Single beam digitally modulated lidar for autonomous vehicle distance sensing

According to one aspect, a relatively low-cost sensor for use on an autonomous vehicle is capable of detecting moving objects in a range or a zone that is between approximately 80 meters and approximately 300 meters away from the autonomous vehicle. A substantially single fan-shaped light beam is scanned for a full 360 degrees in azimuth. Using frequency-modulated-continuous-wave (FMCW) or phase coded modulation on the beam, with back end digital signal processing (DSP), moving objects may effectively be distinguished from a substantially stationary background.

TECHNICAL FIELD

The disclosure relates to autonomous vehicles and, more particularly, to sensors used in autonomous vehicles.

BACKGROUND

Light Detection and Ranging (lidar) is a technology that is often used in autonomous vehicles to measure distances to targets. Typically, a lidar system or sensor includes a light source and a target. The light source emits light towards a target that scatters the light. The detector receives some of the scattered light, and the lidar system determines a distance to the target based on characteristics associated with the received scattered light, or the returned light.

Lidar systems generate three-dimensional point clouds of a surrounding environment. While the point clouds are used to identify the location of obstacles, it is often difficult to determine the velocity of non-stationary obstacles using the point clouds.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

In one embodiment, a relatively low-cost lidar sensor is provided that is capable of detecting moving objects in a range or a zone that is between approximately 80 meters and approximately 300 meters away from the autonomous vehicle. A substantially single fan-shaped light beam is scanned for a full 360 degrees in azimuth. Using coherent detection, such as frequency-modulated continuous-wave (FMCW) or phase-coded modulation, on the beam with back end digital signal processing (DSP), moving objects may effectively be distinguished from a substantially stationary background. This lidar sensor is useful on a vehicle, such as, but not limited to an autonomous vehicle.

Example Embodiments

As the number of autonomous vehicles on roadways is increasing, the ability for autonomous vehicles to operate safely is becoming more important. For example, the ability of sensors used in autonomous vehicles to accurately identify obstacles and to determine the velocity at which non-stationary obstacles are moving is critical. In fact, this is important on non-autonomous vehicles that have some driver assistance capabilities.

In one embodiment, a sensor that is reliable, and relatively low cost, is capable of detecting moving obstacles that are between approximately 80 meters (m) and approximately 300 m away from the sensor. In some instances, the sensor may be arranged to detect moving obstacles that are between approximately 120 m and approximately 200 m away from the sensor. Such a sensor may be a lidar sensor that uses a single divergent, or fan-shaped, beam which is scanned substantially only in azimuth. When an autonomous vehicle is at a distance of between approximately 120 m and approximately 200 m away from an object, the autonomous vehicle is generally concerned with moving objects, and not as concerned with substantially stationary objects. As such, any potential inability to distinguish between objects at different elevations using a single divergent beam scanned substantially only in azimuth is generally not critical. For example, other sensors on an autonomous vehicle may be used to distinguish between objects at different elevations as the autonomous vehicle nears the objects.

Referring initially toFIG.1, an autonomous vehicle fleet will be described in accordance with an embodiment. An autonomous vehicle fleet100includes a plurality of autonomous vehicles101, or robot vehicles. Autonomous vehicles101are generally arranged to transport and/or to deliver cargo, items, and/or goods. Autonomous vehicles101may be fully autonomous and/or semi-autonomous vehicles. In general, each autonomous vehicle101may be a vehicle that is capable of travelling in a controlled manner for a period of time without intervention, e.g., without human intervention. As will be discussed in more detail below, each autonomous vehicle101may include a power system, a propulsion or conveyance system, a navigation module, a control system or controller, a communications system, a processor, and a sensor system.

Dispatching of autonomous vehicles101in autonomous vehicle fleet100may be coordinated by a fleet management module (not shown). The fleet management module may dispatch autonomous vehicles101for purposes of transporting, delivering, and/or retrieving goods or services in an unstructured open environment or a closed environment.

FIG.2is a diagrammatic representation of a side of an autonomous vehicle, e.g., one of autonomous vehicles101ofFIG.1, in accordance with an embodiment. Autonomous vehicle101, as shown, is a vehicle configured for land travel. Typically, autonomous vehicle101includes physical vehicle components such as a body or a chassis200, as well as conveyance mechanisms, e.g., wheels. In one embodiment, autonomous vehicle101may be relatively narrow, e.g., approximately two to approximately five feet wide, and may have a relatively low mass and relatively low center of gravity for stability. Autonomous vehicle101may be arranged to have a working speed or velocity range of between approximately one and approximately forty-five miles per hour (mph), e.g., approximately twenty-five miles per hour. In some embodiments, autonomous vehicle101may have a substantially maximum speed or velocity in range between approximately thirty and approximately ninety mph.

