Patent Application
20220099803
The present disclosure relates to optical sensing systems such as a light detection and ranging (LiDAR) system, and more particularly to, LiDAR systems having a scanner covered by a diffraction grating for steering the optical beams.
Optical sensing systems such as LiDAR systems have been widely used in advanced navigation technologies, such as to aid autonomous driving or to generate high-definition maps. For example, a typical LiDAR system measures the distance to a target by illuminating the target with pulsed laser light beams and measuring the reflected pulses with a sensor such as a photodetector or a photodetector array. Differences in laser light return times, wavelengths, and/or phases can then be used to construct digital three-dimensional (3D) representations of the target. Because using a narrow laser beam as the incident light can map physical features with very high resolution, a LiDAR system is particularly suitable for applications such as sensing in autonomous driving and high-definition map surveys.
The pulsed optical beams (e.g., laser beams) emitted by a LiDAR system are typically directed to multiple directions to scan a field of view (FOV). For example, a scanner of the LiDAR system may be configured to scan the FOV by rotating around a rotation axis.
When scanning the FOV, the outgoing optical beams of the scanner needs to be substantially orthogonal to the rotation axis of the scanner. Otherwise, the scanning path would show a curved pattern instead of a linear one. Curved scanning path may cause distortions in perception. For example, a curved scanning path leads to distorted point cloud data, which in turn causes inaccuracy in the LiDAR observation. Curved scanning path may also lead to reduced effective FOV. Therefore, when merging data of different FOVs scanned by a curved scanning path, the FOVs have to be truncated due to reductions in the effective FOV.
Embodiments of the disclosure provide a transmitter of an optical sensing system. The transmitter includes an emitter configured to emit optical beams. The transmitter also includes a scanner configured to rotate around a rotation axis and steer the optical beams. The scanner includes a surface covered by a diffraction grating configured to diffract an incident optical beam non-orthogonal to the rotation axis of the scanner to form an outgoing optical beam substantially orthogonal to the rotation axis of the scanner.
Embodiments of the disclosure also provide a method for scanning an object using an optical sensing system. The method includes emitting an optical beam, by an emitter, incident on a scanner non-orthogonal to a rotation axis of the scanner. The method also includes diffracting the incident optical beam, by the scanner, to form an outgoing optical beam. The outgoing optical beam has components of a plurality of orders, and the component of a predetermined order is substantially orthogonal to the rotation axis of the scanner. The method further includes steering the component of the predetermined order of the outgoing optical beam to scan the object.
Embodiments of the disclosure further provide an optical sensing system. The system includes an emitter configured to emit optical beams. The system further includes a scanner configured to rotate around a rotation axis and steer the optical beams. A surface of the scanner is covered by a diffraction grating configured to diffract an incident optical beam non-orthogonal to the rotation axis of the scanner to form an outgoing optical beam substantially orthogonal to the rotation axis of the scanner. The system also includes a receiver configured to detect steered optical beams reflected by an object.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
The optical sensing system may be used to scan objects, and the detecting result (e.g., point cloud data) can be used for advanced navigation technologies, such as to aid autonomous driving or to generate high-definition maps. For example, the optical sensing system may include a transmitter configured to emit optical beams (e.g., laser beams) steered to scan an object and a receiver configured to receive/detect optical beams reflected by the object. The detected optical beams may be processed to obtain detecting results such as point cloud data.
In some embodiments, the transmitter may include one or more emitters, configured to emit optical beams. The transmitter may also include a scanner, configured to rotate around a rotation axis and steer the optical beams to scan an FOV. For example, outgoing optical beams of the scanner may transmit along a plurality of scanning angles within a scanning range. Different optical beams emitted by different emitters may be configured to scan different FOVs covering different scanning ranges (e.g., each with a 45-degree range, a 60-degree range, etc.). The scanning may obtain point cloud data which can be used for advanced navigation technologies, such as to aid autonomous driving or to generate high-definition maps.
