LiDAR

Abstract

The LiDAR has a light source, a light-receiving sensor, and a diffraction member. The light source and the light-receiving sensor are arranged as separate-axis systems. The diffraction member selectively diffracts a part of the light output from the light source in a direction in which deviation of the imaging position that occurs in short-range distance measurement is cancelled, and causes the part of the light to be incident on the light-receiving sensor.

Description

LiDAR

[0001] The present invention relates to LiDAR.

[0002] LiDAR (Light Detection and Ranging) measures the distance to a subject based on the time-varying change in light intensity detected by a light-receiving sensor. LiDAR light sources and light-receiving sensors can be arranged in two ways: coaxially or separately. A coaxial configuration requires the laser polarization direction to be aligned, and measures to prevent stray light are also necessary, but a separately-axial configuration does not have such restrictions.

[0003] JP 2018-091630 A JP 2021-148477 A

[0004] In a separate-axis configuration, a shift occurs in the imaging position of reflected light from an object during short-distance distance measurement. For example, when the object is far away, light output from a certain channel of the light source is always received by the same pixel of the light-receiving sensor. However, when the object is close, even if light is output from the same channel, the pixel that receives the light changes depending on the distance to the object. Patent Document 2 employs a method in which the position of the pixel to be driven during short-distance distance measurement is shifted depending on the distance to the object. However, this method has the problem of making the driving of the light-receiving sensor complicated.

[0005] Therefore, the present disclosure proposes LiDAR that can improve the accuracy of short-distance distance measurement.

[0006] According to the present disclosure, a LiDAR is provided that has a light source and a light receiving sensor arranged as separate axis systems, and a diffraction element that selectively diffracts a portion of the light output from the light source in a direction that offsets the shift in imaging position that occurs in close-range ranging, and makes the light incident on the light receiving sensor.

[0007] 1 is a diagram showing the influence of parallax occurring in a LiDAR of a different axis system; FIG. 2 is a diagram showing the shift in imaging position due to parallax; FIG. 3 is a diagram showing the relationship between the amount of spot shift and the amount of light required for distance measurement; FIG. 4 is a diagram showing an example of the configuration of the main parts of the LiDAR of the present disclosure; FIG. 5 is a diagram explaining a countermeasure against parallax using a diffractive member; FIG. 6 is a diagram explaining a countermeasure against parallax using a diffractive member; FIG. 7 is a diagram showing the intensity distribution of laser light at the aperture position of the collimator; FIG. 8 is a diagram showing the intensity distribution of laser light on a diffractive member; FIG. 9 is a schematic diagram of a phase grating; FIG. 10 is a diagram showing the real part, imaginary part, amplitude, phase of f(x) in equation (3), and the result of fast Fourier transform; FIG. 11 is a diagram showing an example of a desirable emission pattern; FIG. 12 is a diagram showing a first modified example of a diffractive member; FIG. 13 is a diagram showing a second modified example of a diffractive member;

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following embodiments, the same components are designated by the same reference numerals, and redundant description will be omitted.

[0009] The description will be given in the following order: [1. Effect of parallax occurring in LiDAR of a different axis system] [2. Shift in imaging position due to parallax and amount of light required for distance measurement] [3. Example of main configuration of LiDAR disclosed herein] [4. Countermeasure against parallax using diffractive members] [5. Area design of DOE] [6. Design of phase grating-based DOE] [7. Effects] [8. Modification 1] [9. Modification 2]

[0010] [1. Effect of Parallax Occurring in Separate-Axis LiDAR] FIG. 1 is a diagram showing the effect of parallax occurring in a separate-axis LiDAR 1.

[0011] The LiDAR 1 emits light (signal light) and measures the distance to the subject SB based on information about the reflected light. The LiDAR 1 has a light projection system 2 (Tx system) and a light receiving system 3 (Rx system). The light projection system 2 has a light source 10 and a collimator 30. The light receiving system 3 has a light receiving sensor 20 and a collimator 40.

