MEMS phased arrays for light detection and ranging applications

Abstract

An optical scanner is described that includes a microelectromechanical system phased array suitable for use in a light detection and ranging system. Generally speaking, the scanner includes an optical transmitter having a first phased array for receiving light from a light source, forming an illumination stripe in a far-field scene, and modulating the phase of the light to sweep or steer the stripe across the scene in two dimensions. An optical receiver in the scanner includes a second phased array for receiving light from the far-field scene and directing at least some of the light onto a detector. The second phased array is configured to descan the received light by directing light reflected from the far-field scene onto the detector while rejecting background light. In one embodiment, the second phased array directs light from a slice of the far-field scene onto a 1D detector array.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is an international application of U.S. non-provisional application No. 17 / 001,477, filed on August 24, 2020, and claims the benefit of priority under 35 U.S.C. 119(e) to U.S. provisional patent application serial number 62 / 947,514, filed on December 12, 2019, and U.S. provisional patent application serial number 62 / 891,977, filed on August 27, 2019, both of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates generally to light detection and ranging (LIDAR) systems, and more particularly to LIDAR systems including phased arrays based on microelectromechanical systems devices (MEMS) and methods of operating the same. Background Art

[0004] Light detection and ranging, or LIDAR, systems are widely used in a variety of applications, including automotive, robotics, and unmanned or autonomous vehicles, for mapping, object detection and identification, and navigation. Generally speaking, LIDAR systems work by illuminating a target in a far-field scene with a beam from a coherent light source (usually a laser) and detecting the reflected light with a sensor. The differences in the return time and wavelength of the light are analyzed in the LiDAR system to measure the distance to the target and, in some applications, render a digital 3D representation of the target.

[0005] Conventional LiDAR systems use mechanical scanners, such as spinning or moving mirrors, to steer a light beam across a target. However, these mechanical LiDAR systems are rather bulky and relatively expensive devices, making them unsuitable for many applications.

[0006] A more recent technology is solid-state LiDAR systems, in which the scanner is replaced with a MEMS-based spatial light modulator (SLM) to form a MEMS phased array built entirely on a single substrate or chip. Solid-state LiDAR systems have the potential to provide cheaper, more compact systems with higher resolution than traditional LiDAR systems. While, at least in theory, they can provide much faster beam steering than traditional mechanical LiDAR systems, the large scan angles required to achieve a large field of view (FOV) and resolution require small sizes for the MEMS mirrors and components, approaching the wavelength of light typically used in LiDAR systems. This, in turn, increases the cost and complexity of MEMS phased arrays, making it difficult to maintain the speed advantage of DMD-based MEMS phased arrays over the mechanical scanners of traditional LiDAR systems.

[0007] Therefore, there is a need to provide a MEMS phased array and a method of operating the same for fast beam steering and large scanning angles used in LiDAR applications. Summary of the Invention

[0008] An optical scanner including a microelectromechanical system (MEMS)-based spatial light module to form a MEMS phased array (hereinafter referred to as a MEMS phased array) suitable for use in a LiDAR system and methods of manufacturing and operating the same are provided.

[0009] In one embodiment, the optical scanner includes: an optical transmitter including a plurality of first MEMS phased arrays configured to receive light from a coherent light source and modulate the phase of at least some of the received light to scan a far-field scene in two dimensions (2D); and an optical receiver including a plurality of second MEMS phased arrays configured to receive light from the far-field scene and direct at least some of the received light onto a detector. Generally, the second MEMS phased array is configured to de-scan the received light by directing light from the coherent light source reflected from the far-field scene onto the detector while rejecting background light.

[0010] In an alternative embodiment, the optical scanner can be implemented using a single shared MEMS phased array, wherein the MEMS phased array is configured to: modulate the phase of light from a coherent light source at a first time to scan a far-field scene at the first time; and descan the received light at a second time by directing light from the coherent light source reflected from the far-field scene onto a detector and rejecting background light.

[0011] In another aspect, a method for operating an optical scanner comprising a plurality of MEMS phased arrays is provided. Generally, the method begins by illuminating a first microelectromechanical system (MEMS) MEMS phased array with light from a coherent light source. Next, the first MEMS phased array is controlled to modulate the phase of the light from the coherent light source, and the modulated light is projected from the first MEMS phased array to a far-field scene to scan the far-field scene in two dimensions (2D). Finally, light from the far-field scene is received on a second MEMS phased array, and the received light is descanned by controlling the second MEMS phased array to direct light reflected from the far-field scene originating from the coherent light source onto a detector while rejecting background light. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the present invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings and appended claims, in which:

[0013] Figure 1is a block diagram illustrating an embodiment of a light detection and ranging (LiDAR) system including a solid-state optical scanner;

[0014] Figures 2A to 2C is a schematic diagram illustrating a method by which a microelectromechanical system device (MEMS) phased array may be operated to steer a light beam or light scanning strip;

[0015] Figure 3 is a schematic diagram of a LiDAR system including an optical scanner with a MEMS phased array, illustrating an embodiment of a method by which a MEMS can be used to scan a far-field scene;

[0016] Figure 4 is a graph showing the change in frequency of outgoing pulses of a LiDAR system using frequency modulated continuous wave (FMCW) technology over time;

[0017] Figure 5A is a block diagram illustrating an embodiment of a solid-state optical scanner including a MEMS phased array in an optical transmitter of the scanner;

[0018] Figure 5B It shows Figure 5A A block diagram of another embodiment of a solid-state optical scanner comprising a first MEMS phased array in an optical transmitter of the scanner and a second MEMS phased array in an optical receiver of the scanner;

[0019] Figure 5C It shows Figure 5A A block diagram of yet another embodiment of a solid-state optical scanner including a shared MEMS phased array in both the transmit and receive optical paths;

[0020] Figure 6 is a block diagram illustrating an embodiment of an optical scanner including a MEMS phased array in an optical receiver of the scanner;

[0021] Figure 7A and Figure 7B is a diagram illustrating an embodiment of a MEMS-based ribbon-type spatial light modulator (SLM) for forming a MEMS phased array suitable for use in an optical scanner;

[0022] Figure 8 yes Figure 7A and Figure 7B Schematic representation of the spacing and amplitude of multiple individual ribbons of a beam-steering SLM;

[0023] Figure 9 Arranged in a shimmering pattern Figure 7A and Figure 7B Schematic representation of the spacing and amplitude of a portion of a linear array of SLM modulators;

[0024] Figure 10 Is for Figure 9 A plot of intensity versus steering angle for the array shown in shows the suitability of MEMS phased arrays for applications requiring fast beam steering and large scan angles;

[0025] Figure 11 It will Figure 7A and Figure 7B Schematic diagram of the ribbon-type SLM modeled as a capacitor-on-a-spring;

[0026] Figure 12 Including damping structure Figure 7A and Figure 7B A cross-sectional side view of a portion of the SLM;

[0027] Figure 13 is a diagram illustrating a top view of an embodiment of a MEMS phased array including a plurality of strip-type SLMs having one-dimensional (1D) arrays that are stacked to increase the axial dimension parallel to the long axis of the MEMS phased array across which modulated light can be scanned;

[0028] Figure 14 is a diagram illustrating a top view of an embodiment of a MEMS phased array including a plurality of strip-type SLMs having a one-dimensional (1D) array arranged in parallel;

[0029] Figures 15A to 15C is a diagram illustrating another embodiment of a MEMS phased array comprising a single strip-type SLM, wherein each of the strips of the SLM is divided along its length by pillars to form a plurality of parallel 1D arrays;

[0030] Figure 16A shows a cross section of an elongated element or ribbon of a ribbon-type SLM having a blazed profile according to another embodiment;

[0031] Figure 16B and Figure 16C shows cross-sectional views of an embodiment of a ribbon-type SLM including blazing ribbons in an inactive state and a fully activated state, respectively;

[0032] Figure 17 is an optics diagram showing illumination and projection optics of an optical scanner that includes a MEMS phased array to steer light across a far-field scene;

[0033] Figure 18A is an optics diagram illustrating the illumination and projection light paths for a single pixel along the horizontal or longitudinal axis of an optical scanner including a MEMS phased array to steer light across a far-field scene;

[0034] Figure 18B It shows Figure 18A 0th order beam and diffracted + / -1st order beams on the Fourier aperture of the projection optics shown in FIG;

[0035] Figure 19 is a schematic block diagram of a compact optical scanner including a compact MEMS phased array and showing folded optical paths for illumination, projection, and reception optics;

[0036] Figure 20A is a schematic block diagram showing a top view of a lens array;

[0037] Figure 20B yes Figure 20A A cross-sectional view of a lens array;

[0038] Figure 20C Is shown by Figure 20A Optical device diagram of 0th order illumination of a single modulator in a strip MEMS phased array of a single element of a lens array; and

[0039] Figure 21 is a flow chart of a method for operating an optical scanner including a MEMS phased array for use in a light detection and ranging (LiDAR) system. DETAILED DESCRIPTION

[0040] An optical scanner and its manufacture and operation method are provided, which includes a microelectromechanical system (MEMS) MEMS phased array suitable for use in a light detection and ranging (LiDAR) system. In the following description, many specific details, such as specific materials, dimensions and processing parameters, are set forth to provide a thorough understanding of the present invention. However, specific embodiments may be practiced without one or more of these specific details or in combination with other known methods, materials and equipment. In other cases, well-known semiconductor design and manufacturing techniques are not described in particular detail to avoid unnecessarily confusing the present invention. References throughout this specification to "embodiments" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrase "in an embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment of the present invention. In addition, specific features, structures, materials or characteristics may be combined in any suitable manner in one or more embodiments.

