Vertical beam regulation with MEMS phased arrays for lidar applications

Abstract

A light detection and ranging (LIDAR) system includes a scanning system with random access pointing. The scanning system includes: a light source that generates coherent light; a micro-electro-mechanical system (MEMS) phased array that steers the coherent light in a vertical direction; and a resonance scanner that scans the coherent light in a horizontal direction. Coherent light is projected onto a far-field scene. The MEMS phased array diverts the coherent light to direct the projected light onto selected spots on the far field scene in a random access manner.

Description

Cross - Reference to Related Applications

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 400,178, filed Aug. 23, 2022, which is hereby incorporated by reference in its entirety. Technical Field

[0002] The present disclosure generally relates to scanning systems, and more particularly to light detection and ranging (LIDAR) systems. Background Art

[0003] LIDAR systems are widely used for mapping, object detection and recognition, and navigation in a number of different applications including advanced driver - assistance systems (ADAS), autonomous vehicles, robots, etc. Generally, a LIDAR system works by illuminating a target in a far - field scene with coherent light from a light source (usually a laser) and detecting the returned light with a sensor. The LIDAR system analyzes the differences in the light return time and wavelength to measure the distance to the target and, in some applications, presents a digital 3 - D representation of the target in the form of a point cloud.

[0004] Traditional LIDAR systems employ mechanical scanners, such as rotating or moving mirrors, to scan the light beam onto the target. However, these mechanical scanners are quite bulky and relatively expensive, making them unsuitable for many applications.

[0005] More recent technology is solid - state LIDAR systems, where the scanner is replaced by a micro - electromechanical system (MEMS) phased array, which includes a MEMS - based spatial light modulator (SLM). U.S. Patent Publication No. US 2021 / 0072531A1, titled “MEMS PHASED - ARRAY FOR LIDAR APPLICATIONS,” filed Aug. 24, 2020, discloses an example use of a MEMS phased array in a LIDAR system.

[0006] An example MEMS - based SLM is a grating light valve device, which is commercially available from Silicon Light Machines, Inc. The device is a known strip-shaped SLM. Briefly, the strip-shaped SLM can be arranged as a one-dimensional (1-D) phased array, and the one-dimensional (1-D) phased array includes a plurality of strips serving as modulation elements. The strips include reflective surfaces that can be actuated to deflect vertically towards the substrate through a gap or cavity when a voltage is applied between the electrodes of the strip and a base electrode formed in or on the substrate. The strips can be individually addressed for actuation. Steering is achieved by actuating the strips to reflect or diffract light incident thereon.

[0007] Another example of a MEMS-based SLM is a spatial light modulator device, which is also a known device commercially available from Silicon Light Machines Corporation. The spatial light modulator device is a two-dimensional (2-D) equivalent of the 1-D device, and the spatial light modulator device includes a two-dimensional pixel array as a modulation element. The 2-D pixel arrangement enables a larger number of pixels for continuous throughput enhancement. SUMMARY OF THE INVENTION

[0008] In one embodiment, a LIDAR system includes a scanning system with random access pointing. The scanning system has: a light source that generates coherent light; a MEMS phased array that steers the coherent light in a vertical direction; and a resonant scanner that scans the coherent light at a resonant frequency in a horizontal direction. The coherent light is projected onto a far-field scene. The MEMS phased array steers the coherent light to direct the projected light in a random access manner to a selected spot on the far-field scene. Return light from the far-field scene can be received by one or more detectors in a monostatic or bistatic configuration.

[0009] After reading the present disclosure in its entirety, including the drawings and the claims, these and other features of the present disclosure will be apparent to those of ordinary skill in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more complete understanding of the subject matter can be obtained by reference to the detailed description and the claims when considered in conjunction with the following drawings, in which like reference numerals refer to like elements throughout the drawings. The drawings are not drawn to scale.

[0011] FIG. 1 is a schematic top view of a 1-D phased array that can be used as a MEMS phased array in an embodiment of the present invention.

[0012] FIG. 2 is a schematic cross-sectional view of a strip taken along section A-A of FIG. 1.

[0013] FIGS. 3 and 4 are schematic axonometric views that illustrate the general operation of a MEMS phased array including a strip-shaped SLM.

[0014] Figure 5 is a schematic diagram of a scanning system according to an embodiment of the present invention.

[0015] Figure 6A and Figure 6B illustrates an example application of random access pointing according to an embodiment of the present invention.

[0016] Figure 7A and Figure 7B illustrates another example application of random access pointing according to an embodiment of the present invention.

[0017] Figures 8A to 8D illustrates the steering and axial scanning of the lens effect of the MEMS phased array of a scanning system according to an embodiment of the present invention using Figure 5

[0018] Figure 9A and Figure 9B illustrates the difference between fixed vertical scan angle resolution and variable vertical scan angle resolution.

