Lidar system including a multi-faceted deflector

Abstract

A LIDAR system including a multi-faceted deflector. A system and method for scanning of a coherent LIDAR. The system includes a motor, a laser source, and a deflector, where the laser source is configured to produce a light beam. A first facet of a plurality of facets has a facet normal direction. The deflector is coupled to the motor and configured to rotate about an axis of rotation to deflect the light beam from the laser source. The laser source is configured to direct the light beam such that the light beam is incident on the deflector at a first incident angle in a first plane, where the first plane contains the axis of rotation, where the first incident angle is spaced apart from the facet normal direction of the first facet. A second facet of the plurality of facets includes an optical element configured to deflect the light beam at the first incident angle into a deflection angle.

Description

[0001] This application is a divisional application of parent application having application number 201980087974.9, applicant Blackmore Sensors and Analytics LLC, filing date December 31, 2019, and title “LIDAR System Including Multi-Faceted Deflector”.

[0002] Cross Reference to Related Applications

[0003] This application claims the benefit of and priority to U.S. Provisional Application No. 62 / 788,415, filed January 4, 2019, the entire disclosure of which is incorporated by reference herein. BACKGROUND

[0004] Distance optical detection using lasers, often referenced by the mnemonic LIDAR, for light detection and ranging, sometimes also called laser radar, is used for a variety of applications, from height finding to imaging to collision avoidance. LIDAR provides finer range resolution with smaller beam size compared to conventional microwave ranging systems, such as radio wave detection and ranging (RADAR). Optical detection of range can be accomplished by several different techniques, including: direct ranging based on round trip time of optical pulses to an object; and chirped detection based on frequency difference between a transmitted chirped optical signal and a returned signal scattered from an object; and phase coded detection based on a sequence of single frequency phase changes distinguishable from natural signals. SUMMARY

[0005] The present application relates to optical scanning systems, and more particularly to optical scanning systems using multi-faceted deflectors.

[0006] Aspects of the present disclosure relate generally to light detection and ranging (LIDAR) in the field of optics, and more particularly to systems and methods of multi-faceted deflectors for scanning for coherent LIDAR to support operation of a vehicle.

[0007] One implementation disclosed herein relates to a system for a multi-facet deflector for scanning of a coherent LIDAR to support operations of a vehicle. In some implementations, the LIDAR system includes a motor. In some implementations, the LIDAR system includes a light source configured to produce a light beam. In some implementations, the LIDAR system includes a deflector including a plurality of facets. In some implementations, a first facet of the plurality of facets has a facet normal direction. In some implementations, the deflector is coupled to the motor and configured to rotate about an axis of rotation to deflect the light beam from the laser source. In some implementations, the laser source is configured to direct the light beam such that the light beam is incident on the deflector in a first plane at a first angle of incidence. The first plane contains the axis of rotation. The first angle of incidence is spaced apart from the facet normal direction. In some implementations, the system includes a second facet of the plurality of facets including an optical element configured to deflect the light beam at the first angle of incidence into a deflection angle.

[0008] In some implementations, the optical element is a reflective blazed grating having a facet ruling normal direction equal to half of the first angle of incidence for each ruling on the facet. In some implementations, the light beam is incident on the deflector in the first plane at a second, different angle of incidence in the first plane, where the second angle of incidence is within 40 degrees of the first angle of incidence. In some implementations, the second facet of the deflector is covered by a second optical element having a second pitch different from the pitch of the optical element of at least one facet of the deflector. In some implementations, where the second facet of the deflector is covered by the second optical element, the second optical element deflects the light beam at the first angle of incidence into a second deflection angle different from the deflection angle.

[0009] In another aspect, the disclosure relates to a deflector for scanning of a coherent LIDAR to support operations of a vehicle. In some implementations, the deflector includes a body having a plurality of outwardly facing facets relative to an axis of the body. In some implementations, a facet of the plurality of outwardly facing facets has a facet normal direction. In some implementations, a facet of the plurality of outwardly facing facets is covered by an optical element, where the optical element has a pitch less than ten times a working wavelength and in a range of 0.8 microns to 10 microns.

[0010] Other aspects, features, and advantages will become apparent from the following detailed description, taken in connection with the accompanying drawings, which illustrate, by way of example, various implementations, in which: BRIEF DESCRIPTION OF DRAWINGS

[0011] Implementations are illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which like references indicate similar elements, in which:

[0012] Figure 1A is a block diagram illustrating example components of a high resolution coherent LIDAR system, in accordance with an implementation;

[0013] Figure 1B is a block diagram illustrating an example system including at least one high resolution LIDAR system mounted on a vehicle, in accordance with an implementation;

[0014] Figure 2A is a block diagram illustrating a sawtooth scan pattern for a high resolution Doppler system used in some implementations;

[0015] Figure 2B is an image illustrating an example velocity point cloud produced by a high resolution Doppler LIDAR system, in accordance with an implementation;

[0016] Figure 3A is a block diagram illustrating a top view of example components of a scanning optic, in accordance with an implementation;

[0017] Figure 3B is a diagram illustrating an exploded view of a deflector assembly, in accordance with an implementation;

[0018] Figure 4A is a block diagram illustrating an example scanning system with off-axis impact beams in a plane perpendicular to the axis of rotation;

[0019] Figure 4B depicts an arrangement of scanning spots using impact beams in or near a (horizontal) plane perpendicular to the axis of rotation;

[0020] Figure 5A is a block diagram illustrating an example scanning system with on-axis impact beams, in accordance with an implementation, where the on-axis impact beams are in a plane containing the axis of rotation;

[0021] Figure 5BAn arrangement of scan spots using an impinging beam that leaves a (horizontal) plane perpendicular to the axis of rotation is depicted;

[0022] Figure 6A is a block diagram illustrating a blazed grating used as a facet of a polygonal deflector according to an implementation;

[0023] Figure 6B is a block diagram illustrating an example scanning system using a polygonal deflector with blazed grating facets and an impinging beam on an axis in a plane containing the axis of rotation according to an implementation;

[0024] Figure 6C An arrangement of scan spots using a blazed grating polygonal deflector and an impinging beam at or near twice the blaze angle according to an implementation is depicted;

[0025] Figure 6D is Figure 5B a repeat of Figure 6C for ease of comparison; and

[0026] Figure 7 is a plot of the efficiency of a blazed grating versus wavelength for a number of candidate wavelengths. DETAILED DESCRIPTION

[0027] To obtain acceptable ranging accuracy and detection sensitivity, direct long-range LIDAR systems use short-pulse lasers with low pulse repetition rates and very high pulse peak powers. The high pulse power leads to rapid degradation of optical components. Chirped and phase-coded LIDAR systems use longer optical pulses with relatively lower peak optical power. In this configuration, the ranging accuracy increases with the chirp bandwidth or the length and bandwidth of the phase code, rather than with the pulse duration, so that excellent ranging accuracy can still be obtained.