[0012] For example, the LiDAR 1 has a solid-state structure. The light source 10 has multiple channels (light-emitting elements 11: see FIG. 4 ) that can emit light individually. For example, the light source 10 is a VCSEL array in which multiple VCSELs (Vertical Cavity Surface Emitting Lasers) that serve as the light-emitting elements 11 are two-dimensionally arranged. The light-receiving sensor 20 is a SPAD sensor that uses a SPAD (Single Photon Avalanche Diode) as the light-receiving element in the pixel PX (see FIG. 5 ).

[0013] The light source 10 and the light receiving sensor 20 may be arranged in a coaxial system or in separate axes. A coaxial system means an arrangement in which the light source 10 and the light receiving sensor 20 have a common optical axis. A separate axes system means an arrangement in which the light source 10 and the light receiving sensor 20 do not have a common optical axis. In the present disclosure, a configuration in which the light source 10 and the light receiving sensor 20 are arranged in separate axes is adopted.

[0014] In the separate-axis configuration, a shift occurs in the imaging position of the light reflected from the subject SB during short-distance distance measurement. This is because the light source 10 (light projection position) and the light-receiving sensor 20 (light reception position) are positioned with a shift equal to the baseline length. Because this is similar to the difference in how an object appears at two observation points, in the following explanation, the shift between the light projection position and the light reception position corresponding to the baseline length will be referred to as "parallax."

[0015] For example, in the LiDAR 1, a correspondence is established between the channel (light-emitting channel) that outputs light and the pixel PX (corresponding pixel) where the image is formed through prior alignment. During distance measurement, the light-emitting channel and the corresponding pixel are driven in synchronization. Even if alignment is performed so that light from a certain channel of the light source 10 is received by a certain pixel of the light-receiving sensor 20 at a distant location, the image formation position of the reflected light from the subject SB will shift at close range. This creates a problem in that the position of a nearby subject SB cannot be accurately measured.

[0016] [2. Deviation of Imaging Position Due to Parallax and Light Amount Required for Distance Measurement] Figure 2 is a diagram showing deviation of imaging position due to parallax. Deviation of imaging position means deviation from the pixel PX (corresponding pixel) where the image should originally be formed due to alignment. If the magnitude of the deviation is referred to as spot deviation, the spot deviation increases as the distance to the subject SB decreases. The example in Figure 2 shows the spot deviation when the base line length (the length between the optical axes of the light source 10 and the light receiving sensor 20) is approximately 30 mm and the angle of view per pixel PX is approximately 0.3°.

[0017] FIG. 3 is a diagram showing the relationship between the amount of spot shift and the amount of light required for distance measurement. The amount of light output from the light source 10 and returning from the subject SB (light reflected from the subject SB) is inversely proportional to the square of the distance to the subject SB. Considering the relationship between the amount of spot shift and the distance to the subject SB shown in FIG. 2, the relationship between the amount of spot shift and the amount of light required for distance measurement is as shown in FIG. 3. The greater the amount of spot shift, the less light is required for distance measurement. In the example of FIG. 3, at a distance corresponding to a spot shift of 1 pixel PX or more, distance measurement is possible with an amount of light of 1% or less.

[0018] Based on the above considerations, the inventors have discovered that short-distance distance measurement is possible even with a separate-axis system configuration if a portion of light can be asymmetrically spread and incident on the target pixel PX. "Spreading light asymmetrically" means selectively spreading light in a direction that offsets the shift in the imaging position that occurs in short-distance distance measurement. This configuration can be realized using a technique such as computer-generated holograms. Specific explanations are provided below.

[0019] 3. Example of the Configuration of Main Parts of the LiDAR of the Present Disclosure] FIG. 4 is a diagram illustrating an example of the configuration of main parts of the LiDAR 1 of the present disclosure.

