Patent Description:
Lidar is an active remote sensing technology that uses light from a transmitter reflected by objects within a field of view (FOV) to determine the range or distance to the objects. This information can be processed to generate an image or otherwise used for mapping, object identification, object avoidance, navigation, etc. in various types of vehicles, such as automotive vehicles or drones, for example. While a number of lidar solutions have been proposed and may be acceptable for particular applications, various strategies have associated disadvantages that may make them unsuitable in other applications. For example, various lidar systems have limited power and associated limited detection range to maintain eye safety, use moving parts to mechanically scan the FOV, have limited frame rates, and are limited in adverse environmental conditions, such as fog, haze, rain, snow, etc..

[<NUM>-A] D1 (<CIT>) discloses a three-dimensional range imager including a laser light source providing a modulated light signal, a multiplexer, an optical fiber connecting the light source to the multiplexer, a plurality of optical fibers connected at first ends to the multiplexer and at second ends to a first fiber array, and a transmitter optic disposed adjacent the first fiber array for projecting a pixel pattern of the array onto a target. A second fiber array in a receiver receives light from the target. A processor generates pixel range data with each pixel corresponding to one of the fibers of the second fiber array.

[<NUM>-B] D2 (<NPL>) discloses a laser radar having an all solid state scanner with a magneto-optic design including birefringent wedges and a Faraday rotator to define the angle of deflection and magneto-optic material for polarization switching to provide non-mechanical beam steering.

[<NUM>-C] D3 (<CIT>) discloses a compact fiber-based scanning laser detection and ranging system including a pulsed <NUM> wavelength fiber laser and a detector that may be implemented using an avalanche photodiode. The disclosed system uses a monostatic fiber-based transmitter/receiver, a fiber beam scanner based on a laterally vibrating fiber, and a position sensor to monitor the transmitted beam position.

D4 (<CIT>) discloses a LIDAR scanner for a vehicle, configured such that an area where a vertically elongated transmitted beam intersects a laterally elongated light reception area forms a detection area. Both the vertically elongated transmitted beam and the laterally elongated light reception area are scanned in perpendicular directions using respectively rotating mirrors.

D5 (<CIT>) discloses a hybrid LIDAR system having an optical beam scanner configured to transform a light beam from a light source into an elongated optical beam, such as an ellipse, to illuminate an elongated illumination area in the field-of-view. A receiver optical subsystem projects an image of objects in the elongated illumination area onto a detector array which provides information regarding the vertical positions of the reflected beam from different vertical positions in the elongated illumination area.

A real-time scanning lidar system and method include various embodiments that incorporate all-optical switching so that no moving parts are required. Various embodiments facilitate scanning of a larger field of view (FOV) in three-dimensional space to provide multi-dimensional real-time data, such as location, range, polarization, velocity, etc., with respect to objects within the FOV.

According to a first aspect, the invention provides a scanning lidar system as specified in claim <NUM>.

According to another aspect, the invention provides a method as specified in claim <NUM>.

Further embodiments are specified in the appended dependent claims.

One or more embodiments may provide advantages for various applications. For example, various embodiments according to the disclosure provide a scanning lidar operating at an eye-safe wavelength that does not require any moving parts by using magneto-optic switches orthogonally oriented fiber arrays to scan a field of view and receive reflected light to create an image or multi-dimensional data representing the FOV. One or more embodiments provide improved range, frame rate, reliability, scalability, and robust operation under adverse weather conditions making them suitable for use in autonomous vehicles and drones, for example.

As used in this description, an image or related terminology is not limited to a visual representation and refers more generally to a data representation of a field of view (FOV). Different types of data, such as location/position, distance/range, intensity, polarization, velocity, etc., may be collected for each measured point or pixel within the FOV to provide a multi-dimensional data array that may be processed by a controller without generating a visual representation of the data. Similarly, references to a pixel do not imply or require a visual representation or display of associated data, or an area on a display screen, but refer more generally to a discrete measurement point or observation point within the FOV, with underlying discrete measurements for a particular pixel location referred to as sub-pixels that may be used to improve or enhance the resolution within the pixel. For example, sub-pixels corresponding to measurements generated for a particular (x, y) pixel location from different laser pulses or different characteristics/properties of the laser pulse provide additional data that may be used to detect or identify time domain or spatial domain changes within the pixel to enhance resolution.

A vehicle is used in its most general sense as something used to carry, transport, or convey something or self-propelled mechanized equipment.