Autonomous vehicle101includes a plurality of compartments210. Compartments210may be assigned to one or more entities, such as one or more customer, retailers, and/or vendors. Compartments210are generally arranged to contain cargo, items, and/or goods. Typically, compartments210may be secure compartments. It should be appreciated that the number of compartments210may vary. That is, although two compartments210are shown, autonomous vehicle101is not limited to including two compartments210.

The autonomous vehicle101may further include a sensor pod220that is mounted on an arc structure230on the top of the autonomous vehicle101.

FIG.3is a block diagram representation of an autonomous vehicle, e.g., autonomous vehicle101ofFIG.1, in accordance with an embodiment. An autonomous vehicle101includes a processor300, a propulsion system310, a navigation system320, a sensor system330, a power system340, a control system350, and a communications system360. It should be appreciated that processor300, propulsion system310, navigation system320, sensor system330, power system340, and communications system360are all coupled to a chassis or body of autonomous vehicle101.

Processor300is arranged to send instructions to and to receive instructions from or for various components such as propulsion system310, navigation system320, sensor system330, power system340, and control system350. Propulsion system310, or a conveyance system, is arranged to cause autonomous vehicle101to move, e.g., drive. For example, when autonomous vehicle101is configured with a multi-wheeled automotive configuration as well as steering, braking systems and an engine, propulsion system310may be arranged to cause the engine, wheels, steering, and braking systems to cooperate to drive. In general, propulsion system310may be configured as a drive system with a propulsion engine, wheels, treads, wings, rotors, blowers, rockets, propellers, brakes, etc. The propulsion engine may be a gas engine, a turbine engine, an electric motor, and/or a hybrid gas and electric engine.

Navigation system320may control propulsion system310to navigate autonomous vehicle101through paths and/or within unstructured open or closed environments. Navigation system320may include at least one of digital maps, street view photographs, and a global positioning system (GPS) point. Maps, for example, may be utilized in cooperation with sensors included in sensor system330to allow navigation system320to cause autonomous vehicle101to navigate through an environment. In one embodiment, navigation system320includes perception software.

Sensor system330includes any sensors, as for example lidar, radar, ultrasonic sensors, microphones, altimeters, and/or cameras. Sensor system330generally includes onboard sensors that allow autonomous vehicle101to safely navigate, and to ascertain when there are objects near autonomous vehicle101. In one embodiment, sensor system330may include propulsion systems sensors that monitor drive mechanism performance, drive train performance, and/or power system levels. A lidar sensor included in sensor system330may be a lidar sensor that utilizes a single, substantially divergent beam that has an elevational component but is scanned substantially only in azimuth, as described in further detail below. Moreover, the lidar sensor used in sensor system330may employ modulation and demodulation techniques described in further detail below. One or more components of the sensor system330may reside in the sensor pod220shown inFIG.2.

Power system340is arranged to provide power to autonomous vehicle101. Power may be provided as electrical power, gas power, or any other suitable power, e.g., solar power or battery power. In one embodiment, power system340may include a main power source, and an auxiliary power source that may serve to power various components of autonomous vehicle101and/or to generally provide power to autonomous vehicle101when the main power source does not have the capacity to provide sufficient power.

Communications system360allows autonomous vehicle101to communicate, as for example, wirelessly, with a fleet management system (not shown) that allows autonomous vehicle101to be controlled remotely. Communications system360generally obtains or receives data, stores the data, and transmits or provides the data to a fleet management system and/or to autonomous vehicles101within a fleet100. The data may include, but is not limited to including, information relating to scheduled requests or orders, information relating to on-demand requests or orders, and/or information relating to a need for autonomous vehicle101to reposition itself, e.g., in response to an anticipated demand.

In a range of between approximately 80 m to approximately 300 m away from an autonomous vehicle, autonomous vehicle perception software is much more concerned with the azimuth of objects than with the elevation of objects. Thus, rather than use data obtained from a lidar sensor to create a point cloud by scanning a narrow beam in both azimuth and elevation, a substantially two-dimensional (2D) point cloud may be created by scanning a single, divergent beam substantially only in azimuth. Each point in a 2D point cloud may have an x-coordinate and a y-coordinate, and the 2D point cloud may be drawn on a flat map. The divergent beam may be a fan-shaped beam. In one embodiment, the beam is diverged or defocused in an elevation direction, and is relatively tightly focused in an azimuth direction.

It has been determined that for certain applications, such as vehicle-based applications, it is not necessary to have such a large amount of data for purposes of ranging of objects approximately 80-200 m from the vehicle. Moreover, for some applications, it is not necessary to determine the full three-dimensional shape of objects in vicinity of the lidar sensor, rather it is sufficient to determine that there is an object moving relative to the lidar sensor, and the velocity at which the object is moving.

There is a trend in the development of lidar sensors to improve their range and point-cloud density capabilities. However, these lidar sensors tend to be quite expensive and can generate a large amount of point-cloud data, which as a result, requires expensive processing capabilities to process the point-cloud data.