[0020] The LiDAR 1 of the present disclosure includes a diffractive element 50 that asymmetrically spreads incident light. The diffractive element 50 selectively diffracts a portion of the light output from the light source 10 in a direction (cancellation direction) that cancels out the shift in the imaging position that occurs during close-range ranging, and causes the light to be incident on the light-receiving sensor 20. The cancellation direction refers to the direction toward the pixel PX (corresponding pixel) that is associated with the light-emitting channel by prior alignment. For example, if the light-receiving sensor 20 is on the right side of the light source 10, the cancellation direction is the right direction. If the light-receiving sensor 20 is on the left side of the light source 10, the cancellation direction is the left direction.

[0021] By spreading the light asymmetrically in the offset direction, even when a shift in the imaging position occurs, as in close-range ranging, a portion of the light can be incident on the corresponding pixel. As shown in FIG. 3, close-range ranging is possible even with weak light. Therefore, distance measurement is possible even with a configuration that diffracts only a portion of the light. In fact, in close-range ranging, where the received light intensity tends to be high, the received light signal is likely to become saturated. This problem becomes more pronounced with SPAD. Therefore, the configuration of the present disclosure, which can reduce the received light intensity of the corresponding pixel in close-range ranging, is advantageous in improving measurement accuracy.

[0022] For example, the diffractive member 50 is provided at the aperture portion of a collimator. The collimator may be the collimator 30 of the light projection system 2 or the collimator 40 of the light receiving system 3. In the example of Fig. 4, the diffractive member 50 is provided at the aperture portion of the collimator 30 of the light projection system 2.

[0023] For example, the collimator 30 has a first lens group 31 and a second lens group 32. The first lens group 31 is responsible for widening the FoV (Field of View). The second lens group 32 is responsible for focusing. The diffractive element 50 is disposed on the optical path between the first lens group 31 and the second lens group 32. At the aperture portion, the image height is converted into a ray angle. Although the diffractive element 50 has incident angle dependency in the exit angle and exit intensity, the angular range of incident light at the aperture portion is small. Therefore, it is less susceptible to the influence of incident angle dependency.

[0024] For example, the diffractive member 50 has a plurality of DOEs (Diffractive Optical Elements) 51, each of which has a different diffraction angle for first-order diffracted light. In the example of FIG. 4 , four DOEs 51, "DOE1," "DOE2," "DOE3," and "DOE4," are provided. The plurality of DOEs 51 selectively diffract light at different angles in offset directions. The DOEs 51 can be created using a technique such as computer-generated holography. For example, the DOEs 51 are printed on the surface of a transparent substrate such as glass or plastic.

[0025] For example, the diffractive member 50 has a circular transparent substrate portion 53 that matches the shape of the opening of the diaphragm portion, and a plurality of DOEs 51 that are arranged in the circumferential direction of the transparent substrate portion 53 along the edge of the transparent substrate portion 53. The diffractive member 50 includes a central portion of the transparent substrate portion 53 that is surrounded by the plurality of DOEs 51 as a non-diffraction portion 52 that does not diffract light from the light source 10. The center of the non-diffraction portion 52 coincides with the center of the pupil. The non-diffraction portion 52 is arranged in the center of the pupil, and the plurality of DOEs 51 are arranged in the peripheral portion of the pupil.

[0026] 5 and 6 are diagrams illustrating a method for reducing parallax using a diffractive member 50. FIG.

[0027] A different ranging area is associated with each of the multiple DOEs 51. "Range measurement area" refers to an individual area divided according to the distance from the LiDAR 1. For example, a first ranging area, a second ranging area, a third ranging area, and a fourth ranging area are associated with "DOE1," "DOE2," "DOE3," and "DOE4," respectively. The fourth ranging area is the ranging area closest to the LiDAR 1. The third ranging area, the second ranging area, and the first ranging area are set in order from the fourth ranging area to the farthest area. A ranging area (fifth ranging area) farther than the first ranging area is associated with the non-diffraction section 52, which does not diffract light.

[0028] Each DOE 51 has a diffraction angle capable of offsetting the shift in the imaging position that occurs in the corresponding ranging area. The diffraction angle of "DOE4," which corresponds to the fourth ranging area closest to the LiDAR 1, is the largest. The diffraction angles of "DOE4," "DOE3," "DOE2," and "DOE1" decrease in order according to the proximity of the ranging area.

