LIDAR SYSTEM WITH Fly-EYE LENS ARRAY

Abstract

An optical system comprising: a sensor array having a field of view; an emitter array including a plurality of emitter units mounted on a surface of the common substrate and arranged in a two-dimensional array, in which each emitter unit of the plurality of emitter units is spaced apart from an adjacent emitter unit by a first pitch, and emits a light pulse having a predetermined beam divergence; and a fly-eye element spaced apart from the emitter array and configured to spread light received from each of the plurality of emitter cell elements into an entire field of view of the sensor array, the fly-eye element comprising a first lenslet array and a second lenslet array spaced apart from each other, wherein the individual lenslets in the first lenslet array and the second lenslet array are spaced apart from each other in at least one dimension by a second pitch different from the first pitch, and wherein each individual lenslet in the first lenslet array is aligned with a corresponding lenslet in the second lenslet array.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. non-provisional patent application No. 18 / 447,471, filed on August 10, 2023, and the benefit of U.S. Provisional Patent Application No. 63 / 373,033, filed on August 19, 2022, which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to light detection and ranging (lidar) systems. Background Art

[0004] Various light detection and ranging (LiDAR) systems measure the distance to a target by illuminating the target with a laser and measuring the reflected light with a sensor. Various techniques, including direct or indirect time-of-flight measurements and frequency modulated continuous wave (FMCW) measurements, can be used to make a digital 3D representation of a target. LiDAR systems can be used for a variety of applications where 3D depth images are useful, including archeology, geography, geology, forestry, mapping, construction, medical imaging, and military applications, among other applications. Autonomous vehicles can also use LiDAR for obstacle detection and avoidance and vehicle navigation.

[0005] Some lidar systems include mechanical, moving parts that physically scan the transmitting and receiving elements at a rotation angle of less than or equal to 360° to capture images of the scene in the field. An example of such a system that can be used for obstacle detection and avoidance in a vehicle is generally referred to as a rotating or rotating lidar system. In a rotating lidar system, the lidar sensor is usually mounted in a housing to a column that rotates or turns a full 360 degrees. The lidar sensor includes a coherent light emitter (e.g., a pulsed laser in the infrared or near-infrared spectrum) to illuminate the scene around the vehicle as the lidar sensor continuously rotates through the scene. As the coherent light emitters rotate, they emit pulses of electromagnetic radiation from the lidar system to different directions in the scene. Part of the radiation incident on the surrounding objects in the scene is reflected from these objects around the vehicle, and these reflections are then detected by the imaging system portion of the lidar sensor at different time intervals. The imaging system converts the detected light into an electrical signal.

[0006] In this way, information about objects surrounding the lidar system, including their distance and shape, is collected and processed. The lidar system's digital signal processing unit can process the electrical signals and reproduce information about the objects in a depth image or 3D point cloud, which can be used as an aid for obstacle detection and avoidance as well as vehicle navigation and other purposes. In addition, image processing and image stitching modules can acquire information and assemble a display of objects around the vehicle.

[0007] Another type of mechanical lidar system uses, for example, a MEMS mirror to steer a laser beam along a predetermined scan pattern. The laser in such a system may be a single laser directed into the field by a mirror according to a two-dimensional scan pattern, or may be an array of lasers directed into the field according to a one-dimensional or two-dimensional scan pattern.

[0008] Solid-state LiDAR systems also exist that do not include any moving mechanical parts. Rather than spinning around in the scene, some solid-state LiDAR systems illuminate the entire portion of the scene they want to capture with light and sense the reflected light. In some solid-state systems, the emitter includes one or more emitters that can emit light simultaneously to illuminate the entire scene, and each detector observes a discrete portion of that scene. Since there are no moving mechanical parts, solid-state LiDAR systems can be very reliable and rugged, and can also be less obtrusive in design than spinning LiDAR systems.

[0009] Some manufacturers are developing solid-state LiDAR systems that use vertical cavity surface emitting lasers (VCSELs) as the illumination source. VCSELs are generally lower power illumination sources than other types of lasers such as edge emitting lasers (EELs). However, VCSELs have advantages that EELs do not have. Generally, VCSELs are smaller, more durable, faster, and more cost-effective than EELs. In addition, due to the vertical emission characteristics of VCSELs, they can be packaged together so that many individual VCSELs are mounted on a single chip as part of a dense array.

[0010] In order to fully illuminate the desired field of view within a range suitable for some applications (such as autonomous driving), a relatively large number of VCSELs need to be activated simultaneously, which poses various design challenges in terms of power management, uniformity of illumination in the far field, and other issues. In addition, if solid-state LiDAR is to be widely used to achieve autonomous driving in automobiles and similar applications, the price of solid-state LiDAR devices needs to be competitive with other technologies. Summary of the invention

[0011] Some embodiments of the present disclosure relate to stationary solid-state LiDAR systems, where there are no rotating columns, no MEM scanning mirrors, and no other moving parts. The embodiments can illuminate the far field in a highly uniform manner, imaging the scene with high resolution and low power consumption, and high reliability. In addition, the embodiments can have a small form factor, so that the LiDAR system can be unobtrusively located on the vehicle and used for autonomous driving and other applications.