[0019] Figure 10A and Figure 10B illustrates beam separation according to an embodiment of the present invention.

[0020] Figure 11A is Figure 5 a schematic diagram of a scanning system of

[0021] Figure 11B is Figure 5 a schematic diagram of a scanning system of

[0022] Figure 11C illustrates the usage where a LIDAR system of a scanning system according to an embodiment of the present invention including Figure 5 can receive return light from a retroreflector on a road.

[0023] Figure 12A , Figure 12B , Figure 13A and Figure 13B illustrates a scanning system according to an embodiment of the present invention of Figure 5 configured to adjust the horizontal field of view for different driving conditions.

[0024] Figure 14A and Figure 14B is a schematic diagram of a scanning system of Figure 5 configured for a single - station configuration according to an embodiment of the present invention.

[0025] Figure 15A , Figure 15B and Figure 15C are schematic diagrams of a Figure 5 scanning system configured in a bistatic configuration according to an embodiment of the present invention.

[0026] Figure 16A and Figure 16B are schematic diagrams of a scanning system according to another embodiment of the present invention.

[0027] Figures 17 to 19 Schematically shows a receiver configuration that can be employed in a Figure 16A and Figure 16B scanning system according to an embodiment of the present invention.

[0028] Figure 20 is a flowchart of an operation method of a LIDAR system according to an embodiment of the present invention. Detailed Description

[0029] In the present disclosure, numerous specific details, such as examples of systems, materials, components, and methods, are provided to provide a thorough understanding of the embodiments of the present invention. However, those of ordinary skill in the art will recognize that the present invention can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the present invention.

[0030] For illustrative purposes, use cases of embodiments of the present invention are explained in the context of a car traveling along a road. However, it should be noted that the embodiments are equally applicable to other LIDAR use cases, including ADAS and other sensing systems on manned or autonomous aircraft, vessels, spacecraft, drones, and general transportation vehicles.

[0031] FIG. 1 is a schematic top view of a 1-D phased array 110 that can be used as a MEMS phased array in an embodiment of the present invention. In one embodiment, the phased array 110 is a grating light valve device commercially available from Silicon Light Machines Corporation. It can be understood that embodiments of the present invention are equally applicable to other types of MEMS-based SLMs. For example, embodiments of the present invention can be applicable to planar SLMs, such as planar light valve devices commercially available from Silicon Light Machines Corporation.

[0032] The phased array 110 includes a plurality of modulation elements, which are a plurality of addressable electrostatic actuation strips 112 in the example of FIG. 1. The phased array 110 can have thousands of strips 112, but only a few are shown and labeled for clarity. It should be noted that the strips 112 can be arranged and controlled in groups, and one or more strips 112 in a group can be in a fixed position (i.e., immovable) relative to the other strips 112 in the group. The actuation of the strips 112 is controlled by drive signals from a drive controller (not shown). The long axis of the strip view is as shown in the direction of arrow 113, and the phased array axis view is as shown in the direction of arrow 114.

[0033] FIG. 2 is a schematic cross-sectional view of the strip 112 taken along section A-A of FIG. 1. In the example of FIG. 2, the strip 112 includes a reflective layer 156 having a reflective surface 153. The elastic mechanical layer 154 supports the reflective layer 156 above the surface 151 of the substrate 157. The electrode 155 can be deflected towards the substrate 157 via an electrostatic force through a gap or cavity 158, which is generated when a voltage is applied between the electrode 155 and a base electrode 152 formed in or on the substrate 157.

[0034] The mechanical layer 154 can include a strained silicon nitride film (SiNx) and is flexibly supported above the surface 151 of the substrate 157 at both ends of the strip 112 by a plurality of posts or structures (also typically made of SiNx). The reflective layer 156 can include a suitable metal, dielectric, or semiconductor material compatible with standard MEMS manufacturing techniques and can be patterned using standard lithography techniques to form the reflective surface 153. The electrode 155 (which is a conductive layer) can be formed above the mechanical layer 154 and in direct physical contact with the mechanical layer 154 (as shown), or formed below the mechanical layer 154. The electrode 155 can be a conductive or semi-conductive material compatible with standard MEMS manufacturing techniques. For example, the electrode 155 can include a doped polysilicon layer or a metal layer. Alternatively, if the reflective layer 156 is metallic, the reflective layer 156 can also serve as the electrode 155.

[0035] FIGS. 3 and 4 are schematic phased array axis views, which illustrate the general operation of a MEMS phased array including a strip type SLM. Modulation elements (such as strips) can be operated in groups of two or more. For illustrative purposes, FIGS. 3 and 4 show strips operating in groups of four.