[0029] 5 shows the projection areas PA of each DOE 51 and non-diffractive portion 52. The projection areas PA refer to areas where light passing through the DOE 51 or non-diffractive portion 52 is projected onto a plane directly facing the diffractive member 50. The projection areas PA of "DOE1," "DOE2," "DOE3," "DOE4," and the non-diffractive portion 52 are denoted by "PA1," "PA2," "PA3," "PA4," and "PA5," respectively. The shape and size of each projection area PA are the same as those of the light-emitting surface of the light-emitting element 11. The projection areas "PA1" to "PA5" are arranged adjacent to each other with no gaps in the shift direction D, which is parallel to the base length.

[0030] Each DOE 51 has an area large enough to acquire the amount of received light required for distance measurement in the corresponding distance measurement area. Since the shorter the distance to the subject SB, the higher the received light intensity, the smaller the amount of received light required for the DOE 51 associated with the closer distance measurement area. Therefore, the area of ​​each DOE 51 is set to be smaller the larger the diffraction angle of the first-order diffracted light. DOE4, which has the largest diffraction angle, has the smallest area. The areas increase in the order of DOE4, DOE3, DOE2, and DOE1 according to the size of the diffraction angle.

[0031] For example, the area of ​​the non-diffraction section 52 is larger than the total area of ​​the multiple DOEs 51. As mentioned above, the signal strength of the light receiving sensor 20 decreases as the object SB becomes more distant. Therefore, to accurately measure long distances, it is necessary to increase the amount of signal light. The light that passes through the non-diffraction section 52 (non-diffracted light) is used for long-distance distance measurement. If the area of ​​the non-diffraction section 52 is increased, the intensity of the non-diffracted light used for long-distance distance measurement increases, improving the accuracy of long-distance distance measurement.

[0032] For example, the amount of light passing through the non-diffraction portion 52 (non-diffracted light) can be 90% or more of the amount of light output from the light source 10. With this configuration, 90% or more of the light output from each channel is used for long-distance ranging. Light diffracted by the diffraction member 50 (diffracted light) is lost in long-distance ranging, but as long as the amount of light is 10% or less, the ranging range does not decrease excessively.

[0033] In the example of FIG. 5 , the amount of non-diffracted light is 98% of the amount of light output from the light source 10. 98% of the light from the light source 10 that passes through the non-diffraction section 52 is emitted at a normal angle of view (projection area "PA5"). 1% of the light that passes through "DOE1" is emitted at an adjacent angle of view (projection area "PA1"). 0.5% of the light that passes through "DOE2" is emitted at an angle of view (projection area "PA2") next to the light from "DOE1". 0.25% of the light that passes through "DOE3" is emitted at an angle of view (projection area "PA3") next to the light from "DOE2". 0.13% of the light that passes through "DOE4" is emitted at an angle of view (projection area "PA4") next to the light from "DOE3".

[0034] When the subject SB is at a long distance as shown in FIG. 5, 98% of the light intensity is focused on the corresponding pixel of the light receiving sensor 20. When the subject SB is at a short distance as shown in FIG. 6, as the distance from the subject SB decreases, the light from the DOE 51 is focused on the corresponding pixel in the order of 1%, 0.5%, 0.25%, and 0.13%. In this case, the light receiving sensor 20 only needs to drive the corresponding pixel corresponding to the light emission channel. The light emission timing of each channel can be shifted. The light receiving sensor 20 selectively drives the corresponding pixel in accordance with the light emission timing of the light emission channel. Only the corresponding pixel needs to be driven. No extra pixel driving is required. Therefore, the driving does not become complicated.

[0035] 7 and 8, the area design of the DOE 51 will be described. Fig. 7 is a diagram showing the intensity distribution of the laser light LS at the stop position of the collimator 30. Fig. 8 is a diagram showing the intensity distribution of the laser light LS on the diffractive member 50.