[0041] Figure 1 is a block diagram illustrating an embodiment of a LiDAR system 100 including a solid-state optical scanning system or optical scanner 102 according to the present disclosure. Figure 1, the LiDAR system 100 typically includes a microcontroller or controller 104 to control the operation of other components of the LiDAR system (including the optical scanner 102) and to interface with a host system (not shown). The controller 104 includes a processor and data processing circuitry to analyze signals from the optical scanner 102 to detect and measure the position of objects in the far-field scene 106, estimate the time of flight (TOF) of the distance between the object and the LiDAR system 100 or the host, and detect and measure the speed and direction of moving objects in the far-field scene by repeating the aforementioned measurements over time. Generally, the controller 104 also includes additional circuitry and memory to measure the size of discrete objects sensed in the far-field scene 106 and identify discrete objects, such as cars or pedestrians. Optionally, the controller 104 may also include memory and circuitry to generate a three-dimensional (3D) model of the far-field scene 106.

[0042] The optical scanner 102 includes an optical transmitter 108 for generating, transmitting, and scanning light across a far-field scene 106 in at least two dimensions, and an optical receiver 110 for receiving reflected light from the far-field scene. Generally speaking, both the optical transmitter 108 and the optical receiver 110 are solid-state. Solid-state means that both the light scanning element of the optical transmitter 108 and the light collecting element of the optical receiver 110 are made or fabricated on silicon, semiconductor, or other types of substrates using micro-electromechanical systems devices (MEMs) and semiconductor or integrated circuit (IC) fabrication techniques. In particular, the beam steering or light scanning element of the optical scanner 102 is made using multiple MEMS phased arrays to replace mechanical scanners, such as spinning or moving mirrors used in conventional LiDAR systems. In some embodiments, such as Figure 1 As shown in FIG, substantially the entire LiDAR system, including the optical scanner 102, the controller 104, and any interface to a host system (not shown in this figure), is integrally formed on a single integrated circuit, IC 112. Because the optical scanner 102 does not include the moving or rotating elements of a conventional LiDAR system, the resulting optical scanner and LiDAR system are more resilient to vibrations and can be smaller and less expensive.

[0043] Now refer to Figures 2A to 2C Methods or approaches for operating an optical MEMS-based phased array to achieve beam steering or scanning are described. Generally speaking, an optical MEMS-based phased array (hereinafter referred to as a MEMS phased array) uses a row of modulators that can change the direction of a coherent beam of light by adjusting the relative phase of the signal from one element to the next. Figures 2A to 2CTwo adjacent light reflecting elements 202 or pixels forming a MEMS phased array 200 are schematically shown. Although only two pixels or light reflecting elements 202 are shown, it should be understood that a MEMS phased array used in LiDAR applications will typically include hundreds to thousands of light reflecting elements. In particular, Figure 2A and Figure 2B , represents the extremes of angular scanning (i.e., from 0 degrees or back reflection perpendicular to the long axis 208 of the MEMS phased array 200 to ±1 orders). As shown in these figures, the maximum possible phase slope between adjacent pixels or light reflecting elements 202 is 1π or a quarter wavelength (λ / 4) deflection. Figure 2C shows a configuration where the deflection between adjacent pixels or light reflecting elements 202 is λ / x (where x is an integer greater than four (4)) to redirect light to Figure 2A and Figure 2B The configuration of the intermediate angle between.

[0044] refer to Figure 2A By illuminating the MEMS phased array 200 with coherent incident light 204 and individually addressing or deflecting the light reflecting elements 202 from a rest or non-deflected state by different amounts relative to the wavelength (λ) of the incident light 204, a wavefront 206 reflected from the MEMS phased array 200 may be directed at an angle relative to the long axis 208 of the MEMS phased array. Stay away from MEMS phased array propagation. Figure 2A The light reflecting element 202 is shown in a stationary or non-deflected state, wherein the reflected light is propagated or manipulated in a direction parallel to an axis 208 of the MEMS phased array. Figure 2C 2. A state is shown in which the light reflecting element 202 has been deflected by an amount equal to 0.25 times the wavelength (λ) of the incident light 204 and causes the reflected light to be reflected at a first angle relative to the axis 208 of the MEMS phased array. The light reflecting element 202 in a state of being manipulated or transmitted. Figure 2B A state is shown in which the light reflecting element 202 has been deflected by an amount equal to x < 0.25 times the wavelength (λ) of the incident light 204 and causes the reflected light to be reflected at a second angle relative to the axis 208 of the MEMS phased array. The light reflecting element 202 in a state of being manipulated or transmitted.

[0045] It should be noted that 0.25 times the wavelength (λ) of the incident light 204 is the maximum value that adjacent light reflecting elements 202 can be deflected without introducing phase ambiguity and resulting in a binary pattern that produces positive and negative 1st order beams. represents the maximum angular field of view (FOV), which is determined by the angles between the first-order reflected rays, over which the modulated light or modulated light band can be steered or scanned. The actual values ​​of these angles for the first-order reflected rays depend on the width or spacing between the light-reflecting elements 202 and the wavelength (λ) of the incident light 204, but are generally given by the following equations:

[0046]

[0047] Here, λ is the wavelength of the incident light, and d is the width of the light reflecting element 202 .

[0048] Now refer to Figure 3 Methods of operating a LiDAR system including a MEMS phased array to scan a far-field scene are described. Figure 3 FIG3 is a schematic functional diagram of a portion of a LiDAR system 300 including a controller 301 and a solid-state optical scanner 302 having an optical transmitter 304 having at least one MEMS phased array 306 configured to receive light from a light source through shaping or illumination optics (not shown in this figure), modulate the phase of at least some of the received light, and transmit or project a beam of phase-modulated light through projection optics 308 to manipulate an illumination line or strip 310 to scan a far-field scene 312. The MEMS phased array 306 manipulates the beam to scan the far-field scene 312 by varying the phase modulation of light incident on different portions of the MEMS phased array. Generally, the first MEMS phased array 306 is configured to scan the far-field scene 312 in at least two dimensions (2D), including an angular dimension (θ) and an axial dimension (indicated by arrow 314) parallel to the long axis of the MEMS phased array.

[0049] It should be noted that although the optical scanner 302 is schematically shown as including a single MEMS phased array 306, this is not required in every embodiment and is not typically the case. Rather, as described in detail below, it is often beneficial for the optical scanner 304 to include multiple adjacent MEMS phased arrays 306 operating in unison or a single MEMS phased array having multiple adjacent arrays to increase the aperture width or length to increase the power or radiant flux of light transmitted or received and to improve the point spread resolution of the system.

[0050] The optical scanner 302 also includes an optical receiver 316 that includes collection or receiving optics 318 to capture light from the far-field scene 312 , which is then directed onto a detector 320 .

[0051] refer to Figure 3, depth or distance information can be obtained from the LiDAR system 300 to a target or object 322 in the far-field scene 312 using any of a variety of standard LiDAR technologies, including pulse, amplitude modulated continuous wave (AMCW), or frequency modulated continuous wave (FMCW). In pulse and AMCW LiDAR systems, the amplitude of the intensity of the transmitted light is pulsed or modulated with a signal, and the TOF from the LiDAR system 300 to the object 322 is obtained by measuring the amount by which the returning signal is delayed in time. The distance to the reflecting object is obtained by multiplying half of this time by the speed of light.

[0052] Figure 4 is a graph showing changes in the frequency of outgoing pulses of transmitted light of a LiDAR system using FMCW technology over time. Figure 3 and Figure 4 In FMCW LiDAR, the frequency of the outgoing chirp or pulse 400 of the transmitted light varies continuously over time as the light band 310 is continuously scanned across the far-field scene 312. The time to the object 322 can be determined by comparing the frequency of the light reflected from the object with the frequency of the local oscillator, and the distance to the object can be derived by using the speed of light as previously described. FMCW LiDAR systems have an advantage over amplitude modulation in that the local oscillator provides inherent amplification of the detected signal.