[0036] When all the strips are in a stationary state, the strip-type SEM operates as a reflector, and when the strips are at varying deflection levels, the strip-type SEM operates as a diffraction grating. That is, a group of strips can be operated in a reflector mode or a diffraction mode. When all the strips in the group are at the same distance relative to the surface of the substrate, such as when all the strips in the group are in a stationary state, the group of strips operates in the reflector mode. Figure 3 shows a group of strips in the reflector mode. In the reflector mode, the incident light (see Figure 3, 211) is reflected back to the light source (see Figure 3, 212).

[0037] When the strips in the group are at varying distances relative to the surface of the substrate, the group of strips operates in the diffraction mode. According to drive signals from a drive controller, one or more strips can be individually addressable to deflect a certain distance from the surface of the substrate to form a modulation pattern. Figure 4 shows a group of strips in the diffraction mode. In the diffraction mode, the incident light incident on the strips (see Figure 4, 213) is diffracted, thereby changing the angle of the outgoing light (see Figure 4, 214).

[0038] The strip-type SLM is capable of near-infrared scanning (NIR) up to a wavelength of 1550 nm and has a point-to-point refresh rate of over 100 kHz. As will be made more apparent below, embodiments of the present invention operate a MEMS-based phased array to direct the projected light to a far-field scene in a random access manner. Thus, embodiments of the present invention allow a LIDAR system to dynamically select a specific area to sense and dynamically adjust the amount of data points that can be sensed.

[0039] LIDAR systems in automotive and other vehicle applications benefit from non-linear vertical resolution. For example, for a car (e.g., a sedan or a truck) traveling along a flat road, the most important region of interest is the center, where many data points are collected to look for in-plane hazards. The next most important region is downward, to look for hazards along the ground. The least important region for flat-ground travel is upward, as hazards generally do not come from the sky during normal car use.

[0040] Mechanical mirror scanners or MEMS mirror scanners are either too slow or must move symmetrically around the resonance center. Typical LIDAR systems based on these mirror scanners must rely on a sparser point cloud or less significant oversampling regions within a typical vertical field of view (FOV) (40°, + / -20°). Mirror scanners in the linear region are slower and typically have a fixed resolution across the FOV. However, resonant mirror scanners can be fast and can have the ability to limit or expand the FOV by changing the drive amplitude. Still, mirror scanners have issues with pointing stability and will oversample the edges of the FOV in a Lissajous-type pattern. Even when these issues are overcome, the FOV of a resonant mirror scanner can only be expanded symmetrically around a fixed center with a symmetric resolution.

[0041] In one embodiment, a MEMS phased array, such as phased array 110 of FIG. 1, is controlled to modify the resolution and timing of the scan to create an arbitrary point cloud configuration to match road conditions. Generally, the basic steering of the incident light on the MEMS phased array is achieved by deflecting the strips into a linear phase pattern commonly referred to as a blazed grating or a phase ramp. The slope of the phase ramp is determined by the pixel pitch of the strips and the wavelength of the light source. The MEMS phased array can also be used as a full phase modulator, allowing for other effects in addition to random access pointing, such as 1-D lens effects, aberration correction, and amplitude control.

[0042] Figure 5 is a schematic diagram of a scanning system 250 according to an embodiment of the present invention. A LIDAR system can incorporate the scanning system 250 to scan a far-field scene 282.

[0043] In Figure 5 the example, a light source 271 (e.g., a laser source) generates coherent light. Illumination optics 272 are disposed along the optical path between the light source 271 and the MEMS phase array 273. The illumination optics 272 illuminate the MEMS phased array 273 with the light generated by the light source 271.

[0044] The MEMS phased array 273 functions as a vertical scanner of the scanning system 250. In one embodiment, the MEMS phased array 273 is a strip-type SLM, such as phased array 110 of FIG. 1. That is, in one embodiment, the MEMS phased array 273 has strips as modulation elements. The MEMS phased array 273 turns the light generated by the light source 271 in the vertical direction onto the far-field scene 282 by means of a resonant horizontal scanner 275 and projection optics 276.

[0045] The relay optical device 274 is disposed along the optical path between the MEMS phased array 273 and the resonant horizontal scanner 275. The relay optical device 274 guides the light deflected by the MEMS phased array 273 onto the resonant horizontal scanner 275.

[0046] For example, the resonant horizontal scanner 275 can be a resonant mechanical mirror or a resonant MEMS mirror. The resonant horizontal scanner 275 scans the light deflected by the MEMS phased array 273 in the horizontal direction at a resonant frequency onto the far-field scene 282 by means of the projection optical device 276.