[0028] The use of a wide-band radio frequency (RF) electrical signal to modulate an optical carrier has enabled useful optical bandwidths. Recent advances in LIDAR include the use of the same modulated optical carrier as a reference signal, and the combination of this reference signal with a return signal at an optical detector to produce, in the resulting electrical signal, a relatively low beat frequency in the RF band that is proportional to the frequency or phase difference between the reference and return optical signals. This beat frequency detection of the frequency difference at the detector is called heterodyne detection. It has several advantages known in the art, such as the use of off-the-shelf RF components and inexpensive availability.

[0029] Recent work has shown novel arrangements of optical components and coherent processing for detecting Doppler shifts in the returned signal that not only provide improved ranging, but also provide the relative signed velocity of the vector between the LIDAR system and each external object. These systems are referred to herein as high-resolution ranging Doppler LIDAR. See, for example, World Intellectual Property Organization (WIPO) publications based on Patent Cooperation Treaty (PCT) patent applications PCT / US 2017 / 062703 and PCT / US 2018 / 016632.

[0030] These improvements provide ranging with or without target velocity in a pencil thin laser beam with appropriate frequency or phase content. When such a beam is swept over a scene using a scanner (also referred to herein as a "deflector"), information about the position and velocity of surrounding objects can be obtained. This information is expected to be of value in defense and control systems for autonomous vehicles such as self-driving cars or driver-assisted cars.

[0031] The sampling and processing that provide ranging accuracy and target velocity accuracy involve integrating one or more laser signals of different durations over a time interval referred to as the integration time. Covering a scene in time for a vehicle control system involves repeating measurements with sufficient accuracy (typically involving one or more signals over a time of one to tens of microseconds) before objects progress too far into the space in front of the facility or vehicle (typically covering distances of about one to tens of meters over a certain time of about one second to a few seconds), typically sufficient to sample a variety of angles (typically thousands of angles) around the facility or vehicle to understand the environment around the facility or vehicle. The number of different angles that can be covered in a certain time (often referred to as the period or sampling time) depends on the sampling rate.

[0032] Opto-mechanical-electrical deflection of laser light is conventionally used for beam-steering (scanning) in LIDAR systems. These conventional LIDAR systems on a macroscopic scale involve selection of reflective, refractive, and diffractive elements according to material properties to direct spatially coherent light sources in selected directions. These systems utilize high-performance galvanometer scanners that operate under complex second-order electromagnetic state systems, making high-power data and extensive tuning necessary.

[0033] However, the reflective surfaces of conventional scanners often produce irregular scan patterns that complicate detection or recognition of objects in the vicinity of the scanning system, especially on a ground vehicle.

[0034] Accordingly, the present disclosure relates to systems and methods for a multi-faceted deflector for scanning of a coherent LIDAR to support operation of a vehicle. That is, the present disclosure describes systems and methods of LIDAR beam scanning in which by replacing the reflector surface of the scanner with a grating, it is possible to achieve near horizontal tilt / declination angles (respectively, vertically above and below the horizontal direction at zero tilt angle) with wider horizontal coverage, thereby improving the ability of the LIDAR system to detect and identify objects in its vicinity.

[0035] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid unnecessarily complicating the present disclosure.

[0036] 1. Distance detection overview

[0037] Distance measurement using an optical phase-coded signal, for a portion of the transmitted signal, the transmitted signal is in phase with the carrier (phase = 0) and then changes by one or more phase changes denoted by the symbol ΔΦ (hence, phase = ΔΦ) in a very short time interval, about the transmitted signal repeatedly switches between two or more phase values. The shortest interval of constant phase is a coding parameter called the pulse duration τ, and is usually the duration of several periods of the lowest frequency in the frequency band. The reciprocal I / τ is the baud rate, where each baud represents one symbol. The number N of such constant phase pulses during the time of the transmitted signal is the number N of symbols and represents the length of the coding. In binary coding, there are two phase values, and the phase of the shortest interval can be considered 0 for one phase value and 1 for the other phase value, so the symbol is one bit, and the baud rate is also called the bit rate. In multi-phase coding, there are multiple phase values. For example, 4 phase values such as ΔΦ * {0, 1, 2, and 3} for ΔΦ = π / 2 (90 degrees), which are equal to {0, π / 2, π, and 3π / 2}, respectively; and thus the 4 phase values represent 0, 1, 2, 3, respectively. In this example, each symbol is two bits, and the bit rate is twice the baud rate.

[0038] For optical ranging applications, the carrier frequency is the optical frequency fc, and the RF f0is modulated onto the optical carrier. The number of symbols N and the duration τ are chosen to achieve the desired ranging accuracy and resolution. The pattern of symbols is chosen to be distinguishable from other coded signal sources and noise sources. Thus, the strong correlation between the transmitted signal and the return signal is a strong indication of a reflected or backscattered signal. The transmitted signal consists of one or more blocks of symbols, where each block is long enough to provide a strong correlation with a reflected or backscattered echo even in the presence of noise.

[0039] In chirp detection, the laser power is turned on at time zero for a finite pulse duration τ. The frequency of the pulse increases from fi to f2 over the duration τ of the pulse, thus having a bandwidth B = f2 - fi. The rate of change of frequency is (f2 - fi) / τ.

[0040] The return signal is simply the transmitted reference signal attenuated in strength and delayed by Δt. When the return signal is received from an external object after a distance of 2R, where R is the distance to the target, the return signal, which started at delay time Δt, is given by 2R / c, where c is the speed of light in the medium (approximately 3 x 10 8 meters per second, m / s). The amount of frequency change over this time depends on the distance, called f R , which is given by the rate of change of frequency multiplied by the delay time. This is given by equation la.

[0041] f R = (f2 - fi) / τ * 2R / c = 2BR / cτ (la)

[0042] In a time domain mixing operation called de-chirping, the value of f R is measured by the frequency difference between the transmitted signal and the return signal. Thus, the distance R is given by equation lb.