[0053] Using information about TOF, the controller 301 in the LiDAR system can then calculate the position of the target 322 in the far-field scene 312 along the Y-axis 326 from the steering direction of the MEMS phased array 306 as light is transmitted from the MEMS phased array and from the sensed position of the object along an axis of the detector 320 (indicated by arrow 328) parallel to the long axis of the detector.

[0054] Now refer to Figures 5A to 5C and Figure 6 The block diagram depicts an embodiment of an optical scanner according to the present disclosure, which is particularly suitable for use in a LiDAR system to scan and / or identify objects or targets in a far-field scene, such as people, buildings, and cars.

[0055] refer to Figure 5A In a first embodiment, an optical scanner 500 includes an optical transmitter 504 and an optical receiver 506. The optical transmitter 504 generally includes a light source 508; a shaping or illumination optic 510 that illuminates a MEMS phased array 512 with light from the light source; and an imaging or projection optic 514 that transmits or projects phase-modulated light from the MEMS phased array into a far-field scene 516 to scan the far-field scene in at least two dimensions.

[0056] The light source 508 may include any type and number of light emitting devices capable of continuously emitting or pulsing coherent light at a sufficient power level or power density and at a single wavelength or frequency or within a narrow wavelength or frequency range to enable phase and / or amplitude modulation of the light from the MEMS phased array 512. Generally, the light source 508 is a continuous wave light source that continuously emits light modulated in amplitude (for AMCW LiDAR) or frequency (for FMCW LiDAR). Because objects in the far-field scene are continuously illuminated, the light source can operate at less power than the high peak power of a pulsed system. The light source 508 may include multiple lasers or laser emitters, such as diode lasers or vertical cavity surface emitting lasers (VCSELS). In one embodiment, the light source 508 includes a VCSEL array with multiple laser emitters to increase optical power while meeting or extending eye-safe power limits. In another embodiment, the light source 508 includes a plurality of high power lasers producing powers from about 5000 milliwatts (mW) to about 40,000 mW at wavelengths (λ) from about 750 nm to about <2000 nm.

[0057] The illumination optics 510 may include a plurality of elements, including lenses, integrators, mirrors, and prisms, configured to transmit light from the light source 508 to the first MEMS phased array 512 to illuminate a line of a specified width and substantially cover the full width and / or length of the MEMS phased array. In one embodiment, the illumination optics 510 includes a microlens or lens array (described in more detail below) to individually illuminate one or more modulators in the first MEMS phased array 512.

[0058] The projection optics 514 may also include lenses, integrators, mirrors, and prisms and is configured to transmit light from the MEMS phased array 512 to illuminate a line or strip in the far-field scene 516. Generally, the projection optics 514 include magnification optics or elements, such as Fourier transform (FT) lenses and mirrors, to increase the field of view (FOV) of the optical scanner 500. In one embodiment, the projection optics 514 include a lens array to disperse light in a first direction to form an illuminated strip perpendicular to the direction in which the projected light is moved or manipulated in the far-field scene 516.

[0059] The optical receiver 506 typically includes receiving optics 518 to collect or receive light from the far-field scene and direct or transmit the received light to a detector 520 or detector array. As with the illumination and projection optics, the receiving optics 518 may include lenses, integrators, mirrors, and prisms and is configured to receive light from the far-field scene 516 and transmit the light from the far-field scene 516 to the detector 520. In one embodiment, the receiving optics 518 includes a lens array to increase the effective fill factor of the detector 520.

[0060] In general, detector 520 may include any type of detector sensitive to light in the wavelengths generated by light source 508, including one or more rolling shutter cameras, a one- or two-dimensional array of photodiode detectors, or a single photon avalanche diode (SPAD) array. Figure 5A In the embodiment shown in , the receiving optics will be 2D and the detector is a 2D array of detectors or a 2D detector array. The LiDAR system used in the automotive detector 520 can use lower density, higher sensitivity devices (such as APDs) for long range detection.

[0061] exist Figure 5B In another embodiment shown in FIG, optical receiver 506 is a directional optical receiver including a second MEMS phased array 522 to de-scan collected or received light by selectively directing light reflected from slices of far-field scene 516 onto detector 520 while substantially rejecting background light. For example, the second MEMS phased array directs light from a light source reflected from far-field scene 516 onto detector 520 by adapting the direction in which the second MEMS phased array steers the light based on information about the direction in which the first MEMS phased array 512 steers the light beam. Optionally, as in the embodiment shown, optical receiver 506 may also include detector optics 524 to transmit light from the second MEMS phased array 522 to detector 520. As with illumination optics 510, projection optics 514, and receiving optics 518, detector optics 524 may include lenses, integrators, mirrors, and prisms and may be configured to substantially fill or overfill detector 520. In one embodiment, receive optics 518 includes a lens array to increase the effective fill factor of stacked phased array 522 .

[0062] In some embodiments, where the detector 520 comprises a one-dimensional (1D) detector array and the optical receiver 506 is a directional receiver, the second MEMS phased array 522 selectively directs light reflected from a slice of the far-field scene 516 onto the 1D detector array while rejecting light reflected from outside the slice from the far-field scene, as well as background light.

[0063] As Figure 5AIn the embodiment shown in FIG, an optical scanner 500 includes an optical transmitter 504 and an optical receiver 506. The optical transmitter 504 further includes a light source 508 and illumination optics 510 that illuminate a first MEMS phased array 512 with light from the light source; and projection optics 514 that transmit or project phase-modulated light from the MEMS phased array into a far-field scene 516. In addition to a second MEMS phased array 522, the optical receiver 506 also includes a detector 520 and receiving optics 518 to collect or receive light from the far-field scene 516 and direct or transmit the light to the second MEMS phased array 522 and onto the detector 520. Because the second MEMS phased array 522 directs light from the light source reflected from the far-field scene onto the detector 520, the size or width of the detector 520 can be reduced compared to a case where the second MEMS phased array 522 is not provided. That is, the detector may comprise a ID array detector because the second MEMS phased array 522 is capable of imaging a slice of the 2D scene 516 onto the detector 520. The full scene is reconstructed by scanning the second MEMS phased array.

[0064] exist Figure 5C In yet another embodiment shown in , the optical scanner 500 includes a shared MEMS phased array 526 configured to modulate the phase of light from the light source 508 at a first time to scan the far-field scene 516, and to descan the collected or received light at a second time by directing light from the light source reflected from the far-field scene onto the detector 520 while substantially rejecting background light. Figure 5A and Figure 5B In the embodiment shown in FIG, an optical scanner 500 includes an optical transmitter 504 and an optical receiver 506. In addition to a light source 508 and a shared MEMS phased array 526, the optical transmitter 504 also includes illumination optics 510 for illuminating the MEMS phased array with light from the light source, and projection optics 514 for transmitting or projecting phase-modulated light from the MEMS phased array into a far-field scene 516. In addition to a detector 520 and the shared MEMS phased array 526, the optical receiver 506 also includes receiving optics 518 for collecting or receiving light from the far-field scene 516, and optionally, detector optics 524 for directing or transmitting light to the shared MEMS phased array and onto the detector 520.

[0065] exist Figure 6In another embodiment shown in FIG, an optical scanner 600 may include a MEMS phased array 602 in the scanner's optical receiver 604 and a spatial light modulator (SLM 606) in an optical transmitter 608. The SLM 606 in the optical transmitter 608 need not include solid-state devices, but may instead include a mechanical scanner (such as a spinning or moving mirror) to steer a light beam throughout a far-field scene 610. As with the embodiments described above, in addition to the MEMS phased array 602, the optical receiver 604 includes receiving optics 612 to collect or receive light from the far-field scene 610 and direct or transfer the light to the MEMS phased array and from there to a detector 614. Additionally, the optical transmitter 608 includes a light source 616, illumination optics 618 that illuminate the SLM 606 with light from the light source, and projection optics 620 that transmit or project the phase-modulated light from the MEMS phased array into the far-field scene 610.

[0066]

[0046] Embodiments of a MEMS-based spatial light modulator (SLM) for forming a MEMS phased array suitable for use in an optical scanner will now be described.

[0067] One type of MEMS-based SLM suitable for use in a MEMS phased array of a LIDAR system to modulate or steer a light beam is a ribbon-type SLM or ribbon MEMS phased array, which includes a plurality of electrostatically deflectable ribbons, such as the Grating Light Valve (GLV) commercially available from Silicon Light Machines of Sunnyvale, California. TM ). A ribbon SLM typically comprises a one-dimensional (1D) linear array consisting of thousands of independent, addressable, electrostatically actuated movable structures (such as elongated elements or ribbons), each of which has a light reflective surface supported on the surface of a substrate. Each ribbon includes an electrode and is deflectable toward the substrate through a gap or cavity by means of an electrostatic force generated when a voltage is applied between the electrodes in the ribbon and a base electrode formed in or on the substrate. The ribbon electrodes are driven by drive channels in a driver that may be integrally formed on the same substrate as the array. Ribbon SLMs are suitable for a wide variety of LiDAR applications because they are small, fast, low-cost systems that are easy to manufacture, integrate and package while still being able to provide large diffraction angles. Additionally, ribbon SLMs are capable of operating to produce 3D scans or models when used in conjunction with rolling shutter cameras, photodiode detector arrays and SPAD arrays, as well as a variety of illumination sources, including laser arrays or bars having multiple semiconductor diode lasers or VCSELs.