[0047] The projection optical device 276 is disposed along the optical path between the resonant horizontal scanner 275 and the far-field scene 282. The projection optical device 276 projects the light scanned by the resonant horizontal scanner 275 onto the far-field scene 282.

[0048] The receiving optical device 280 guides the return light from the far-field scene 282 onto one or more detectors 279. The detectors 279 can include a 1-D array or a 2-D array of photodetectors, such as single-photon avalanche diode sensors (SPADs). Depending on the application, the scanning system 250 can have additional (e.g., filtering optical devices) or fewer optical devices.

[0049] The drive controller 278 includes circuitry configured to generate drive signals that deflect the strip elements of the MEMS phased array 273 into a desired modulation pattern, drive the resonant horizontal scanner 275 to scan in the horizontal direction at a resonant frequency, and coordinate the timing with the system controller 277, the light source 271, and the detector 279. The drive controller 278 can be implemented using discrete circuitry, an application-specific integrated circuit (ASIC), a system-on-chip (SOC), a microcontroller with associated software, etc.

[0050] As employed in a LIDAR system, the system controller 277 is configured to determine the desired modulation pattern of the strip elements of the MEMS phased array 273 based on the point cloud determined from the return light and other sensing data from other sensors 281 (e.g., cameras, radars). The system controller 277 can process the sensing data from the detector 279 and from other sensors 281 according to conventional LIDAR algorithms to sense the far-field scene 282 for navigation, object detection, ADAS, and / or other LIDAR applications. The system controller 277 can be implemented using a general-purpose computer with associated software.

[0051] In the absence of a drive signal to the MEMS phased array 273, the projected light will scan a single horizontal line on the far-field scene 282. The drive signal to the MEMS phased array 273 can be shaped to drive the strip elements of the MEMS phased array 273 into a modulation pattern that steers the projected light from a first spot directly to a second spot without having to point to another spot in between, thereby allowing random access pointing to the far-field scene 282. Random access pointing aids in intelligent point cloud collection because important regions of the far-field scene 282 can be sensed more relative to other regions.

[0052] Figure 6A and Figure 6B illustrates an example application of random access pointing according to an embodiment of the present invention. In Figure 6A and Figure 6B example, vehicle 251 is equipped with a LIDAR system 240 having a scanning system 250. In Figure 6A , the scanning system 250 scans (see line 252) the far-field scene in the direction of travel of the vehicle 251. In Figure 6B , the vertical FOV and vertical resolution of the scanning system 250 are adjusted (see line 253) to scan more intermediate regions relative to the upper region of the far-field scene. The vertical FOV and vertical resolution of the scanning system 250 can be adjusted by shaping the drive signal generated by the drive controller 278 to modulate the strip elements of the MEMS phased array 273 into a pattern that steers the projected light to scan more intermediate regions.

[0053] Figure 7A and Figure 7B illustrates another example application of random access pointing according to an embodiment of the present invention. In Figure 7A and Figure 7B example, vehicle 251 is equipped with a LIDAR system 240 having a scanning system 250. When traveling along a flat road, the region of interest is mainly along the horizontal plane in the direction of travel, and secondly towards the ground plane. That is, when driving along a flat section of a highway, there is little need to scan upwards. Additionally, the horizontal plane can have objects at close or far distances (e.g., the next car in front of vehicle 251 may be several vehicle lengths away or two hundred meters ahead), and scanning downwards will reflect the projected light off the road at a generally predictable distance based on the height of the sensors of the scanning system 250.

[0054] Random access pointing allows for more frequent sampling of the horizontal plane when traveling along flat sections of the highway because there is a higher likelihood that important objects are on the same plane as vehicle 251, the unpredictability of the positions of these objects increases, and the fact that more distant objects that are more likely to be found on the travel plane of vehicle 251 will benefit from more interrogations due to reduced returned light compared to closer objects, as Figure 7A shown. Other sensors 281 of the scanning system 250, such as cameras and radars, can also provide additional information such that the projected light is biased to sample more of the ground or sky based on sensor fusion information. As an example, when vehicle 251 approaches a hillside, the camera, radar, and / or other sensors 281 of the scanning system 250 will detect the road slope and, in response, cause the drive controller 278 to drive the MEMS phased array 273 to effectively move the center of the system vertical FOV upward to continue scanning for obstacles further along the road, as Figure 7B shown.

[0055] As described by J.R. Landry et al. in IEEE Photonics Technology Letters, Vol. 32, No. 14, pp. 859 - 862, July 15, 2020, "Random Access Cylindrical Lensing and Beam Steering Using a High-Speed Linear Phased Array", adding cylindrical and linear phase profiles produces a lensing effect that allows for both steering and axial scanning. The lensing effect allows the MEMS phased array to change the vertical far-field diffraction angle of the projected beam.

