The present disclosure relates to a light detection and ranging (LiDAR) system, and more particularly to, a micro shutter array for filtering out ambient light when detecting optical signals in a scanning LiDAR system.
In a scanning LiDAR system, a biaxial architecture has some advantages such as simpler optics, less limitation on a scanner, and a larger aperture which is not limited to the scanner size. One requirement of the biaxial architecture though is that the field of view (FOV) of the receiving optics has to be large enough to cover all scanned points in the far field. However, if the receiving optics is made to be large, in real-world LiDAR applications, it will also collect a large amount of ambient light, such as light from the direct or indirect sunlight reflected off far-field objects. The larger the receiving FOV, the more collected ambient light. Ambient light introduces noises for backend processing and thus lowers the detection accuracy. Therefore, there is a trade-off between the receiving FOV that affects the detection range and the signal-to-noise ratio that affects the detection accuracy in existing biaxial scanning LiDAR systems.
Embodiments of the disclosure address the above problems by including a micro shutter array for filtering out the ambient light when detecting the optical signals in a biaxial scanning LiDAR system.
Embodiments of the disclosure provide an exemplary optical sensing system. The optical sensing system includes a laser emitter configured to sequentially emit a series of optical signals and a steering device configured to direct the series of optical signals in different directions towards an environment surrounding the optical sensing system. The optical sensing system further includes a receiver configured to receive the series of optical signals returning from the environment. The receiver includes a micro shutter array disposed in a light path of the returning series of optical signals and configured to sequentially open only a portion of the micro shutter array at a specified location at each time point, to allow the returned series of optical signals to sequentially pass through the micro shutter array. The receiver further includes a photodetector configured to receive the optical signals sequentially passed through the micro shutter array.
Embodiments of the disclosure also provide an exemplary optical sensing method using a micro shutter array. The method includes sequentially emitting, by a laser emitter of an optical sensing system, a series of optical signals. The method further includes directing, by a steering device of the optical sensing system, the series of optical signals in different directions towards an environment surrounding the optical sensing system. The method additionally includes receiving the series of optical signals returned from the environment, by a micro shutter array disposed in a light path of the returning optical signals, where the micro shutter array sequentially opens only a portion of the micro shutter array at a specified location at each time point, to allow the returned series of optical signals to sequentially pass through the micro shutter array. The method additionally includes receiving, by a photodetector, the optical signals sequentially passed through the micro shutter array.
Embodiments of the disclosure further provide an exemplary receiver of an optical sensing system. The exemplary receiver includes a micro shutter array disposed in a light path of returning series of optical signals and configured to sequentially open only a portion of the micro shutter array at a specified location at each time point, to allow the returned series of optical signals to sequentially pass through the micro shutter array. The exemplary micro shutter array further includes a photodetector configured to receive the optical signals sequentially passed through the micro shutter array.
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 present disclosure, 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.
Embodiments of the present disclosure provide a micro shutter array in a receiver of a biaxial scanning LiDAR system. According to one example, the micro shutter array may be disposed between a receiving lens and a condenser lens of the receiver. The micro shutter array may include a plurality of micro shutter elements arranged in a one-dimensional, two-dimensional, or three-dimensional array, where each micro shutter element may be controlled to switch between an open and a closed state. Accordingly, when an optical signal returned from the environment of the LiDAR system is received by the receiver in a biaxial scanning LiDAR system, the micro shutter array may be controlled to allow only a spatially selected portion to be opened, to allow the returned optical signal to pass through the spatially selected portion of the micro shutter array and detected by a photodetector of the receiver.
In some embodiments, the spatially selected portion is selected based on the location where the returned optical signal is incident on the micro shutter array after collimation by the receiving lens, where the incident location of the returned optical signal is also determined by the angular direction at which a scanner of the LiDAR system is pointing during a scanning process. Accordingly, when the scanner of the LiDAR system scans the environment by continuously changing the angular direction, the location where the returned optical signal is incident on the micro shutter array may also continuously change, and the changing pattern may correspond to a pattern that the scanner of the LiDAR system follows during the scanning process. To allow the returned optical signals to pass through the micro shutter array, the micro shutter array may be then controlled to sequentially open different portions of the micro shutter array, where each portion is spatially selected based on the location where the returned optical signal is incident on the micro shutter array.