An optical switch refers to an all-optical switch that maintains the signal as light from input to output in contrast to an electro-optic switch that converts the optical signal to an electric signal and back to an optical signal to route light signals or pulses from one channel to another, i.e. from an input to one of a plurality of outputs, or from one of a plurality of inputs to an output. The all-optical switch may be controlled by an electric signal or electronic controller to provide spatial domain switching of optical signals or pulses. An optical switch with no moving parts refers to a device that does not have any moving mechanical components to perform the switching operation, i.e. excludes movable mirrors such as those provided in MEMS based photonic switches.

An optical element refers to any element or component that acts upon light including discrete elements such as mirrors, lenses (including graded index or gradient index lenses), prisms, gratings, etc. as well as integrated optics and holographic optical elements that may also act on incident light to redirect the light and/or modify one or more properties of the light.

<FIG> is a block diagram illustrating operation of a representative embodiment of a system or method for scanning lidar. System <NUM> includes a transmitter <NUM> configured to illuminate a field of view (FOV) <NUM> having at least one object <NUM> with reflected light from object <NUM> being detected by a receiver <NUM>. Transmitter <NUM> includes a laser <NUM> and a first optical switch <NUM> configured to receive laser pulses from the laser <NUM>. In various embodiments, laser <NUM> is a fiber laser operating in a pulsed mode in the SWIR range with an output nominal wavelength between <NUM> and <NUM>. In at least one embodiment laser <NUM> operates at a nominal output wavelength of <NUM> in the eye-safe region so that transmitter <NUM> may operate with higher power to provide longer range and improved imaging/sensing performance. Laser <NUM> may be operated to provide a data frame rate of between <NUM>-<NUM>, for example, with laser pulse rates between <NUM>-<NUM>, for example. Of course, the data frame rate and laser pulse repetition rate will vary based on the particular application and implementation.

In the representative embodiment illustrated in <FIG>, first optical switch <NUM> is an electronically controlled all-optical <NUM> x N switch to transfer optical pulses output by fiber laser <NUM> from the input of switch <NUM> to one of the N outputs as controlled by an associated controller, such as controller(s) <NUM>. In one embodiment, optical switch <NUM> is implemented by a <NUM> x <NUM> magneto-optical switch similar to commercially available switches offered by Agiltron, Inc. of Woburn, MA, USA or Primanex, Inc. of Qingdao, Shandong, China. A magneto-optical switch includes a Faraday rotator to switch the optical pulses so that the switch includes no moving parts to perform the switching operation.

Each of the outputs of switch <NUM> is coupled to an associated fiber positioned in a linear array along a first axis or direction. In one embodiment, the linear array of transmitter fibers <NUM> is oriented vertically. The outputs of fibers <NUM> are positioned at the focal plane of transmission optics <NUM>, which may be implemented by at least one optical element configured to receive the laser pulses from fibers <NUM> and to redirect the laser pulses such that the light <NUM> is directed into a different angle to illuminate a corresponding portion of the FOV <NUM> containing one or more objects <NUM>. The at least one optical element may include a diverging lens or one or more asymmetric, aspherical, and/or cylindrical optical elements to provide an oval or elliptical output beam at a specified angle based on the desired coverage portion of FOV <NUM> (best illustrated in <FIG>). The at least one optical element may include one or more lenses with each lens associated with a single one of fibers <NUM>, a group of fibers <NUM>, or all fibers <NUM>.

Receiver <NUM> receives central light rays <NUM> and off-axis light rays <NUM>, <NUM> within reflected light <NUM> from object <NUM> within the FOV <NUM>. Receiver optics <NUM> includes at least one optical element configured to collect and receive the laser pulses reflected from the FOV <NUM> and to redirect received reflected pulses to at least one of a second plurality of fibers <NUM>. Fibers <NUM> are arranged in a linear array oriented orthogonally relative to the linear array of the transmitter fibers <NUM>. In one embodiment, fibers <NUM> are oriented horizontally (best shown in <FIG>). Of course, the orientation of the linear fiber arrays of the transmitter and receiver may be reversed with the transmitter fibers oriented horizontally and the receiver fibers oriented vertically. Other orthogonal orientations are also possible depending on the particular application and implementation.

In the representative embodiment of <FIG>, receiver optics <NUM> are configured to collect and redirect off-axis reflected light rays <NUM> to an associated fiber <NUM>, while representative central rays <NUM> are collected and redirected to a fiber <NUM> and representative off-axis rays <NUM> are collected and redirected to a fiber <NUM> within fiber array <NUM>. Receiver optics <NUM> includes at least one optical element, which may include collection optics upstream of beam shaping optics configured to form beams having an elliptical cross section. The at least one optical element may include a converging lens or one or more asymmetric, aspherical, and/or cylindrical optical elements to provide an oval or elliptical output beam. The at least one optical element may include one or more lenses with each lens associated with a single one of fiber array <NUM>, a group of fibers within fiber array <NUM>, or all fibers of fiber array <NUM>.