[0012] In some embodiments, an optical system is provided, which includes: a sensor array having a field of view; an emitter array, the emitter array including a plurality of emitter units mounted on a surface of a common substrate and arranged in a two-dimensional array, wherein each of the plurality of emitter units is spaced apart from its adjacent emitter unit by a first spacing and emits a light pulse having a predetermined beam divergence; and a fly's eye element, which is spaced apart from the emitter array and is configured to spread light received from each of the plurality of emitter units into the entire field of view of the sensor array, the fly's eye element including a first lenslet array and a second lenslet array spaced apart from each other, wherein individual lenslets in the first lenslet array and the second lenslet array are spaced apart from each other in at least one dimension by a second spacing different from the first spacing, and wherein each individual lenslet in the first lenslet array is aligned with a corresponding lenslet in the second lenslet array.

[0013] In another embodiment, the optical system includes: a sensor array having a field of view, the sensor array including a plurality of single photon avalanche diodes (SPADs); an emitter array including a plurality of emitter units mounted on a surface of a common substrate and arranged in a two-dimensional array, wherein each of the plurality of emitter units is spaced apart from its adjacent emitter unit by a first spacing and emits a light pulse having a predetermined beam divergence; a fly's eye element spaced apart from the emitter array, the fly's eye element being positioned to receive light from the emitter array and being configured to generate a flood illumination distribution that macroscopically matches the field of view of the sensor array, the fly's eye element including a first lens array and a second lenslet array spaced apart from each other, wherein individual lenslets in the first lenslet array and the second lenslet array are spaced apart from each other in at least one dimension by a second spacing different from the first spacing, and wherein each individual lenslet in the first lenslet array is aligned with a corresponding lenslet in the second lenslet array; and a timing generator and driver circuit operably coupled to control the emitter array to emit radiation pulses at a desired time and frequency. In some implementations, the optical system can be part of a solid-state lidar system that does not include any moving parts.

[0014] In other embodiments, a solid-state laser radar system is provided, which includes: a sensor array having a field of view; an emitter array, the emitter array including a plurality of emitter units mounted on a surface of a common substrate and arranged in a two-dimensional array, wherein each of the plurality of emitter units is spaced apart from its adjacent emitter unit by a first spacing and emits light having a predetermined beam divergence; and a fly's eye element, which is spaced apart from the emitter array, the fly's eye element being positioned to receive light from the emitter array and being configured to generate a flood illumination distribution that macroscopically matches the field of view of the sensor array, the fly's eye element including a first lens array and a second lenslet array spaced apart from each other, wherein individual lenslets in the first lenslet array and the second lenslet array are spaced apart from each other in at least one dimension by a second spacing different from the first spacing, and wherein each individual lenslet in the first lenslet array is aligned with a corresponding lenslet in the second lenslet array.

[0015] In various embodiments, the optical system and / or solid-state laser radar system may include one or more of the following features. The light cone generated by each transmitter unit in the transmitter array may have a lower divergence angle on the X-axis than the light beam generated by the fly's eye element. The individual lenslets in the first array and the second array may be spaced apart from each other by a second spacing along the X-axis, and may be spaced apart from each other by a third spacing along the Y-axis that is different from the first spacing and the second spacing. The system may further include a collimating lenslet array disposed between the transmitter array and the fly's eye element. Each lenslet in the collimating lenslet array is aligned with a corresponding transmitter unit in the transmitter array and is spaced apart from adjacent lenslets in a plurality of collimating lenslets by a first spacing. The fly's eye element may be a single monolithic optical component, wherein the single monolithic optical component has a first lenslet array formed on a first side of the optical component and a second lenslet array formed on a second side of the optical component opposite to the first side. The second spacing may be less than the first spacing. The system may further include a timing generator and a driver circuit that are operably coupled to control the transmitter array to emit radiation pulses at a desired time and frequency. The emitter array may include a plurality of individual VCSEL chips mounted on a common substrate. The driver circuit may be mounted on a common substrate near the VCSEL chip. And, the fly's eye element may be mounted to the common substrate. The first lenslet array and the second lenslet array in the fly's eye element may be spaced apart from each other by the focal length (f) of the lenslets. The sensor array may include a plurality of single photon avalanche diodes (SPADs). The fly's eye element may be designed to produce a flood illumination distribution that macroscopically matches the field of view of the sensor array. The sensor array may include a plurality of sensors arranged in a two-dimensional array. Each sensor in the sensor array may include a single photon avalanche diode (SPAD) array. Each sensor in the sensor array may be coupled to a memory circuit configured to accumulate histogram data of the sensor.