In some embodiments, the micro shutter array may be coated with a reflective material that has a high reflectivity. Accordingly, by controlling the micro shutter array to sequentially open only a spatially selected portion at each time point during a scanning process, the majority of the micro shutter array remains closed during the scanning process. Therefore, most of the ambient light, including the direct or indirect sunlight reflected off far-field objects, may be reflected back without passing through the micro shutter array for detection by the photodetector of the LiDAR system. This then allows the signal-to-ratio to remain high for a biaxial LiDAR system, even when the receiving optics FOV is large. That is, the detection range of the disclosed biaxial scanning LiDAR system can be increased without the sacrifice of detection accuracy of the LiDAR system. Other advantages of the disclosed micro shutter array include its easy integration into the existing biaxial scanning LiDAR systems, without changing many of the other components, especially the transmitting part included in these LiDAR systems. The features and advantages described herein are not exhaustive and many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings and the following descriptions.
The disclosed LiDAR system containing a micro shutter array can be used in many applications. For example, the disclosed LiDAR system can be used in advanced navigation technologies, such as to aid autonomous driving or to generate high-definition maps, in which the optical sensing system can be equipped on a vehicle.
As illustrated in
Consistent with some embodiments, LiDAR system 102 and sensor 110 may be configured to capture data as vehicle 100 moves along a trajectory. For example, a scanning system of LiDAR system 102 may be configured to scan the surrounding environment. LiDAR system 102 measures distance to a target by illuminating the target with laser beams and measuring the reflected/scattered pulses with a receiver. The laser beams used for LiDAR system 102 may be ultraviolet, visible, or near-infrared, and may be pulsed or continuous wave laser beams. In some embodiments of the present disclosure, LiDAR system 102 may capture point cloud data including depth information of the objects in the surrounding environment, which may be used for constructing a high-definition map or 3-D buildings and city modeling. As vehicle 100 moves along the trajectory, LiDAR system 102 may continuously capture data including the depth information of the surrounding objects (such as moving vehicles, buildings, road signs, pedestrians, etc.) for map, building, or city modeling construction.
Laser emitter 208 may be configured to emit laser beams 207 (also referred to as “native laser beams”) to scanner 210. For instance, laser emitter 208 may generate laser beams in the ultraviolet, visible, or near-infrared wavelength range, and provide the generated laser beams to scanner 210. In some embodiments of the disclosure, depending on underlying laser technology used for generating laser beams, laser emitter 208 may include one or more of a double heterostructure (DH) laser emitter, a quantum well laser emitter, a quantum cascade laser emitter, an interband cascade (ICL) laser emitter, a separate confinement heterostructure (SCH) laser emitter, a distributed Bragg reflector (DBR) laser emitter, a distributed feedback (DFB) laser emitter, a vertical-cavity surface-emitting laser (VCSEL) emitter, a vertical-external-cavity surface-emitting laser (VECSEL) emitter, an extern-cavity diode laser emitter, etc., or any combination thereof. Depending on the number of laser emitting units in a package, laser emitter 208 may include a single emitter containing a single light-emitting unit, a multi-emitter unit containing multiple single emitters packaged in a single chip, an emitter array or laser diode bar containing multiple (e.g., 10, 20, 30, 40, 50, etc.) single emitters in a single substrate, an emitter stack containing multiple laser diode bars or emitter arrays vertically and/or horizontally built up in a single package, etc., or any combination thereof. Depending on the operating time, laser emitter 208 may include one or more of a pulsed laser diode (PLD), a CW laser diode, a Quasi-CW laser diode, etc., or any combination thereof. Depending on the semiconductor materials of diodes in laser emitter 208, the wavelength of emitted laser beams 207 may be at different values, such as 760 nm, 785 nm, 808 nm, 848 nm, 870 nm, 905 nm, 940 nm, 980 nm, 1064 nm, 1083 nm, 1310 nm, 1370 nm, 1480 nm, 1512 nm, 1550 nm, 1625 nm, 1654 nm, 1877 nm, 1940 nm, 2000 nm, etc. It is understood that any suitable laser source may be used as laser emitter 208 for emitting laser beams 207 at a proper wavelength.
Scanner 210 may include various optical elements such as prisms, mirrors, gratings, optical phased array (e.g., liquid crystal-controlled grating), or any combination thereof. When a laser beam is emitted by laser emitter 208, scanner 210 may direct the emitter laser beam towards the environment, e.g., object(s) 212, surrounding LiDAR system 102. In some embodiments, object(s) 212 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, at each time point during a scanning process, scanner 210 may direct laser beams 209 to object(s) 212 in a direction within a range of scanning angles by rotating a deflector, such as a micromachined mirror assembly.