[0036] Generally, the intensity distribution of the cross section of the beam output from a laser is close to a Gaussian shape as shown in Figure 7. The light emitted from each channel of the light source 10 is all Gaussian, and the intensity distribution in the cross section of the aperture portion of the collimator 30 is also close to that Gaussian shape. Therefore, the intensity is high at the center of the cross section of the aperture portion and low at the periphery of the cross section of the aperture portion. On the other hand, when the light emitted from the collimator 30 travels sufficiently far, the beam cross section approaches the shape (aperture shape) of the light-emitting surface of the light-emitting element 11. This is because the expansion corresponding to the aperture shape of the light-emitting element 11 is greater than the beam diameter of the light emitted from a point on the light-emitting surface.

[0037] Most of the light that passes through the non-diffractive portion 52 in the center of the aperture is projected onto a projection area "PA5" with 98% intensity. Light that passes through "DOE1," which has the largest area in the periphery of the aperture, is projected onto a projection area "PA1" with 1% intensity. "DOE2" has half the area of ​​"DOE1," and light that passes through it is projected onto a projection area "PA2" with 0.5% intensity. "DOE3" has half the area of ​​"DOE2," and light that passes through it is projected onto a projection area "PA3" with 0.25% intensity. "DOE4" has half the area of ​​"DOE3," and light that passes through it is projected onto a projection area "PA4" with 0.13% intensity.

[0038] In this way, the volumetric component of the laser cross-sectional profile at the aperture of the collimator 30 (the product of the ratio of the DOE 51 and the ratio of the light intensity) is the energy distribution ratio in the angular distribution of light intensity after passing through the collimator 30. The area design of each DOE 51 is determined based on the desired light intensity. The type and number of DOEs 51 are determined based on the angle to which the asymmetric spread should be achieved in response to the amount of spot shift due to parallax.

[0039] 6. Design of Phase Grating-Based DOE The design of the phase grating-based DOE 51 will be explained with reference to FIGS.

[0040] 9 is a schematic diagram of a phase grating PG. The phase grating PG has a concave-convex shape with a refractive index n, height t, and period a. A phase difference occurs due to the optical path difference between the part of the concave-convex portion with a refractive index of n and the air part with a refractive index of 1, causing interference. Due to the interference, m-th order diffracted light is emitted. The emission angle θ of the m-th order diffracted light ｍ is determined by the following formula (1): ｉ is the angle of incidence on the phase grating, and λ is the wavelength.

[0041]

[0042] The intensity of each m-th order light is determined by the height t of the uneven shape. More generally, according to the concept of Fraunhofer diffraction, the in-plane coordinates of the uneven shape are (x, y), and the structural scale π(x ２ +y ２ The angular distribution of the emitted intensity u(x ０ , y ０ ) is expressed by the following formula (2): As shown in formula (2), the output intensity angular distribution u(x ０ , y ０ ) is obtained by Fourier transform of the uneven shape f(x, y). A is a constant. k is the wave number.

[0043]

[0044] Therefore, the incident light is directed to a certain angular position (x ０ , y ０ ) and becomes asymmetric as a result of the Fourier transform. This function is well known and is shown in the following formula (3).

[0045]

[0046] It is important that the real part is an even function and the imaginary part is an odd function. If the deviation direction D is the x-direction, we only need to consider the emission of light along the x-axis, so we will proceed with the discussion using this f(x).

[0047] 10 shows the real part, imaginary part, amplitude, and phase of f(x) in equation (3), as well as the result of fast Fourier transform. The amplitude is the in-plane distribution of light intensity in the DOE 51 and corresponds to the transmittance distribution of the DOE 51. The phase is the in-plane distribution of the optical phase due to the optical path difference, so when the refractive index is constant, the phase corresponds to the concave-convex shape of the DOE 51 itself. Therefore, the DOE 51 corresponding to f(x) in equation (3) has a sawtooth concave-convex shape with uniform transmittance.

[0048] The Fourier transform of this DOE pattern results in a distribution with a peak only to the right of the center line at an output angle of 0°. This means that incident light is output only to positions in a certain angular direction. It can be seen from equation (1) that this output angle itself is determined by the period of the DOE pattern.