[0016] The nature and advantages of the embodiments in the disclosed embodiments may be better understood with reference to the following detailed description and accompanying drawings. However, it should be understood that each figure is provided for illustrative purposes only and is not intended to be a limitation of the scope of the invention. In addition, as a general rule, unless clearly contrary to the description, when the same reference numerals are used for elements in different drawings, these elements are generally the same or at least similar in function or purpose. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a simplified block diagram of a light detection and ranging (lidar) system according to some embodiments;

[0018] Figure 2 is a simplified block diagram of components of a time of flight measurement system or circuit according to some embodiments;

[0019] Figure 3 is a simplified cross-sectional diagram of an optical system according to some embodiments;

[0020] Figure 4A is a simplified diagram depicting light output from a single emitter unit into a fly's eye element according to some embodiments;

[0021] Figure 4B is a simplified top plan view of an array of emitters according to some embodiments, the array of emitters being Figure 4A A portion of the optical system depicted in;

[0022] Figure 5A is a simplified diagram depicting light intensity levels received at a fly's eye element according to some embodiments;

[0023] Figure 5B is to describe when receiving Figure 5A The light beam depicted in is a simplified diagram of the light intensity level of a target light beam output from a fly's eye element according to some embodiments;

[0024] Figure 6 is a simplified cross-sectional diagram of an optical system according to some embodiments;

[0025] Figure 7 is a simplified cross-sectional diagram of an optical system according to some embodiments; and

[0026] Figure 8 is a simplified diagram of a car according to some embodiments, in which four solid-state lidar sensors are included at different locations along the car. DETAILED DESCRIPTION

[0027] Embodiments of the present disclosure are described herein with reference to solid-state LiDAR applications and systems. A solid-state LiDAR system may include an array of emitter elements and an array of sensors. As described herein, one or more emitter elements may define an emitter unit, and one or more photodetectors may define a sensor. Some embodiments of the solid-state LiDAR systems described herein may acquire images by emitting short duration (pulses) of light from an array or a subset of the array of emitter units over the entire field of view of the system. In contrast, a scanning LiDAR system generates image frames by raster scanning light emissions (continuously) over a field of view or scene, for example, using a point scan or line scan to emit the illumination power required for each point, and scanning sequentially to reconstruct the entire field of view.

[0028] Example LiDAR System

[0029] Figure 1An exemplary light-based 3D sensor system 100, such as a light detection and ranging (lidar) system, according to some embodiments of the present disclosure is illustrated. The lidar system 100 may include a control circuit 110, a timing circuit 120, a driver circuit 125, an emitter array 130, and a sensor array 140. The emitter array 130 may include a plurality of emitter units 132 arranged in an array (e.g., a one-dimensional or two-dimensional array), and the sensor array 140 may include a plurality of sensors 142 arranged in a two-dimensional array. The sensors 142 may be depth sensors, such as time-of-flight (ToF) sensors. In some embodiments, each sensor 142 may be, for example, an array of single photon detectors, such as a single photon avalanche diode (SPAD). In some embodiments, each sensor 142 may be coupled to an in-pixel storage block (not shown) that accumulates histogram data for the sensor 142, and the combination of the sensor and the in-pixel memory circuit is sometimes referred to as a "pixel" 142. Each emitter unit 132 of the emitter array 130 may include one or more emitter elements and emits radiation pulses (e.g., light pulses) or continuous wave signals at a time and frequency controlled by the timing generator or driver circuit 125. In some embodiments, the emitter unit 132 may be a pulsed light source such as an LED or a laser such as a vertical cavity surface emitting laser (VCSEL) that emits a light cone (e.g., infrared light) having a predetermined beam divergence.

[0030] The emitter array 130 may project a pulse of radiation into a field in front of the lidar system 100. Some of the emitted radiation may then be reflected back from an object in the field of view, such as a target 150. The reflected radiation may then be sensed or detected by a sensor 142 within the sensor array 140. The control circuit 110 may implement a pixel processor that measures and / or calculates the distance to the target 150. In some embodiments, the control circuit 110 may measure and / or calculate the flight time of the radiation pulse in the trip from the emitter array 130 to the target 150 and back to the detector 142 within the sensor array 140 using direct or indirect time of flight (ToF) measurement techniques. In other embodiments, the control circuit 110 may measure and / or calculate the distance to the target 150 by detecting the frequency of a continuous beam emitted from the emitter array 130 and reflected back from the target 150 using a frequency modulated continuous wave (FMCW).