Each fiber of fiber array <NUM> is coupled to a different input of a second optical switch <NUM>. Optical switch <NUM> may be implemented by an all optical switch with no moving parts similar to first optical switch <NUM>. In one embodiment optical switch <NUM> is a M x <NUM> magneto-optical switch that sequentially connects one of the M inputs coupled to an associated fiber within fiber array <NUM> to an output connected to detector(s) <NUM> as controlled by associated controller(s) <NUM>. In one embodiment optical switch <NUM> is a <NUM> x <NUM> magneto-optical switch such that system <NUM> provides a <NUM> x <NUM> array of pixels or data for a <NUM>° horizontal by <NUM>° vertical FOV as described in greater detail herein. Of course, the vertical and horizontal extent, number of pixels, and FOV covered need not be symmetric or proportional to the representative embodiments and will vary by application and implementation.

In one embodiment, at least one controller <NUM>, <NUM> is a microprocessor-based controller having associated non-transient memory or computer readable media for storing data representing instructions executable by the controller(s) to perform one or more control functions or algorithms and is thereby configured to control the first optical switch <NUM> to direct the laser pulses from fiber laser <NUM> from an input of the first optical switch <NUM> to each of the plurality of outputs coupled to associated fibers <NUM> in turn. The at least one controller <NUM>, <NUM> controls the second optical switch <NUM> to direct light from each of the second plurality of fibers <NUM> in turn to the output of the second optical switch <NUM>, and to process signals from the at least one detector <NUM> to generate data representing the field of view. Each of detector(s) <NUM> may be implemented by a photodiode such as an avalanche photodiode (APD), a PIN diode, a Schottky barrier photodiode, or any other optical detector with similar sensitivity that provides the desired signal-to-noise ratio (SNR) for a particular application. Where more than one controller is provided, the controllers may communicate to exchange data and/or coordinate or cooperate to perform a particular task, function, algorithm, etc..

In general, the processes, methods, or algorithms disclosed herein can be performed by a processing device, controller, or computer, which can include any existing programmable electronic control unit or dedicated electronic control unit or controller. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media including electronic, magnetic, and/or optical storage devices. Certain processes, methods, or algorithms may also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable dedicated or custom hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers, or any other hardware components or devices, or a combination of hardware, software and firmware components. Similarly, illustration or description of a process, algorithm or function in a particular sequence or order may not be required to perform the described operation or outcome. Some processes, functions, algorithms, or portions thereof may be repeatedly performed, performed in a different sequence, or omitted for particular applications.

<FIG> is a diagram illustrating a transmission beam cross-section or front view for a linear array of fibers in a representative embodiment. As illustrated in <FIG>, the optics in the transmitter may not be symmetric but rather asymmetric, aspherical, or cylindrical in nature, so that each beam of the output light <NUM> is shaped by the non-spherical optics to have an oval or elliptical beam cross section or front view. Each beam has a very wide angular divergence in the horizontal plane or direction <NUM> and narrow angular divergence in the vertical plane or direction <NUM>, or vice versa. In one embodiment, the horizontal angular divergence is <NUM> degrees with a vertical angular divergence of <NUM> degree. This beam shape can be achieved, for example, by placing a small aspherical/cylindrical lens in front of every fiber <NUM> within linear array <NUM> or a larger lens common to groups or all fibers as previously described. As such, the transmitter directs each laser pulse across a wide horizontal coverage and narrow vertical coverage or vice versa. Additional vertical coverage for the FOV is provided by scanning the laser pulses using the optical switch across adjacent fibers to cover the desired FOV. Each pulse may be separated in time to reduce or eliminate overlap.

<FIG> is a diagram illustrating a cross-section of received reflected light directed into a linear array <NUM> of fibers <NUM> arranged orthogonally relative to the linear array <NUM> of transmission fibers <NUM> (<FIG>) in a representative embodiment. As previously described, the receiver optics is configured to receive the laser pulses reflected from the FOV and to redirect received reflected light to each of the fibers <NUM>. The fibers are scanned or switched by the associated optical switch to direct the received light to the detector(s). As described with respect to <FIG>, the received light is directed or coupled to one of the plurality of fibers <NUM> in the linear array <NUM>. The receiving "beams" in space look very similar to the transmission beams only rotated by <NUM> degrees, as generally illustrated in <FIG>. The shaping of the receiving beams to the oval or elliptical cross section is performed using similar techniques and components as described above with respect to shaping the transmission beam. In one embodiment, the received light "beams" each cover an angle in the horizontal direction <NUM> of <NUM>° and an angle in the vertical direction <NUM> of <NUM>°.