[0068] Now refer to Figure 7A and Figure 7BAn embodiment of a ribbon-type SLM is described. For the sake of clarity, many details of MEMS in general and MEMS-based SLMs in particular that are known and irrelevant to the present invention have been omitted from the following description. The drawings described are merely schematic and non-limiting. In the drawings, the size of some elements may be exaggerated and not drawn to scale for illustrative purposes. Dimensions and relative dimensions may not correspond to actual reductions in practice of the present invention.

[0069] refer to Figure 7A and Figure 7B In the illustrated embodiment, the SLM is a one-dimensional (1D) ribbon-type SLM 700 that includes a linear array 702 composed of thousands of individually addressable electrostatically actuated ribbons 704, each of which has a light-reflecting surface 706 supported on a surface of a substrate 708. Each ribbon 704 includes an electrode 710 and is deflectable toward the substrate 708 through a gap or cavity 712 by an electrostatic force generated when a voltage is applied between the electrode in the ribbon and a base electrode 714 formed in or on the substrate. The ribbon electrodes 710 are driven by drive channels 716 in a driver 718 that can be integrally formed on the same substrate 708 as the linear array 702.

[0070] exist Figure 7B Shown in Figure 7A Schematic cross-sectional side view of an elongated element or ribbon 704 of an SLM 700. Figure 7B , the ribbon 704 includes a resilient mechanical layer 720 for supporting the ribbon above a surface 722 of a substrate 708; a conductive layer or electrode 710; and a reflective layer 724 including a reflective surface 706 overlying the mechanical layer and the conductive layer.

[0071] Generally, the mechanical layer 720 comprises a taut silicon nitride membrane (SiNx) and is flexibly supported above the surface 722 of the substrate 708 by a plurality of posts or structures (also typically made of SiNx) at both ends of the ribbon 704. The conductive layer or electrode 710 can be formed on the mechanical layer 720 and in direct physical contact with the mechanical layer 720 (as shown), or formed below the mechanical layer. The conductive layer or ribbon electrode 710 can comprise any suitable conductor or semiconductor material compatible with standard MEMS manufacturing techniques. For example, the electrode 710 can comprise a doped polysilicon (poly) layer or a metal layer. Alternatively, if the reflective layer 724 is metallic, it can also serve as the electrode 710.

[0072] The separate discrete reflective layer 724 , where included, may comprise any suitable metallic, dielectric, or semiconductor material that is compatible with standard MEMS fabrication techniques and capable of being patterned using standard photolithographic techniques to form the reflective surface 706 .

[0073] In the embodiment shown, multiple strips are grouped together to form a plurality of MEMS pixels 726 , with one or more strips in the array being driven by a single driver channel 716 .

[0074] Figure 8 How can it be adjusted Figure 7A and Figure 7B Schematic representation of the overall spacing and amplitude of the SLM ribbon in the steering beam. Figure 8 To steer a normally incident light beam 802 by reflecting a steering angle θ, ribbons 804 are arranged in a "blazed" pattern 806 with a pitch or period Λ. As the blazed pitch Λ decreases, the light is steered within a larger angle θ. It should be noted that the blazed period Λ can take integer or non-integer values ​​to allow for continuous modulation of the steering angle θ. The maximum steering angle is achieved when the blazed period includes two ribbons.

[0075] Figure 9 Schematic representation of a portion of a linear array 902 in a ribbon-type SLM, shown in cross-section along the long axis of the ribbon. The deflection of ribbon 906 is varied to impose a monotonic phase change along the array. Note that once the phase change exceeds one wave (i.e., a half-wave deflection), the deflection pattern can be continued via modular division by the wavelength forming the blazed group 903. An SLM with a programmable MEMS element (ribbon 906) allows light to be continuously scanned across an angle, making it particularly useful in steering applications such as LIDAR.

[0076] Figure 10 is a plot of intensity versus steering angle and shows Figure 9 The suitability of a ribbon-type SLM for phased array applications is schematically shown in FIG. Figure 10 , it can be seen that along Figure 9 The periodic spatial pattern of the ribbon SLM shown in produces a phased array reflection, and varying the spatial period and amplitude of the pattern varies the reflected beam angle, thereby allowing the ribbon SLM to rapidly cycle through the pattern to sweep the beam from field to field. In particular, it should be noted that as the period of the spatial pattern on array 902 increases, i.e., as each period includes a greater number of ribbons, the maximum intensity 1008 of the light reflected from array 902 shifts to the left, as indicated by arrow 1010. As the spatial period decreases, or the number of ribbons in each period decreases, the maximum intensity 1008 of the light reflected from array 902 shifts to the right, as indicated by arrow 1012.

[0077] The high switching speed of ribbon SLMs makes them attractive for MEMS phased array applications such as LiDAR. However, there are two challenges in designing ribbon SLMs for LiDAR. First, a large stroke is typically used, that is, the amount by which a single ribbon can be deflected. It is generally recommended that ribbon SLMs have a stroke of up to or exceeding half the wavelength of the light being modulated or steered. For example, it has been found that a stroke of approximately 0.8 μm is desirable to achieve sufficient phase shift in LiDAR applications using a wavelength of 1550 nm. The stroke of a phase modulator scales linearly with wavelength.

[0078] The second challenge of ribbon-type SLMs for MEMS phased arrays is that the ribbons should include narrow ribbon widths to achieve wide angular swing. Generally speaking, it is recommended that ribbons in ribbon-type SLMs for MEMS phased array applications have ribbon widths of approximately <5 μm or less, and in some embodiments can be as narrow as 0.5 μm.

[0079] These requirements of large stroke and narrow ribbon width make it difficult to switch ribbon SLMs at high rates (which is desired for beam steering) because the narrow ribbon over a large air gap has very poor damping and behaves like a guitar string, taking a long time to settle, thus limiting the rate at which the beam can be steered.

[0080] Now refer to Figure 11 Describe the effect of air gap and ribbon width on settling time. Figure 11 This is a schematic diagram showing how the ribbon of a ribbon-type SLM is modeled as a capacitor on a spring. Figure 11 , the voltage potential V(t) applied between the ribbon 1102 and the grounded lower electrode or substrate electrode 1104 generates an electrostatic Coulomb attraction that deflects the ribbon toward the substrate electrode by a distance x. The electrostatic force is offset by the elastic restoring force (at Figure 11 Once the electrostatic force is removed, the mechanical layer (represented by spring 1106) Figure 7B The elastic restoring force of the stretched silicon nitride membrane (shown as mechanical layer 720 in FIG) allows the ribbon 1102 to return to a neutral state or position. In addition, there is a damping force caused by the squeeze film effect (in Figure 11 (represented by damper 1108 in the figure), this squeeze-film effect is proportional to the instantaneous velocity of the ribbon and slows or dampens the movement of ribbon 1102. Squeeze-film damping is a strong function of both the ribbon width and the air gap thickness. The settling time is proportional to the cube of the air gap thickness and inversely proportional to the cube of the ribbon width. Therefore, to achieve sufficient damping with a narrow ribbon, a very thin air gap is recommended.

[0081] Coulomb attraction (F coulomb ) is given by:

[0082]

[0083] Where ε0 is the permittivity of free space, A is the effective capacitance area of ​​the strip (in square meters (m2) 2 ), G is the gap thickness, and x is the linear displacement of the ribbon relative to the substrate electrode (in meters).

[0084] Elastic recovery force (F Elastic ) is given by:

[0085]

[0086] Where k is the spring constant of the mechanical layer and x is the linear displacement of the ribbon 1102 relative to the substrate electrode 1104 (in meters).

[0087] Damping force (F Damping ) is given by:

[0088]

[0089] Where b is the damping constant of the air gap and dx / dt is the velocity of the center of the ribbon 1002 relative to the substrate electrode 1004 (in meters per second).

[0090] Therefore, in equilibrium, these three forces (Coulomb attraction, elastic restoring force and damping force) must be balanced.

[0091] However, as the ribbon 1102 displaces more than 1 / 3 of the total thickness of the gap (G) between the ribbon and the substrate electrode 1104 in a neutral state, the electrostatic force can overwhelm the elastic restoring force. This results in a potentially destructive phenomenon commonly referred to as "snap-down" or "pull-in," in which the ribbon 1102 snaps into contact with the substrate electrode 1104 and remains stuck there even when the electrostatic force is removed. Generally, it has been observed that snap-down occurs at a characteristic displacement of x = G / 3, where the ribbon 1102 has deflected one-third of the original gap thickness. Therefore, the ribbons in conventional ribbon-type SLMs are typically operated or driven to not deflect more than a distance of G / 3 to prevent snap-down. Unfortunately, this leaves the lower 2 / 3 of the gap G empty, which in turn leads to poor squeeze-film damping.