[0031] As described in more detail below, in some embodiments, the emitter array 130 may include an array (e.g., a one-dimensional or two-dimensional array) of emitter units 132, wherein each emitter unit is a unique semiconductor chip having a plurality of independent VCSELs (sometimes referred to herein as emitter elements) formed on the chip. A fly's eye element 136 may be disposed in the optical path of the emitter unit such that light projected by the emitter unit passes through the fly's eye element 136 before exiting the lidar system 100. In some embodiments, an additional optional optical element 134 (e.g., a microlens array that collimates or reduces the divergence angle of light received at the optical element 134 and passes the altered light to the fly's eye element 136) may be included in the optical path of the system 100 between the emitter array 130 and the fly's eye element 136. For convenience, the optical element 134 is sometimes referred to herein as a "collimating lens array 134" or a "collimating lenslet array 134").

[0032] The fly's eye element 136 can be designed to spread the light received at the fly's eye element over an area in the far field that can be referred to as the field of view of the emitter array (or the illumination field of the emitter array). Typically, the emitter array 130, the collimating lens array 134 (if included), and the fly's eye element 136 cooperate to spread the light from the emitter array 130 over the entire field of view of the emitter array. Further details of example implementations of the emitter array 130, the collimating lens array 134, and the fly's eye element 136 are discussed below.

[0033] The driver circuit 125 may include one or more driver circuits, each driver circuit controlling one or more emitter units. The driver circuit may be operated in response to a timing control signal referenced to a master clock and / or a power control signal that controls the peak power and / or repetition rate of the optical output of the emitter unit 132. In some embodiments, each of the emitter units 132 in the emitter array 130 is connected to and controlled by a separate circuit in the driver circuit 125. In other embodiments, a group of emitter units 132 in the emitter array 130 (e.g., emitter units 132 that are spatially close to each other or in a common column of the emitter array) may be connected to the same circuit within the driver circuit 125. The driver circuit 125 may include one or more driver transistors configured to control the modulation frequency, timing, and amplitude of the optical emission signal output from the emitter unit 132.

[0034] In some embodiments, a single event of emitting light from multiple emitter units 132 can illuminate an entire image frame (or field of view); this is sometimes referred to as a "flash" lidar system. Other embodiments may include non-flash or scanning lidar systems in which different emitter units 132 emit pulses of light, for example, into different portions of the field of view at different times. The maximum optical power output of the emitter units 132 can be selected to produce a signal-to-noise ratio for the echo signal from the farthest, least reflecting target under the brightest background illumination conditions that can be detected in accordance with the embodiments described herein. In some embodiments, an optional filter (not shown) (such as a bandpass filter) can be included in the optical path of the emitter units 132 to control the emission wavelength of the light.

[0035] Light output from the transmitter unit 132 may impinge on the lidar system 100 and be reflected back to the lidar system by one or more targets 150 in the field of view. The reflected light may be detected by one or more of the sensors 142 (e.g., after being collected by the receiver optics 146) as an optical signal (also referred to herein as a return signal, echo signal, or echo), converted into an electrical signal representation (sometimes referred to herein as a detection signal), and processed (e.g., based on time-of-flight techniques or FMCW techniques) to define a 3-D point cloud representation 160 of the field of view 148 of the sensor array 140. The operation of the lidar system according to embodiments of the present disclosure as described herein may be performed by one or more processors or controllers (such as the control circuit 110).

[0036] The sensor array 140 includes a sensor array 142 (sometimes referred to as pixels). In some embodiments, each sensor or pixel may include one or more photodetectors, such as SPADs. And in some specific embodiments, the sensor array is a very large array consisting of hundreds of thousands or even millions of densely packed SPADs. Receiver optics 146 and receiver electronics (including timing circuits 120) can be coupled to the sensor array 140 to power, enable and disable all or part of the sensor array 140 and provide timing signals thereto. In some embodiments, the sensors can be activated or deactivated with at least nanosecond accuracy (e.g., time periods, bins, or intervals of 1ns, 2ns, etc.), and in various embodiments, can be individually addressable, group addressable, and / or globally addressable. The receiver optics 146 may include a body optical lens configured to collect the maximum field of view that can be imaged by the laser radar system 100, which in some embodiments is determined by the aspect ratio of the two-dimensional sensor array in combination with the focal length of the receiver optics 146.

[0037] In some embodiments, the receiver optics 146 may further include a lens (not shown) for improving the collection efficiency of the detection pixels and / or an anti-reflective coating (also not shown) for reducing or preventing the detection of stray light. In some embodiments, a spectral filter 144 may be positioned in front of the sensor array 140 to pass or allow "signal" light (i.e., light having a wavelength corresponding to the wavelength of the optical signal output from the transmitter unit) to pass, but substantially reject or prevent non-signal light (i.e., light having a wavelength different from the wavelength of the optical signal output from the transmitter unit) from passing. The spectral filter may be, for example, a bandpass filter that passes a very narrow band of wavelengths (e.g., electromagnetic radiation) centered at the operating wavelength of the transmitter array.