FIG.4Ais a diagrammatic representation of a single beam that is scanned substantially only in azimuth in accordance with an embodiment. As shown, a lidar sensor400is configured to generate a single beam410that is arranged to scan with respect to a z-axis. Lidar sensor400may be a single beam digitally modulated lidar sensor. Typically, single beam410may scan approximately 360 degrees with respect to the z-axis. That is, an overall scanning angle θ may be approximately 360 degrees.

Beam410is shown in an xy-plane for ease of illustration, i.e., beam410is shown as including an azimuthal component. Beam410may have any suitable operating wavelength, e.g., an operating wavelength of approximately 1550 nanometers.

In general, beam410is a divergent beam and has an elevational component in addition to an azimuthal component.FIG.4Bis a diagrammatic representation of a single divergent beam that has a component in elevation and is scanned substantially only in azimuth in accordance with an embodiment. Lidar sensor400is arranged to produce a single divergent beam410′ that is scanned about a z-axis. Beam410′ is substantially fan-shaped, and has an elevational component. In one embodiment, the elevational component of beam410′ is an angle ϕ that is in a range of between approximately −10 degrees and approximately 10 degrees. Beam410′ may have any suitable operating wavelength, e.g., an operating wavelength of approximately 1550 nanometers.

FIG.5illustrates the single divergent or fan-shaped beam410′ that may be generated by the lidar sensor400. One advantage of the single divergent beam410′ is that a single instance of modulation, demodulation, and related signal processing resources may be used. Thus, there are cost and simplicity advantages to this approach.

Divergent beam410′ may, in one embodiment, be a substantially flat fan or sheet of light that is illuminated substantially simultaneously. That is, divergent beam410′ may be a single sheet of light that is effectively flashed as one beam, rather than being divided into multiple beams that are narrow in elevation.

When a single light beam is used for a full 360-degree scan in azimuth, substantially only a single copy of a lidar modulator, demodulator, and signal processing chain may be used. As a result, scanning may be provided at a desired scan rate at a lower cost, for example, than systems that scan narrow light beams in both azimuth and elevation.

Whereas newer high-resolution lidar sensors may have multiple beams that cover a fan shape in elevation, the lidar sensor arrangement depicted inFIGS.4A,4B and5involves a single beam that covers a fan shape in elevation. A lidar sensor that employs a single divergent beam generates one measurement for each intersection event of the beam by an object, which reduces the complexity of the computations needed to be performed on returned light. The lidar sensor400may be rotated about a circle, such as around a vehicle, at a rate of approximately 10 rotations/sec. This is sufficient to determine that there is an object moving with respect to the lidar sensor, and at what velocity the object is moving relative to the lidar sensor (or relative to a vehicle on which the lidar sensor is mounted).

FIG.6is a block diagram representation of lidar sensor400capable of scanning a beam substantially only in azimuth in accordance with an embodiment. The lidar sensor400includes a light source or emitter430that includes a divergent beam generator435, a beam steering mechanism440, a detector450, and a housing460. As will be appreciated by those skilled in the art, lidar sensor400may include many other components e.g., lenses such as a receiving lens. Such various other components are not shown inFIG.6for simplicity.

Light emitter430may generally emit a light at any suitable wavelength, e.g., a wavelength of approximately 1550 nanometers. It should be appreciated that a wavelength of approximately 1550 nanometers may be preferred for reasons including, but not limited to including, eye safety power limits and wide availability of 1550 nanometer lasers. In general, however, suitable wavelengths may vary widely.

Light source430may include the divergent beam generator435. In one embodiment, divergent beam generator435may create a single divergent beam, and light source430may be substantially rigidly attached to a surface, e.g., a surface of an autonomous vehicle, through housing460. In other words, light source430may be arranged not to rotate.

Beam steering mechanism440is arranged to steer a beam generated by divergent beam generator435. In one embodiment, beam steering mechanism440may include a rotating mirror that steers a beam substantially only in azimuth, e.g., approximately 360 degrees in azimuth. Beam steering mechanism may be arranged to rotate clockwise and/or counterclockwise. The rotational speed of beam steering mechanism440may vary widely. The rotating speed may be determined by various parameters including, but not limited to including, a rate of detection, and/or field of view.

Detector450is arranged to receive light after light emitted by light source430is reflected back to lidar sensor400. Housing460is arranged to contain light source430, beam steering mechanism440, and detector450. The detector450may be, for example, a photodiode or an array of photodiodes or other suitable photosensor arrangement.

Reference is now made toFIG.7for a more detailed description of the lidar sensor400in more detail, and in particular further details of the light source430, divergent beam generator435and beam steering mechanism440, according to an example embodiment. Light from light source430is directed into an optical fiber432that in turn is coupled to the divergent beam generator435. The divergent beam generator435includes a collimation lens437and a divergence lens439. The collimation lens437narrows the light carried from the light source430on the optical fiber432and the divergence lens439diverges collimated light from the collimation lens437to produce the single divergent beam410′.

