject to the Petzval condition (…). / n), color difference conditions ( / Vd), F-number, and field of view constraints indirectly limit the aberration contribution and tolerance sensitivity. The larger the optical power, the greater the aberration contribution and tolerance sensitivity. It is necessary to balance this by using multiple sets of low optical power to share the burden, high refractive index combined with positive optical power, and shape factor curvature optimization.

[0010] In some embodiments, the large-area lidar receiving lens of the present invention has four lenses: the second lens is a spherical concave-concave lens with negative optical power; the third lens is a spherical convex-concave lens with positive optical power; and the fourth lens is an aspherical concave-convex lens with negative optical power.

[0011] In some embodiments, the large-target laser radar receiving lens of the present invention has three lenses: the second lens is an aspherical convex-concave lens with negative optical power; and the third lens is an aspherical convex-concave lens with negative optical power.

[0012] In some embodiments, the focal length of the large-area lidar receiving lens of the present invention is f, the entrance pupil diameter is EPD, and the following relationship is satisfied: relative aperture f / EPD≤1.7.

[0013] In some embodiments, the light transmission diameter of the first lens of the present invention is D1, the total optical length of the large target surface lidar receiving lens is TTL, the maximum pixel diameter is IMH, the field of view is FOV, and the entrance pupil diameter is EPD, satisfying the following relationships: IMH / TTL≥0.33, D1 / TTL≤0.65, FOV / f×EPD≥0.22 (radians).

[0014] In some embodiments, the present invention further includes a narrowband filter; the narrowband filter is disposed on the object side of the first lens or the image side of the fourth lens; the narrowband filter is tilted at 2-4°.

[0015] According to another aspect of the present invention, a lidar is also provided, including the aforementioned large-area lidar receiving lens.

[0016] The present invention has the following beneficial effects: 1. By using a four- or three-element lens structure and precisely controlling the optical power distribution and the coordinated constraints of the target surface, structure, and aperture, the following effects can be achieved: Large target area high-fidelity imaging: with an IMH ≥ 15.8mm image circle, the RMS blur spot across the entire field of view is ≤20μm, and the edge illumination uniformity is ≥60%.

[0017] 2. Ultra-high light-gathering efficiency: The f / 1.7 design increases the photon flux per unit area by approximately 40% (compared to an f / 2.0 lens). 3. Shorter than similar large-area lenses by 32%–41%, meeting space constraints. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a large-target-area lidar receiving lens according to one embodiment of the present invention; Figure 2 for Figure 1 The diagram shows the dot matrix of the large-target lidar receiving lens. Figure 3a for Figure 1 The field curve of the large-target lidar receiving lens is shown. Figure 3b for Figure 1 The distortion curve of the large-target lidar receiving lens is shown. Figure 4 for Figure 1 The MTF curve of the large-target lidar receiving lens is shown. Figure 5 for Figure 1 The relative illumination curve of the large-target lidar receiving lens is shown. Figure 6 This is a schematic diagram of the structure of a large-target laser radar receiving lens according to another embodiment of the present invention. Figure 7 for Figure 6 The diagram shows the dot matrix of the large-target lidar receiving lens. Figure 8a for Figure 6 The field curvature diagram of the large-target lidar receiving lens is shown. Figure 8b for Figure 6 The distortion curve of the large-target lidar receiving lens is shown. Figure 9 for Figure 6The MTF curve of the large-target lidar receiving lens is shown. Figure 10 for Figure 6 The relative illumination curve of the large-target lidar receiving lens is shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort should fall within the protection scope of this invention.

[0020] Figure 1 The structure of a large-target lidar receiving lens according to one embodiment of the present invention is shown schematically.

[0021] Reference Figure 1 As shown, the large target surface lidar receiving lens provided in this embodiment includes, in sequence from the object side to the image side along the optical axis: a filter 8, an aperture 7, a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, and a cover plate protective glass 5.

[0022] The first lens 1 has positive optical power, with its object-side surface being convex and its image-side surface being concave; the second lens 2 has negative optical power, with both its object-side surface and image-side surface being concave; the third lens 3 has positive optical power, with both its object-side surface being convex and its image-side surface being concave; and the fourth lens 4 has negative optical power, with both its object-side surface being concave and its image-side surface being convex.

[0023] Table 1: Surface type, radius of curvature, thickness, material refractive index and Abbe number of each lens of the large target surface lidar receiving lens in this embodiment. The units of radius of curvature and thickness are millimeters (mm).