Although the orthogonally positioned linear arrays of fibers are illustrated as a vertical transmission array and a horizontal receiver array, any other orthogonal orientation is possible. Similarly, although the representative embodiments include examples having a transmission fiber array with <NUM> fibers and a receiver fiber array of <NUM> fibers, the transmission and receiver arrays may contain different numbers of fibers depending on the particular application. Likewise, although transmission optics generate beams having angular divergence of <NUM> x <NUM> degrees and receiver optics to generate light having angular divergence of <NUM> x <NUM> degrees, the transmitter and receiver optics may be selected to provide different angular divergences depending on the particular application.

<FIG> illustrates multi-dimensional data generated from detector signals associated with overlapping points or pixels corresponding to a combination of the optically switched or scanned transmitted and received light pulses. The transmitted elliptical pulses <NUM> are scanned using the transmitter optical switch to direct pulses into each fiber sequentially or in turn as indicated at <NUM>. The received light or "beams" <NUM> are scanned using the receiver optical switch to direct light from each receiver fiber to the detector as represented at <NUM>. The intersection of the transmitted and received beam provides an array of pixels <NUM> representing the data generated by the detector signals for a particular position/location. As such, if the transmitter optical switch is configured to direct one or more laser pulses to fiber indexed i and the receiving optical switch is configured to direct received light from fiber number j to the detector(s), then the light signal that will be received at the detector will come from the angle defined by the (i, j)th element of the 2D pixel array of pixels <NUM> defined by the combination of the transmitting and receiving beams. As defined in greater detail below, multiple laser pulses may be provided to one transmitter/receiver fiber pair before operating the switches to scan to the next adjacent transmitter/fiber pair to provide multiple measurements for each pixel <NUM> to improve SNR as described below. Similarly, switching may occur after each laser pulse with multiple data associated with each pixel combined or otherwise processed to provide desired performance.

In one representative embodiment, each laser pulse associated with each of <NUM> transmission fibers has an instantaneous FOV of <NUM>° x <NUM>°. Each receiver instantaneous FOV is <NUM>° x <NUM>° and the laser is scanned from top down and the receiver from left to right, creating a matrix of pixels <NUM> that include <NUM> x <NUM> (or more generally N x M) pixels defined by the intersection of the transmitted and received light. The scanning is based on transmitter/receiver optical switches implemented by <NUM> x <NUM> magneto-optic switches with a switching time of less than 10µsec. The fiber laser characteristics are assumed to provide PRF*<NUM>*<NUM> pulses/second or approximately <NUM> pulses/second to provide the desired SNR with an average laser power of <NUM> * <NUM> microjoules = 3W. Representative signal calculations are shown below.

The instantaneous peak power that falls on the target is provided by: <MAT> Assuming a target size as small as the minimal resolution for the system to detect, St, the reflected signal from this target object is given by: <MAT> In a worst case scenario, the reflected signal from the target object is distributed evenly over half a dome toward the transmitter unit, and therefore the collecting optics in the receiver collects the following amount of power from the target object: <MAT> Inserting the values for each one of the parameters above gives: <MAT>.

While it may be difficult to detect such a signal from a single pulse, repeating the pulses to generate sub-pixel measurements for each pixel with a frame rate of <NUM>, for example, can provide an improvement factor of <NUM> for the SNR, so the effective received signal will be: <MAT> This signal level can clearly be detected by a sensitive photodiode such as an avalanche photodiode or similar optical detector.

The laser pulse frequency can be increased with an upper system constraint established by a rate at which transmitted pulses may overlap or intersect at the receiver if the pulses are close enough in time, i.e. a pulse is transmitted before the previously transmitted pulse has been reflected by an object and detected by the receiver. Assuming a buffer time of <NUM> microseconds (<NUM>) between pulses to prevent the pulses from intermixing, the maximum laser frequency for a typical application would be <NUM>. This repetition rate may provide a corresponding rate of <NUM> sub-pixels/sec and an average laser power of 15W. As 15W is a rather large laser average power, multiple detectors may be provided to operate in parallel to cover the FOV of the system. For example, a system having four avalanche photodiodes in parallel instead of a single detector as described above facilitates a <NUM> laser (<NUM>. 8W average laser power) while providing <NUM> sub-pixels/sec data rate. Similarly, a system having eight detectors with a <NUM> laser frequency can generate <NUM> sub-pixels/sec. A representative system having multiple detectors operating in parallel is illustrated and described with respect to <FIG>. Of course, the polarization filters would be omitted so that all parallel detectors are detecting the same characteristic of the received light.