The beam steering mechanism440may include a rotating structure442to which is attached a mirror444. In addition, the divergence lens439is attached to the rotating structure442. An electric motor446is coupled to the rotating structure442to rotate the rotating structure442in the direction of the arrow shown inFIG.7. The mirror444reflects the single divergent beam410′ to produce a reflected single divergent beam410′ that spans an elevation relative to the xy-plane and is rotated in the azimuth direction (relative to the z-axis) as the motor446rotates the rotating structure442to which the mirror444and divergence lens439are mounted.

In one form, the mirror444may be a flat mirror. In another form, the mirror444is a curved mirror, in which case the divergence function of the divergence lens439may be performed by the mirror444. Thus, the only components that rotate are the mirror444and the divergence lens439, or in one variation, only a curved mirror rotates. The light source430, optical fiber432and collimation lens437need not rotate.

The arrangement depicted inFIG.7may achieve a 360 degree rotational scan, and as fast as 600 rpm (10 cycles/sec). No active components are in motion, and there is no need for any vertical scanning (in elevation) since the beam already has a diverging pattern in elevation. Further still, there are no Doppler effects introduced by the mirror rotation.

FIG.8Ashows that the divergence lens439may be a cylindrical lens. The divergence lens439receives a narrow beam of light and produces the divergent beam410′.

FIG.8Bshows still another variation in which a diffraction grating470is used instead of a divergence lens. The diffraction grating470may take the form of a microscopic grid of wires. The diffraction grating470is a passive optical device in which light going in one end emerges out the other end with its properties changed. The diffraction grating470produces divergence only where selected exit angles are represented by beam power, rather than the continuum of angles provided by a cylindrical lens, for example.

Further still, an optical prism may be used instead of a divergence lens or diffraction grating, in order to generate the diverging beam pattern.

In general, a mechanism that allows a beam associated with a lidar sensor to be scanned substantially only in azimuth may be less complex than a mechanism which allows for both azimuthal and elevational scanning. For example, in order to support scanning substantially only in azimuth, because no elevational scanning is supported, a relatively simple rotating mirror may be used to support scanning.

Supporting substantially only azimuthal scanning allows issues associated with rotating joints, e.g., issues associated with power and/or data transfer across rotating joints, to be avoided.

FIG.9is a process flow diagram that illustrates a method500of using a single beam digitally modulated lidar, e.g., a single fan-shaped beam, to facilitate the detection of moving objects in accordance with an example embodiment. The method500begins at operation510in which vehicle, e.g., an autonomous vehicle, on which the lidar is mounted, drives. As the vehicle drives, or is otherwise propelled, the lidar sensor scans a divergent beam, or a fan-shape beam, substantially only in azimuth, in operation520. It should be appreciated that the divergent beam generally has an elevational component, but is scanned substantially only in azimuth. In one embodiment, scanning the single, divergent beam substantially only in azimuth allows for the creation of a 2D point cloud and the detection of moving objects within a range or zone, e.g., within a zone that is between approximately 80 m and approximately 300 m away from the vehicle.

At operation530, coherent detection is applied returned light from the single divergent beam. Applying coherent detection may include, but is not limited to, applying a frequency-modulated continuous-wave (FMCW) or a phase-coded modulation to the single divergent beam. In addition, back end digital signal (baseband demodulation) processing may be applied as appropriate. That is, baseband modulation and baseband demodulation/digital signal processing may be applied to the single divergent beam. The application of FMCW or phase coded modulation, in addition to back end signal processing, allows the velocity profile of objects at each range to be recovered in operation540. Further details about the modulation of the light beam and digital signal processing of returned light are described below. Once the velocity profile of the objects is recovered, the method of using a single beam digitally modulated lidar is completed.

Coherent detection enables direct measurement of an objected detected by the single divergent beam. That is, by modulating the light beam that is sent into a target area, the velocity of any detected object can be determined by observing how the light beam intersects with surfaces of the object and changes the modulation of returned light from the object. Therefore, there is no need to rescan the object and perform complex computations on the point-cloud to determine velocity of the object. In a few msec (ms), and one scan, it is possible to determine the direction of movement and velocity of an object.

Referring next toFIG.10, a system600is shown that uses baseband modulation and baseband digital signal processing techniques in connection with a lidar sensor, in accordance with an embodiment. The system600generally includes a “stable” light source610, or a light source that produces a beam of light with a relatively narrow line width. Stable light source610may produce a beam of light that may be a single divergent beam as described above in connection withFIGS.1-9, or in general, any light beam (e.g., non-divergent light beam). That is, the system600, and its variations depicted inFIGS.11and12, may be used with any type of light beam for one-dimensional lidar, two-dimensional lidar as well as three-dimensional lidar.