[0024] In Table 1, aperture 7 is located on the object side of the first lens 1; d2: thickness of the first lens 1; d3: air gap between the first lens 1 and the second lens 2; d4: thickness of the second lens 2; d5: air gap between the second lens 2 and the third lens 3; d6: thickness of the third lens 3; d7: air gap between the third lens 3 and the fourth lens 4; d8: thickness of the fourth lens 4; d9: air gap between the fourth lens 4 and the cover glass 5; d10: thickness of the cover glass 5; d11: air gap between the image side of the cover glass 5 and the imaging surface 6.

[0025] In this embodiment, both the object-side surface and the image-side surface of the fourth lens 4 are aspherical. The surface shape z of each aspherical lens can be defined using, but is not limited to, the following aspherical formula: in, N α is the number of Zernike coefficients in the series; i For even-order aspherical surfaces; A i For the first i The coefficients of the Zernike Standard polynomial are higher-order aspherical coefficients; c represents the curvature of the associated aspherical vertex. r Let be the radial ray coordinates; ρ be the normalized radial ray coordinates. These are the angular coordinates of the light rays. All the units for the above parameters correspond to lens units.

[0026] Table 2: Higher-order coefficients A4, A6, A8, A10, A12, A14 and A16 used for each aspherical mirror in Example 1.

[0027] Table 3: Parameters in this embodiment include the effective focal lengths f1 to f4 of each lens, the total effective focal length f of the large target surface lidar receiving lens, the distance TTL between the object side surface of the first lens 1 and the imaging surface on the optical axis, the light transmission diameter D1 of the first lens 1, the total optical length TTL of the large target surface lidar receiving lens, the maximum pixel diameter IMH, the field of view FOV, the focal length f of the large target surface lidar receiving lens, and the entrance pupil diameter EPD.

[0028] As shown in Table 3, the large-area lidar receiving lens in this embodiment meets the following requirements: IMH / TTL≥0.33, D1 / TTL≤0.65, FOV / f×EPD≥0.22. The relative aperture f / EPD≤1.7. The large target surface exhibits compactness, with the image height accounting for 18% of the total length, and a large aperture ratio, with the entrance pupil exceeding half of the total length, reflecting the large aperture of f / 1.7.

[0029] The image quality of the large-area lidar receiving lens in this embodiment is evaluated from the following aspects: spot diagram, field curvature, distortion, modulation transfer function (MTF), and relative illumination. The test wavelength range is 895nm–915nm (covering the typical operating band of near-infrared lidar), and the full field of view is ±10.9° (corresponding to a vertical detection range of 21.8°).

[0030] Figure 2 schematically shown Figure 1 The diagram shows a dot matrix of the large-target lidar receiving lens.

[0031] refer to Figure 2 As shown, within the entire field of view of this large-target lidar receiving lens, the RMS (root mean square) blur diameter at each field of view point is <20 μm, and the RMS value at the center field of view (0°) differs from the RMS value at the edge field of view (±10.9°) by <2 μm. This specification indicates that the receiving lens possesses excellent on-axis and off-axis focusing capabilities within its design band, meeting the requirements of high-resolution detectors (such as SPAD arrays with pixel sizes ≤30 μm).

[0032] Figure 3a schematically shown Figure 1 The field curve of the large-target lidar receiving lens is shown.

[0033] refer to Figure 3a The field curvature diagram of the large-target lidar receiving lens is shown. The horizontal axis represents the image plane defocusing amount (unit: mm), and the vertical axis represents the field of view (°). The solid line represents the field curvature in the meridional direction, and the dashed line represents the field curvature in the sagittal direction. This diagram shows that the maximum deviation between the meridional and sagittal field curvatures is controlled within ±0.2 mm.

[0034] Figure 3b schematically shown Figure 1 The distortion curve of the large-target lidar receiving lens is shown.

[0035] refer to Figure 3b The relative distortion curve of the large-area lidar receiving lens is shown: the horizontal axis represents the distortion percentage (%), and the vertical axis represents the field of view angle (°). This figure shows that the maximum absolute value of the relative distortion within the entire field of view is less than 0.6%, and it shows a gradual trend.

[0036] Figure 4 schematically shown Figure 1 The MTF curve of the large-target lidar receiving lens is shown.