Alternatively, or in combination, search resources may be allocated based on detection of objects in previous frames. This strategy will effectively increase the resolution of detection without the need to increase the number of overall pixels in the system by allocating additional search sub-pixels directed only to areas where objects were detected in previous frames.

<FIG> illustrates a modular configuration or architecture for a scanning lidar sensor having a controller or central unit (CU) and at least one optical head (OH) of a representative embodiment. The various modular configurations or architectures illustrate in <FIG> are understood to have components similar to those described with respect to the embodiment of <FIG> unless otherwise stated, and are not described again in detail. However, various components may be arranged differently within either the CU or OH depending on the particular embodiment, and additional components may be used to facilitate specific embodiments.

System <NUM> includes a CU module <NUM> with a first housing and OH module <NUM> in a second housing coupled by a fiber bundle <NUM>. In the representative embodiment of <FIG>, CU module <NUM> includes fiber laser <NUM>, first optical switch <NUM>, controller(s) <NUM>, second optical switch <NUM> and detector(s) <NUM>. Fiber laser <NUM> is coupled to first optical switch <NUM> via fiber <NUM>, or may be directly coupled. Transmitter fibers <NUM> are coupled to the output of first optical switch <NUM>. Similarly, receiver fibers <NUM> are coupled to second optical switch <NUM>. Fiber bundle <NUM> includes transmitter fibers <NUM> and receiver fibers <NUM>. OH <NUM> includes transmitter optics <NUM> and receiver optics <NUM>. As such, OH module <NUM> contains only optical fibers and optical components, and is connected to the CU <NUM> through optical fiber bundle <NUM>. As illustrated and described in greater detail with respect to <FIG>, multiple OH modules can be connected to a single CU module to expand the covered FOV of the system. In this embodiment, the CU module <NUM> contains the laser, optical switches, detection electronics, and processor. The OH module <NUM> is relatively small in dimensions and can be remotely located relative to the CU module <NUM>. As such, the OH module <NUM> may be placed in various locations of a vehicle, drone, robot, etc..

<FIG> illustrates a modular configuration or architecture for a scanning lidar sensor having a central unit with an optical splitter upstream of a transmitter optical switch coupled to multiple optical heads in another representative embodiment. System <NUM> includes a plurality of OH modules <NUM> coupled to a remotely located CU module <NUM>. CU module <NUM> includes laser <NUM> and a fiber splitter <NUM>, implemented by a <NUM> x <NUM> fiber splitter in this representative embodiment. Controller(s) <NUM> and detector(s) <NUM> may be located either within CU module <NUM> or one or more OH modules <NUM>. Plurality of OH modules <NUM> include four OH modules <NUM>, <NUM>, <NUM>, and <NUM> in this representative embodiment. Each of the OH modules includes a transmitter optical switch <NUM>, a receiver optical switch <NUM>, transmitter linear array and associated optics <NUM>, and a receiver linear array and associated optics <NUM>. As such, system <NUM> includes one CU <NUM> and N independent OH modules <NUM> (<NUM> in this example), each covering a specific part of the overall FOV of the system. This architecture maintains independency for each OH <NUM> to have its own associated scan pattern, but the overall solution may be more expensive and have larger size and complexity.

<FIG> illustrates a modular configuration or architecture for a scanning lidar sensor having a central unit with an optical splitter downstream of a transmitter optical switch coupled to multiple optical heads in another representative embodiment. System <NUM> includes a plurality of OH modules <NUM> and a single CU module <NUM>. The CU module <NUM> includes a laser <NUM>, a transmit switch <NUM> with output fibers <NUM> connected each connected to one of a plurality of fiber splitters <NUM>. In the representative embodiment illustrated, (<NUM>) - <NUM> x <NUM> fiber splitters <NUM> are provided so that each of the fiber splitters <NUM> is coupled to all of the OH modules <NUM> by associated transmission fibers <NUM>. Controller(s) <NUM> and Detector(s) <NUM> may also be provided either within CU module <NUM> or one or more OH modules <NUM>.