The system600further includes an optical transmitter620, a baseband modulator module/block630, an optical receiver640and a baseband demodulator (digital signal processing) module/block650. The optical transmitter620includes an optical mixer625that mixes the light beam from the light source610with a baseband modulated light beam to impose baseband modulation on the light beam from the light source610. The baseband modulation may be in the form of FMCW, phase coded modulation or any other suitable modulation scheme now known or hereinafter developed. Thus, baseband modulation is effectively applied to a light beam that is transmitted into a target area. The modulated light beam may be a single divergent (fan-shaped) beam that is scanned in an azimuth direction, as described above, or any type of beam.

Returned light from the target area is received (e.g., by a suitable photodetector) and directed to optical receiver640. The optical receiver640includes an optical mixer645that mixes the returned light with light from the light source610and the mixed light output of the mixer645is (digitized) and supplied to baseband demodulator block650.

Traditional lidar sensors illuminate a target area with light pulses (turned on and off) and evaluate roundtrip time of light. Coherent detection is different. In the system600, the stable light source610is continuously on (no pulsing) and the light beam is mixed with a baseband modulation and then sent into a target area. The differences between characteristics of the modulation applied on the transmitted beam and the modulation detected on the returned light are used to directly determine movement (velocity) of a detected object. There is no need to perform roundtrip timing analysis between light pulses because the timing aspects are determined by the differences in transmitted modulation and received modulation.

The system600may achieve greater sensitivity, allowing for greater range of detection (with lower levels of light), and to directly determine velocity of an object from a single scan event.

The use of coherent detection in the manner depicted byFIG.10may be applied to any light beam structure, and is not limited to use with the single divergent beam structure described herein. However, a more robust lidar sensor may be realized by combining the single divergent light beam with the coherent detection aspects depicted inFIG.10.

While system600is one example of a suitable coherent lidar signal processing chain, it should be appreciated that many other coherent lidar signal processing chains may be implemented. Other examples of suitable coherent lidar signal processing chains are be described below with reference toFIGS.11-13.

FIG.11shows another suitable coherent lidar signal processing system600′ that uses baseband modulation and baseband digital signal processing, in accordance with an example embodiment. System600′ is similar to system600ofFIG.11, except that the optical transmitter620′ and optical receiver640′ include additional components instead of a single mixer. The system600′ employs in-phase and quadrature optical beam components in the optical transmitter620′ and optical receiver640′. Specifically, the optical transmitter620′ includes a phase shifter622, first and second mixers624and626, respectively, and an optical combiner/summer628. Similarly, the optical receiver640′ includes a phase shifter642and first and second mixers644and646, respectively.

In the transmit path, the light beam from the stable light source610is coupled to the phase shifter622and to the first mixer624of the optical transmitter620′. The phase shifter622shifts the phase of the light beam from the light source610by approximately ninety (90) degrees, for example, and supplies the resulting phase shifted light beam to the second mixer626. The baseband modulator block630applies baseband modulation to the light beam from the light source610at first mixer624. First mixer624outputs a first modulated light beam and corresponds to an in-phase beam component. The baseband modulator block630also applies baseband modulation to the phase shifted light beam at second mixer626, and second mixer626outputs a second modulated (phase shifted) light beam, and corresponds to a quadrature beam component. The optical combiner/summer628combines the first modulated (in-phase) light beam from first mixer624and the second modulated (quadrature) light beam from second mixer626to produce a modulated transmit beam that is directed to a target area.

In the receive path, the light beam from the light source610is coupled to the phase shifter642and to the first mixer644of the optical receiver640′. The phase shifter642shifts the phase of the light beam from the light source610by approximately ninety (90) degrees to produce a phase shifted light beam. The first mixer644mixes received/returned light from the target area with the light beam from the light source610and supplies the resulting first returned (in-phase) light beam to the baseband demodulator block650. The second mixer646mixes the received/returned light from the target area with the phase shifted light beam and supplies the resulting second returned (quadrature) light beam to the baseband demodulator block650. The baseband demodulator block650demodulates the outputs from the first and second mixers644and646, respectively. The differences between the baseband modulation applied in the transmit path by the baseband modulation block630and the baseband modulation on the outputs from the first and second mixers644and646, respectively, may be analyzed to determine presence of an object in the target area and velocity of the object.