[0037] refer to Figure 4The modulation transfer function (MTF) curve of the large-area lidar receiving lens shown represents the modulation index of the large-area lidar receiving lens at different spatial frequencies under various fields of view. The horizontal axis represents the spatial frequency (unit: lp / mm), and the vertical axis represents the MTF value. This figure shows that MTF@20lp / mm>0.7. Within the range of 0 to 20lp / mm, the MTF curve decreases smoothly and uniformly from the center to the edge of the field of view, exhibiting good imaging quality at both low and high frequencies.

[0038] Figure 5 schematically shown Figure 1 The relative illumination of the large-target lidar receiving lens is shown.

[0039] refer to Figure 5 The figure shows the relative illumination curve of the large-area lidar receiving lens, with the horizontal axis representing the field of view angle (°) and the vertical axis representing the contrast ratio. This figure indicates that the minimum relative illumination within the entire field of view (10.9°) is >0.68.

[0040] In summary, the large-area lidar receiving lens in this embodiment has excellent optical quality, making its light-gathering efficiency and imaging accuracy suitable for SPAD large array detectors.

[0041] Figure 6 The structure of a large-target lidar receiving lens according to another embodiment of the present invention is shown schematically.

[0042] Reference Figure 6 As shown, the large target surface lidar receiving lens provided in this embodiment includes, in sequence along the optical axis from the object side to the image side: a filter 8, a first lens 1, a second lens 2, a third lens 3, and a cover plate protective glass 8.

[0043] The first lens 1 has positive optical power, with its object side being convex and its image side being concave; the second lens 2 has negative optical power, with its object side being convex and its image side being concave; and the third lens 3 has negative optical power, with its object side being concave and its image side being convex.

[0044] Table 4: Surface type, radius of curvature, thickness, material, refractive index, and Abbe number of each lens of the large-target lidar receiving lens in this embodiment. The units for radius of curvature and thickness are millimeters (mm).

[0045] In Table 4, the aperture stop is located on the object side of the first lens 1; d2: thickness of the first lens 1; d3: air gap between the first lens 1 and the second lens 2; d4: thickness of the second lens 2; d5: air gap between the second lens 2 and the third lens 3; d6: thickness of the third lens 3; d7: air gap between the third lens 3 and the object side of CG; d12: thickness of CG; d13: air gap between the image side of the cover glass and the imaging surface.

[0046] In this embodiment, the object-side surface and image-side surface of the second lens 2 to the third lens 3 are both aspherical. The surface shape z of each aspherical lens can be defined using, but is not limited to, the following aspherical formula: in, N The number of Zernike coefficients in the series; α i For even-order aspherical surfaces; A i For the first i The coefficients of the Zernike Standard polynomial are higher-order aspherical coefficients; c Represents the curvature of the relevant aspherical vertex; r Let be the radial ray coordinates; ρ be the normalized radial ray coordinates. These are the angular coordinates of the light rays. All the units for the above parameters correspond to lens units.

[0047] Table 5: Higher-order coefficients A4, A6, A8, A10, A12, A14 and A16 that can be used for each aspherical mirror in this embodiment.

[0048] Table 6: In this embodiment, the effective focal lengths f1 to f3 of each lens, the total effective focal length f of the large target surface lidar receiving lens, the distance TTL between the object side surface of the first lens 1 and the imaging surface on the optical axis, the light transmission diameter of the first lens 1 is D1, the maximum pixel diameter is IMH, the field of view is FOV, the focal length of the large target surface lidar receiving lens is f, and the entrance pupil diameter is EPD, etc.

[0049] In this embodiment, the large-area lidar receiving lens meets the following requirements: IMH / TTL≥0.33, D1 / TTL≤0.65, FOV / f×EPD≥0.22, and relative aperture f / EP≤1.7.

[0050] Figure 7 schematically shown Figure 6 The diagram shows a dot matrix of the large-target lidar receiving lens.

[0051] Figure 7 The diagram shown is a dot plot of the large target surface lidar receiving lens in this embodiment. Within the entire field of view, the RMS (root mean square) blur diameter of each field point is <10um.

[0052] Figure 8a schematically shown Figure 6 The field curve diagram of the large-target lidar receiving lens is shown.

[0053] refer to Figure 8a As shown, the horizontal axis of the receiving lens of this large-target lidar represents the image plane defocusing amount (unit: mm), and the vertical axis represents the field of view (°). The solid line represents the field curvature in the meridional direction, and the dashed line represents the field curvature in the sagittal direction. This figure shows that the maximum deviation of the meridional field curvature is controlled within ±0.034 mm, and the maximum deviation of the sagittal field curvature is controlled within ±0.196 mm.