[0056] Figures 8A to 8D Illustrated is the steering and axial scanning by the lensing effect of the MEMS phased array 273 of the scanning system 250 according to an embodiment of the present invention. In Figures 8A to 8D , the Fourier lens 301 is disposed along the optical path between the MEMS phased array 273 and the far-field scene. The drive controller 278 is depicted as having a waveform of the drive signal to the MEMS phased array 273. The x-axis of the waveform indicates "pixels" (i.e., modulation elements), and the y-axis of the waveform indicates the corresponding voltage of the drive signal.

[0057] In Figure 8A , the drive controller 278 does not generate a drive signal to the MEMS phased array 273. This causes the beam from the MEMS phased array 273 to be focused on the center of the nominal reference plane 302. Figures 8B to 8Dshows a drive controller 278 that generates a drive signal that applies a combination of a ramp and a cylindrical phase to scan a light beam from the MEMS phased array 273 upward on a reference plane 302 ( Figure 8B ), at the center but beyond the reference plane 302 ( Figure 8C ), and below the center but in front of the reference plane 302.

[0058] The optical system of the scanning system 250 can be designed such that the default diffraction angle is minimized in the highest range case. For example, an autonomous vehicle traveling at highway speeds would like the light beam from the light source 271 to be collimated to optimize the spot power at 200 - 300 m ahead. Applying positive focusing to the light beam can achieve a tighter diffraction angle, but the minimum angle will generally be determined by the system aperture and cannot be improved much. However, positive focusing can correct alignment errors and thus improve the far - field power. That is, the lens effect can fix the alignment error to obtain better collimation, thereby increasing the far - field power and thus the range. On the other hand, negative cylindrical focusing will cause the light beam to diverge, resulting in the beam spot diverging faster. In cases where high resolution is not as important as high speed, especially when the expected reflector is closer to the vehicle, this enlarged beam spot may be useful. As an example, a 0.1° spot will cover 35 cm at 200 m, but only 3.5 mm at 20 m. This precision is likely unnecessary at the traveling speed, and a 1° spot will have a similar resolution at 20 m as a 0.1° spot at 200 m.

[0059] Figure 9A and Figure 9B illustrates the difference between a fixed vertical scan angle resolution ( Figure 9A ) and a variable vertical scan angle resolution ( Figure 9B ). In Figure 9A , the vehicle 351 is equipped with a LIDAR system that includes a conventional mirror scanner in both the vertical and horizontal directions. The mechanical steering of the light beam (see 352) results in a fixed angular resolution. In Figure 9B , the vehicle 251 is equipped with a LIDAR system 240 that includes a scanning system 250. The MEMS phased array 273 of the scanning system 250 allows adjustment of the vertical diffraction angle through the lens effect (see 353) to dynamically match the road conditions.

[0060] Wide-angle far-field projection requires a wide-angle lens, which typically causes large aberrations. A common aberration is field distortion, which can cause the spot to deviate significantly from its desired position. For barrel distortion, the spots are shifted significantly towards the center, and their diffraction angles will change slightly. This distortion can be measured as part of calibration and actively corrected using a MEMS phased array. For a point that is horizontally centered but vertically skewed, the MEMS phased array can simply readjust the spot position by a predetermined angle. For pure horizontal skew with a spot scanning system, a high MEMS phased array refresh rate enables fast switching that allows variable pulse delays. The desired delay is determined by the amount of skew and the sub-axis scanning pattern. For spots that are off the central axis, a combination of vertical angle and timing delay can be used.

[0061] The fully arbitrary phase control of the MEMS phased array enables additional features beyond random access pointing. For example, instead of scanning a single beam, the MEMS phased array can preferentially split the beam across multiple spots by introducing a high-period grating stage or through holographic optimization. Figure 10A and Figure 10B Illustrates beam splitting according to an embodiment of the present invention. Generally, the MEMS phased array can create multiple vertical spots for a LIDAR system with a 1-D detector array. In Figure 10A a simple grating pattern of the strip elements of the MEMS phased array 273 creates spots at fixed positions. In Figure 10B a holographic global optimization of the strip elements of the MEMS phased array 273 creates arbitrarily placed spots.

[0062] Splitting the beam can be useful when less power is required and there is a detector array for differentiating returns. Similarly, especially for a single detector system, the MEMS phased array can transfer additional light outside its FOV, thereby dimming the projected beam. For example, this technique can be used to increase eye safety when scanning nearby objects identified as human, or to suppress the return light from retroreflective surfaces, which can be several orders of magnitude stronger than diffuse objects. Additionally, by comparing the return light from a turbulent medium with the predicted deviation in a non-turbulent medium caused by the shift of the phase wavefront, using one-dimensional ghost imaging, the shift but known phase wavefront can be used to mitigate scattering, such as scattering from fog or rain.