In the embodiment of <FIG>, OH modules <NUM> include a first OH module <NUM>, a second OH module <NUM>, a third OH module <NUM>, and a fourth OH module <NUM> remotely located from CU module <NUM> and coupled by one or more fiber bundles <NUM>. Each OH module <NUM> includes a receiver optical switch <NUM>, transmitter linear array and transmitter optics <NUM>, and receiver linear array and receiver optics <NUM>. In this embodiment, system <NUM> includes a single CU module <NUM> and N non-independent OH modules <NUM>, where each scan step is done in parallel in each OH module <NUM>, <NUM>, <NUM>, and <NUM>. This facilitates smaller OH modules <NUM> that are generally lower cost, but the scan pattern of the overall field of view is fixed and is a replica of the scan pattern of one of the OH modules <NUM>.

<FIG> illustrates a representative embodiment of a vehicle having a scanning lidar sensor with a rotating optical head and/or one or more stationary optical heads. Vehicle <NUM> includes a plurality of OH modules <NUM> coupled to a remotely located CU module <NUM>. OH modules may be placed at various positions around the vehicle <NUM> such as OH modules <NUM>, <NUM> positioned on respective side-view mirrors, OH modules <NUM>, <NUM> placed on a front grille or bumper. Fixed OH modules may also or alternatively placed at any number of positions including different faces/corners of the vehicle <NUM>, inside headlights, frames, mirrors, etc. One or more embodiments may utilize the headlight integrated optics to collect light for the OH units.

Alternatively, or in combination, vehicle <NUM> may include an OH module <NUM> connected to a motor/actuator <NUM> that rotates to scan <NUM>° as represented at <NUM>. One or more rotating units may integrate an OH module with a rotating mirror, or deliver the light from an OH module through a rotating mirror on the roof or side of a vehicle. The CU module may deliver the laser light to/from the rotating OH module through one or more free space optical elements with no physical connection between the rotating OH module and the fixed CU module.

<FIG> is a block diagram illustrated a scanning lidar with optical switches and multiple detectors to detect polarization of reflected light according to various embodiments. System <NUM> includes a laser <NUM> configured to transmit polarized pulses. In the illustrated embodiment, system <NUM> includes a polarizer <NUM> between laser <NUM> and transmitter optical switch <NUM>. Polarizer <NUM> may be omitted if laser <NUM> generates polarized light suitable for the application. Optical switch <NUM>, transmitter fibers <NUM> and transmitter linear array and optics <NUM> are configured to preserve the polarization of the polarized pulses to deliver associated polarized output beams <NUM> similar to the previously described embodiments. Reflected light <NUM> from objects within the FOV passes through receiver collection optics and beam shaping optics and into the receiver linear array <NUM> of fibers <NUM>. Switch <NUM> scans fibers <NUM> to sequentially couple each of fibers <NUM> to optical splitter <NUM>, which splits or redirects the light to outputs <NUM> connected to detectors <NUM>, <NUM>, <NUM>, and <NUM> operating in parallel. Each detector <NUM>, <NUM>, <NUM>, and <NUM> may have an associated polarization filter <NUM>, <NUM>, <NUM>, and <NUM> to detect light having corresponding polarizations.

As illustrated in <FIG>, the laser pulses transmitted through each one of the fibers <NUM> is polarized, with the collection optics of the system, including the free space optical elements <NUM>, <NUM> and the receiving optical fibers <NUM> selected to maintain the polarization of the reflected signal from the target object. As such, system <NUM> can collect information not just on the reflectance of the target object or its shape, but also on its Degree Of Polarization (DOP) and Angle Of Polarization (AOP). Because each detector <NUM>, <NUM>, <NUM>, and <NUM> has a different linear polarizer <NUM>, <NUM>, <NUM> aligned at angles of <NUM>, <NUM>, and <NUM> degrees or circular polarizer <NUM> in front of its front surface, the different polarization components of each reflected signal may be used to calculate the DOP and AOP of natural and/or man-made targets very accurately. DOP/AOP information may be used to advantage in driver assistance systems and autonomous vehicles.

AOP and/or DOP images are very robust and survive strong interference by the atmosphere such as scattering through fog, haze or rain. In such atmospheric conditions, the reflected signal intensity from a target tends to diminish and be masked by the light reflected and scattered by the particles or water droplets in its optical path. However, DOP/AOP information from the target is maintained and therefore can be used to sense or see through fog and haze to much longer ranges relative to simple intensity information. Polarization information may also help detect and classify small objects on smooth surfaces (such as a flat tire on the road, or a pit or crack in a road) that are almost undetectable by using just the intensity image of the reflected signal. Polarization information may also help detect and classify surface characteristics to alert a driver, such as a road surface containing water, oil, ice, black ice etc..