[0049] In this disclosure, the desired output pattern is one with peaks at regular intervals where the intensity gradually decreases on one side only. Fig. 11 shows an example of a desirable output pattern. If a pattern like that shown in Fig. 11 can be realized with a single DOE 51, it would be good to use that. However, to obtain such a distribution, the function of the following formula (4) is required as f(x). ｋ is a magnitude constant.

[0050]

[0051] In the example of Figure 11, the following formula (5) is used for the real part of f(x), and the following formula (6) is used for the imaginary part of f(x). Focusing on the amplitude, it can be seen that the structure has a certain period. As can be seen from formula (1), this period is on the wavelength scale, but it is difficult to realize a material with a complex transmittance structure on such a scale. When k in formula (4) is k≧2, functions with different periods have beats in amplitude, so it seems difficult to create a DOE 51 that emits asymmetric and multiple branched beams. For this reason, the structure of Figure 4, which combines multiple DOEs 51 with k=1, is preferable.

[0052]

[0053]

[0054] [7. Effects] The LiDAR 1 has a light source 10, a light receiving sensor 20, and a diffraction element 50. The light source 10 and the light receiving sensor 20 are arranged as separate axial systems. The diffraction element 50 selectively diffracts a portion of the light output from the light source 10 in a direction that offsets the shift in the imaging position that occurs during short-distance ranging, and causes the light to be incident on the light receiving sensor 20.

[0055] This configuration reduces the influence of parallax in short-distance distance measurement. This improves the accuracy of short-distance distance measurement. It also avoids complicating the operation of the light receiving sensor 20. Furthermore, in short-distance distance measurement, only a portion of the light output from the light source 10 is used for distance measurement. This has the advantage that the light receiving signal is less likely to become saturated in short-distance distance measurement, where the intensity of received light tends to be high.

[0056] The diffractive member 50 has a plurality of DOEs 51 each having a different diffraction angle for first-order diffracted light.

[0057] This configuration makes it easier to obtain a diffraction member 50 with desired diffraction characteristics.

[0058] The diffractive member 50 is provided at the aperture portion of the collimator.

[0059] This configuration reduces the angular range of light incident on the diffractive member 50. Therefore, the diffraction characteristics (exit angle and exit intensity) are less susceptible to the influence of the incidence angle dependency.

[0060] The diffractive member 50 has a circular transparent substrate portion 53 that matches the shape of the aperture of the diaphragm portion, and a plurality of DOEs 51 that are arranged in the circumferential direction of the transparent substrate portion 53 along the edge of the transparent substrate portion 53 .

[0061] According to this configuration, it is possible to effectively use light from the edge of the transparent substrate portion 53, which has a relatively large aberration, to perform short-distance distance measurement.

[0062] The area of ​​each DOE 51 is set to be smaller as the diffraction angle of the first-order diffracted light increases.

[0063] This configuration effectively suppresses saturation of the optical signal during short-distance measurement. That is, in short-distance measurement, the intensity of the reflected light from the subject SB tends to be high, so it is desirable to reduce the area of ​​the DOE 51 and reduce the intensity of the diffracted light. Since the diffraction angle needs to be larger as the subject SB gets closer, reducing the area of ​​the DOE 51 with a large diffraction angle helps to suppress saturation of the optical signal during short-distance measurement.

[0064] A different distance measurement area is associated with each of the DOEs 51. Each DOE 51 has a diffraction angle capable of offsetting the shift in the imaging position occurring in the corresponding distance measurement area, and an area capable of acquiring the amount of received light required for distance measurement in the corresponding distance measurement area.

[0065] This configuration can improve the accuracy of distance measurement in various distance measurement areas.

[0066] The diffractive member 50 includes a central portion of a transparent substrate portion 53 surrounded by a plurality of DOEs 51 as a non-diffraction portion 52 that does not diffract light from the light source 10. The area of ​​the non-diffraction portion 52 is larger than the total area of ​​the plurality of DOEs 51.

[0067] This configuration increases the intensity of the non-diffracted light used for long-distance distance measurement, thereby improving the accuracy of long-distance distance measurement.