[0043] R = f R c τ / 2B (lb)

[0044] Of course, if the return signal arrives after the pulse has been completely transmitted, i.e., if 2R / c is greater than τ, then equations la and lb are not valid. In this case, the reference signal is delayed by a known or fixed amount to ensure that the return signal overlaps the reference signal. Multiplying the fixed or known delay time of the reference signal by the speed of light c gives an additional distance that is added to the distance calculated from equation lb. Although there can be an absolute distance offset due to uncertainty in the speed of light in the medium, this is a near constant error, and the relative distance based on the frequency difference is still very accurate.

[0045] 2. Optical detection hardware overview

[0046] To depict the new scanning technique, some general hardware methods are described. Figure 1A is a block diagram showing example components of a high-resolution coherent LIDAR system 100 according to an implementation. Optical signals are represented with arrows. Electrical wired or wireless connections are represented with unarrowed segmented lines. A laser source 112 emits a carrier or beam 101 that is phase or frequency modulated in a modulator 182a before or after a beamsplitter 116 to produce a phase-coded or chirped optical signal 103 with a duration D. The beamsplitter 116 splits the modulated (or, as shown, unmodulated) optical signal for use in a reference path 120. A target beam 105 (also referred to herein as a transmitted signal) is produced that has the vast majority of the energy of the beam 101. A modulated or unmodulated reference beam 107a is also produced that has much less energy, but enough to produce good mixing with a return beam 191 scattered from an object (not shown). In the implementation shown, the reference beam 107a is separately modulated in a modulator 182b. The reference beam 107a passes through the reference path 120 and is directed to one or more detectors as a reference beam 107b. In some implementations, the reference path 120 introduces a known delay sufficient for the reference beam 107b to arrive at the detector array 130 with scattered light from objects outside the LIDAR in a range of interest. In some implementations, the reference beam 107b is referred to as a local oscillator (LO) signal, referring to older methods of producing the reference beam 107b locally from a separate oscillator or light source.

[0047] The transmitted signal is then transmitted to illuminate an area of interest, typically through some scanning optics 118. The detector array is a single paired or unpaired detector or paired or unpaired one-dimensional (ID) or two-dimensional (2D) array arranged in a plane generally perpendicular to the beams 191 returned from objects. The reference beam 107b and the return beam 191 are combined in zero or more optical mixers 184 to produce an optical signal with characteristics to be properly detected. The acquisition system 140 records the frequency, phase, or amplitude, or some combination of the interference pattern for each detector multiple times during the signal duration D. The number of temporal samples processed per signal duration or integration time affects the down-range extent.

[0048] The number or integration time is often a practical consideration selected based on the number of symbols per signal, the signal repetition rate, and the available camera frame rate. The frame rate is the sampling bandwidth, often called the "digitizer frequency." The only fundamental limits on the range extent are the coherence length of the laser and the length of the chirp or unique phase code before it repeats (for clear ranging). This is possible because any digital record of the returned heterodyne signal or bits can be compared or cross-correlated with any portion of the transmitted bits from the history of previous transmissions.

[0049] The acquired data can be used by a processing system 150, such as a computer system or chip set. According to one or more implementations described below, a scanner control module 154 provides scan signals to drive the scanning optics 118. In some implementations, a signed Doppler compensation module (not shown) in the processing system 150 determines the sign and magnitude of the Doppler shift and the correction distance based thereon along with any other corrections, if any. The processing system 150 also includes a modulation signal module (not shown) to send one or more electrical signals that drive the modulators 182a, 182b. In some implementations, the processing system also includes a vehicle control module 152 to control a vehicle on which the system 100 is mounted.

[0050] Any known device or system can be used to implement the laser source 112, modulators 182a, 182b, beam splitter 116, reference path 120, optical mixer 184, detector array 130, scanning optics 118, or acquisition system 140. Optical coupling, either flood or focused on the target or focused past the pupil plane, is not shown. As used herein, an optical coupler is any component that affects the propagation of light within spatial coordinates to direct light from one component to another, especially components such as vacuum, air, glass, crystal, mirrors, lenses, optical circulators, beam splitters, phase plates, polarizers, optical fibers, optical mixers, and the like, used alone or in some combination.

[0051] In some implementations, a vehicle is controlled based at least in part on data received from a high resolution Doppler LIDAR system mounted on the vehicle. Figure 1Bis a block diagram showing an example system 102 including at least one high resolution LIDAR system mounted on a vehicle 160, according to an implementation. The vehicle has a center of mass indicated by star 161 and travels in a forward direction given by arrow 163. In some implementations, the vehicle 160 includes components that operate in response to signals from a processor, such as a vehicle control module 152 of a processing system 150, such as a steering or braking system (not shown). In some implementations, the vehicle has an on-board processor 164, such as a chipset. In some implementations, the on-board processor 164 is in wired or wireless communication with a remote processor. In an implementation, the processing system 150 of the LIDAR system is communicatively coupled with the on-board processor 164, or the processing system 150 of the LIDAR is used to perform the operations of the on-board processor 164, such that the vehicle control module 152 causes the processing system 150 to emit one or more signals to the steering or braking system of the vehicle to control the direction and speed of the vehicle.

[0052] The high resolution Doppler LIDAR uses a scanning beam 172 that scans from one side through an azimuthal field of view 174 and through a vertical angle (see, e.g., FIG. 1) to the other side (represented by future beam 173), illuminating a spot in the environment around the vehicle 160. In some implementations, the field of view is 360 degrees in azimuth. In some implementations, the tilt angle field of view is from about +10 degrees to about -10 degrees or a subset thereof. Figure 2A ) to the other side (represented by future beam 173), illuminating a spot in the environment around the vehicle 160. In some implementations, the field of view is 360 degrees in azimuth. In some implementations, the tilt angle field of view is from about +10 degrees to about -10 degrees or a subset thereof.

[0053] In some implementations, the vehicle includes auxiliary sensors (not shown), such as GPS sensors, odometry, tachometers, temperature sensors, vacuum sensors, voltage or current sensors, and other sensors known in the art. In some implementations, a gyroscope 166 is included to provide rotational information.

