Light receiving device and lidar system

Abstract

This invention provides a light receiving device, including a photodetector and a plurality of light-diffusing units. The photodetector includes multiple pixels, each pixel including multiple cells, which are used to convert received optical signals into electrical signals. Each light-diffusing unit corresponds to at least one pixel of the photodetector and is used to diffuse the received incident light beam onto the plurality of cells contained in the corresponding at least one pixel. This light receiving device can be applied in a lidar system. The solution of this invention increases the dynamic range of the detector and the lidar system, improving detection efficiency.

Description

Technical Field

[0001] This invention relates to the field of optical detection, and more particularly to an optical receiving device and a lidar system. Background Technology

[0002] Photodetectors have applications in many fields, such as in the receiving devices of lidar (light detection and ranging) systems. The working principle of a lidar system is to emit a laser beam of a specific frequency towards a designated area. When the laser encounters an object during its flight, it is reflected off its surface, with a portion of the reflected laser light reaching the lidar receiver as an echo. The lidar receiver compares the received echo signal with the emitted signal to obtain relevant information about the object, such as distance, angle, and reflectivity.

[0003] There are various types of photodetectors, such as avalanche photodiodes (APDs), single-photon avalanche photodiodes (SPADs), and silicon photomultipliers (SiPMs). Among them, the SiPM consists of an array of avalanche diodes operating in Geiger mode, including photon counters for multiple pixels. A pixel contains many independent photosensitive units, called cells, and the response signals of multiple photosensitive units are accumulated and output through a shared output channel. SiPMs are characterized by high sensitivity, low bias voltage, and compact structure.

[0004] When using SiPM as a photodetector, the received light signal is focused by the receiving lens, and the focused light signal is incident on a small portion of the SiPM photosensitive surface pixels, resulting in a small dynamic range and low detection efficiency. Summary of the Invention

[0005] This invention provides an optical receiving device and a lidar system, which increases the dynamic range of the detector and lidar system and improves detection efficiency.

[0006] In a first aspect, embodiments of the present invention provide a light receiving device, comprising: a photodetector and a plurality of light-diffusing units; wherein the photodetector includes a plurality of pixels, each pixel including a plurality of cells, the cells being used to convert received optical signals into electrical signals; each light-diffusing unit corresponds to at least one pixel of the photodetector, and is used to diffuse the received incident light beam onto the plurality of cells contained in the corresponding at least one pixel. The light-diffusing units diffuse the incident light onto the plurality of cells, thereby increasing the dynamic range of the entire detector and improving detection efficiency.

[0007] In one possible design, the light-diffusing unit includes a light-diffusing mirror with a reflective coating on its sidewalls, which diffuses the received light beam onto the plurality of pixels contained in at least one pixel of the photodetector. The use of the light-diffusing mirror ensures that the incident light can be uniformly diffused to the light-emitting surface.

[0008] In one possible design, the length L of the homogenizing mirror satisfies the condition: L≥d / (2*tan(θ / 2)); where d is the length of the shorter side of the cross-section of the homogenizing mirror, and θ is the divergence angle of the light beam entering the mirror. This dimensional characteristic improves the diffusion effect.

[0009] In one possible design, the homogenizing unit also includes a diffuser placed in front of the incident surface of the homogenizing mirror; the diffuser is used to diffuse the received incident beam to the incident surface of the homogenizing mirror. This further improves the homogenizing effect.

[0010] In one possible design, the homogenizing unit also includes a microlens disposed on the incident surface of the homogenizing unit; the microlens is used to converge the received incident light beam onto the incident surface of the diffuser or homogenizing mirror. The use of a microlens increases the incident angle of the incident light.

[0011] In one possible design, the components within the light-diffusing unit are connected using photosensitive adhesive. The use of photosensitive adhesive reduces the energy loss of the incident light.

[0012] In one possible design, the photodetector is a silicon photomultiplier tube (SiPM). The use of a SiPM allows the detector to have higher sensitivity.

[0013] In one possible design, multiple light-diffusing units are secured by structural clamps, improving the durability of the light receiving device.

[0014] In one possible design, the light-diffusing unit corresponds to multiple pixels, and the multiple light-diffusing units form an internally unisolated prism, forming a row layout, column layout, or irregular layout, thereby making the application scenarios of the light receiving device more extensive.