[0068] The amount of light passing through the non-diffraction portion 52 is 90% or more of the amount of light output from the light source 10 .

[0069] With this configuration, the long distance measurement range does not become excessively low.

[0070] The effects described in this specification are merely examples and are not limiting, and other effects may also be present.

[0071] 8. Modification 1 FIG. 12 is a diagram showing a first modification of the diffraction member 50. As shown in FIG.

[0072] 4, the multiple DOEs 51 are provided on one surface of the transparent substrate unit 53. The optical function is provided only on one surface of the transparent substrate unit 53, and no optical function is provided on the other surface of the transparent substrate unit 53. Therefore, in this modification, some optical function is provided on the other surface of the transparent substrate unit 53, thereby realizing a multifunctional diffractive member 50.

[0073] For example, the diffractive member 50 of this modified example has multiple DOEs 51 on one surface 50A of the transparent substrate portion 53, and a magnifying optical element 54 on the other surface 50B of the transparent substrate portion 53. The magnifying optical element 54 magnifies the light from the light-emitting surface at a magnification corresponding to the reciprocal of the area occupancy of the light-emitting surface in the light source 10. This configuration suppresses a decrease in resolution due to a low area occupancy of the light-emitting surface. Note that, although the surface 50A is the front surface and the surface 50B is the back surface in the example of Fig. 12, the relationship between the front and back may be reversed.

[0074] For example, a magnifying optical element "DOE5" that emits 2x2 branched light is printed on the other surface 50B of the transparent substrate portion 53. A rectangular VCSEL array with a square aperture and an area occupancy rate of 25% is used as the light source 10. This simultaneously achieves uniform illumination suited to the high resolution of the SPAD side and a solution to parallax.

[0075] 13 and 14 are diagrams showing a second modified example of the diffraction member 50. FIG.

[0076] In the example of Fig. 4, a diffractive member 50 is inserted in the aperture portion of the collimator 30 of the light-projecting system 2. In this case, if a highly reflective material such as a retroreflector is present near the angle of view of the corresponding pixel in the light-receiving system 3, there is a possibility that flare noise will occur on the light-receiving side due to light from an unintended angle of view. If such a problem occurs, a diffractive member 50 can be installed in the light-receiving system 3 as shown in Figs. 13 and 14.

[0077] For example, the diffractive member 50 in this modified example is installed in the aperture portion of the collimator 40 in the light-receiving system 3. With this configuration, unintended reflected light caused by diffraction is less likely to be detected by the light-receiving sensor 20. For example, if the light is expanded on the light-projecting system 2 side, unintended reflected light may occur before reaching the light-receiving system 3, potentially causing flare. If the light is expanded on the light-receiving system 3 side, the optical path to the light-receiving sensor 20 is short, making such a problem less likely to occur.

[0078] In this modification, unlike the example in FIG. 8 , the light distribution within the aperture is not Gaussian but uniform. Therefore, it is necessary to design the area of ​​the DOE 51 to match this profile. For example, in the aperture portion on the light-receiving system 3 side, the light intensity distribution within the plane is uniform, so the area of ​​the DOE 51 itself determines the light intensity distribution ratio when spreading the light asymmetrically. In this case, it is advisable to print "DOE1" to "DOE4" on the edge of the aperture, where aberration is relatively large. The reason for this is that the central portion, which has small aberration and good light-gathering performance, is intended to be used for long-distance distance measurement, where efficient signal capture is required.