Receiver 204 may be configured to detect returned laser beams 211 reflected by object(s) 212. Upon contact, laser light can be reflected/scattered by object(s) 212 via backscattering, such as Raman scattering, and fluorescence. Returned laser beams 211 may be in a same or different direction from laser beams 209. In some embodiments, receiver 204 may collect laser beams returned from object(s) 212 and output signals reflecting the intensity of the returned laser beams.
As described above and as illustrated in
Photodetector 220 may be configured to detect the focused laser spot 217. In some embodiments, photodetector 220 may include a single sensor element that continuously detects the focused laser spots passed through micro shutter array 216 and focused by condenser lens 218. In some embodiments, photodetector 220 may be a photosensor array that includes multiple sensor elements. Different focused laser spots 217 may be detected by different sensor elements included in the photosensor array. In some embodiment, a focused laser spot detected by photodetector 220 may be converted into an electrical signal 219 (e.g., a current or a voltage signal). Electrical signal 219 may be an analog signal which is generated when photons are absorbed in a photodiode included in photodetector 220. In some embodiments, photodetector 220 may be a PIN detector, an avalanche photodiode (APD) detector, a single photon avalanche diode (SPAD) detector, a silicon photo multiplier (SiPM) detector, or the like.
Readout circuit 222 may be configured to integrate, amplify, filter, and/or multiplex signal detected by photodetector 220 and transfer the integrated, amplified, filtered, and/or multiplexed signal 221 onto an output port (e.g., controller 206) for readout. In some embodiments, readout circuit 222 may act as an interface between photodetector 220 and a signal processing unit (e.g., controller 206). Depending on the configurations, readout circuit 222 may include one or more of a transimpedance amplifier (TIA), an analog-to-digital converter (ADC), a time-to-digital converter (TDC), or the like.
Controller 206 may be configured to control transmitter 202 and/or receiver 204 to perform detection/sensing operations. For instance, controller 206 may control laser emitter 208 to emit laser beams 207, or control photodetector 220 to detect optical signal returning from the environment. In some embodiments, controller 206 may also control data acquisition and perform data analysis. For instance, controller 206 may collect digitalized signal information from readout circuit 222, determine the distance of object(s) 212 from LiDAR system 102 according to the travel time of laser beams, and construct a high-definition map or 3-D buildings and city modeling surrounding LiDAR system 102 based on the distance information of object(s) 212. In some embodiments, controller 206 may combine the digitalized signals from a series of laser beams passed through different portions of micro shutter array 216 in constructing a high-definition map or 3-D buildings and city modeling surrounding LiDAR system 102. The specific details regarding the pass-through of micro shutter array 216 by a series of laser beams will be described hereinafter in conjunction with
As illustrated, LiDAR system 102 may further include a receiving lens 214, a condenser lens 218, and a micro shutter array 216 disposed between receiving lens 214 and condenser lens 218. In addition, LiDAR system 102 may also include a photodetector 220 and readout circuit(s) 222, which is coupled to controller 206. In some embodiments, LiDAR system 102 may further include a MEMS driver 302b coupled to micro shutter array 216, where MEMS driver 302b may drive the micro shutter elements included in micro shutter array 216 to individually open or close according to a predefined pattern, as further described below.
Receiving lens 214 may collimate the optical signals received from the environment. In some embodiments, to improve the detection range of LiDAR system 102, e.g., to detect a building that is 100 m or higher surrounding the LiDAR system, the FOV of receiving lens 214 may be configured to be large. With the increased FOV, when receiving the optical signals from the environment, besides the laser beams reflected from objects (e.g., far-field object(s) 212), receiving lens 214 may also receive a large amount of ambient light from the environment. For instance, direct or indirect sunlight reflected off far-field objects may be also received by receiving lens 214. The larger the FOV of the receiving lens, the more ambient light received from the environment, which introduces more noise for backend processing. Accordingly, the detection accuracy is reduced if more ambient light is detected by photodetector 220 of LiDAR system 102.