[0054] 3. Polygonal scan overview

[0055] Figure 2Ais a block diagram showing a simple zigzag scan pattern of a LIDAR system used in some prior art implementations. The scan sweeps through a range of azimuthal (horizontal) and tilt / declination angles (above and below the vertical, respectively, in the horizontal direction at zero tilt angle). In various implementations described below, other scan patterns are used. Any scan pattern known in the art can be used in various implementations. For example, in some implementations, adaptive scanning is performed using the methods described in Crouch’s PCT patent applications entitled “Method and system for adaptive scanning with optical ranging systems” or “Method and system for automatic real-time adaptive scanning with optical ranging systems,” the entire contents of which are incorporated by reference as if fully set forth herein. Figure 2B is an image showing an example velocity point cloud produced by a high resolution Doppler LIDAR system, according to an implementation.

[0056] Figure 3Ais a block diagram illustrating a top view of example components of a scanning optic 300 according to an implementation. The scanning optic 300 is an implementation of the scanning optic 118 of the system 100, with features discussed herein. The scanning optic 300 includes a deflector assembly 350 composed of a first polygon deflector 344a coupled to a motor 357 (not shown) and configured to rotate about an axis of rotation 343 at a first angular velocity 349a. In the illustrated implementation, the deflector assembly 350 also includes a second polygon deflector 344b coupled to the motor 357 and configured to rotate about the axis of rotation 343 at a second angular velocity 349b. While two polygon deflectors 344a, 344b are depicted in the scanning optic 300, in other implementations fewer or more than two polygon deflectors are included in the scanning optic 118. In the illustrated implementation, the first angular velocity 349a has a first fixed rotational speed that is different (e.g., less or opposite) than a second fixed rotational speed of the second angular velocity 349b. For example, the first fixed rotational speed of the first angular velocity 349a is in a range of about 1000 revolutions per minute (rpm) to about 5000 rpm, and the second fixed rotational speed of the second angular velocity 349b is in a range of about 300 rpm to about 1000 rpm. As another example, the first angular velocity 349a and the second angular velocity 349b have different directions (e.g., clockwise and counterclockwise). While five-sided regular polygon (penta) deflectors are depicted for the two polygon deflectors, in other implementations other regular or irregular polygon deflectors are used. In some implementations, a single beam is alternately directed to multiple polygon deflectors; and, in other implementations, multiple different beams are each directed to a different set of one or more polygon deflectors. In some implementations, the polygon deflectors have reflective facets and are referred to as polygon reflectors.

[0057] In one implementation in which the reflector rotates in opposite directions, the ratio of the mass of the second polygon deflector 344b to the mass of the first polygon deflector 344a is approximately equal to the ratio of the rotational speed of the first angular velocity 349a to the rotational speed of the second angular velocity 349b. This advantageously ensures that the assembly of polygon deflectors 344a, 344b has no net angular momentum during rotation, which enables stability of the scanning optic 300 during operation when a vehicle on which the scanning optic 300 is disposed is turned or otherwise rotated.

[0058] Figure 3Bis a schematic diagram showing an exploded view of a deflector assembly 350 according to an implementation. In the implementation shown, the deflector assembly 350 includes a first polygonal deflector 344a operatively coupled to a motor 357 and a second polygonal deflector 344b operatively coupled to the motor 357 through the first polygonal deflector 344a. The first polygonal deflector 344a is rotatably mounted to a drive shaft 358 and a planetary bearing 359 of the motor 357. The first polygonal deflector 344a includes a recess (not shown) to receive the drive shaft 358 and the planetary bearing 359. The second polygonal deflector 344b is rotatably mounted to the first polygonal deflector 344a with a planetary gear 354 and a driver sun gear 356 positioned within a ring gear 352. The ring gear 352 is received within a cavity (not shown) on a lower surface of the second polygonal deflector 344b. One or more parameters (e.g., diameter, number, etc.) of the planetary gear 354, the driver sun gear 356, and / or the ring gear 352 are selected to adjust a ratio of a magnitude of a rotational speed of a first angular velocity 349a of the first polygonal deflector 344a to a magnitude of a rotational speed of a second angular velocity 349b of the second polygonal deflector 344b. In various implementations, the ratio is in a range of about 3 to about 10 or in a range of about 3 to about 30. Any suitable motor known in the art can be used as the motor 357, such as a motor manufactured by Nidec Motor Corporation of Torrance, California. Any suitable gears can be used for one or more of the ring gear 352, the planetary gear 354, or the driver sun gear 346, such as available from Gears, Inc., including S1EO5ZM05S072 inner ring gears coupled with options from Ground Metric Spur Gear Products. Gears, Inc., including S1EO5ZM05S072 inner ring gears coupled with options from Ground Metric Spur Gear Products.

[0059] When a beam hits the surface of a deflector, the beam is deflected by a deflection angle relative to the incoming beam (e.g., by the angle of specular reflection of the reflecting surface on the face of the deflector). It is a common practice for the reflecting face of the deflector to lie in a plane perpendicular to the radial of the rotation axis 343 of the deflector assembly 350, and to illustrate the problem with the current use of reflecting surfaces, such an arrangement is assumed in the following. However, similar problems arise if the face is not so oriented. For the sake of illustration, it is further assumed that the rotation axis points towards the local plumb line measuring the down-angle; and that the plane perpendicular to the rotation axis is horizontal, with the azimuth angle lying in it. However, the same problems and principles exist regardless of the direction in which the rotation axis points.

[0060] Horizontal scanning is typically done with the beam from the source / detector optics hitting a point inside the deflector, typically inside a circle inscribed in the polygon deflector, in the horizontal plane, such as the intersection of the axis of rotation and the horizontal plane. If the beam is directed outside this inscribed circle, there will be some angles of deflector rotation that do not intersect the faces of the deflector, and thus there will be angles that are not deflected at all. In some arrangements, such gaps in any deflection can be desirable. If the beam is directed at the axis of rotation (as depicted in Figure 3A Figure 1), then at some angle of rotation, the reflecting face of the deflector will be perpendicular to the impinging beam and will return the beam toward the source, which interferes with the beam leaving the device to scan the nearby area outside the device.

[0061] Figure 4A Figure 2 is a block diagram showing an example scan with off-axis impinging beams in a (horizontal) plane perpendicular to the axis of rotation. The beam from the source / detector optics 410 impinges on the face of a polygon deflector 444 that rotates about an axis of rotation 443. Both the face of the polygon deflector 444 and the axis of rotation are perpendicular to the plane of the drawing sheet. In this configuration, the beam is not directed to the axis of rotation and no beam is reflected back to the source / detector optics 410. The azimuthal reflection angle varies in a field of view 420 between an angle Bl 421 when the beam first impinges on the face and an angle B2 422 when the face rotates out of the beam. This azimuthal angle field of view 420 is asymmetric about the azimuthal angle B3 423 that is perpendicular to the face of the deflector. The field of view 420 is less than if the beam from the source / detector optics 410 were directed toward the axis of rotation 443; however, the reflected beam is prevented from being blocked by the source / detector optics 410. The field of view 420 increases as the size of the polygon deflector 444 increases. Increasing the size of the polygon deflector can be disadvantageous for scanning systems on vehicles that have space or weight constraints.