<FIG> illustrates a representative embodiment of a system or method for improving resolution within a pixel of a laser scanned FOV by manipulating or scanning polarization of the transmitted and received light using a Faraday rotator and phase mask to generate sub-pixel data. This strategy may be employed in one or more of the previously described embodiments, or other laser scanning systems to increase the resolution of scan of the system. The system or method involve inserting a polarization phase mask and polarization manipulation component into the optical train of both the transmitted and received light. The polarization manipulation may be performed electronically such that there are no moving parts in the scanning process as previously described with respect to one or more embodiments. There are various ways to provide polarization manipulation within the optical path of the transmitted and received beams other than illustrated in <FIG> that are within the scope of the claimed subject matter and will be recognized by those of ordinary skill in the art.

System <NUM> includes an optical path <NUM> for the transmitted and received beams that includes a linear polarizer <NUM> positioned upstream of a Faraday rotator (FR) <NUM>, which, in turn is positioned upstream of a phase mask (PM) <NUM> and a second linear polarizer <NUM>. System <NUM> may be placed in front of each transmission fiber in any of the previously described embodiments, for example.

Phase mask <NUM> may comprise a liquid crystal polymer (LCP) retarder, which is half-wave retarder designed to affect the radial and azimuthal polarization of optical fields. A commercially available vortex retarder, for example, has a constant retardance across the clear aperture but its fast axis rotates continuously over the area of the optic. There is no practical limit to the flexibility in designing the fast axis distribution on the phase mask to produce a desired distribution of polarized light immediately downstream of the phase mask. In the representative embodiment of <FIG>, phase mask <NUM> is a half-wave retarder phase mask that includes three columns <NUM>, <NUM>, and <NUM> each having a retardation axis rotated at a different angle. This design allows the Faraday rotator (FR) <NUM> to turn or rotate the input linear polarization produced by the linear polarizer <NUM> to be parallel to one of the retardation axes <NUM>, <NUM>, <NUM> on the phase mask <NUM>. The FR <NUM> is controlled electronically by supplying variable voltage. If the selected polarization direction is parallel to the retardation axis in the first column <NUM> of the PM, the intensity of the light that follows the second polarizer <NUM> will have peak intensity along the line of column <NUM>, with reducing intensity toward column <NUM> and <NUM> that have axes rotated relative to the input polarizer <NUM>. The FR <NUM> can then select a second angle of rotation that will align the polarization to the second column <NUM> of the PM <NUM>. In that case the peak intensity following the second polarizer <NUM> will move to the second column <NUM> and the other columns <NUM>, <NUM> will have lower intensity and look much darker. In a similar manner, the FR <NUM> can select any column <NUM>, <NUM>, <NUM> to be enhanced in intensity after the second polarizer <NUM> and therefore "scan" the peak intensity across the horizontal direction with three sub-pixels. Similar optics may be placed in front of the receive channel of the system with the same scan mechanism, but with the receiver PM rotated <NUM> degrees relative to the transmission PM. This will allow the transmitter/receiver pair to enhance a different square in the PM and therefore a different portion of the selected pixel based on the nine possible sub-pixels of the field of view of each of the fibers. This strategy may be applied to a single pixel location to provide sub-pixel resolution by scanning the polarization using the FR across the PM, which results in scanning the peak intensity of the received pulses across a pixel rather than a portion or region of the FOV represented by a group of pixels.

The combination of the transmitter and receiver polarization scan patterns provides the ability to emphasize the power of a specific pixel within a group of pixels, or a particular region within a single pixel as generally represented in <FIG>.

With reference to <FIG>, pattern <NUM> represents peak intensity distribution of a transmitted beam having system <NUM> in the optical path after the light exits the second polarizer <NUM> with the <CIT> controlled to align with the first column <NUM> of PM <NUM>. This results in column <NUM> having higher peak intensity relative to column <NUM> and column <NUM>. Pattern <NUM> represents peak intensity distribution of received light having a system <NUM> in the optical path, but with PM <NUM> rotated by <NUM> degrees and the FR controlled in a coordinated manner as the FR in the transmission path, after the received light exits polarizer <NUM>. This results in the top row <NUM> having higher peak intensity than the middle row <NUM> and bottom row <NUM>. The combined transmitter/receiver scan <NUM> illustrates the resulting distribution of power or intensity with pixel or sub-pixel <NUM> having a higher peak intensity than surrounding sub-pixels/pixels. By switching or scanning the polarization state, the position of the brightest pixel or sub-pixel can be quickly shifted to various positions to scan an area of interest with variable intensity to improve resolution.