Turning now toFIG.12, a block diagram is shown of a lidar sensor system700according to another example embodiment. The lidar sensor system700includes a fixed/stable continuous wave (CW) laser710, an optical splitter712, an optical phase modulation (PM) modulator720, an optical amplifier725(such as an erbium doped fiber amplifier (EDFA)), an optical coupler730, a beam direction/steering and reception assembly735, an optical coupler/combiner740, and a photodetector745. The lidar sensor system700further includes a controller750that in turn includes a baseband modulator block752, a baseband demodulator block754, a detection processor block756, a digital-to-analog converter (DAC)760, an analog-to-digital converter (ADC)765and an amplifier770. The DAC760converts the digital baseband modulation produced by the baseband modulator block752to an analog signal that is supplied to the PM modulator720. The ADC765converts the analog receive signal at the output of the amplifier770to a digital signal and directs it to the baseband demodulator block754. The controller750may be implemented in digital signal processor (DSP) that includes fixed or programming digital logic gates, such as in a Field Programming Gate Array (FPGA).

In the lidar sensor system700, the optical splitter712, optical PM modulator720, and optical amplifier725form an optical transmitter. Similarly, the optical combiner740and photodetector745form an optical receiver.

The fixed CW laser710provides a continuation light beam, of a suitable wavelength, to the optical splitter712. The optical splitter712splits the light beam and directs it to both the optical PM modulator720and to the optical coupler/combiner740. As described further below, the unmodulated light beam directed by the optical splitter712to the optical coupler/combiner740is used as a reference with respect to the received/return light.

The optical PM modulator720applies phase modulation to the light beam according to the baseband modulation contained in output of the DAC760, to produce a phase modulated light beam. The optical amplifier725amplifies the phase modulated light beam, that is then coupled to the optical coupler730, which in turn directs the amplified phase modulated light beam to the beam direction/steering and reception assembly735. The beam direction/steering and reception assembly735sends the amplified phase modulated light beam to the target area and collects returned/received light from the target area. In one example, the light beam may be a single divergent light beam as described above, and the beam direction/steering and reception assembly735may take the form of the beam steering mechanism described above in connection withFIGS.7,8A and8B.

The received/returned light is directed by the optical coupler730to the optical combiner740. The optical combiner740combines the unmodulated light beam from the fixed CW laser710with the received/returned light, and the resulting combined light beam is detected by the photodetector745. In one form, the optical combiner740may include a direct downmixing path and a phase shifted downmixing path, similar to that inFIG.11.

The photodetector745converts the combined light beam to an electrical receive signal. The amplifier770amplifies the electrical receive signal and supplies an amplified electrical receive signal to the ADC765. The ADC765converts the amplified electrical receive signal to a digital receive signal for processing by the baseband demodulator block754and by the detection processor756. The baseband demodulation block754performs baseband demodulation of the digital receive signal, including dechirping in the digital domain, in order to recover the baseband modulation on the returned light. The detection processor756analyzes/compares the modulation recovered in the digital receive signal with the modulation generated by the baseband modulation block752. For example, the detection processor756may analyze the differences between the modulation applied to the light beam that is transmitted into the target area and the modulation recovered in the digital receive signal to determine velocity of a moving object in the target area of the lidar sensor system700.

Unlike a conventional optical communication system in which node is not attempting to receive the same optical beam that it transmitted, in a lidar sensor system, the received signal is derived from the transmitted signal. In other words, a lidar sensor is looking for returned light from a target area that results from the reflection/scattering of the light that the sensor transmits into the target area. A lidar sensor uses the received light to estimate the range and velocity of an object reflecting light transmitted from the lidar sensor.

Turning now toFIG.13, a more detailed diagram of a portion of the lidar sensor system700is shown for purposes of describing signal processing operations that may be performed to detect range and velocity of a target. The baseband modulation block752may include a numerically controlled oscillator (NCO)780and the baseband demodulation block754may include a Fast Fourier Transform (FFT) block782. A de-chirp block784is provided that receives the output of the NCO780and is used de-chirp (perform symbol multiplication) the output of the ADC765.

The NCO780may generate a linear frequency modulation signal, also known as a “chirp” that is supplied to the DAC760to drive the PM modulator720shown inFIG.12. An example of a waveform of the linear frequency modulation signal is shown at790inFIG.13. The linear frequency modulation signal is also supplied to the de-chirp block784. In the receive/return path, the ADC765converts return signal to a digital signal and passes the digital signal to the de-chirp block784. The de-chirp block784generates a de-chirp signal that is supplied to the FFT block782. The FFT block782obtains the frequency components of the de-chirp signal. An example of the frequency components generated by the FFT block782is shown at792. Using well known principles of FMCW techniques, the frequency components generated by the FFT block782may be analyzed, such as by the detection processor756shown inFIG.12, to obtain the range and velocity of one or more targets in the field of view of the lidar sensor.

FIG.14is a block diagram representation of another example of a coherent lidar sensor system800in accordance with an embodiment. The system800includes a tunable stable light source810that cooperates with a synthesizer820to generate a light beam. The light beam, once transmitted, may be received and processed using baseband digital signal processing block830after the received/returned light is mixed by a mixer840with the output of the tunable stable light source810.