[0062] Figure 4B Figure 3 depicts an arrangement that uses impinging off-axis beams in or near a (horizontal) plane perpendicular to the axis of rotation to scan a target plane that is perpendicular to the plane containing the axis of rotation, as in Figure 4AThe target plane is 200 meters from the axis of rotation. The horizontal axis represents distance in the horizontal plane in meters; while the vertical axis represents distance in the vertical plane in meters, both relative to the position (0,0) in the horizontal plane and the beam reflected normal to the current face of the polygon deflector 444. The off- horizontal spot is produced by stepping the source / detector optics 410 in vertical angles from about 0 (1°) to a maximum of + / - 10 degrees. Note that the illumination spot is not symmetric about reflection normal to the deflector face; however, it is more symmetric in the vertical direction. A relatively useful rectangular spot array is found in the range of about -75 meters to about +100 meters vertically and about -200 meters to about +500 meters horizontally. This relatively regular array simplifies detection or recognition of objects near the scanning system. In addition, a spot array with tens of meters of vertical spread near horizontal is particularly useful for land and sea surface vehicles where the surface is at near horizontal (small down tilt) angles and there is little advantage to steep down tilt or tilt angles.

[0063] To use the wider azimuthal field of view available for on-axis impact angles of the beam on the face of the polygon deflector without being blocked by the source / detector optics, a non-horizontal impact beam has been used, as depicted in Figure 5A Figure 5A is a block diagram showing an example scan with an on-axis impact beam in a plane containing the axis of rotation. The beam from the source / detector optics 510 impacts on the face (plane normal to the drawing) of a polygon deflector 544 that rotates about the axis of rotation 543 in the plane of the illustration. This rotation is imparted by the motor and suspension components 550 of the deflector assembly. In this configuration, no beam is reflected back to the source / detector optics 510 that are located above the horizontal plane (at the horizontal plane at a down tilt angle D3 423 equal to zero). As a result, a non-zero down tilt angle D4 is imposed on the reflected beam. When the down tilt angle of the source / detector optics 510 is varied from a down tilt angle Di to an angle D2 522, a down tilt field of view 520 is covered. As the polygon rotates, the azimuthal reflection angle varies in a field of view (not shown) between an angle A (when the beam first impacts on the face) to an angle -A (when the face rotates away from the beam). This azimuthal field of view is symmetric about the azimuthal angle normal to the face of the deflector. Because the azimuthal angle of the impact beam is close to the angle toward the axis of rotation 543, a much larger azimuthal field of view is obtained than the field of view 420 depicted in Figure 4A . Thus, a smaller polygon deflector can be used to achieve the same horizontal range in a given range. Using a smaller polygon is advantageous for scanning systems on vehicles that have space or weight constraints.

[0064] A disadvantage of the non-zero down tilt angle is that the vertical displacement increases more rapidly with distance to the target plane than the Figure 4A ​the increase is faster when the horizontal impact occurs. Figure 5B An arrangement is depicted using scanning spots of an impact beam that leaves a (horizontal) plane perpendicular to the axis of rotation. The target plane is at a distance R from the axis of rotation. The horizontal axis represents the distance in the horizontal plane in km (1 km = 10 3 m); while the vertical axis represents the distance in the vertical plane in km, both relative to the position 0,0 in the horizontal plane and the beam reflected normal to the current face of the polygonal deflector 544. The spots on different vertical lines are created by stepping the source / detector optics 510 in the vertical angle between D1 521 and D2 522. Note that, in contrast to the previous embodiment, the illumination spots are now symmetric about the reflection normal to the face of the deflector and are wider in azimuth; but, in the vertical direction, less symmetric. As mentioned above, for a ground vehicle, for example, the relatively useful rectangular region of interest lies at small down-tilt angles for distances of the order of 0 to -0.1 R. In contrast, for an airborne vehicle, the region of interest lies at large down-tilt angles for distances of the order of 0 to +0.1 R. Figure 4B Figure 5B The pattern of illumination spots in the previous embodiment far exceeds the useful area in azimuth on the left and right sides of the field of view. The useful near-horizontal spots at the outer edges of the field of view lose something gained in the range of azimuth. This relatively irregular array complicates detection or recognition of objects near the scanning system, especially on a ground vehicle.

[0065] 4. Polygonal grating

[0066] In various implementations, it is recognized that the advantages of near-horizontal tilt / down-tilt angles shown in the pattern of Figure 4B Figure 5B In some implementations, the horizontal or near-horizontal tilt / down-tilt angles can be within +10 degrees to -10 degrees of the facet normal direction. In some implementations, the horizontal or near-horizontal tilt / down-tilt angles can be within +5 degrees to -5 degrees of the facet normal direction.

[0067] Figure 6A is a block diagram showing a blazed grating serving as a face (or facet) of a polygonal deflector according to an implementation. Like every grating, the blazed grating has a constant line spacing d, which determines the magnitude of the wavelength demultiplexing caused by the grating. In a blazed grating, the grating lines, hereinafter called rulings, have a triangular, sawtooth cross section, forming a step structure. The steps are tilted with respect to the polygonal face, hereinafter called facet, by a so-called blaze angle θ B The angle between the facet normal and the ruling normal is therefore θ B ​​The blaze angle is optimized to maximize the efficiency of the wavelength of light used, and typically includes a reflective surface of the surface at the blaze angle. Descriptively, this means that θ B so that both the beam diffracted by the ruling and the beam reflected at the step are deflected in the same direction. At angles near the blaze angle, most of the incident energy is still deflected with high efficiency. In the Littrow configuration, the angle of incidence and the angle of deflection are equal. In the non-Littrow configuration of the blaze grating used in some implementations herein, the angle of incidence is not at the facet normal, while the deflected beam is at the facet normal, so the blaze angle is chosen to be half of the angle of incidence or near half of the angle of incidence, or half of some angle of incidence within a range of angles of incidence. This allows the source / detector optics at the angle of incidence to not be in the path of the deflected beam at all azimuthal angles, thus allowing a smaller polygonal deflector to be used to obtain a wider azimuthal field of view, while still having the deflected beam near horizontal to avoid large vertical deflection that is of little interest for many applications such as ground vehicles.