[0054] Figure 8b schematically shown Figure 6 The distortion curve of the large-target lidar receiving lens is shown.

[0055] refer to Figure 8b As shown, the horizontal axis of the relative distortion curve of the large-target lidar receiving lens represents the distortion percentage (%), and the vertical axis represents the field of view angle (°). This figure indicates that the maximum absolute value of the relative distortion across the entire field of view is less than 0.9%.

[0056] Figure 9 schematically shown Figure 6 The MTF curve of the large-target lidar receiving lens is shown.

[0057] refer to Figure 9 As shown, the modulation transfer function (MTF) curve of the large-area lidar receiving lens represents the modulation index of the large-area lidar receiving lens at different spatial frequencies under various fields of view. The horizontal axis represents the spatial frequency (unit: lp / mm), and the vertical axis represents the MTF value. This figure shows that MTF@20lp / mm > 0.65.

[0058] Figure 10 schematically shown Figure 6 The relative illumination curve of the large-target lidar receiving lens is shown.

[0059] refer to Figure 10As shown, the relative illumination curve of the large-area lidar receiving lens has the horizontal axis representing the field of view angle (°) and the vertical axis representing the contrast ratio. The figure shows that the minimum relative illumination within the entire field of view (10.9°) is >0.9. In this embodiment, the lidar receiving lens uses two aspherical lenses, which provides stronger light confinement.

[0060] In summary, the large-area lidar receiving lens in this embodiment has excellent optical quality, making its light-gathering efficiency and imaging accuracy suitable for SPAD large array detectors.

[0061] In the description of this specification, the references to terms such as "certain embodiments," "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0062] In this invention, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; "link" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A large-area lidar receiving lens, characterized in that, Includes: the first lens to the Nth lens arranged sequentially from the object side to the image side, where N is 3 or 4; The first lens is a spherical convex-concave lens with positive optical power; The second lens is a lens with negative optical power; The Nth lens is an aspherical concave-convex lens with negative optical power; The optical power of a lens with positive optical power ranges from 0 < Φ < 0.04, while the optical power of a lens with negative refractive power ranges from -0.04 < Φ < 0.

2. The large-target-area lidar receiving lens according to claim 1, characterized in that: N=4； The second lens is a spherical concave-convex lens with negative optical power; The third lens is a spherical convex-concave lens with positive optical power; The fourth lens is an aspherical concave-convex lens with negative optical power.

3. The large-target-area lidar receiving lens according to claim 2, characterized in that... The focal length of the receiving lens of the large target surface lidar is f, the entrance pupil diameter is EPD, and the following relationship is satisfied: relative aperture f / EPD≤1.

7.

4. The large-target-area lidar receiving lens according to claim 2, characterized in that... The first lens has a light transmission diameter of D1, the large target surface lidar receiving lens has an optical total length of TTL, a maximum pixel diameter of IMH, a field of view of FOV, and an entrance pupil diameter of EPD, satisfying the following relationships: IMH / TTL≥0.33, D1 / TTL≤0.65, FOV / f×EPD≥0.

22.

5. The large-target-area lidar receiving lens according to claim 2, characterized in that... It also includes narrowband filters; The narrowband filter is disposed on the object side of the first lens or the image side of the fourth lens; the narrowband filter is tilted at 2-4°.

6. The large-target-area lidar receiving lens according to claim 1, characterized in that: N=3； The second lens is an aspherical convex-concave lens with negative optical power; The third lens is an aspherical concave-convex lens with negative optical power.

7. The large-target-area lidar receiving lens according to claim 6, characterized in that... The focal length of the receiving lens of the large target surface lidar is f, the entrance pupil diameter is EPD, and the following relationship is satisfied: relative aperture f / EPD≤1.

7.

8. The large-target-area lidar receiving lens according to claim 6, characterized in that... The first lens has a light transmission diameter of D1, the large target surface lidar receiving lens has an optical total length of TTL, a maximum pixel diameter of IMH, a field of view of FOV, and an entrance pupil diameter of EPD, satisfying the following relationships: IMH / TTL≥0.33, D1 / TTL≤0.65, FOV / f×EPD≥0.

22.

9. The large-target-area lidar receiving lens according to claim 6, characterized in that... It also includes narrowband filters; The narrowband filter is disposed on the object side of the first lens or the image side of the third lens; the narrowband filter is tilted at 2-4°.

10. A lidar, characterized in that: Includes the large-area lidar receiving lens as described in any one of claims 1-9.

Images