[0092] Therefore, to achieve adequate damping with narrow ribbons, it is desirable to create a very thin die gap, close to the physical stroke (x) of the application, while to avoid pull-in, it is desirable to create a larger "electrical gap".

[0093] Reducing the die gap while maintaining or increasing the electrical gap can be accomplished by inserting a dielectric between the ribbon and the substrate electrode. In one embodiment, a solid dielectric film beneath the ribbon is used to improve damping (and heat transfer) in this way. For a dielectric thickness G, the equivalent electrical thickness is G / ε r , where ε r is the relative permittivity. For example, for r =3.9 relative dielectric constant of silicon dioxide solid dielectric film and having ε r =1 relative dielectric constant of the vacuum or air gap, in order to increase the electrical gap by 1μm, it is necessary to provide approximately 4μm of additional dielectric material above the substrate electrode and between the ribbon and the substrate electrode. It should be noted that it can be difficult or impractical to integrate thick films (i.e., films with a thickness greater than about 2μm) into existing MEMS processes for manufacturing ribbon-type SLMs because inherent film stresses can cause voids or delamination in such thick films, and film roughness can become excessive with increasing thickness. For this reason, low dielectric constant materials are often used.

[0094] In another embodiment, the die gap is reduced while maintaining or increasing the electrical gap by using an electrically permeable damping structure formed above the substrate electrode during manufacturing. Generally speaking, the electrically permeable damping structure includes a dielectric layer suspended above the substrate electrode and separated from the substrate electrode by a first gap or first air gap, wherein the dielectric layer at least defines the top surface of the air gap. It should be noted that although the first gap is referred to as an air gap, it need not be filled with air, but instead can be evacuated or filled with a mixture of other gases. In some embodiments, the dielectric layer can substantially surround the air gap to form an airtight or hermetically sealed cavity. In other embodiments, the first air gap opens to the MEMS environment, including a second gap or air gap between the electrically permeable damping structure and the lower surface of the ribbon, and the entire environment of the ribbon-type SLM can be evacuated or filled with a fill gas and hermetically sealed. Suitable fill gases can include pure forms or mixtures of one or more of nitrogen, hydrogen, helium, argon, krypton, or xenon.

[0095] In one embodiment, the ribbon SLM includes an electrically permeable damping structure to provide large stroke while maintaining good damping, thereby enabling fast beam steering and large scan angles, and exceeding the wavelength of the modulated or steered light to accommodate light with long wavelengths up to about 10 μm. Figure 12 This damping structure is included Figure 7A and Figure 7B Cross-sectional side view of a portion of a ribbon-type SLM. Figure 12, the ribbon-type SLM 1200 includes a bottom or lower electrode 1202 formed above a substrate 1204 and a static electrically permeable damping structure formed above the bottom electrode. Generally speaking, the electrically permeable damping structure includes: a first air gap 1206; a dielectric layer 1208 suspended above the lower electrode 1202 and separated from the lower electrode 1202 by the first air gap; and a second air gap 1210 above the dielectric layer, separating the movable lengths of the plurality of ribbons 1212 of the ribbon-type SLM 1200 from the dielectric layer. As in the case of the combination Figure 7A and Figure 7B In the depicted embodiment of a ribbon-type SLM, each ribbon 1212 includes a mechanical layer typically formed of a tensioned silicon nitride layer and a ribbon or top electrode coupled to one of a plurality of drive channels (not shown) via a bus 1214, and each ribbon 1212 is configured to be deflected toward the bottom electrode by an electrostatic force generated between the top electrode and the bottom electrode. Figure 7A and Figure 7B In the embodiment of FIG. 1 , the drive channels are integrally formed on the same substrate 1204 as the linear array of ribbons 1212 .

[0096] Optionally, as in the embodiment shown, the device may further include a thin intervening dielectric layer 1216, such as silicon dioxide, between the substrate 1204 and the lower electrode 1202 to electrically insulate the lower electrode.

[0097] In operation, the ribbons 1212 can be independently deflected toward the bottom electrode 1202 by a distance substantially equal to the thickness of the second air gap 1210. In general, the thickness of the second air gap 1210 is ˜G / 3 and the thickness of the first air gap 1206 is ˜2G / 3, where G is the distance between the bottom electrode 1202 and the ribbon 1212 in an undeflected or resting state. It has been found that for a ribbon-type SLM 1200 with ribbons 1212 having a width transverse to the long axis of the linear array from 10 μm to 0.5 μm and operating at near-infrared wavelengths suitable for LiDAR applications, an electrically permeable damping structure such as described above and having a first air gap 1206 of approximately 2.5 μm and a second air gap 1210 of up to approximately 1.5 μm improves settling time while maintaining high switching speeds and substantially preventing pull-in or drop-out of the ribbon 1212. Note that the ratio of the second air gap thickness to the first air gap thickness can be reduced to accommodate narrower ribbons requiring more damping. By changing the thickness ratio but maintaining the same total thickness (first air gap + second air gap), the overall desired stroke is maintained.

[0098] In one embodiment, such as Figure 13In the embodiment shown in , the MEMS phased array 1300 may include a plurality of strip-type SLMs 1302a, 1302b, each having a one-dimensional (1D) array 1304a, 1304b, arranged in a line along a common or shared long axis 1306, and operated to increase the area over which modulated light can be scanned, and stacked to increase the axial dimension parallel to the long axis of the array. Figure 13 , each of the arrays 1304a, 1304b includes hundreds or thousands of independently addressable electrostatically actuated strips 1308a, 1308b. Figure 7A and Figure 7B In the depicted ribbon-type SLM 700, each of the ribbons 1308a, 1308b has a light-reflecting surface, includes electrodes, and is deflectable toward a substrate 1310 through a gap or cavity by electrostatic forces generated when a voltage is applied between the electrodes in the ribbon and a base electrode in the substrate. Each of the ribbons 1308a, 1308b is driven by a drive channel 1312a, 1312b in a driver 1314a, 1314b, which may be integrally formed on the same substrate 1310 as the arrays 1304a, 1304b.

[0099] In some embodiments (such as the illustrated embodiment), each of the strip-type SLMs 1302a, 1302b, including the arrays 1304a, 1304b and the drivers 1314a, 1314b, is integrally formed on a single shared substrate 1310. Alternatively, each of the strip-type SLMs 1302a, 1302b may be integrally formed on separate substrates that are then packaged in a single shared integrated circuit (IC) package. In yet another alternative embodiment, each of the strip-type SLMs 1302a, 1302b is individually packaged and then mounted to a single shared printed circuit board (PCB).

[0100] exist Figure 14 and Figures 15A to 15C In other embodiments shown in FIG, a MEMS phased array may include multiple strip-type SLMs or a single strip-type SLM with multiple one-dimensional (1D) arrays arranged and operated in parallel to increase the active aperture of the optical scanner. Increasing the functional area of ​​the MEMS phased array in this way allows for simpler optics, increased field of view (FOV) and system point spread resolution, and improved sensitivity by collecting more light during the descanning operation.

[0101] Figure 1414 is a diagram illustrating a top view of an embodiment of a MEMS phased array 1400 including a plurality of ribbon-type SLMs 1402A and 1402B, each including an array 1404 of a plurality of ribbons 1406 arranged in parallel. Generally speaking, as in the illustrated embodiment, the ribbon-type SLMs 1402A and 1402B are integrally formed on a shared substrate 1408, and the ribbons 1406 are driven by drive channels 1416 in a driver 1418, which may be integrally formed on the same substrate 1408 as the array 1404. Alternatively, in an embodiment not shown, all of the plurality of ribbon-type SLMs 1402A and 1402B may be driven by a single shared driver 1418.

[0102] Figures 15A to 15C 1 is a diagram illustrating another embodiment of a MEMS phased array 1500 comprising a single strip-type SLM 1502, wherein each of the strips 1504 of the SLM is divided along its long axis by pillars 1506 to form a plurality of parallel 1D arrays 1508a, 1508b, and 1508c. Although only three parallel 1D arrays 1508a, 1508b, 1508c are shown, it will be understood that the strip-type SLM 1502 can be divided into any number of parallel 1D arrays (from 2 to over 50). Figure 15B The undeflected or stationary state is shown in Figure 15A Schematic cross-sectional side view of the movable belt 1504 of the SLM 1502. Figure 15C The deflected or active state is shown in Figure 15A Schematic cross-sectional side view of the movable belt 1504 of the SLM 1502. Figure 7A and Figure 7B In the embodiment of the SLM 700 depicted, the ribbon 1504 includes a resilient mechanical layer 1510 for supporting the ribbon above a bottom electrode 1512 formed on a surface of a substrate 1514; a ribbon or top electrode 1516; and a reflective layer 1518 including a light reflecting surface covering the mechanical layer or top electrode. Figure 7A In the embodiment shown in FIG. 1 , the SLM 1502 further includes a plurality of drive channels 1520 in a driver 1522 that is integrally formed on the same substrate 1514 as the linear 1D arrays 1508 a , 1508 b , and 1508 c .