[0068] Figure 6B is a block diagram showing an example scanning system using a polygonal deflector with a facet of a blaze grating and an on-axis impinging beam in a plane containing the axis of rotation, according to an implementation. The beam from the source / detector optics 610 impinges on a facet (normal to the plane of the drawing) of a polygonal deflector 644 that rotates about the axis of rotation 643 in the plane shown. This rotation is imparted by the motor and suspension components 550 of the deflector assembly. In this configuration, no beam is deflected back to the source / detector optics 610 below the horizontal plane (the horizontal plane has a down angle E3 623 equal to zero). However, the source / detector optics 610 cause the beam to impinge on the facet at an angle that is twice or near twice the blaze angle below the horizontal, so all deflected beams are horizontal or near horizontal at angle E3 623. When the impinging beam is at α = 2θ B Upon incidence, the deflected beam E3 623 is horizontal, as shown by the dotted line arrow. The beam returning from the object follows the same angle in the opposite direction, as shown by the dashed line arrow. As the angle of incidence of the source / detector optics 510 varies from slightly less than twice the blaze angle to slightly more than twice the blaze angle, the deflected beam has a tilt / down angle that varies from slightly above horizontal E1 621 (positive tilt angle) to slightly below horizontal E2 622 (negative deflection angle or positive down angle). Thus, a near horizontal tilt / down field of view 620 is covered. As the polygon rotates, the azimuthal reflection angle varies in the field of view (not shown) between angle A when the beam first impinges on the facet to -A when the facet rotates away from the beam. This azimuthal field of view is symmetric about the azimuthal angle normal to the facet of the deflector.

[0069] Because the azimuth angle of the impinging beam is close to the angle toward the axis of rotation 643, a much larger azimuth field of view is obtained than Figure 4A the field of view 420 depicted. Thus, a smaller polygon deflector can be used to achieve the same horizontal range in a given range. Using a smaller polygon is advantageous for scanning systems on vehicles that have space or weight constraints. Because the deflection angle is close to horizontal, there is no distortion of the vertical range in the target plane, as Figure 5B depicted.

[0070] Figure 6C An arrangement of scanning spots using a blazed-grating polygon deflector and impinging beams at or near twice the blaze angle is depicted, according to an implementation. The target plane is at a distance R from the axis of rotation. The horizontal axis represents distance in the horizontal plane in km; while the vertical axis represents distance in the vertical plane containing the axis of rotation in km, both relative to the beam reflected at the current face of the polygon deflector 544 at position (0, 0) in the horizontal plane and normal to the face. The spots on different vertically separated rows are produced by stepping the source / detector optics 610 at a vertical angle close to twice the blaze angle. Note that in contrast to Figure 4B the illumination spots are now symmetric about reflection from the face of the deflector normal to the face and much wider in azimuth. Note that in contrast to Figure 6D the illumination spots in Figure 5B are repeated Figure 6D in contrast, the vertical distribution is much more vertically symmetric. As noted above, for a ground vehicle, for example, for a distance of about 0 to + / - 0.1 R, the relatively useful rectangular region of interest is at a small tilt angle and a downward deflection angle. In contrast, the pattern of illumination spots in

[0071] far exceeds the useful region in azimuth on the left and right sides of the field of view. The content of the nearly horizontal spots that are useful at the outer edges of the field of view has been recovered by using a polygon deflector with a face that contains a blazed grating. This less regular array simplifies detection or recognition of objects near the scanning system, especially on a ground vehicle.

[0072] The physical phenomenon of diffraction is described in equation 2

[0073] where d is the ruling spacing, a is the angle of incidence, β is the angle of deflection, both relative to the facet normal, λ is the optical wavelength, and m is the mode number, where most of the energy goes into mode m = 1. In various implementations, the deflected beam is designed to be normal to the facet and different from the incident beam, so β = 0; thus the angle of incidence a is given by equation 2b.

[0074] a = (arcsin(m λ / d)) (2b)

[0075] By choosing the line spacing d, the order m, and the incidence angle a for a given optical wavelength used in a coherent LIDAR, the exit beam can be normal to the polygon surface and behave like a horizontal planar polygon deflector.

[0076] To maximize the optical efficiency to the m=l order, an appropriate blazed grating can be used. The blaze wavelength is usually defined for a Littrow configuration (i.e., when the incidence angle and the deflection angle are equal). However, in this case, Figure 6A The grating configuration shown in FIG. 2 is not at the Littrow angle; therefore, the appropriate blaze wavelength is different from the standard Littrow blaze wavelength. In this case, Figure 6A In FIG. 2, the deflected beam is designed to be normal to the facet, β = 0, so the blaze angle is chosen to be half of the incidence angle to maximize the efficiency of the first order of deflection. Therefore, the blaze angle is given by equation 3.

[0077] θ B = (arcsin(mλ / d) / 2 (3)

[0078] Therefore, in some implementations, it is advantageous to jointly select and optimize the incidence angle a, the grating line spacing d, and the blaze angle θ B to obtain high diffraction efficiency, which affects the exit beam and the incident beam.

[0079] There are at least two practical choices for how to set the axes with a diffractive polygon. The first is to use galvanometers (e.g., a set of motor-driven mirrors that are used to steer the laser beam through a lens), where the vertical scan direction is stationary for a facet, then steps a small amount when the beam is “broken” by the transition between facets, and is stationary again on the next facet. The second option is to use a different line spacing, d, on the diffractive grating of each facet. This results in a different diffracted beam angle for each facet, effectively scanning horizontally for one facet, then another horizontal scan for the next facet, but at a different vertical angle. Therefore, a substantial amount of vertical scan range should be achievable for a diffractive polygon.

[0080] In some implementations, the impinging beam is composed of multiple beams separated by a small vertical angle, e.g., 4 beams with an angular separation of 0.57° or less. Therefore, if the polygon is a four-sided object with an angular spread of 2.28° for each set of beams (including extra space), then the blaze angle is different on each facet, a total vertical field of view of 10° or less can be achieved with a line spacing of 0.57° for each line. If the angle between beams is increased, or the number of facets is increased, then the vertical field of view will increase.