[0038] The sensors 142 of the sensor array 140 are connected to the timing circuit 120. The timing circuit 120 can be phase locked to the driver circuit 125 of the emitter array 130. The sensitivity of each sensor or sensor group in the sensor 142 can be controlled. For example, when the detector element includes a reverse biased photodiode, an avalanche photodiode (APD), a PIN diode, and / or a Geiger-mode avalanche diode (i.e., SPAD), the reverse bias can be adjusted. In some embodiments, a higher over-bias voltage provides a higher sensitivity.

[0039] In some embodiments, the control circuit 110, which may be, for example, a microcontroller or microprocessor, provides different transmitter control signals to the driver circuits 125 of different transmitter units 132 and / or provides different signals (e.g., strobe signals) to the timing circuits 120 of different sensors 142 to enable / disable different sensors 142 to detect the return signal from the target 150. The control circuit 110 may also control a memory storage operation for storing data indicated by the detection signal in a non-transitory memory or memory array included therein or different therefrom.

[0040] Figure 2 Components of a ToF measurement system or circuit 200 in a lidar application according to some embodiments described herein are also illustrated. Circuit 200 may include a processor circuit 210 (such as a digital signal processor (DSP)), a timing generator 220 that controls the timing of an illumination source (illustrated by way of example with reference to laser emitter array 230) and a sensor array (illustrated by way of example with reference to sensor array 240). Processor circuit 210 may also include a sequencer circuit ( Figure 2 not shown).

[0041] Processor circuit 210 and timing generator 220 can implement Figure 1 Some of the operations of the control circuit 110 and the driver circuit 125. Similarly, the transmitter array 230 and the sensor array 240 may represent Figure 1 2 and 3. The emitter array 130 and sensor array 140 in FIG. 2 are shown in FIG. 2. The laser emitter array 230 may emit laser pulses 235 at times controlled by the timing generator 220. Light 245 from the laser pulses 235 may be reflected back from a target (illustrated by way of example as object 250) and may be sensed by the sensor array 240. The processor circuit 210 implements a pixel processor that may measure or calculate the flight time of each laser pulse 235 and its reflected signal 245 in the journey from the emitter array 230 to the object 250 and back to the sensor array 240.

[0042] The processor circuit 210 may provide analog and / or digital implementations of logic circuits that provide the necessary timing signals (such as quenching and gating or gating signals) to control the operation of the single photon detectors of the array 240 and process the detection signals output therefrom. For example, the individual single photon detectors of the sensor array 240 may be operated so that they generate detection signals in response to incident photons during a gating interval or gating window defined only by the gating signal. Photons incident outside the gating window have no effect on the output of the single photon detectors. More generally, the processor circuit 210 may include one or more circuits configured to generate detector control signals that control the timing and / or duration of activation of the sensor pixels 142 (or specific single photon detectors therein) and / or generate corresponding emitter control signals that control the output of light signals from the emitter unit 132.

[0043] The processor circuit 210 can identify a detection event based on one or more photon counts indicated by a detection signal output from the sensor array 240, which can be stored in the non-transitory memory 215. In some embodiments, the processor circuit 210 may include a correlation circuit or correlator that identifies a detection event based on photon counts from two or more detectors (referred to herein as correlated photon counts) within a predefined time window relative to each other, wherein the detection signal indicates the arrival time of the incident photon within the correlation window. Since photons corresponding to the light signal output from the emitter array 230 (also referred to as signal photons) can arrive relatively close in time compared to photons corresponding to ambient light (also referred to as background photons), the correlator is configured to distinguish signal photons based on respective arrival times relative to each other within the correlation time. For example, such a correlator and gating window are described in U.S. Patent Publication No. 2019 / 0250257, entitled “Methods and Systems for High-Resolution Long Range Flash Lidar,” the entire contents of which are incorporated herein by reference for all purposes.

[0044] The processor circuit 210 may be small enough to allow for a three-dimensional stacked implementation, such as where the sensor array 240 is "stacked" on top of the processor circuit 210 (and other related circuitry) that is sized to fit within the area or footprint of the sensor array 240. For example, some embodiments may implement the sensor array 240 on a first substrate and the transistor array of the circuit 210 on a second substrate, where the first and second substrates / wafers are joined in a stacked arrangement, as described, for example, in U.S. Patent Application No. 16 / 668,271, entitled "High Quantum Efficiency Geiger-Mode Avalanche Diodes Including High Sensitivity Photon Mixing Structures and Arrays," filed on October 30, 2019, the disclosure of which is incorporated herein by reference for all purposes.

[0045] The pixel processor implemented by the processor circuit 210 can be configured to calculate an average ToF accumulated over hundreds or thousands of laser pulses 235 and an estimate of the return of photons in the reflected light 245. The processor circuit 210 can be configured to count incident photons in the reflected light 245 to identify a detection event within a laser cycle (or a portion thereof) (e.g., based on one or more SPADs within the sensor array 240 having been "triggered").