[0103] In another embodiment, the MEMS phased array comprises a blazed grating strip or ribbon MEMS array wherein each elongated element or strip of the strip SLM has a reflective surface with a blazed profile. By blazed profile is meant wherein each strip has a reflective surface across the width of the strip that is angled at a blazed angle relative to the surface of the SLM or the surface of the substrate on which the SLM is fabricated. In some embodiments, the reflective surface has a stepped profile to produce effective blazed at the blazed angle. The blazed angles on the strips adjust the power and contrast in the modulated light from the SLM at the zeroth (0th) order and higher, thereby providing higher contrast at the 0th order and higher contrast and / or power at the first (1st) order and higher. For scanning operations, in conjunction with the above description of Figures 8 to 10 The described blazing operation or method uses blazed ribbons to offset the center of the "scan envelope" (the angle between + / - 1 order in an SLM with flat ribbons) toward the 1st order and away from the zeroth (0) order or angle of incidence. The advantage of offsetting the center of the "scan envelope" is that any reflections from any other surface of the SLM exposed by the gaps between the ribbons will appear only in the zeroth order and therefore will not be scanned, resulting in a more optically efficient system with greater or higher contrast.

[0104] Now refer to 16A to 16C An embodiment of a ribbon-type SLM comprising ribbons having a blazed profile is described. Figure 16A A cross-sectional view of a single elongated element or ribbon 1602 is shown, having a stepped profile to produce an effective blazed surface 1604 at a blaze angle γ. Ribbon 1602 generally includes a rectangular body 1606 and a stepped reflector 1608. Rectangular body 1606 may comprise silicon nitride, and stepped reflector 1608 may comprise an optically reflective material, such as aluminum. Stepped reflector 1608 forms a first surface 1610 and a second surface 1612 of ribbon 1602. First and second surfaces 1610, 1612 are generally separated by a height difference of one-eighth of a wavelength, λ / 8, of incident light to form a blaze profile 1614. Blaze profile 1614 forms an effective blazed surface 1604 at a blaze angle γ, where blaze angle γ is given by the expression γ = arctan(λ / (4A)).

[0105] exist Figure 16B16 shows a first cross-sectional view of a portion of a blazed ribbon or ribbon MEMS phased array 1616 in an inactive state having ribbons 1602 at a grating pitch A and a first surface 1610 defining a grating plane 1618. In the inactive state, there is generally zero electrical bias between the ribbons 1602 and a lower or bottom electrode 1620. Incident light (I) of wavelength λ strikes the blazed ribbon MEMS phased array 1616 at an angle normal to the grating plane 1618 and diffracts the light into a plurality of diffraction orders D0, D1, D2, D3 based on the profile of the blazed ribbon 1602. -1 In the inactive state, the zeroth order diffraction D0 is normal to the grating plane 1618. The diffraction orders D1 and D -1 At a first diffraction angle θ1 given by the expression θ1 = arcsin(λ / A), where A is the grating pitch of the first surface 1610 and the second surface 1612 of the ribbon 1602. For the illustrated embodiment having the first surface 1610 and the second surface 1612 separated by a height difference of one-eighth of a wavelength λ / 8, the diffraction angle θ1 is about four times the blaze angle γ or less than about 15°. Ignoring first light loss due to absorption by the stepped reflector 1608 and second light loss of the incident light I passing through the gaps between adjacent pairs of ribbons 1602, half of the light incident on the blazed ribbon MEMS phased array 1616 is diffracted into the zeroth diffraction order D0, while a quarter of the incident light I is diffracted into the first diffraction orders D1 and D -1 Each of them.

[0106] exist Figure 16C 16 shows a second cross-sectional view of the blazed ribbon MEMS phased array 1616 in an activated state, wherein the ribbon 1602 is moved toward the substrate 1622 by applying an electrical bias between the ribbon and the bottom electrode 1620. In general, as in the embodiment shown, the blazed ribbon MEMS phased array 1616 uses a similar circuit as described above with respect to FIG. Figures 8 to 10 Describes the flash operation or method to operate. Figure 16C To steer a normally incident light beam (I) through a first-order reflection steering angle θ3, ribbons 1602 having blazed profiles 1614 are arranged in a "blazed" pattern 1624 with a pitch or period Λ. In the activated state, incident light I having a wavelength λ is diffracted into a first angle θ1 by the profile of the blazed ribbon 1602 as described above, and further diffracted or steered by a first-order diffraction angle θ2 generated by the blazed pattern 1624 and given by the expression θ2 = arcsin(λ / Λ), where Λ is the blazed pitch Λ of the blazed pattern 1624. It should be noted that the blazed period Λ can assume integer or non-integer values ​​to allow for continuous modulation of the steering angle θ3. As the blazed pitch Λ decreases, the light is steered over a larger angle from θ1 to θ3.

[0107] Figure 17 is an optics diagram showing illumination optics 1702 and projection optics 1704 for an optical scanner that includes multiple MEMS phased arrays 1706 to steer light 1708 to scan a far-field scene 1710. Figure 17 In the embodiment shown in FIG, illumination optics 1702 may include an array of lens arrays or micro-cylindrical lenses 1712 to form individual light beams from a coherent light source, and an imaging lens 1716 to focus the collimated light onto individual modulators of a MEMS phased array 1706. In the embodiment shown, the optical coherent light source includes an array of light emitting devices, such as VCSEL lasers 1718. In pulsed or flash LiDAR where the VCSEL array 1718 is used to generate the coherent light source, illumination optics 1702 and projection optics 1704 can achieve peak powers greater than 5 watts (W) using 10 nanosecond (ns) pulses at a repetition rate of up to 1 MHz, while each beam projected into the far-field scene has an average power of less than about 2.5 microwatts (mW), making it eye-safe.

[0108] Projection optics 1704 may include one or more lenses, such as a Fourier lens 1720 and a fisheye lens 1722, to spread light from the MEMS phased array into the far-field scene in at least the angular dimension (transverse to the axial dimension in which the light is scanned by phase modulation of the MEMS phased array 1706). Figure 17 In pulsed or flash LiDAR using a VCSEL array 1718 to generate a coherent light source, the illumination optics 1702 and projection optics 1704 can achieve peak power greater than 5 watts (W) with 10 nanosecond (ns) pulses at a repetition rate of up to 1 MHz, while each beam projected into the far-field scene has an average power of less than about 2.5 microwatts (mW), making it Class 1 and eye-safe. Furthermore, for a MEMS phased array 1706 with a single element size of 4.25 μm and a housing aperture of 3 mm, the MEMS phased array can provide a 25.5-degree FOV with more than 1,000 resolvable lines.

[0109] In some embodiments, at least one of the illumination optics, projection optics, or reception optics includes anamorphic optics for focusing light from a light source onto a MEMS phased array and / or for focusing modulated light from the MEMS phased array into a far-field scene. It is desirable that the anamorphic optics provide a vertical or transverse numerical aperture (NA) along the vertical axis of the MEMS phased array (transverse to the direction of light scanning) that is less than the diffraction angle of modulated light reflected from the array along the vertical or transverse axis of the scanning direction, and provide a horizontal or longitudinal NA that is greater than the vertical or transverse NA along the horizontal or longitudinal axis of the array, as the field of view and resolution requirements for the vertical and horizontal axes may differ. The horizontal axis optics will match the FOV of the phased array device to the horizontal scan requirements of the system, while the FOV for the vertical scan is determined by the vertical numerical aperture, as set by the illumination or detector array system.