By blocking the ambient light from being detected by photodetector 220, micro shutter array 216 may increase the detection accuracy of LiDAR system 102 even when the FOV of the receiving lens is large. As illustrated, micro shutter array 216 may be disposed along the light path of the returned optical signals right after receiving lens 214. The optical signals, including the returned laser beams and the ambient light, may be collimated and directed by receiving lens 214 towards micro shutter array 216. Micro shutter array 216 may serve as a filter to allow the returned laser beams to pass through while blocking most of the ambient light. To achieve such a filtering effect, micro shutter array 216 may include a plurality of micro shutter elements arranged in a two-dimensional array, where each micro shutter element may include a coated reflective surface facing receiving lens 214. A micro shutter element can be in one of an open state for allowing light and laser beams to pass through or in a closed state for blocking light and laser beams to pass through. At any moment during a scanning process, the majority of the micro shutter elements may remain closed and thus the majority of the ambient light may be reflected back towards receiving lens 214. Only a spatially selected portion of micro shutter elements may be in an open state for allowing the returned laser beams to pass through the micro shutter array. A very limited portion of the ambient light, if any, may also pass through the spatially selected portion of the micro shutter elements in the open state. The spatial location of the selectively opened portion may correspond to the incident position of the returned laser beam, which may be further determined by the angular direction at which a scanner of the LiDAR system is pointing during a scanning process, as further described in detail in
For instance, in part (a) of
It is to be noted that while only one micro shutter element is controlled to open at one time point in the illustrated
Similarly, a MEMS driver 302amay be coupled to micro shutter array 216, to drive a micro shutter element to open or close. In some embodiments, multiple MEMS drivers 302b may be included in the LiDAR system, where each MEMS driver 302b may control only one or just a few micro shutter elements included in the micro shutter array 216. In some embodiments, different MEMS mechanisms may be employed to drive a micro shutter element to open or close. For instance, a comb drive-based rotation mechanism may be employed to drive a micro shutter element to rotate around a hinge (like a door or window) so as to open or close the micro shutter element. Alternatively, a micro shutter element may be controlled, e.g., by a different comb-drive-based mechanism, to slide behind or in front of another micro shutter element(s), so as to “open” the micro shutter element to allow a returned laser beam to pass through the “hole” opened by the micro shutter element. Other MEMS driving mechanisms to open a micro shutter element are also possible and are contemplated.
Similar to MEMS driver 302a, MEMS driver 302b may be also integrated in a controller 702b and/or coupled to controller 206, which provides instructions to MEMS driver 302b to drive a micro shutter element to open or close during a scanning process. For instance, the instructions may instruct whether and/or when to open/close a specific micro shutter element, and which pattern should follow when multiple micro shutter elements are sequentially opened. Controller 702b (or controller 206 if there is no controller 702b) may communicate with controller 702a (or controller 206 if there is no controller 702a), to identify the scanning pattern that the scanner follows in a scanning process, and then determine the pattern in which the micro shutter elements should be sequentially opened, so that a returned laser beam can timely pass through an opened portion of the micro shutter array. Based on the determined pattern for sequentially opening the micro shutter elements, a corresponding instruction may be generated and provided to MEMS driver 302a, which then drives the micro shutter array to open the micro shutter elements following the determined pattern. That is, through communication between the controllers controlling the operations of the scanner and the micro shutter array, the micro shutter elements may be controlled to open/close timely and sequentially, so as to achieve the filtering function of the micro shutter array.
In some embodiments, to assemble the whole FOV detection signal from the sequentially detected signals, a controller (e.g., controller 206) may record the location information of an opened micro shutter element when the intensity information of the returned laser beam passed through that micro shutter element is detected by the photodetector of the LiDAR system. By combining the location information and the corresponding light intensity information corresponding to each opened micro shutter element during a scanning process, the whole FOV detection signal may be then obtained for detecting far-field objects in the environment.
It is to be noted that, in some embodiments, not all micro shutter elements in a micro shutter array need to be open and/or closed during a scanning process. In some embodiments, the number of micro shutter elements constructed for a micro shutter array may be larger than the number of micro shutter elements required for covering the whole receiving optics FOV in a scanning process. For instance, in the micro shutter array illustrated in
In step S802, an optical source (e.g., laser emitter 208) inside a transmitter of an optical sensing system (e.g., transmitter 202 of LiDAR system 102) may emit a series of optical signals for optical sensing of the environment. Here, the optical signals emitted by the optical source may have a predetermined beam size and divergence. In some embodiments, the emitted optical signals may have a high intensity and a large divergence, to allow detection of the objects in a wide range.