[0046] The timing and duration of the detection window can be controlled by the strobe signal (strobe #i or strobe ) is controlled by the ToF measurement system 200. Many repetitions of strobe #i can be grouped (e.g., in pixels) to define subframes of strobe #i, where subframes i=1 to n define an image frame. Each subframe of strobe #i can correspond to a corresponding distance subrange of the entire imaging distance range. In a single-strobe system, the subframe of strobe #i can correspond to the entire imaging distance range and is identical to the image frame because there is a single strobe pulse. The time between emitter unit pulses (which defines the laser cycle, or more generally, the emitter pulse frequency) can be selected to define or otherwise correspond to the desired overall imaging distance range of the ToF measurement system 200. Therefore, some embodiments described herein can utilize range gating to activate and deactivate the sensor with a variable delay relative to the emission of the laser for a duration within the laser cycle or "detection window" time, thereby capturing reflected relevant signal photons corresponding to a specific distance subrange at each window / frame, for example to limit the number of ambient photons collected in each laser cycle.

[0047] Strobe can turn off and on individual photodetectors or groups of photodetectors (e.g., for pixels), for example to save energy during time intervals outside the detection window. For example, a SPAD or other photodetector can be turned off during idle time, such as before the next laser cycle after an integrated burst of time bins. As another example, the SPAD can also be turned off while all or part of a histogram is being read out from the non-transitory memory 215. Yet another example is when the counter for a particular time bin reaches the maximum value of the allocated bits in the histogram stored in the non-transitory memory 215 (also referred to as "bin saturation"). The control circuit can provide a strobe signal to activate a first subset of sensors while inactivating a second subset of sensors. Additionally or alternatively, circuits associated with the sensors can also be turned off and on at specified times.

[0048] The sensors can be arranged in a variety of ways for detecting reflected pulses. For example, the sensors can be arranged in an array, and each sensor can include an array of photodetectors (e.g., SPADs). The signal from the photodetector indicates when a photon is detected and how many photons may be detected. For example, a SPAD can be a semiconductor photodiode operated with a reverse bias voltage that generates an electric field of sufficient amplitude so that a single charge carrier introduced into the device depletion layer can cause a self-sustaining avalanche via impact ionization. The induced charge carrier can be photoelectrically generated by a single incident photon that hits a high field region. The avalanche is actively (e.g., by reducing the bias voltage) or passively (e.g., by using a voltage drop across a series-connected resistor) quenched by a quenching circuit to allow the device to be "reset" to detect other photons. This single-photon detection operating mode is often referred to as a "Geiger mode," and the avalanche can generate a current pulse that causes the photons to be counted. Other photodetectors can generate analog signals (in real time) that are proportional to the number of photons detected. Signals from independent photodetectors can be combined to provide a signal from a sensor, which can be a digital signal. This signal can be used to generate a histogram.

[0049] Transmitter Module

[0050] Return to reference Figure 1 In some embodiments, the circuits and emitter units that combine to generate and project light pulses into a field can be manufactured together as part of a single component, referred to herein as an emitter module. For example, in some embodiments, the emitter array 130 can be formed from a plurality of individual VCSEL chips mounted on a common substrate. The driver circuit 125 can be formed on the common substrate near the VCSEL chips to improve the electrical characteristics of the system, and the optical element 134 (if included) and the fly's eye element 136 can be mounted to the common substrate as part of the emitter module.

[0051] In a solid-state system lidar system, in which there are no moving parts (e.g., no motors to rotate the lidar system, and no MEMs mirrors or similar devices to scan a relatively small laser array across the system's field of view), the emitter array 130 needs to project a sufficient amount of optical power to illuminate the entire field of view of the lidar system at the distance for which the lidar system is designed. While in some embodiments, the emitter array 130 can be formed from a single semiconductor chip densely packed with thousands of VCSELs that illuminate the desired field of view, it can be challenging to manage thermal issues associated with such a chip and to integrate the necessary electronics to efficiently drive the emitter units, all of which can increase the cost of developing a solid-state lidar system around a single large array VCSEL chip.

[0052] Rather than using a single large array (VCSEL) chip as the emitter array 130, some embodiments take advantage of the relatively low price of commercially available high power VCSEL chips and mount multiple such VCSEL chips on a common circuit board. To illustrate, consider an embodiment in which approximately 10,000 watts of transmitter power is required to fully and adequately illuminate the desired field of view within the expected range limits of the lidar system. In such an embodiment, if the emitter array 130 includes multiple VCSEL chips that output 300 watts of peak power per chip, at least 33 individual VCSEL chips are required to illuminate the field of view. Further details of embodiments of emitter arrays including multiple individual VCSEL chips are described below.