In some embodiments, point clouds captured in different FOVs may be merged to generate point clouds of an FOV with a larger range in angular degree (e.g., an FOV with 360-degree). In order to merge point clouds of different FOVs, the point clouds are better obtained by linear beam scanning paths. Curved beam scanning paths (e.g., as shown in
In order to improve the linearity of the scanning path, the outgoing optical beams of the scanner need to be substantially orthogonal to the rotation axis of the scanner. Embodiments of the present disclosure provide systems and methods for scanning an object using an optical sensing system (e.g., a LiDAR system) with an improved scanner. The scanner may include a surface covered by a diffraction grating configured to diffract an incident optical beam non-orthogonal to the rotation axis of the scanner to form an outgoing optical beam substantially orthogonal to the rotation axis of the scanner. Accordingly, emitter(s) of the transmitter may be more flexibly placed in the LiDAR. For example, they no longer need to be placed to emit beams orthogonal to the rotation axis of the scanner to reduce/eliminate the scanning curvature problem. This can significantly increase the accuracy and performance of the optical sensing system.
As illustrated in
Consistent with some embodiments, LiDAR system 202 and sensor 210 may be configured to capture data as vehicle 200 moves along a trajectory. For example, a transmitter of LiDAR system 202 may be configured to scan the surrounding environment. LiDAR system 202 measures distance to a target by illuminating the target with pulsed laser beam and measuring the reflected pulses with a receiver. The laser beam used for LiDAR system 202 may be ultraviolet, visible, or near infrared. In some embodiments of the present disclosure, LiDAR system 202 may capture point clouds including depth information of the objects in the surrounding environment. As vehicle 200 moves along the trajectory, LiDAR system 202 may continuously capture data.
In some embodiments, transmitter 302 can sequentially emit a stream of pulsed laser beams in different directions (e.g., in different angles) within its scanning range as it moves (e.g., rotates, swings, etc.), as illustrated in
In some embodiments of the present disclosure, laser source 306 may include a pulsed laser diode (PLD), a vertical-cavity surface-emitting laser (VCSEL), a fiber laser, etc. For example, a PLD may be a semiconductor device similar to a light-emitting diode (LED) in which the laser beam is created at the diode's junction. In some embodiments of the present disclosure, a PLD includes a PIN diode in which the active region is in the intrinsic (I) region, and the carriers (electrons and holes) are pumped into the active region from the N and P regions, respectively. Depending on the semiconductor materials, the wavelength of laser beam 307 provided by a PLD may be smaller than 1,100 nm, such as 405 nm, between 445 nm and 465 nm, between 510 nm and 525 nm, 532 nm, 635 nm, between 650 nm and 660 nm, 670 nm, 760 nm, 785 nm, 808 nm, or 848 nm. It is understood that any suitable laser source may be used as laser source 306 for emitting laser beam 307.
Scanner 310 may be configured to steer a laser beam 309 (also referred to as “outgoing laser beam” with respect to scanner 310) in the first direction to scan an object 312. Scanner 310 may be configured to rotate around a rotation axis (e.g., along Z axis, not shown), thus steering laser beams 309 in different directions within a scanning range extending along the Y-axis. Consistent with the present disclosure, and as will be described in more details below in connection with
Object 312 may be made of a wide range of materials including, for example, non-metallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules.
In some embodiments, receiver 304 may be configured to detect a returned laser beam 311 returned from object 312. The returned laser beam 311 may be in a different direction from laser beam 309. Receiver 304 can collect laser beams returned from object 312 and output electrical signal reflecting the intensity of the returned laser beams. Upon contact, laser light can be reflected by object 312 via backscattering, such as Rayleigh scattering, Mie scattering, Raman scattering, and fluorescence. As illustrated in
Detector 316 may be configured to detect returned laser beam 311 returned from object 312. In some embodiments, detector 316 may convert a laser light (e.g., returned laser beam 311) collected by lens 314 into an electrical signal 318 (e.g., a current or a voltage signal). Electrical signal 318 may be generated when photons are absorbed in a photodiode included in detector 316. In some embodiments of the present disclosure, detector 316 may include a PIN detector, a PIN detector array, an avalanche photodiode (APD) detector, a APD detector array, a single photon avalanche diode (SPAD) detector, a SPAD detector array, a silicon photomultiplier (SiPM/MPCC) detector, a SiP/MPCC detector array, or the like.