[0015] In one possible design, the light-emitting end face of the homogenizing unit is the same size as the photosensitive surface in the detector pixel, reducing incident light energy loss.

[0016] Secondly, embodiments of the present invention provide a lidar system, including a light source, a scanner, a receiving lens, the aforementioned light receiving device, and a processor; wherein the light source is used to output a laser beam; the scanner is used to scan within a set area; the receiving lens is used to converge the echo light signal reflected by an object into the light receiving device; the light receiving device is used to convert the echo light signal into an echo electrical signal; and the processor is used to analyze the echo electrical signal and control the light source, scanner, and light receiving device. This lidar system has a large dynamic range and high detection efficiency.

[0017] Thirdly, embodiments of the present invention provide a detection method applied to the aforementioned lidar system, comprising: outputting a control signal to a light source to drive the light source to output a laser beam; outputting a control signal to a scanner to drive the scanner to scan according to a set mode; receiving an echo signal output by a light receiving device, processing it, and obtaining information about the object corresponding to the echo. This increases the dynamic range of the detection and improves the detection efficiency. Attached Figure Description

[0018] Figure 1 A schematic diagram of a lidar system structure is provided in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the photosensitive surface of a SiPM detector provided in an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram showing the relationship between the homogenizing unit and the SiPM detector provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the bonding between the homogenizing unit and the SiPM detector provided in an embodiment of the present invention;

[0022] Figure 5 This is a schematic diagram of the uniform light unit structure provided in an embodiment of the present invention;

[0023] Figure 6 This is a schematic diagram of light reflection from a uniform mirror provided in an embodiment of the present invention;

[0024] Figure 7 A schematic diagram showing the uniform light unit provided in an embodiment of the present invention being fixed by a structural component;

[0025] Figure 8 A schematic diagram of a scanning detection method provided in an embodiment of the present invention;

[0026] Figure 9 This is a schematic diagram of the merging of the homogenizing mirror body according to an embodiment of the present invention;

[0027] Figure 10 A three-dimensional schematic diagram of the columnar microlens provided in an embodiment of the present invention;

[0028] Figure 11 A schematic diagram showing the existence of edge grooves between the photosensitive surfaces of the detector provided in this embodiment of the invention;

[0029] Figure 12 Provided for embodiments of the present invention Figure 11 A schematic diagram of the corresponding homogenizing unit;

[0030] Figure 13 This is a schematic diagram of the optical path of a light receiving device excluding a homogenizing mirror, provided in an embodiment of the present invention.

[0031] Figure 14 Provided for embodiments of the present invention Figure 13 The corresponding schematic diagram of echo photon reception;

[0032] Figure 15 This is a schematic diagram of the optical path of a light receiving device including a light-uniforming mirror, provided in an embodiment of the present invention.

[0033] Figure 16 Provided for embodiments of the present invention Figure 15 The corresponding schematic diagram of echo photon reception. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0035] This invention provides an optical receiving device and a lidar system using the optical receiving device. For example... Figure 1 As shown, the lidar system 10 comprises a light source 101, a scanner 102, a receiving lens 103, a light receiving device 104, and a processor 105.

[0036] Light source 101 is used to output laser beam.

[0037] Scanner 102 is used to perform two-dimensional scanning within a set area.

[0038] The receiving lens 103 is used to focus the echo light signal reflected by the object 11 into the light receiving device 104.

[0039] The optical receiver 104 is used to convert the echo optical signal into an echo electrical signal.

[0040] The processor 105 controls the light source 101, scanner 102, and light receiver 104, and analyzes the echo electrical signals to obtain relevant parameters of the object 11. After the two-dimensional scan is completed, the processor 105 finally analyzes and obtains a point cloud image.

[0041] The light receiving device 104 includes a photodetector, which can be a silicon photomultiplier tube (SiPM). The SiPM comprises multiple pixels, typically forming a two-dimensional pixel array, such as M*N pixels, where M and N are positive integers greater than 1. Each pixel comprises multiple cells, each cell being an independent photosensitive unit used to convert the received light signal into an electrical signal. The electrical signals from multiple cells within a single pixel are accumulated and output through a shared output channel.