In one embodiment, to a first order, the sensitivity or signal-to-noise ratio may be approximately the same when comparing a narrow beam scanned N times in elevation to a single divergent beam integrated N times, using coherent integration, over the same field of view. In such an embodiment, to a second order, a higher sensitivity may be achieved by a single divergent beam than by a narrow beam, as there may effectively be no down time between scans when a single divergent beam is used. As such, objects may be illuminated for a longer amount of time. Further, because a coherent processing time is generally longer for a single divergent beam than for a narrow beam, velocity resolution may be better when using the single divergent beam.

Although only a few embodiments have been described in this disclosure, it should be understood that the disclosure may be embodied in many other specific forms without departing from the spirit or the scope of the present disclosure. By way of example, although a single divergent, fan-shaped beam has been described as suitable for being scanned substantially only in azimuth, a narrow beam may instead be scanned substantially only in azimuth. For an embodiment in which a narrow beam is used, a coherent processing time may be reduced.

Coherent detection has been described as including the use of FMCW or phase coded modulation on a beam. Coherent detection is not limited to the use of FMCW or phase coded modulation on a beam. In general, coherent detection improves the sensitivity associated with a lidar device, and provides a desirable range with respect to a divergent beam.

While a light source has been described as being substantially stationary with respect to an autonomous vehicle, e.g., not rotating, it should be appreciated that in some embodiments, a light source may rotate to scan a beam in azimuth. In other words, any suitable method may be used to provide a beam and to cause the beam to be scanned substantially only in azimuth.

An autonomous vehicle has generally been described as a land vehicle, or a vehicle that is arranged to be propelled or conveyed on land. It should be appreciated that in some embodiments, an autonomous vehicle may be configured for water travel, hover travel, and or/air travel without departing from the spirit or the scope of the present disclosure.

The embodiments may be implemented as hardware, firmware, and/or software logic embodied in a tangible, i.e., non-transitory, medium that, when executed, is operable to perform the various methods and processes described above. That is, the logic may be embodied as physical arrangements, modules, or components. For example, the systems of an autonomous vehicle, as described above with respect toFIG.3, may include hardware, firmware, and/or software embodied on a tangible medium. A tangible medium may be substantially any computer-readable medium that is capable of storing logic or computer program code which may be executed, e.g., by a processor or an overall computing system, to perform methods and functions associated with the embodiments. Such computer-readable mediums may include, but are not limited to including, physical storage and/or memory devices. Executable logic may include, but is not limited to including, code devices, computer program code, and/or executable computer commands or instructions.

It should be appreciated that a computer-readable medium, or a machine-readable medium, may include transitory embodiments and/or non-transitory embodiments, e.g., signals or signals embodied in carrier waves. That is, a computer-readable medium may be associated with non-transitory tangible media and transitory propagating signals.

The steps associated with the methods of the present disclosure may vary widely. Steps may be added, removed, altered, combined, and reordered without departing from the spirit of the scope of the present disclosure. Therefore, the present examples are to be considered as illustrative and not restrictive, and the examples are not to be limited to the details given herein, but may be modified within the scope of the appended claims.

Data relating to operations described herein may be stored within any conventional or other data structures (e.g., files, arrays, lists, stacks, queues, records, etc.) and may be stored in any desired storage unit (e.g., database, data or other repositories, queue, etc.). The data transmitted between entities may include any desired format and arrangement, and may include any quantity of any types of fields of any size to store the data. The definition and data model for any datasets may indicate the overall structure in any desired fashion (e.g., computer-related languages, graphical representation, listing, etc.).

In one form, a method is provided for performing lidar sensing. The method includes: generating a single divergent light beam; scanning the single divergent light beam in an azimuth direction into a target area; and applying coherent detection based on returned light from the target area to detect one or more objects in the target area. The single divergent light beam may have an elevational component. The single divergent light beam may be a fan-shaped light beam. The operation of generating the single divergent light beam may include generating the single divergent light beam from a stable light source. The operation of scanning may include scanning the single divergent beam approximately 360 degrees around a vehicle to detect the one or more objects in the target area with respect to the vehicle. Moreover, the scanning of the single divergent beam may be achieved by rotating a mirror in the azimuth direction into the target area.

The method may further include, based on the coherent detection, deriving a velocity of the one or more objects in the target area. Further still, the method may include applying baseband modulation to the single divergent light beam, and wherein applying coherent detection includes recovering a modulation of the returned light and analyzing frequency components of the returned light in order to detect the one or more objects in the target area and a velocity of the one or more objects.

In another form, a lidar sensor apparatus is provided that comprises: a light emitter configured to generate a single divergent light beam that has an elevational component; a beam steering mechanism configured to scan the single divergent light beam in an azimuth direction into a target area; and a detector configured to apply coherent detection based on returned light from the target area to detect one or more objects in the target area.