[0081] In an example implementation, the wavelength is about 1550 nanometers (nm, 1 nm = 10 -9lines per millimeter (mm, 1 mm = 10 micrometers, pm = 10"6meters). For a mode 1 diffraction and a grating with 600 lines per millimeter (1 / d) of 1.666 micrometers, 1 micrometer = 1 micrometer, pm = 10 -6 meters), an incident angle of about 68 degrees to avoid source / detector optics achieving a deflected beam normal to the facet. The blaze angle is half of about 34 degrees. In contrast, the Littrow configuration and the same pitch has a blaze wavelength of about 1874 nm.

[0082] Advantageously, the vast majority of the diffracted energy goes into the first mode, making the signal-to-noise ratio in the return beam as large as possible. For a properly tuned system, the optical energy that goes into the first mode can be as high as 90% efficiency for high precision gratings. Figure 7 is a plot of the efficiency of a blazed grating for multiple candidate wavelengths in the Littrow configuration versus wavelength. While not directly applicable, it demonstrates the suitability of a blazed grating to efficiently inject energy from a non-normal incident angle into a horizontally deflected beam, allowing avoidance of source / detector optics. The plot shows how much light is transmitted into the first diffraction order (m = 1) for various grating pitches (reciprocal of the ruling pitch d) optimized for light of different wavelengths from 1200 nm to 1850 nm in the Littrow configuration. At 1200 nm, a grating ruling of 300 lines per millimeter (mm, 1 mm = 10 -3 meters) provides about 74% efficiency in the Littrow configuration. At 1300 nm, a grating ruling of 400 lines per millimeter provides about 88% efficiency in the Littrow configuration. At 1700 nm, a grating ruling of 300 lines per millimeter provides about 82% efficiency in the Littrow configuration. At 1850 nm, a blazed grating ruling of 600 lines per millimeter provides about 76% efficiency in the Littrow configuration. Such performance is adequate for many example implementations.

[0083] Thus, in a first set of implementations, an optical scanning system includes a motor 357, a light source for a light beam (e.g., source / detector optics 610), and a polygon deflector 644 (also referred to herein as a "multi-faceted deflector"). Each facet in the multi-faceted deflector has a facet normal direction. The multi-faceted deflector is operatively coupled to the motor and is structured to rotate about an axis of rotation at an angular velocity to deflect the light beam from the source. The source is structured so that the light beam is incident on the multi-faceted deflector in a first plane containing the axis of rotation at an incident angle in the first plane that is spaced apart from the facet normal direction of each facet. At least one facet is covered by a grating having a facet ruling pitch selected to deflect the light beam at the first incident angle into a deflection angle that is within ten degrees of the facet normal direction.

[0084] In some implementations of the first set, the echelette is a reflective blazed echelette in which the facet ruling normal direction is equal to half of a first angle of incidence on each ruling on the facet. In some implementations of the first set, the beam is incident on the multi-faceted deflector in a first plane at a different second angle of incidence in the first plane that is within 40 degrees of the first angle of incidence. In some implementations of the first set, the first facet of the multi-faceted deflector has a different echelette pitch than a different second facet of the multi-faceted blazed echelette, whereby an incident beam at the first angle of incidence is deflected by the first facet by a first deflection angle and by the second facet by a different second deflection angle. In some implementations of the first set, the beam source is a source of multiple beams and the multiple beams approach the rotation axis at multiple different angles of incidence.

[0085] In a second set of implementations, a multi-faceted deflector for an optical scanning system includes a body having a plurality of outwardly facing facets relative to a central axis of the body. Each facet in the multi-faceted deflector has a facet normal direction and is covered with a reflective blazed echelette having a facet ruling pitch in the range of 0.8 microns to 10 microns. A high efficiency ruling pitch d is typically greater than 50% of the operating wavelength λ. However, to achieve sufficient diffraction angles, the pitch is advantageously less than 10x the operating wavelength. Thus, an echelette ruling pitch d in the range of 0.5λ to 10λ is advantageous, and even more advantageous is an echelette ruling pitch d in the range of 2λ to 5λ.

[0086] In some implementations, each facet also has a facet ruling normal direction at a blaze angle in the range of 10 degrees to 40 degrees from the facet normal direction of each ruling on the facet, such that the maximum angle of incidence allows the source / receiver to not be impinged upon or otherwise interfered with by the outgoing scanned deflected beam. A maximum diameter of a cross-section of the multi-faceted deflector in a plane perpendicular to the central axis is in the range of 0.5 centimeters to 10 centimeters. To take advantage of useful smaller polygons when using echelette facets, a diameter of close to 5 centimeters (2 inches) is used. Thus, in some implementations, the cross-section has a maximum diameter in the range of from 4 centimeters to 6 centimeters or 0.5 centimeters to 5 centimeters.

[0087] In various implementations, the one or more facets each have a normal direction that is perpendicular to the central axis; while in some implementations, the one or more facets each have a tilted face with a normal direction that is not perpendicular to the central axis. In various implementations, a cross-section of the multi-faceted deflector perpendicular to the central axis has a regular or irregular polygonal shape. In various implementations, two or more multi-faceted deflectors each having at least one grating facet that moves in unison or at different rates or even in opposite directions are combined in a deflector assembly as part of the LIDAR scanning optics 118.

[0088] 5. Variations, extensions, and modifications

[0089] In the foregoing specification, the disclosure has been described in connection with specific implementations thereof. It will be evident, however, that various modifications and changes can be made thereto without departing from the broader spirit and scope of the disclosure. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Throughout the specification and claims, the word "comprise" and variations thereof are not intended to imply that there is no further item, element, or step. Furthermore, the word "an" or "one" is intended to mean one or more than one, unless the context clearly indicates otherwise. Throughout the specification and claims, the expression "at least one of A and B" is intended to mean A or B or both A and B.

[0090] Notwithstanding that the numerical ranges and parameters setting forth the broadest scope of the numeric ranges and parameters are approximations, the numerical values set forth in the specific non-limiting examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, unless otherwise clearly indicated, the numerical values presented herein have one or more of their digits set forth with an "about" or "approximately” to indicate that an exact value is not to be understood as being strictly requisite. Also, the phrase "about" is used to indicate that a value is within a reasonable expected range of the stated value, and that slight variances are expected to be within the range of error inherent in the testing methodologies used. For example, "about 1.1" means from 1.05 to 1.15. The term "about" is used to indicate that a value is within a reasonable expected range of the stated value, and that slight variances are expected to be within the range of error inherent in the testing methodologies used. For example, "about 1.1" means from 1.0 to 1.2. If the minimum and maximum values are not clearly indicated, the term "about" means a range of values within twice the value of the least significant figure of the term. For example, "about 100" means a range of values from 50 to 200. Further, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a range of "less than 10" for a positive parameter can include any and all subranges between the minimum of zero (0) and the maximum of 10, that is, any and all subranges having a minimum of zero (0) or more and a maximum of 10 or less, for example 1 to 4.