[0063] Figure 11A is a schematic diagram of a scanning system 250, where the strip elements of the MEMS phased array 273 are modulated into a standard blazed steering pattern. The beam from the MEMS phased array 273 (see 371) passes through a 4f system 373. The 4f system 373 magnifies the steering angle and filters out first-order and higher-order light.

[0064] Figure 11BIt is a schematic diagram of a scanning system 250, where the strip elements of the MEMS phased array 273 are modulated to have a blazed steering pattern with a binary phase grating pattern. As Figure 11A shown, Figure 11B the 4f system 373 in Figure 11B amplifies the steering angle and filters out the first-order and higher-order light. Adding the binary phase grating pattern to the amplitude control of the strip elements of the MEMS phased array 273 allows the 4f system 373 to also block the side lobes (see Figure 11C for 381 and 382), to prevent the return light from the retroreflector from overwhelming the sensors of the LIDAR system.

[0065] Figure 12A and Figure 12B and Figure 13A and Figure 13B illustrate a scanning system 250 configured to adjust the horizontal FOV for different driving conditions according to an embodiment of the present invention. In Figure 12A and Figure 13A , the MEMS phased array 273 of the scanning system 250 is set in the plane of the figure page. The light source 271 generates coherent light, which is steered by the MEMS phased array 273 in the vertical plane and scanned by the resonant horizontal scanner 275 in the horizontal plane. The return light from the far-field scene is captured by the detector 279 (see Figure 5 ; Figure 12A and Figure 12B and Figure 13A and Figure 13B not shown in), and the detector can be a 1D detector array or a 2D detector array. The resolution of the scanning system 250 is determined by the resolution of the MEMS phased array 273 and the system numerical aperture.

[0066] Figure 12A depicts the resonant horizontal scanner 275, whose FOV amplitude is symmetrically adjusted to be narrow for high-speed driving, such as on a highway. Figure 12B shows a high-resolution point cloud (depicted as dots), which is due to the narrower horizontal FOV. Figure 13A depicts the resonant horizontal scanner 275, whose FOV amplitude is symmetrically adjusted to be wider for urban driving or situations with many obstacles. Figure 13B shows a lower-resolution point cloud due to the wider horizontal FOV. It should be noted that resonant scanners are generally affected by inertia and thus usually decelerate when rotating.

[0067] The scanning system 250 can be configured for single-station, dual-station, or other detector configurations. Figure 14A and Figure 14BSchematic diagram of a scanning system 250 configured for single - station configuration according to an embodiment of the present invention. In Figure 14A and Figure 14B a light source 271 and a detector 279, both commonly labeled "400", are disposed at the same general location. Thus, the projected light and the returned light share the same optical components. The illumination optical component 272 includes a collimating lens. The magnification and filtering optical component 403 (e.g., a 4f system) serves as a relay and filtering optical component.

[0068] In Figure 14A the drive controller 278 drives the resonant - level scanner 275 with a sinusoidal drive signal and drives the MEMS phased array 273 to perform random - access pointing of the projected light as described above. Figure 14A The nominal (depicted as a solid line) and scanned (depicted as a dashed line) projected light are shown.

[0069] Figure 14B The returned light (depicted as a dashed line) and the projected light (depicted as a solid line) sharing the same optical components in a single - station configuration are shown. The drive controller 278 drives the MEMS phased array 273 to steer the returned light towards the detector 279 and reject out - of - plane light. The MEMS phased array 273 is configured to have an appropriately large aperture to ensure that the returned light is collected by one or more detectors 279 disposed directly adjacent to the light source 271.

[0070] Since both the returned light and the projected light pass through the magnification and filtering optical component 403, any magnification of the FOV angle will come at the cost of a smaller system aperture, and similarly match the FOV of the MEMS phased array 273 to the system FOV. The dual - station configuration overcomes this limitation of the single - station configuration. In the dual - station configuration, the light source and the detector are not adjacent to each other, and the returned light needs to be guided towards the detector.

[0071] Figure 15A 、 Figure 15B and Figure 15C Schematic diagram of a scanning system 250 configured for dual - station configuration according to an embodiment of the present invention. In Figure 15A 、 Figure 15B and Figure 15C the illumination optical component 272 includes a collimating lens. Compared with the single - station configuration, the path of the returned light does not require magnification and is separated from the path of the projected light. This allows the MEMS phased array 273 to have a larger aperture.

[0072] In Figure 15A the drive controller 278 drives the resonant - level scanner 275 with a sinusoidal drive signal and drives the MEMS phased array 273 to perform random - access pointing of the projected light as described above. Figure 15AShows the nominal (depicted as a solid line) and scanned (depicted as a dashed line) projected light according to the scan of the resonance level scanner 275. Figure 15B Shows the nominal (depicted as a solid line) and steered (depicted as a dashed line) projected light according to the steering of the MEMS phased array 273.