[0053] As described above, in some embodiments, the emitter array 130 and the fly's eye element 136 (and the optical element 134, if included) can cooperate to evenly spread the light from the emitter array 130 throughout the illumination field of the emitter array. Each emitter unit 132 emits a light cone having a specific divergence angle. For example, as a non-limiting example, in various embodiments, the emitter unit can emit a light cone having a divergence angle between 15 and 25 degrees FWHM (full width at half maximum). In some specific implementations, each emitter unit can emit a light cone having a divergence angle of approximately 17 degrees. The fly's eye element 136 can be designed to spread the received light to a desired angle in the far field while generating a substantially uniform far-field light pattern as described below. Therefore, the fly's eye element 136 makes the far-field cone angle independent of the cone angle of the independent emitter unit.

[0054] In some embodiments, the fly's eye element 136 is designed to produce a flood illumination distribution that macroscopically matches the field of view of the sensor array 140. For example, the fly's eye element 136 can be designed to spread the received light within the illumination field of the emitter array (sometimes referred to herein as the field of view of the emitter array) so that the entire field of view of the sensor array 140 is substantially equally illuminated (given the constraints of the optical system). Accurately matching the fields of view of the emitter array and the sensor array minimizes the waste of laser light, thereby ensuring that most (if not all) of the light projected into the field of view from the emitter array 130 contributes to the range and accuracy of the lidar system 100. Matching the fields of view of the emitter array and the sensor array can also prevent or minimize the possibility of light striking objects outside the field of view of the sensor array (e.g., highly reflective stop signs), which may otherwise reflect light back to the sensor array, thereby contaminating or corrupting the data collected by the sensor array.

[0055] 1. Fly Eye Components

[0056] Reference now Figure 3 , Figure 3 3 is a simplified schematic diagram of an optical system 300 including an emitter array 310 and a fly's eye optical element 320. The emitter array 310 may represent the emitter arrays 130 and 230 described above, and the fly's eye element 320 may represent the fly's eye element 136 described above. As shown, the emitter array 310 may include a plurality of emitter units 312 arranged in an array. Figure 3 Only a single dimension (e.g., the Y axis) is shown in FIG. 3 , but in a typical embodiment, the emitter units 312 are arranged in a two-dimensional array. The fly's eye element 320 includes two identical lenslet arrays 322, 324, which are spaced apart from the emitter array 310 and are spaced apart from each other by the focal length (f) of the lenslets in the two lens arrays 322, 324.

[0057] Each emitter unit 312 can output a light cone 330 (e.g., infrared light pulses) having a predetermined divergence angle. The light cone 330 is received by the fly's eye element 320 and shaped into a target light beam 340 output from the optical system 300. In some embodiments, the first lens array 322 receives the light cone 330 and focuses the received light cone onto the second lens array 324 (for ease of illustration, Figure 3 Only the light focused by two individual lenslets in the array 322 is depicted in FIG. 3 ). The second lens array 324 images the shape of the lenslets into the far field as a target beam 340. In this way, the fly's eye element 320 can generate a highly uniform (uniform from edge to edge) target beam with a far field cone angle that is independent of the cone angle of each individual emitter unit 312. The spacing and focal length of the fly's eye element 320 can be selected to give the target beam 340 the desired beam requirements.

[0058] Importantly, in some embodiments, the two lens arrays 322, 324 each have the same pitch, which is different from the pitch of the emitter array 310. For example, in one embodiment, the emitter units 312 are spaced apart from each other along the X-axis and the Y-axis at a pitch of 3.6 mm, while the individual lenses in each of the lens arrays 322, 324 are spaced apart from each other along the X-axis at a pitch of 1.2 mm, and along the Y-axis at a pitch of 2.3 mm. Having different pitches between the emitter array 310 and each of the fly's eye lens arrays 322, 324 results in the emitter array having a number of emitter units 312 that is different from the number of lenses in each of the lens arrays 322, 324. For example, in one embodiment, each of the fly's eye lens arrays 322, 324 has over 100 lenslets, while the emitter array 310 includes an array of 6×8 emitter units 312 (for a total of forty-eight (48) emitter units). Having different numbers of optical elements and different spacing between the emitter units and lenslets in the fly's eye array means that each individual emitter unit 312 is not aligned with a specific corresponding lenslet in the fly's eye lens array 322, 324. This design eliminates the necessity of optics to collimate the light beams output from the emitter units 312, which requires that such optics be precisely aligned one-to-one with the emitter units of the emitter array 310. The design also eliminates any need to closely align or precisely register the fly's eye element 320 to the emitter array 310 in the way that some optical systems require that the micro-optical lens array be precisely aligned with the emitter array, so that each emitter element projects its light into a specific corresponding lenslet in the micro-optical array.