In step S804, a steering device of the optical sensing system (e.g., scanner 210 in transmitter 202 of LiDAR system 102) may steer the emitted optical signals toward the environment surrounding the optical sensing system. The steering device may steer the emitted optical signals according to a predefined pattern, so that different parts of the environment may be scanned over a short period of time. For instance, the emitted optical signals may be directed toward far-field objects in the environment according to a predefined scanning pattern (e.g., a two-dimensional scanning pattern). The objects in the environment may then reflect at least a portion of the optical signals toward the LiDAR system. In some embodiments, the LiDAR system may be biaxial and thus the returned optical signals may be directly directed towards a receiving lens (e.g., receiving lens 214) of the LiDAR system without being reflected by the steering device. The receiving lens may collimate the received optical signals. In some embodiments, to increase the detection range, the receiving lens FOV may be large. Therefore, a certain amount of ambient light may be also received by the receiving lens. The received ambient light may be also collimated by the receiving lens.
In step S806, a micro shutter array (e.g., micro shutter array 216) disposed after the receiving lens may receive the series of optical signals collimated by the receiving lens, where the micro shutter array may sequentially open only a portion of the micro shutter array at a specified location at each time point, to allow the returned series of optical signals to sequentially pass through the micro shutter array. As previously described, the micro shutter array may include a plurality of micro shutter elements, where each of the plurality of micro shutter elements may be in one of an open or closed state, and may include a reflective surface that reflects the ambient light if the micro shutter element is in the closed state. To allow the series of optical signals to pass through the micro shutter array, different portions of the micro shutter array may be sequentially opened, where each opened portion may allow a corresponding returned optical signal to pass through. The exact position at which a portion of the micro shutter array to be opened corresponds to an incident location of a returned optical signal on the micro shutter array. Since the returned series of optical signals follow the predefined scanning pattern when the signals are incident on the micro shutter array, the multiple portions included in the micro shutter array may be also controlled to open sequentially following the scanning pattern, to allow each returned optical signal to pass through each corresponding opened portion of the micro shutter array.
As described above, when receiving the returned optical signals, the receiving lens may also receive the ambient light (unless specified, an optical signal throughout the specification may mean a laser light or an optical signal other than the ambient light). The received ambient light may be also collimated towards the micro shutter array. However, different from the returned optical signals that are incident only on a very small portion (e.g., less than 1%) of the micro shutter array, the received ambient light may be incident on the whole surface of the micro shutter array. Since only a small portion of the micro shutter array is controlled to open at any time point, only a very small portion of the ambient light, if any, may thus pass through the opened portion of the micro shutter array with the returned laser beam, and the majority of the collimated ambient light is blocked by the remaining closed majority portion of the micro shutter array. Therefore, even the receiving lens of the LiDAR system has a large FOV aimed at a large detection range, the signal-to-noise ratio may be maintained high for the disclosed LiDAR system due to the blocked ambient light by the micro shutter array.
In step S808, a photodetector (e.g., photodetector 220) of the LiDAR system may receive the series of optical signals sequentially passed through the micro shutter array. The series of optical signals may be sequentially received by the photodetector. When each optical signal is detected by the photodetector, the location information of the corresponding micro shutter element(s) allowing the pass-through of that optical signal is also received and recorded, e.g., by a controller of the LiDAR system. Therefore, after all the returned optical signals are detected, the detection signal for the entire receiving FOV can be then obtained by combining the sequentially detected signals. The whole FOV detection signal can then be used to generate a frame of image or map for the whole receiving lens FOV during an optical sensing process. The generated frame of an image or map may have a high accuracy due to the filtering effect of the micro shutter array that blocks the noise of the ambient light received by the large FOV receiving lens. The disclosed LiDAR system with a micro shutter array may thus achieve both a large detection range and a high accuracy during an optical sensing process.
Although the disclosure is made using a LiDAR system as an example, the disclosed embodiments may be adapted and implemented to other types of optical sensing systems that use receivers to receive optical signals not limited to laser beams. For example, the embodiments may be readily adapted for optical imaging systems or radar detection systems that use electromagnetic waves to scan objects.
Another aspect of the disclosure is directed to a non-transitory computer-readable medium storing instructions which, when executed, cause one or more processors to perform the methods, as discussed above. The computer-readable medium may include volatile or nonvolatile, magnetic, semiconductor-based, tape-based, optical, removable, non-removable, or other types of computer-readable medium or computer-readable storage devices. For example, the computer-readable medium may be the storage device or the memory module having the computer instructions stored thereon, as disclosed. In some embodiments, the computer-readable medium may be a disc or a flash drive having the computer instructions stored thereon.
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.