[0091] Some implementations of the present disclosure are described below in the context of a single front-facing high-resolution Doppler lidar system on a personal automobile; however, implementations are not limited to this context. In other implementations, one or more systems of the same or other high-resolution LIDARs with or without Doppler components, with overlapping or non-overlapping fields of view, or one or more such systems mounted on smaller or larger manned or autonomous vehicles on land, sea, or air. In other implementations, a scanning high-resolution LIDAR is mounted at a temporary or permanent fixed location on land or sea.

Claims

1. A light detection and ranging (LIDAR) system, comprising: a light source configured to output a first light beam; a motor; and a deflector configured to rotate about an axis of rotation by the motor, the deflector comprising a plurality of facets, each facet of the plurality of facets comprising a plurality of gratings, a first facet of the plurality of facets defining a first direction, a first grating of the plurality of gratings of the first facet configured to receive the first light beam at an incident angle different from the first direction and output a second light beam at a deflection angle different from the incident angle, the plurality of gratings of the first facet having a first pitch, and the plurality of gratings of a second facet of the plurality of facets having a second pitch different from the first pitch, such that an incident light beam at a first incident angle is deflected by the first facet into a first deflection angle and by the second facet into a different second deflection angle.

2. The light detection and ranging (LIDAR) system of claim 1, wherein the light source is configured to output the first light beam toward the axis of rotation.

3. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein the first direction is orthogonal to at least one of the first facet or the axis of rotation.

4. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein the first light beam and the second light beam are in a first plane that includes the axis of rotation.

5. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein the motor is a first motor, the light detection and ranging (LIDAR) system further comprises a second motor configured to control the light source to adjust the incident angle of the first light beam, wherein adjusting the incident angle of the first light beam adjusts the deflection angle of the second light beam.

6. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein the deflection angle is within 10 degrees of the first direction.

7. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein each facet of the plurality of facets defines a respective first direction that is perpendicular to the axis of rotation.

8. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein the first grating is a blazed grating.

9. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein a cross-section of the plurality of gratings of the first facet has a triangular shape or a sawtooth shape.

10. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein the light source is configured to output a plurality of first light beams, the plurality of first light beams including the first light beam having an angular spread in a first plane that includes the axis of rotation.

11. The light detection and ranging (LIDAR) system of claim 1 or 2, further comprising: a galvanometer configured to control the incident angle of the first light beam.

12. The light detection and ranging (LIDAR) system of claim 1 or 2, wherein ​ The deflector is a polygonal deflector.

13. An autonomous vehicle control system comprising: a light detection and ranging (LIDAR) system according to claim 1 ; and one or more processors configured to: determine at least one of a distance to an object or a velocity of the object using a third light beam from the object in response to the second light beam; and control operation of an autonomous vehicle using at least one of the distance or the velocity.

14. An autonomous vehicle comprising: a light detection and ranging (LIDAR) system according to claim 1 ; at least one of a steering system or a braking system; and one or more processors configured to: determine at least one of a distance to an object or a velocity of the object using a third light beam from the object in response to the second light beam; and control operation of at least one of the steering system or the braking system using at least one of the distance or the velocity.

15. The autonomous vehicle of claim 14, further comprising: a motor configured to rotate the deflector to scan an azimuthal field of view of the autonomous vehicle using the second light beam.

16. A light detection and ranging (LIDAR) system comprising: a light source configured to output a non-horizontal light beam, the light source being switched between at least two different positions; a motor; and a deflector comprising a plurality of facets, wherein a first facet of the plurality of facets defines a facet normal direction normal to a face of the first facet; and a grating on the first facet, the grating being configured to receive the light beam at an angle of incidence different from the facet normal direction, a facet ruling pitch of the grating being formed so as to deflect the light beam at a deflection angle between 0 degrees and about 10 degrees of the facet normal direction.

17. The light detection and ranging (LIDAR) system of claim 16, wherein: the motor is configured to rotate the deflector about an axis of rotation, and the facet normal direction is perpendicular to the axis of rotation.

18. The light detection and ranging (LIDAR) system of claim 16 or 17, wherein: the grating defines a ruling normal normal to the grating and angled with respect to the facet normal direction.

19. The light detection and ranging (LIDAR) system of claim 16 or 17, wherein: a cross-section of the deflector perpendicular to an axis of rotation of the deflector has an irregular polygonal shape.

20. The light detection and ranging (LIDAR) system of claim 16 or 17, wherein: a diameter of the deflector is greater than or equal to about 0.5 centimeters and less than or equal to about 10 centimeters.

21. The light detection and ranging (LIDAR) system of claim 16 or 17, wherein: the grating is one of a plurality of gratings on the first facet.

22. The light detection and ranging (LIDAR) system of claim 21, wherein: The plurality of gratings forms a sawtooth structure.

23. The light detection and ranging (LIDAR) system of claim 16 or 17, wherein: the light source is configured to output a plurality of light beams including the light beam, the plurality of light beams having an angular spread.

24. The light detection and ranging (LIDAR) system of claim 16 or 17, wherein: the light source is configured to output the light beam toward an axis of rotation of the deflector.

25. An autonomous vehicle control system, the autonomous vehicle control system comprising: the light detection and ranging (LIDAR) system of claim 16; and one or more processors configured to: receive a signal from at least one of a reflection or a scattering of the light beam by an object; determine at least one of a distance to the object or a velocity of the object based on the signal; and control an operation of an autonomous vehicle based on at least one of the distance or the velocity.

26. An autonomous vehicle, the autonomous vehicle comprising: the light detection and ranging (LIDAR) system of claim 16; a steering system; a braking system; and one or more processors configured to: receive a signal from at least one of a reflection or a scattering of a light beam by an object; determine at least one of a distance to the object or a velocity of the object based on the signal; and control an operation of at least one of the steering system or the braking system based on at least one of the distance or the velocity.

27. The autonomous vehicle of claim 26, further comprising: a motor configured to rotate the deflector to scan an azimuthal field of view of the autonomous vehicle using the light beam.

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