[0073] Figure 15C Shows the detector 279 in a bistatic configuration, which receives the nominal (shown as a solid line) and steered (shown as a dashed line) return light according to the return steering of the MEMS phased array 273. The collection lens 451 is located near the projection system but not coaxial with the projection system. The collection lens 451 collects the entire far-field scene onto a single detector or images it onto a detector array.

[0074] It can be understood that the monostatic and bistatic transmit and receive configurations described herein can also be used in the orthogonal direction, such that the MEMS phased array 273 steers in the horizontal dimension.

[0075] In one embodiment, the LIDAR system does not include a separate resonance level scanner. In the embodiment, the MEMS phased array performs both vertical and horizontal scanning. The embodiment provides a higher frame rate at the cost of a larger beam divergence and requires imaging the far field onto a 2D detector array or imaging the far field horizontally and compressing the vertical component onto a 1-D detector. In the latter case, the horizontal resolution is determined by the number of horizontal pixels in the 1-D detector, and the vertical resolution is determined by the resolution of the MEMS phased array. The detector in the embodiment can be arranged in a monostatic or bistatic configuration.

[0076] Figure 16A Is a schematic diagram of a scanning system 500 according to an embodiment of the present invention. In Figure 16A , the coherent light from the light source 501 is collimated by a lens 503 (e.g., a spherical lens), and then focused by a cylindrical lens 504 onto the MEMS phased array 502 (e.g., the 1-D phased array 110 of FIG. 1) to produce a line beam that will illuminate the entire horizontal FOV. There is no separate horizontal scanner in the scanning system 500.

[0077] Figure 16BThe vertical axis of the scanning system 500 is shown. Coherent light from the light source 501 is collimated by the lens 503 to fill the MEMS phased array 502, while being unaffected by the cylindrical lens 504 on this axis, so that the light beam remains collimated in the far field. The MEMS phased array 502 is driven by the drive controller 551 to direct the light beam along the desired vertical angle, thereby creating vertical discrimination for the LIDAR method. However, the line beam does not allow horizontal discrimination like the collimated spot resonance scanning method, so the bistatic receiver must provide horizontal discrimination, such as the flash LIDAR or Time of Flight Camera method.

[0078] Figures 17 to 19 Schematically shows a receiver configuration according to an embodiment of the present invention that can be employed in the scanning system 500.

[0079] In Figure 17 the dash-dotted line (see Figure 17 , 601) represents the first scanning pattern projected onto the far-field scene, and the dashed line (see Figure 17 , 602) represents the second scanning pattern projected onto the far-field scene. The receiving optics 603 includes a spherical imaging lens that images the corresponding return light of the scanning pattern onto the 2-D detector array 604. The return light is imaged onto the 2D detector array 204 as in conventional camera imaging.

[0080] In Figure 18 the dash-dotted line (see Figure 18 , 701) represents the first scanning pattern projected onto the far-field scene, and the dashed line (see Figure 18 , 702) represents the second scanning pattern projected onto the far-field scene. The corresponding return light of the first scanning pattern and the second scanning pattern passes through the deformable optical device 705. The deformable optical device 705 images the horizontal information of the return light as the normal onto the 1-D detector array 704, while compressing the vertical information of the return light onto the 1-D detector array 704. Vertical information discrimination is achieved through the pointing information from the MEMS phased array. That is, the vertical information of the return light can be determined based on the timing and pointing of the projected light steered by the MEMS phased array according to the drive signal from the drive controller.

[0081] In Figure 19 the dash-dotted line (see Figure 19 , 751) represents the first scanning pattern projected onto the far-field scene, and the dashed line (see Figure 19, 752) represents a second scan pattern projected onto the far-field scene. The MEMS phased array 753 (e.g., the 1-D phased array 110 of FIG. 1) (which is also used for both horizontal and vertical scanning of light) turns the corresponding returned light onto the sparse detector 755 by means of receiving optics including a spherical lens 754. The spherical lens 754 is used in a simple Fourier imaging configuration; the spherical lens 754 is placed at a focal length behind the MEMS phased array 753, and the sparse detector 755 is placed at a focal length behind the spherical lens 754. The sparse detector 755 includes a sparsely arranged 1-D detector array, i.e., the detector 755 does not have as many pixel sensors as a normal 2-D detector array. For example, there may be at least one pixel width separating adjacent 1-D detector arrays, and in most embodiments, the number of detector rows will be less than 10, as opposed to the hundreds required for a 2-D detector array. Since the MEMS phased array 753 can be driven to turn the returned light onto a specific detector in the sparse detector 755, the gaps between the 1-D detector arrays in the sparse detector 755 are not a major limitation.