[0079] [Additional Notes] The present technology may also have the following configurations. (1) A LiDAR having a light source and a light receiving sensor arranged as separate axial systems, and a diffractive member that selectively diffracts a portion of light output from the light source in a direction that offsets a shift in imaging position that occurs during short-distance ranging, and causes the light to be incident on the light receiving sensor. (2) The LiDAR described in (1) above, in which the diffractive member has a plurality of DOEs (Diffractive Optical Elements) with different diffraction angles of first-order diffracted light. (3) The LiDAR described in (2) above, in which the diffractive member is provided at an aperture portion of a collimator. (4) The LiDAR described in (3) above, in which the diffractive member has a circular transparent substrate portion that matches the opening shape of the aperture portion, and the plurality of DOEs that are arranged in the circumferential direction of the transparent substrate portion along the edge of the transparent substrate portion. (5) The LiDAR according to (4) above, wherein the area of ​​each DOE is set to be smaller as the diffraction angle of the first-order diffracted light increases. (6) The LiDAR according to (5) above, wherein the plurality of DOEs are respectively associated with different ranging areas, and each DOE has a diffraction angle capable of offsetting the shift in the imaging position occurring in the corresponding ranging area, and has an area capable of acquiring the amount of received light required for ranging in the corresponding ranging area. (7) The LiDAR according to (5) or (6) above, wherein the diffractive member includes a center portion of the transparent substrate portion surrounded by the plurality of DOEs as a non-diffraction portion that does not diffract light from the light source, and the area of ​​the non-diffraction portion is larger than the total area of ​​the plurality of DOEs. (8) The LiDAR according to (7) above, wherein the amount of light passing through the non-diffraction portion is 90% or more of the amount of light output from the light source. (9) The LiDAR according to any one of (4) to (8), wherein the diffractive element has the plurality of DOEs on one surface of the transparent substrate unit, and has an enlarging optical element on the other surface of the transparent substrate unit that enlarges light from the light-emitting surface at a magnification corresponding to the reciprocal of the area occupancy rate of the light-emitting surface of the light source. (10) The LiDAR according to any one of (3) to (9), wherein the diffractive element is installed at an aperture portion of the collimator in a light-receiving system.

[0080] REFERENCE SIGNS LIST 1 LiDAR 3 Light receiving system 10 Light source 20 Light receiving sensor 50 Diffraction member 51 DOE 52 Non-diffraction portion 53 Transparent substrate portion 54 Magnifying optical element 30, 40 Collimator

Claims

1. A LiDAR having a light source and a light receiving sensor arranged as a separate axis system, and a diffraction element that selectively diffracts a portion of the light output from the light source in a direction that offsets the shift in the imaging position that occurs in close-range distance measurement, causing the light to be incident on the light receiving sensor.

2. The LiDAR according to claim 1, wherein the diffractive member has a plurality of DOEs (Diffractive Optical Elements) each having a different diffraction angle of the first-order diffracted light.

3. The LiDAR according to claim 2, wherein the diffractive element is provided at an aperture portion of a collimator.

4. The LiDAR described in claim 3, wherein the diffractive element has a circular transparent substrate portion that matches the opening shape of the aperture portion, and the plurality of DOEs that are arranged in the circumferential direction of the transparent substrate portion along the edge of the transparent substrate portion.

5. The LiDAR according to claim 4, wherein the area of ​​each DOE is set to be smaller as the diffraction angle of the first-order diffracted light is larger.

6. The LiDAR described in claim 5, wherein each of the multiple DOEs is associated with a different ranging area, and each DOE has a diffraction angle capable of offsetting the shift in the imaging position that occurs in the corresponding ranging area, and has an area capable of acquiring the amount of received light required for ranging in the corresponding ranging area.

7. The LiDAR described in claim 5, wherein the diffractive element includes a central portion of the transparent substrate portion surrounded by the multiple DOEs as a non-diffractive portion that does not diffract light from the light source, and the area of ​​the non-diffractive portion is larger than the total area of ​​the multiple DOEs.

8. The LiDAR described in claim 7, wherein the amount of light passing through the non-diffractive portion is 90% or more of the amount of light output from the light source.

9. The LiDAR described in claim 4, wherein the diffractive element has the plurality of DOEs on one surface of the transparent substrate portion, and has a magnifying optical element on the other surface of the transparent substrate portion that magnifies light from the light-emitting surface at a magnification corresponding to the inverse of the area occupancy of the light-emitting surface in the light source.

10. The LiDAR described in claim 3, wherein the diffractive element is installed at the aperture portion of the collimator in the light receiving system.

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