In some embodiments, LiDAR system 300 may further include one or more controllers, such as a controller 320. Controller 320 may control the operation of transmitter 302 and/or receiver 304 to perform detection/sensing operations. Specifically, controller 320 may control the scanning of transmitter 302 (e.g., the rotation of scanner 310) and may control the receiver 304 to receive the optical signals. Controller 320 may also be configured to process the optical beams received accordingly. For example, controller 320 may be configured to merge data of FOVs scanned by laser beams 307 emitted by different laser sources 306 and generate an FOV with larger scanning range (e.g., a 360-degree FOV). Controller 320 may also be configured to obtain point cloud data based on returned laser beams from the scanned FOVs. It is contemplated that to obtain point cloud data of a merged FOV, controller 320 may either merge the raw data (e.g., the captured light signals returned from the scanned FOVs) and obtain the point cloud data of the merged detecting result, or controller 320 may obtain the point cloud data of each scanned FOV and merge the point cloud data of each scanned FOV.
In some embodiments, controller 320 may include components (not shown) such as a communication interface, a processor, a memory, and a storage for performing various control functions. In some embodiments, controller 320 may have different modules in a single device, such as an integrated circuit (IC) chip (implemented as, for example, an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA)), or separate devices with dedicated functions.
In some embodiments, the processor of controller 320 may include any appropriate type of general-purpose or special-purpose microprocessor, digital signal processor, or microcontroller. The memory or storage may be a volatile or non-volatile, magnetic, semiconductor, tape, optical, removable, non-removable, or other type of storage device or tangible (i.e., non-transitory) computer-readable medium including, but not limited to, a ROM, a flash memory, a dynamic RAM, and a static RAM. For example, the memory and/or the storage may be configured to store program(s) that may be executed by the processor to control the operation of scanner 310.
As illustrated in
In some embodiments, surface 401 may be covered with a diffraction grating, such that an incident laser beam (e.g., laser beam 307) non-orthogonal to rotation axis 403 may be diffracted to form an outgoing laser beam (e.g., laser beam 309) orthogonal to rotation axis 403 for scanning object 312. For example, surface 401 may include periodic ridges 405. In some embodiments, the diffraction grating may be designed based on at least an incident angle θ of laser beam 307 and the wavelength of laser beam 307. The incident angle θ is the angle between laser beam 307 and rotation axis 403. Consistent with the present disclosure, incident angle θ does not have to be 90°. In some embodiments, various parameters of the diffraction grating may be determined to design the diffraction grating according to sub-wavelength grating design rules known by a person skilled in the pertinent art. In some embodiments, these parameters of the diffraction grating may include e.g., the depth of each ridge of periodic ridges 405, the spacing between the adjacent periodic ridges, and the material of periodic ridges 405, etc. For example, the spacing may be the length of the pitch between each ridges of periodic ridges 405.