The light emitter, in one form, may include: a stable light source configured to output a light beam; and a divergent beam generator configured to receive the light beam from the stable light source and to generate the single divergent light beam. The beam steering mechanism may include: a mirror that is mounted to a rotating assembly and configured to rotate in order to scan the single divergent light beam in the azimuth direction. In one form, the mirror is a substantially flat mirror.

The divergent beam generator may include, in one form, an optical element configured to generate the single divergent light beam from the light beam output by the stable light source, wherein the optical element is one of: a divergence lens, a diffraction grating and a prism. The optical element may be mounted to the rotating assembly so as to rotate with the mirror. In another form, the divergent the divergent beam generator includes a curved mirror configured to receive the light beam output by the stable light source and to reflect the single divergent light beam into the target area. The beam steering mechanism may include a rotating assembly to which the mirror is attached, the rotating assembly configured to rotate in order to scan the single divergent light beam in the azimuth direction. The beam steering mechanism may be configured to scan the single divergent beam approximately 360 degrees around a vehicle to detect the one or more objects in the target area with respect to the vehicle.

The lidar sensor apparatus may further include a baseband modulator configured to apply baseband modulation to the single divergent light beam, and the detector may include a baseband demodulator configured recover a modulation of the returned light and a detection processor configured to analyze frequency components of the returned light in order to detect the one or more objects in the target area and a velocity of the one or more objects.

In still another form, a lidar sensor system is provided comprising: a stable light source configured to produce a light beam that is substantially continuous; a baseband modulator configured to generate a baseband modulation; an optical transmitter coupled to the baseband modulator and configured to apply the baseband modulation to the light beam and to produce a modulated light beam for transmission into a target area; an optical receiver coupled to the stable light source and configured to receive returned light from the target area; and a baseband demodulator coupled to the optical receiver and configured demodulate the returned light to detect one or more objects in the target area. The baseband modulation may be one of: frequency continuous wave modulation or phase coded modulation.

The lidar sensor system may further include: a divergent beam generator configured to receive the light beam from the stable light source and to generate a single divergent light beam to which the baseband modulator applies the baseband modulation to produce the modulated light beam for transmission into the target area; and a beam steering mechanism configured to scan the single divergent light beam in an azimuth direction into the target area.

The lidar sensor system may further include a detection processor coupled to the baseband demodulator and configured to analyze frequency components of the returned light to determine a velocity of the one or more objects detected in the target area.

In one form, the optical transmitter includes a mixer coupled to an output of the baseband modulator and to the stable light source, the mixer configured to apply the baseband modulation to the light beam, and wherein the optical receiver includes a mixer coupled to the stable light source and configured to mix the returned light with the light beam output by the stable light source.

In another form, the optical transmitter may include: a phase shifter coupled to receive the light beam from the stable light source and configured to phase shift the light beam by approximately 90 degrees to produce a phase shifted light beam; a first mixer coupled to the stable light source and to an output of the baseband modulator, the first mixer configured to apply the baseband modulation to the light beam from the stable light source to produce a first modulated light beam; a second mixer coupled to an output of the baseband modulator and to an output of the phase shifter, the second mixer configured to apply the baseband modulation to the phase shifted light beam to produce a second modulated light beam; and an optical combiner configured to combine the first modulated light beam and the second modulated light beam to produce a modulated transmit light beam for transmission into the target area.

In one form, the optical receiver includes: a phase shifter coupled to receive the light beam from the stable light source and configured to phase shift the light beam by approximately 90 degrees to produce a phase shifted light beam; a first mixer coupled to receive the light beam from the stable light source and the returned light, the first mixer configured to mix the returned light with the light beam to produce a first returned light beam; and a second mixer coupled to receive the phase shifted light beam and the returned light, the second mixer configured to mix the returned light with the phase shifted light beam to produce a second returned light beam; wherein the baseband demodulator is configured to receive as input the first returned light beam and the second returned light beam.

In one form, the lidar sensor system further includes: a digital-to-analog converter coupled to receive an output of the baseband modulator to convert the baseband modulation to an analog modulation signal; and an analog-to-digital converter coupled to convert an analog receive signal derived from the returned light to a digital receive signal to be supplied to the baseband demodulator; wherein the optical transmitter includes an optical phase modulator and an optical amplifier, the optical phase modulator is coupled to receive as input the light beam output by the stable light source and the analog modulation signal, wherein the optical phase modulator is configured to apply the baseband modulation to the light beam to produce the modulated light beam, the optical amplifier configured to amplify the modulated light beam to produce an amplified modulated light beam for transmission into the target area; wherein the optical receiver includes an optical combiner, and a photodetector, the optical combiner configured to receive the returned light and the light beam from the stable light source, wherein the optical combiner is configured to output a combined light beam to the photodetector, wherein the photodetector is configured to convert the combined light beam to the analog receive signal that is coupled to the analog-to-digital converter.