<FIG> is a flowchart illustrating operation of a system or method for lidar scanning using optical switching according to one or more embodiments. The system or method <NUM> include generating laser pulses at <NUM>, which may include generating laser pulses using a fiber laser having an output nominal wavelength of between <NUM> and <NUM>. The system or method include optically switching the laser pulses to each of a first plurality of fibers arranged in a first linear array to illuminate a field of view at <NUM>. This may include shaping the laser pulses to form an elliptical beam with at least <NUM> times greater angular divergence along a first axis relative to angular divergence along a perpendicular second axis as represented at <NUM>.

Block <NUM> represents directing light reflected from an object illuminated by the laser pulses within the field of view to a second plurality of fibers arranged in a second linear array. This may include collecting and shaping light to form elliptical beams with an angular divergence along a second axis at least <NUM> times greater than the angular divergence along a perpendicular first axis at <NUM>. The system or method may also include optically switching light from the second plurality of fibers to direct the light to at least one detector as represented at <NUM>, which may include optically splitting the received light to direct a portion of the received light to each of a plurality of detectors arranged in parallel as indicated at <NUM>. The system or method may further include detecting the angle and/or degree of polarization of the received light as represented at <NUM>. The detector signals are then processed to generate data representing the field of view as represented by block <NUM>.

<FIG> is a flowchart illustrating operating of a system or method for increasing resolution of a laser scanned FOV using polarization manipulation according to one or more embodiments. System or method <NUM> includes generating a laser beam at <NUM>, which may be a pulsed or continuous wave (cw) beam. The laser beam is scanned along a first direction to generate a transmitted beam to illuminate a field of view is indicated at <NUM>. This may include optically switching the laser beam to scan a first linear array of fibers as indicated at <NUM>.

The system or method <NUM> may include directing light reflected from an object illuminated by the transmitted laser beam within the field of view along a second direction orthogonal to the first direction to form a received beam provided to at least one detector as represented at <NUM>. This may include optically switching received light from a linear array of fibers positioned orthogonally relative to the first linear array of fibers as indicated at <NUM>. Block <NUM> represents processing signals from the at least one detector to generate a two-dimensional array of pixels. Block <NUM> represents varying an intensity profile within a selected pixel or group of pixels to move peak intensity in a continuous manner within the selected pixel or across the group of pixels by synchronously varying polarization of the transmitted laser beam and the received beam provided to the at least one detector. This may include directing the transmitted beam and the received light through associated polarizers, Faraday rotators, and phase masks as represented at <NUM>, and synchronously controlling the Faraday rotators to manipulate or vary the polarization as represented at <NUM>.

Claim 1:
A scanning lidar system (<NUM>) comprising:
a transmitter (<NUM>) including a laser (<NUM>) and a first optical switch (<NUM>) configured to receive laser pulses from the laser (<NUM>);
a first plurality of fibers (<NUM>) each coupled to a different one of a plurality of outputs of the first optical switch (<NUM>);
a first at least one optical element (<NUM>) configured to receive the laser pulses from at least one of the first plurality of fibers (<NUM>) and to redirect the laser pulses to illuminate at least a portion of a field of view;
a receiver (<NUM>) including a second optical switch (<NUM>) and at least one detector (<NUM>);
a second plurality of fibers (<NUM>) each coupled to a different input of the second optical switch (<NUM>), an output of the second optical switch (<NUM>) coupled to the at least one detector (<NUM>);
a second at least one optical element (<NUM>) configured to receive the laser pulses reflected from the field of view and to redirect received reflected pulses to at least one of the second plurality of fibers (<NUM>); and
at least one controller (<NUM>, <NUM>) configured to control the first optical switch (<NUM>) to direct the laser pulses from an input of the first optical switch (<NUM>) to each of the plurality of outputs in turn, to control the second optical switch (<NUM>) to direct light from each of the second plurality of fibers (<NUM>) in turn to the output of the second optical switch (<NUM>), and to process signals from the at least one detector (<NUM>) to generate data representing the field of view, the system characterized in that:
outputs of the first plurality of fibers (<NUM>) are positioned in a first linear array (<NUM>) and inputs of the second plurality of fibers (<NUM>) are positioned in a second linear array (<NUM>) orthogonal to the first linear array (<NUM>),
the first at least one optical element (<NUM>) is configured to form a pulsed output beam from each of the first plurality of fibers (<NUM>) having an elliptically shaped cross-section,
the second at least one optical element (<NUM>) is configured to form received pulsed beams having elliptically shaped cross sections, and
the data correspond to pixels (<NUM>), with each pixel (<NUM>) corresponding to an intersection of the elliptically shaped cross sections of the transmitted and received pulsed beams.