[0042] An example of a SiPM detector is as follows Figure 2 As shown, it includes 6*4 pixels, and each pixel includes 6*6 cells. To complete a 1440*900 pixel point cloud image, for a 6*4 pixel SiPM detector, the scanner needs to be set to scan at 240 angles horizontally and 225 angles vertically to finally form a complete point cloud image.

[0043] The light receiving device 104 also includes multiple light-diffusing units, each corresponding to a pixel of the photodetector. The light-diffusing units are used to diffuse the received echo light signal onto the multiple pixels contained in the corresponding pixel.

[0044] like Figure 3 The schematic diagram shows that the light receiving device includes 6*4 light-diffusing units (301), and these 24 light-diffusing units correspond to 6*4 pixels (302) of the photodetector. In actual products, the light-emitting surface of the light-diffusing unit is usually attached to the photosensitive surface of the SiPM detector.

[0045] Figure 4 This is a schematic diagram showing the light-diffusing unit and the SiPM detector attached together. For clarity, the photodetector in the diagram consists of 3*3 pixels, and there are 9 light-diffusing units 401, which correspond one-to-one with the 9 pixels of the SiPM detector 402.

[0046] An embodiment of the present invention provides a uniform light unit structure, such as Figure 5 As shown, it includes: a microlens 501, a diffuser 502, and a light-diffusing mirror 503. The microlens 501, diffuser 502, and light-diffusing mirror 503 are fixedly connected by photosensitive adhesive to form a light-diffusing unit, as shown. Figure 5 As shown on the right.

[0047] Microlens 501 is used to receive the echo incident beam and focus it onto the diffuser. The microlens can enlarge the receiving numerical aperture, allowing beams with larger incident angles to enter the light receiving device. For example, if the spherical radius of curvature of the microlens is designed to be 1.4 mm and the thickness 1 mm, the receiving numerical aperture will be approximately 0.25. The microlens material can be BK7 glass, etc.

[0048] The diffuser 502 is used to diffuse the received incident light beam. The light beam entering the diffuser through the microlens has its divergence angle expanded by the diffuser so that it can be rapidly diffused within the homogenizing mirror, thereby reducing the length of the homogenizing mirror.

[0049] The sidewalls of the homogenizing mirror 503 are typically coated with a reflective film, which further diffuses the light beam passing through the diffuser to multiple pixels in the corresponding photodetector. The homogenizing mirror has a homogenizing effect: when a light beam enters the homogenizing mirror, the reflective film on the sidewalls forms a "photon well." The beam undergoes multiple reflections within the well, resulting in a uniform energy distribution when it reaches the SiPM photosensitive surface of the photodetector. The reflective film prevents photons from passing through the mirror to adjacent homogenizing units, thus avoiding crosstalk.

[0050] The light transmission cross section of a homogenizing mirror can be rectangular, but is usually square. Figure 6 This is a schematic diagram of light reflection from a uniform mirror. Figure 6 The length of the uniform light mirror is L, and the side length of the square cross-section is d. d is generally the same as or slightly larger than the size of the corresponding SiPM detector pixel, so that the light beam reaches the SiPM photosensitive surface.

[0051] The length L of the homogenizing mirror can be designed according to the following condition: L≥d / (2*tan(θ / 2)). Where d is the length of the shortest side of the mirror's cross-section, and θ is the divergence angle of the light beam entering the mirror. For example, in one embodiment, each pixel of the detector is 1mm*1mm in size, and the light-transmitting surface of each homogenizing unit is 1mm*1mm in size, i.e., d=1mm.

[0052] The sidewalls of the homogenizing mirror can be coated with a reflective film, and the upper and lower end faces, as well as the light inlet and outlet end faces, can be coated with an anti-reflective film; the light-transmitting surfaces of the microlenses and diffusers can also be coated with an anti-reflective film. The working end face of the microlens can also be further polished.

[0053] The light receiving device may contain M*N light-diffusing units, corresponding to the M*N pixels of the photodetector. These light-diffusing units can be combined together using some common fastening methods, for example, they can be bonded together with photosensitive adhesive.

[0054] The light-diffusing unit can also be fixed by clamping with structural components. For example... Figure 7 As shown, the 3*3 uniform light units are fixed by a structural component 701, which makes the entire light receiving device less prone to deformation and the detection performance more stable.