In some embodiments, the diffraction grating may be formed based on etching on any suitable substrate (e.g., a silicon substrate). For example, the pattern (e.g., the determined spacing) for forming periodic ridges 405 may be incorporated into suitable existing patterning masks such that the etching of the substrate for forming periodic ridges 405 can be performed with existing etching methods (e.g., dry etching, wet etching, etc.). In some embodiments, in order to increase the reflectivity of the surface, the diffraction grating may be coated with metal materials such as silver, aluminum, etc., or non-metal materials such as silicon oxides and silicon nitrides, etc. In some embodiments, the diffraction grating may be formed by etching a dielectric layer deposited on the substrate. For example, the dielectric layer may be transparent in the operating wavelength (e.g., the wavelength of the incident optical beam and the outgoing optical beam of scanner 400) and may be deposited on a top surface of the substrate. In some other embodiments, the diffraction grating may be formed by etching the substrate coated with dielectric material on its top surface. In some further embodiments, the diffraction grating may be formed by etching a suitable substrate without additional coating. For example, the etched substrate (e.g., an etched silicon substrate) would be fabricated such that it only reflects wavelengths that are transparent to silicon. The wavelengths transparent to silicon can be designed to coincide the operating wavelength of scanner 400. It is understood that the fabricating method for forming the diffraction grating is not limited to the described above. Any suitable method can be used for fabricating the diffraction grating.
In order to make the beam scanning path formed by the outgoing beams substantially linear, the outgoing optical beams (e.g., laser beams 309) have to be substantially orthogonal (e.g., having a 90-degree angle) to rotation axis 403. Based on the embodiments disclosed herein, the term “substantially” can indicate a value of a given quantity that varies within, for example, 5-10% of the defined value such as ±5%, ±7.5%, or ±10% of the defined value.
In some embodiments, by covering surface 401 of scanner 400 with the diffraction grating, an incident laser beam (e.g., laser beam 307) with incident angle θ non-orthogonal to rotation axis 403 can be diffracted to form an outgoing optical beam (e.g., laser beam 309) substantially orthogonal to rotation axis 403.
For example, after being diffracted by the diffraction grating (e.g., periodic ridges 405), laser beam 309 may have components of a plurality of orders such as from −mth to nth orders, where m and n are positive integers as shown in
Among the plurality of orders, the component of the 0th order may typically carry the majority of energy of the laser beam. However, the component of the 0th order may not be necessarily orthogonal to rotation axis 403. For example, when the incident angle θ is not 90°, the 0th-order component will not be orthogonal to rotation axis 403. Instead, as illustrated in
In some embodiments, as scanner 400 rotates around rotation axis 403 during scanning, laser beam 309 may be steered to transmit at the plurality of scanning angles, forming a beam scanning path 407 (e.g., along Y axis, vertical to the shown plane in
As illustrated in
In some embodiments, more than one emitter may be configured to emit laser beams 307 for scanning different FOVs. For example, after being diffracted by periodic ridges 405, laser beams 309 emitted from different emitters (e.g., laser sources 306) may be configured to form different beam scanning paths 407 covering different scanning ranges in the Y axis. In some embodiments, the data of different FOVs may be merged by a controller (e.g., controller 320 in
For example,
In step S502, a scanner (e.g., scanner 310 in
In step S504, an optical beam (e.g., laser beam 307 in
In step S506, the optical beam may be diffracted to form an outgoing beam (e.g., laser beam 309 in
In step S508, energy of the component of the 0th order is substantially redistributed to the component of the predetermined order (e.g., tth order). For example, to ensure energy efficiency, at least 95% of the energy of the component of the incident optical beam may be redistributed to the component of the predetermined order.
In step S510, the outgoing beam is transmitted to scan an object (e.g., object 312 in
In step S512, a controller (e.g., controller 320) may determine whether all scanning angles within a scanning range are scanned. For example, the scanning range can be 45-degree, 60-degree, etc. and a certain angular increment may be used to scan that range. For example, when an 1-degree increment is used, a 45-degree scanning range will be scanned at 45 different scanning angles. If all the scanning angles within the scanning range are scanned (S512: Yes), method 500 ends.
Otherwise, if not all of the scanning angles within the scanning range are scanned (S512: No), method 500 returns to step S502, where the scanner is rotated around the rotation axis to a next scanning angle (e.g., second scanning angle β). Steps S502-S512 are repeated until all scanning angles are scanned.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and related methods. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system and related methods.
It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