[0110] Figure 18A and Figure 18B is an optical device diagram showing a top view and a side view of the light path of the deformed illumination and imaging optical device according to an embodiment of the present disclosure. The top view shows the optical path along the pixel arrangement direction. Figure 18A , the light path begins with a light source, such as a laser 1802, which in this embodiment is shown as comprising a plurality of light emitting or laser diodes 1804 arranged as a bar laser to illuminate a substantially linear portion of a 1D or 2D array 1806 of SLMs through anamorphic illumination optics 1807, which includes a first optical element or lens 1808 and a second optical element or lens 1810. Although in the illustrated embodiment, the anamorphic illumination optics 1807 are depicted or represented by two single lenses 1808 and 1810, it will be understood that the anamorphic illumination optics may include any number of prisms, lenses, and refract and transmit light from the laser 1802 to the linear array 1806 to adequately illuminate the linear array. Lens 1808, often referred to as a FAC lens (fast axis collimator), collimates the laser light from the emitter along the vertical axis or fast axis of the emitter. In the illustrated embodiment, the laser 1802 is a bar laser comprising a plurality of semiconductor diode lasers or emitters arranged along a common long axis. Each emitter of the strip laser acts as a spatial single-mode laser and has a Gaussian beam profile along the vertical axis. Figure 18A As shown in the side view in FIG, an almost perfectly collimated beam can be achieved. Since the size of the modulator along the vertical axis is one or several millimeters, no focusing optics or reduction optics are required. This means that the NA of the illumination beam along the vertical direction is almost zero. If an optical device such as a Powell lens is inserted to convert the Gaussian profile to a top-hat profile, the modulators arranged vertically in a single pixel can be uniformly illuminated. Figure 18AIn the top view in FIG, optical element or lens 1810 is used to illuminate the entire spatial light modulator array along the horizontal axis. A light pipe or fly's eye lens array can be included in optical element or lens 1810 to even out the light from the stripe laser or laser diode 1804. Because the stripe laser has multiple emitters and typically has a width of 10 mm along the horizontal axis, it serves as the NA to some extent. In the example where optical element or lens 1810 is a single cylindrical lens, the NA will be D / 2f, where D is the size of the stripe laser and f is the focal length of the cylindrical lens in optical element or lens 1810. When optical devices for even illumination are inserted into optical element or lens 1810, the NA number is expanded. Therefore, while the NA along the fast or vertical axis is low, the NA along the slow or horizontal axis can be much greater than the fast axis.

[0111] like Figure 18A As disclosed in , the pixel arrangement direction of the linear array 1806 is set to be parallel to the emitter arrangement direction of the strip laser 1802. This configuration can effectively use the diffracted beam. When the focus is on the horizontal axis, the NA of the illumination optics has a certain value due to the size of the emitter array, and the conditions for separating the diffracted beam by the linear array 1806 are limited. The imaging optics 1812 may include a magnifying element, such as a Fourier transform (FT) lens 1816 and a Fourier aperture 1818. As described above, the array includes only one or several pixels in the horizontal direction, and the 1st order beam can be separated from the 0th order beam only when the illumination NA is almost zero. Therefore, a part of the 1st order beam interferes with the 0th order beam. In Figure 18A In FIG, the dashed line shows the 1st order beam, while the thick solid line shows the main 0th order beam. Since the NA of the illumination beam is maintained after being diffracted into the 1st order beam by the linear array 1806, some of the 1st order beam passes through the Fourier aperture 1818. On the other hand, the NA of the illumination optics along the vertical axis is small and the number of modulators in a single pixel is large, so that the diffracted, main beam is separated.

[0112] The modulated light from linear array 1806 is then transmitted through imaging optics 1812 to imaging plane 1814. Figure 18A ), imaging optics 1812 may also include anamorphic optics, represented here by anamorphic lens 1820 and microlens or lens array 1822. This embodiment is particularly advantageous where the pixel size of array 1806 is not square. By using or adding anamorphic imaging optics to imaging optics 1812, a reduced image of the linear array is projected onto the imaging plane in a vertical direction, thereby correcting or compensating for any distortion or non-square pixels in linear array 1806.

[0113] Figure 18BThe 0th order beam and diffracted + / - 1st order beams are shown on the Fourier aperture 1818. Figure 18B , ellipse 1824 represents the 0th order beam, while ellipse 1826 represents the 1st order beam in the vertical direction, and ellipse 1828 represents the 1st order beam in the horizontal direction. The aperture size along the vertical axis (vertical NA 1830) is equivalent to the diffraction angle of the 1st order beam, and the size of the 0th order beam (represented by ellipse 1824) along the horizontal axis is equivalent to the diffraction angle of the 1st order beam. Figure 18A The horizontal NA 1832 of lenses 1808 and 1810 in FIG. 1 is the same. Figure 18B , it can be seen that the 0th order beam (represented by ellipse 1824) can pass through the Fourier aperture 1818, while the + / - 1st order beams along the vertical axis (represented by ellipse 1826) are completely blocked, and the + / - 1st order beams along the horizontal axis (represented by ellipse 1828) are essentially blocked or have their power significantly reduced. This results in a slightly degraded contrast ratio (CR). Therefore, Figure 18A The illumination and imaging optics of the embodiments are suitable for use in LiDAR systems, such as Figure 1 and Figure 3 The LiDAR system shown in FIG.

[0114] The power of a laser stripe comprising multiple laser diodes is not as high as in the examples given above and is typically equal to or less than 100 watts (W). To increase the total irradiation power, multiple laser stripes should be used. Therefore, in some embodiments, vertical stacking of laser stripes can be used to achieve higher power.

[0115] Figure 19 is a schematic block diagram of a compact optical scanner 1902 shown in cross-section, including one or more MEMS phased arrays 1904, 1906 and illustrating a folded light path for illuminating the MEMS phased array, thereby projecting modulated light, and receiving and scanning light onto a detector 1908. Figure 19 As shown in , the folded light path enables a compact optical scanner 1902 size of, for example, approximately 7 cm by 7 cm, with a thickness of approximately 2 cm, or about the size of a deck of playing cards.

[0116] refer to Figure 19, the optical scanner 1902 includes a housing or shell 1910 and one or more openings or apertures 1912, 1914 through which light is projected to scan a far-field scene (not shown in this figure) and light is received back from the far-field scene. Generally, the apertures 1912, 1914 are covered or sealed by lenses 1916, 1918 to further amplify or expand the projected light, focus the received light, and / or provide an environmentally sealed housing 1910 for the optical scanner 1902. In some embodiments (such as the embodiment shown), the lenses 1916, 1918 may include fisheye lenses to further increase the field of view (FOV) of the optical scanner 1902.

[0117] The optical scanner 1902 also includes illumination optics 1920 that direct light from a coherent light source 1922 onto the MEMS phased array 1904; imaging or projection optics 1924 that transmit or project phase-modulated light from the MEMS phased array into a far-field scene; and receiving optics 1926 that receive light from the far-field scene and direct it onto the detector 1908. As in the embodiments described above, the light source 1922 may include any type and number of light emitting devices, such as lasers, diode lasers, or VCSELS. The illumination optics 1920 may include multiple elements, including one or more lenses 1920a and an integrator, mirror, or prism 1920b, configured to transmit light from the light source 1922 to the MEMS phased array 1904 to illuminate a line of a specified width and substantially cover the full width length of the MEMS phased array. The projection optics 1924 may also include a lens 1924a, and an integrator, mirror, or prism 1924b configured to transmit light from the MEMS phased array 1904 to illuminate a line or stripe in the far-field scene. As with the illumination and projection optics, the receiving optics 1926 may include one or more lenses 1926a, 1926b, integrators, mirrors, and / or prisms configured to receive light from the far-field scene and transmit it to the detector 1908. In general, the detector 1908 may include any type of detector sensitive to coherent light of the wavelength generated by the light source 1922, including one or more rolling shutter cameras, a one-dimensional or two-dimensional array of photodiode detectors, or a SPAD array.

[0118] Finally, the housing 1910 of the optical scanner 1902 may also include or house electronic circuitry 1928 required for the operation of the optical scanner (such as a controller, a power supply for the controller, a light source 1922, a MEMS phased array 1904, 1906, and a detector 1908), one or more memories, and an interface to a host system.

[0119] As mentioned above, one or more of the illumination optics 510, projection optics 514, reception optics 518, and detector optics 524 may include microlenses or lens arrays. In particular, the illumination optics in a transmitter including a lens array may be coupled to a light source including a VCSEL array (e.g., a VCSEL array). Figure 17 ) are useful in combination to provide independent optical channels. Lens optical arrays are also particularly useful to distribute light over multiple strip MEMS phased arrays in an optical transmitter or receiver (such as Figure 13 to Figure 1 5) to distribute the light across multiple arrays and / or in projection optics to disperse and form illumination bands in the far-field scene. Finally, lens arrays are useful in receiver array optics to increase the effective fill factor of the receiver array.

[0120] Now refer to 20A to 20C Embodiments of lens arrays suitable for use in some or all of these applications are described. Figure 20A is a schematic block diagram showing a top view of an embodiment of a lens array, Figure 20B yes Figure 20A A cross-sectional view of the lens array, Figure 20B Shown by Figure 20A The 0th order illumination of a single modulator in a strip MEMS phased array with a single element of the lens array. Figure 20A , lens array 2000 includes a molded surface forming a plurality of individual lenses or elements (such as microlenses or cylindrical lenses) that are configured to concentrate (focus or project) light more in one direction than in another direction. In the embodiment shown, lens array 2000 is adapted or configured to focus light onto individual strips or portions of strips divided by pillars in strip MEMS phased array 2002, and the individual lenses or elements include cylindrical lenses 2004, each cylindrical lens 2004 having a major axis that is parallel to the major axis of the lens. Figure 13 As shown in the stacked arrangement or as Figure 14 The long axis 2006 of one or more strip MEMS phased arrays are arranged parallel to the long axis 2006 of the strip as shown in FIG15 and perpendicular to the long axis 2008 of the strip. Figure 20B As shown in the cross-sectional view of lens array 2000 in , cylindrical lenses 2004 focus or concentrate incoming light 2010 onto the center of each individual strip or portion of a divided strip in strip MEMS phased array 2002 .