[0055] The light-emitting surface of each homogenizing unit should cover the effective photosensitive surface of the corresponding pixel. The size of the light-emitting surface should be the same as the size of the corresponding pixel, or the same as the size of the effective photosensitive surface of the corresponding pixel. The exit end should be in contact with the SiPM photosensitive surface to ensure no light leakage at the exit.

[0056] When assembling the light receiving device, the light-emitting surface of the homogenizing unit must be aligned with the photosensitive surface of the SiPM detector pixel. One possible assembly method is as follows:

[0057] Step 1: Attach the light-emitting end face of the homogenizing unit to the photosensitive surface of the SiPM detector without applying adhesive.

[0058] Step 2: Illuminate the light inlet of any homogenizing unit in the light receiving device with a thin beam of light in the working band of the SiPM detector, monitor the output amplitude of the response signal of the corresponding pixel of the SiPM detector, adjust the position of the homogenizing unit up, down, left and right, and fix the position of the homogenizing unit when the output signal amplitude of the SiPM detector is at its maximum.

[0059] Step 3: Apply photosensitive adhesive around the bonding area between the homogenizing unit and the SiPM detector. Once the adhesive dries, the two will bond together. Figure 7 In the image, position 702 shows the bonding area between the homogenizing unit and the SiPM detector.

[0060] Figure 1 In the lidar system shown, the beam inlet end face of the light receiving device 104 is as follows: Figure 7 The incident surface 703 of the homogenizing unit shown should be placed at the focal plane of the receiving lens 103 to avoid photon crosstalk at the entrance end.

[0061] Applied to Figure 1 The present invention also provides a scanning and detection method for the lidar system shown in the embodiment of the present invention, such as... Figure 8 As shown, the steps include the following.

[0062] S1, the processor 105 outputs a control signal to the light source 101, driving the light source to output a laser beam. The output end of the light source 101 may also include a emitting lens to shape the emitted beam into a speckled beam before it enters the scanner 102.

[0063] S2, the processor 105 outputs control signals, such as scanning angle information, to the scanner 102, driving the scanner to scan according to the set mode. In this way, the light beam output by the light source passes through the scanner and is emitted towards the target area.

[0064] S3, the processor 105 receives the echo signal, processes it, and obtains information such as the angle and distance of the object corresponding to the current echo. The light beam output from the scanner 102 is reflected when it encounters an object, and emits an echo beam towards the lidar system. The echo beam is converged by the receiving lens 103 and enters the light receiving device 104. After passing through the beam homogenizing unit, the beam illuminates the photosensitive pixels of the SiPM detector. After photoelectric conversion, an echo electrical signal is output, which the processor receives and processes.

[0065] The processor 105 continues the above process to perform a two-dimensional scan of the target area, thereby forming a point cloud image of the target area.

[0066] In some practical applications, multiple uniform light units can be combined to form row layouts, column layouts, and irregular layouts. For example, such as... Figure 9 As shown, three cubic homogenizing mirrors are merged to form a cuboid homogenizing mirror, corresponding to 1*3 pixels of the SiPM detector. The merging method is as follows: the three homogenizing mirrors with optical path isolation are combined to form a prism without internal isolation. Furthermore, Figure 9 The three spherical microlens groups shown can also be combined to form a cylindrical microlens, such as... Figure 10 The image shown is a three-dimensional view of a columnar microlens.

[0067] This invention also provides a light receiving device applied to an array SiPM detector with a relatively low pixel fill factor. For example... Figure 11 As shown, edge grooves exist between the photosensitive surfaces of the detector pixels. In the figure, each pixel of the detector is 1.0mm x 1.0mm in size, each pixel's photosensitive surface is 0.6mm x 0.6mm in size, the pixel edge groove (gap) width is 0.4mm, and the fill factor is 60%.

[0068] Correspondingly, the structure of the homogenizing unit is as follows: Figure 12 As shown in the figure, the left side is the test image, and the right side is the 3D view. The homogenizing unit includes a microlens 1201, a diffuser 1202, a homogenizing mirror 1203, a fixing structure 1204, and a SiPM detector 1205. As can be seen from the figure, the size of the light-emitting surface of the homogenizing mirror is reduced to the same size as the photosensitive surface of the detector. This allows all photons received at the incident light end face to be guided onto the pixel photosensitive surface, improving light energy utilization and effectively increasing the detector fill factor from 60% to 100%.