[0082] Figure 20 is a flowchart of an operating method 800 of a LIDAR system according to an embodiment of the present invention.

[0083] In step 801, coherent light (e.g., laser) is generated by a light source.

[0084] In step 802, the coherent light from the light source is turned in the vertical direction onto the far-field scene using a MEMS phased array. The MEMS phased array may include a strip-type SLM having electrostatically actuated strips.

[0085] In step 803, the coherent light from the light source is scanned in the horizontal direction onto the far-field scene at a resonant frequency using a resonant scanner. The resonant scanner may be a resonant mirror scanner.

[0086] In step 804, the coherent light turned in the vertical direction by the MEMS phased array and scanned in the horizontal direction by the resonant scanner is projected onto the far-field scene.

[0087] In step 805, the returned light is received from the far-field scene. The returned light may be received by one or more photodetectors in a monostatic configuration or a bistatic configuration. In the monostatic configuration, the light source and the photodetector are adjacent. In the bistatic configuration, the light source and the photodetector are not adjacent. In the bistatic configuration, the MEMS phased array turns the returned light onto the photodetector.

[0088] In step 806, the MEMS phased array steers the coherent light from the light source and directs the projected light to the far-field scene in a random access manner. That is, the MEMS phased array steers the coherent light such that the projected light directly points from the first light spot to the second light spot without having to point to one or more intermediate light spots on the far-field scene between the first light spot and the second light spot.

[0089] In step 807, the field of view of the MEMS phased array is adjusted in response to a detected change in the far-field scene. For example, the field of view of the MEMS phased array can be adjusted upward in response to detecting an approaching hillside.

[0090] Although specific embodiments of the present invention have been provided, it should be understood that these embodiments are for illustrative purposes and not restrictive. Many additional embodiments will be apparent to those of ordinary skill in the art who read this disclosure.

Claims

1. A light detection and ranging (LIDAR) system, comprising: a light source configured to generate a light beam; a microelectromechanical system (MEMS) phased array configured to steer the light beam in a vertical direction onto a far-field scene; a resonant scanner configured to scan the light beam in a horizontal direction onto the far-field scene at a resonant frequency; and a detector configured to receive return light from the far-field scene.

2. The LIDAR system according to claim 1, wherein the detector comprises a two-dimensional (2-D) array of photodetectors.

3. The LIDAR system according to claim 2, wherein the MEMS phased array comprises a strip-type spatial light modulator (SLM), and the strip-type SLM comprises a plurality of electrostatically actuated strips as modulation elements.

4. The LIDAR system according to claim 1, 2, or 3, wherein the resonant scanner comprises a resonant mirror scanner.

5. The LIDAR system according to claim 1, 2, or 3, wherein in a monostatic configuration, the detector is disposed adjacent to the light source.

6. The LIDAR system according to claim 1, 2, or 3, wherein in a bistatic configuration, the detector is not disposed adjacent to the light source.

7. The LIDAR system according to claim 1, 2, or 3, further comprising a 4f system disposed in an optical path between the MEMS phased array and the resonant scanner.

8. The LIDAR system according to claim 1, 2, 3, or 6, wherein the MEMS phased array is configured to steer the return light onto the detector.

9. The LIDAR system according to claim 1, 2, 3, 4, 5, or 6, wherein the LIDAR system is located in a vehicle.

10. The LIDAR system according to claim 1, 2, 3, 4, 5, or 6, wherein the LIDAR system is located in an aircraft.

11. A method of operating a light detection and ranging (LIDAR) system, the method comprising: generating coherent light from a light source; steering the coherent light in a vertical direction onto a far-field scene by a microelectromechanical system (MEMS) phased array; scanning the coherent light in a horizontal direction onto the far-field scene at a resonant frequency by a resonant scanner; and receiving return light from the far-field scene.

12. The method according to claim 11, further comprising: adjusting a field of view (FOV) of the MEMS phased array.

13. The method according to claim 12, wherein the FOV of the MEMS phased array is adjusted in response to detecting a change in the far-field scene.

14. The method according to claim 13, wherein the FOV of the MEMS phased array is adjusted upward in response to detecting that a vehicle comprising the LIDAR system is approaching a hillside.

15. The method according to claim 11, 12, or 13, wherein steering the coherent light in a vertical direction onto the far-field scene by the MEMS phased array comprises: projecting the coherent light as a projection light onto the far-field scene; and Steer the coherent light in the vertical direction to directly point the projected light from a first spot on the far-field scene to a second spot on the far-field scene without pointing the projected light to one or more intermediate spots on the far-field scene between the first spot and the second spot.

Images