[0121] refer to Figure 20CWhen an electrostatic potential difference is applied between the active ribbon 2012 in a ribbon MEMS phased array and the substrate or lower electrode, the ribbon is deflected into a parabolic profile as shown. Consequently, a diffraction grating is established only in a narrow region near the centerline of ribbon 2012. Regions outside this optical "sweet spot 2014" are neither parallel to the surface of the ribbon MEMS phased array nor displaced by the desired amount, thus failing to provide effective steering. To this end, it is desirable to use lens array 2000 to carefully shape or focus the illumination onto the center portion of the ribbon MEMS phased array, or to collimate or project only the light modulated from the center portion of the ribbon. A rule of thumb is that the width of sweet spot 2014 should be on the order of approximately 1 / 10 to 1 / 3 the length of ribbon 2012, depending on the contrast ratio. In addition, particularly with respect to light collected by the receiving optical device and focused onto the strip MEMS phased array in the optical receiver or descanned by the strip MEMS phased array and focused onto the detector, each lens or element focuses only the 0th order light 2016 on the sweet spot 2014 or is modulated by the sweet spot 2014 while rejecting light 2018 of other orders, thereby improving the contrast and resolution of the optical scanner.

[0122] Now refer to Figure 21 A flowchart depicts a method of operating an optical scanner including a first microelectromechanical system (MEMS) phased array for use in a light detection and ranging (LiDAR) system. Figure 21 The method begins by illuminating a first MEMS phased array with light from a coherent light source (2102). The first MEMS phased array is controlled to modulate the phase of the light from the coherent light source and project the modulated light from the first MEMS phased array into a far-field scene (2104), and the first MEMS phased array is further operated or controlled to scan the far-field scene (2106). As described above, the first MEMS phased array is adapted or configured to scan the far-field scene in two dimensions (2D) (including an angular dimension and an axial dimension parallel to the long axis of the first MEMS phased array). Next, light from the far-field scene is received at a second MEMS phased array (2108), and the second MEMS phased array is controlled to descan the received light (2110) by directing substantially only light originating from the coherent light source and reflected from the far-field scene onto a detector while rejecting background light.

[0123] In some embodiments, the first MEMS phased array and the second MEMS phased array are the same shared MEMS phased array, and controlling the first MEMS phased array includes controlling the shared MEMS phased array at a first time to modulate the phase of light from a coherent light source to scan a far-field scene in 2D, and controlling the second MEMS phased array includes controlling the shared MEMS phased array at a second time to descan received light by directing light from the coherent light source reflected from the far-field scene onto a detector and rejecting background light.

[0124] Thus, embodiments of a LIDAR system including a 1D MEMS phased array and methods of operating the same have been described. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be apparent that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the present disclosure. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.

[0125] The Abstract of the present disclosure is provided to comply with 37 CFR §1.72(b), which requires an abstract that will allow the reader to quickly ascertain the nature of one or more embodiments of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Additionally, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of simplifying the disclosure. This method of disclosure should not be interpreted to reflect an intention that the claimed embodiments require more features than are expressly recited in each claim. On the contrary, as reflected in the claims below, the inventive subject matter lies in less than all the features of a single disclosed embodiment. Accordingly, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

[0126] Reference to one embodiment or an embodiment in this description means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of a circuit or method. The appearance of the phrase one embodiment in various places in the specification is not necessarily all referring to the same embodiment.

Claims

1. An optical scanner comprising: an optical transmitter for receiving light from a light source and modulating a phase of at least some of the received light to project the light onto a far-field scene in two dimensions, the two dimensions including a first direction in which the light is dispersed to form an illumination band and a second dimension in which the illumination band is steered by modulating the phase of the light received from the light source; as well as an optical receiver comprising a plurality of first MEMS phased arrays to receive light from the far-field scene and direct at least some of the received light onto a detector, wherein each MEMS phased array comprises a strip MEMS phased array having light-reflecting strips arranged in parallel, wherein the plurality of first MEMS phased arrays are configured to descan the received light by directing light from the light source reflected from the far-field scene onto the detector while rejecting background light, wherein the optical receiver further comprises a receiving optical device for receiving light from the far-field scene and directing the received light onto the plurality of first MEMS phased arrays, and wherein the receiving optical device comprises a first lens array to increase the effective fill factor of the plurality of first MEMS phased arrays, wherein the optical transmitter comprises: a plurality of second MEMS phased arrays for receiving light from the light source and modulating the phase of at least some of the received light to project the light onto the far-field scene in two dimensions; and an illumination optical device for illuminating the plurality of second MEMS phased arrays with light from the light source, and The illumination optical device includes a second lens array for individually illuminating one or more light modulators in the plurality of second MEMS phased arrays.

2. The optical scanner according to claim 1, wherein The optical transmitter also includes a projection optical device for projecting light from the plurality of second MEMS phased arrays to the far-field scene, and wherein the projection optical device includes a third lens array for dispersing the light in the first direction to form the illumination band and increase the field of view FOV of the optical scanner.

3. The optical scanner according to claim 2, wherein The light source includes a vertical cavity surface emitting laser (VCSEL) array including multiple emitters to increase optical power and extend eye-safe power limits.

4. The optical scanner according to claim 1, wherein The detector includes a one-dimensional 1D detector array, and the optical receiver is a directional receiver, in which the first MEMS phased array selectively directs light reflected from a slice of the far-field scene onto the 1D detector array while rejecting light reflected from the far-field scene outside the slice and background light.

5. The optical scanner according to claim 1, wherein The ribbon MEMS phased array includes a plurality of ribbons suspended in parallel rows above a substrate, each ribbon having a light reflecting surface and a length perpendicular to a long axis of the ribbon MEMS phased array, and wherein the ribbon MEMS phased array is configured to deflect at least a certain number of the plurality of ribbons toward the substrate to modulate the phase of light reflected from the certain number of ribbons to scan the far-field scene in an angular dimension and an axial dimension parallel to the long axis of the phased array.

6. The optical scanner according to claim 5, wherein The plurality of first MEMS phased arrays include a plurality of strip-shaped MEMS phased arrays arranged in a line to increase an active aperture of the optical scanner.

7. The optical scanner according to claim 6, wherein The ribbon MEMS phased array further includes a damping structure between the plurality of ribbons and the substrate to enable modulation of the phase of light having a long wavelength.

8. The optical scanner according to claim 5, wherein Each of the plurality of strips is divided by pillars along its length to form a plurality of strip-shaped MEMS phased arrays arranged in parallel to increase the active aperture of the optical scanner.

9. The optical scanner according to claim 5, wherein The ribbon MEMS phased array includes a ribbon including a blazed profile to shift 0th order light reflected from the ribbon MEMS phased array.

10. An optical scanner comprising: MEMS phased array; coherent light source; illumination optics for illuminating the MEMS phased array with light from the coherent light source; projection optics for projecting light from the MEMS phased array to a far-field scene; a receiving optical device for receiving light from the far-field scene and directing the received light onto the MEMS phased array; as well as a detector onto which the MEMS phased array directs at least some of the received light, Wherein, the MEMS phased array is configured as follows: modulating the phase of light from the coherent light source at a first time to project light onto the far-field scene in two dimensions (2D), and The received light is descanned at a second time by directing light from the coherent light source reflected from the far-field scene onto the detector and rejecting background light.

11. The optical scanner according to claim 10, wherein The MEMS phased array comprises a ribbon MEMS phased array comprising a plurality of ribbons suspended in parallel rows above a substrate, each ribbon having a light reflecting surface and a length perpendicular to a long axis of the ribbon MEMS phased array, and wherein the ribbon MEMS phased array is configured to deflect at least a certain number of the plurality of ribbons toward the substrate to modulate the phase of light reflected from the at least certain number of ribbons to project light onto the far-field scene in an angular dimension and an axial dimension parallel to the long axis of the ribbon MEMS phased array.

12. The optical scanner according to claim 11, wherein The MEMS phased array includes a plurality of strip phased arrays arranged in parallel to increase the active aperture of the system.

13. The optical scanner according to claim 11, wherein Each of the plurality of strips is divided by pillars along its length to form a plurality of strip-shaped MEMS phased arrays arranged in parallel to increase the active aperture of the system.

14. The optical scanner according to claim 10, wherein At least one of the illumination optics, the projection optics or the receiving optics comprises folded anamorphic optics.

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