[0069] The technical effects of embodiments of the present invention are illustrated below by way of example. Figure 13 The diagram shows the optical path of a light receiving device without a homogenizing mirror. After passing through the receiving mirror 1301, the echo light is focused onto a local area of ​​the photosensitive surface of a 3*3 pixel SiPM detector. Only a small portion of each pixel, i.e., a small number of pixels, can receive the echo photons. Figure 14 The diagram shows the corresponding echo photon reception, where it can be seen that the echo photons are all concentrated in the center of a 3*3 pixel area.

[0070] like Figure 15The diagram shows the optical path of a light-receiving device with a homogenizing mirror. A 3x3 homogenizing mirror 1503 is added in front of the photosensitive surface of the 3x3 pixel SiPM detector 1502. After passing through the receiving mirror 1501, the echo light is focused onto the incident surface of the homogenizing mirror. After multiple reflections from the sidewalls of the homogenizing mirror, the echo light is evenly distributed across the 3x3 pixel photosensitive surface, meaning that each pixel within the pixel can receive echo photons relatively evenly. Figure 16 The diagram shows the corresponding echo photon reception, where the echo photons are distributed relatively evenly across 3*3 pixels.

[0071] The aforementioned light-receiving device, including the light-diffusing unit, can also be used in products such as security cameras and low-light detection imaging equipment. These products require the detection of weak light signals, and using an array SiPM detector can yield better images.

[0072] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality.

[0073] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. An optical receiving device, characterized in that, include: A photodetector, and multiple light-diffusing units; wherein: The photodetector includes multiple pixels, and each pixel includes multiple cells, which are used to convert received optical signals into electrical signals. Each of the light-diffusing units corresponds to at least one pixel of the photodetector and is used to diffuse the received incident light beam onto the plurality of pixels contained in the corresponding at least one pixel; the light-diffusing unit includes a light-diffusing mirror; the sidewall of the light-diffusing mirror is coated with a reflective film so that the received light beam is diffused onto the plurality of pixels contained in the at least one pixel of the photodetector.

2. The optical receiving device as claimed in claim 1, characterized in that, The length L of the homogenizing mirror body satisfies the following condition: Where d is the length of the short side of the light-transmitting cross section of the uniform mirror, and θ is the divergence angle of the light beam when it enters the mirror.

3. The optical receiving device as described in claim 1 or 2, characterized in that, The light-diffusing unit also includes a diffuser plate disposed in front of the incident surface of the light-diffusing mirror. The diffuser is used to diffuse the received incident beam to the incident surface of the homogenizing mirror.

4. The optical receiving device as described in claim 1 or 2, characterized in that, The light-diffusing unit also includes a microlens disposed on the incident surface of the light-diffusing unit; The microlens is used to focus the received incident light beam onto the diffuser or the incident surface of the homogenizing mirror.

5. The optical receiving device as described in claim 1 or 2, characterized in that, The components in the light-diffusing unit are connected by photosensitive adhesive.

6. The optical receiving device as described in claim 1 or 2, characterized in that, The photodetector is a silicon photomultiplier tube (SiPM).

7. The optical receiving device as described in claim 1 or 2, characterized in that, The multiple light-diffusing units are fixed by structural components.

8. The optical receiving device as described in claim 1 or 2, characterized in that, The light-diffusing unit corresponds to multiple pixels, and the multiple light-diffusing units are a prism without internal isolation, forming a row layout, column layout, or irregular layout.

9. The optical receiving device as described in claim 1 or 2, characterized in that, The light-emitting end face of the uniform light unit has the same size as the photosensitive surface in the detector pixel.

10. A lidar system, characterized in that, It includes a light source, a scanner, a receiving lens, a light receiving device as described in any one of claims 1-9, and a processor; wherein, The light source is used to output a laser beam; The scanner is used to scan within a defined area; The receiving lens is used to converge the echo light signal reflected by the object into the light receiving device; The optical receiving device is used to convert the echo optical signal into an echo electrical signal; The processor is used to analyze the echo electrical signal and control the light source, scanner, and light receiving device.

11. A detection method applied to the lidar system as described in claim 10, characterized in that, include: A control signal is output to the light source to drive the light source to output a laser beam; Output control signals to the scanner to drive the scanner to scan according to the set mode; The echo signal output by the optical receiving device is received, processed, and the object information corresponding to the echo is obtained.

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