[0059] The fly's eye element 320 may be designed with considerations of efficiency, uniformity, and eye safety. In some embodiments, efficiency is maximized by employing emitter units 312 that generate light cones 330 whose divergence angles on both the X-axis and the Y-axis are lower than the divergence angle of the target beam 340 generated by the fly's eye element 320. Selecting emitter units 312 and fly's eye elements 320 with such characteristics ensures that all light generated by the emitter array 310 is projected into the far field through the fly's eye element 320. On the other hand, if emitter units 312 that generate light cones 330 whose divergence angles on one or both of the X-axis and the Y-axis are higher than the divergence angle of the target beam 340 are employed in the optical system 300, some of the light projected by the emitter array 310 will be lost in the far field. In some embodiments, the divergence angle of the light cone 330 may be slightly greater than the divergence angle of the target beam 340 on one of the X-axis or the Y-axis in order to provide a certain amount of tolerance during the manufacturing process of the optical system 300.

[0060] Uniformity can be designed in part by including at least a certain number of lenslets in each of the fly-eye arrays 322, 324. Since each sub-portion of the fly-eye element 320 projects to the entire far-field image, some embodiments include at least 100 lenslets to generate a far-field image with uniformity for some applications. There is a small amount of light loss at the interface between each adjacent lenslet. Therefore, some embodiments select the number of lenslets in each of the fly-eye arrays 322, 324 by balancing the increased uniformity achieved with more lenslets with the light loss level that may be experienced if too many lenslets are included in each of the arrays 322, 324.

[0061] Eye safety can be designed based on the power and wavelength of the light output by the emitter unit 312. The inventors have found that, in some embodiments, reducing the size of the lenslets in the fly's eye element 320 and setting the distance between the emitter array 310 and the fly's eye element 320 to at least a minimum distance (e.g., about 20 mm in some embodiments) can improve eye safety and uniformity.

[0062] As a specific example, see Figure 4A and Figure 4B ,in Figure 4A is a simplified diagram depicting a portion of an optical system 400 designed according to embodiments disclosed herein, and Figure 4B 4 is a simplified top plan view of an emitter array 410 as part of an optical system 400. The optical system 400, which may be an implementation of the optical system 300, includes an emitter array 410 having forty-eight (48) individual emitter units 412 that project infrared light (e.g., 940 nm wavelength) into a fly's eye element 420 that is a distance d from the emitter units, which in the particular implementation shown is twenty (20) mm. For convenience and ease of illustration, the optical system 400 includes an emitter array 410 having forty-eight (48) individual emitter units 412 that project infrared light (e.g., 940 nm wavelength) into a fly's eye element 420 that is a distance d from the emitter units. In the particular implementation shown, the distance is twenty (20) mm. Figure 4A Only a single transmitter unit 412 is shown.

[0063] As shown, the fly's eye element 420 includes two lenslet arrays 422, 424 that are registered and aligned with each other. Each of the lenslet arrays 422, 424 includes four hundred and five (405) lenslets arranged in a 27×15 array. The focal length of the lenslets is 4.44 mm, and the lenslets are spaced at a pitch of 1.2 mm along the X axis and at a pitch of 2.3 mm along the Y axis. The emitter units 412 are spaced at a pitch of 3.6 mm from each other, and each emitter unit is a single VCSEL chip that includes a hexagonal arrangement of 472 VCELs with a pitch of 0.047 mm. The light cone 430 generated by each emitter unit has a divergence angle of 17 degrees, and the fly's eye element reshapes the light cone it receives into a target beam 440 (only a portion generated by a single emitter 412 is shown in FIG. 4), which has a far field angle of 30 degrees on the X axis and a far field angle of 15 degrees on the Y axis.

[0064] Each light cone 430 generated by the emitter unit 412 is spread over a plurality of individual lenslets in the lenslet array 422 and is then focused by the lenslet array 422 such that the emitter unit is imaged at an image plane 450 slightly spaced behind the lenslet array 424. Figure 4A and Figure 4B In the illustrated implementation, imaging the emitter units 412 onto an image plane slightly past the lenslet array 424 slightly reduces the light from each emitter unit to ensure that the target beam 440 is eye-safe at the individual emitter unit level as well as for the entire emitter unit collection.

[0065] Figure 5A is a graph depicting the light intensity levels received at the fly's eye element when each of the forty-eight (48) emitter units 412 in the emitter array of the optical system 400 is flashed simultaneously at an average power of 62 mW, and Figure 5B is a graph depicting the light intensity level of the target light beam output from the fly's eye element. Figure 5A It can be clearly seen that the light spot distribution of the emitter array has some overlap in the center part of the light pattern. The overlap helps with uniformity and allows for lower power used in the secondary source. Figure 4B As shown, the fly's eye element generates a highly uniform target beam in the far field. The target beam is oversized in the X-axis and slightly undersized in the Y-axis.

[0066] 2. Single-chip fly eye component

[0067] In some embodiments, the fly's eye element can be fabricated as a single optical element that includes a first lenslet array on one side of the optical element and a second lenslet array on the opposite side. Figure 6 , Figure 6 6 is a simplified cross-sectional illustration of an optical system 600 according to some embodiments. The optical system 600 includes an emitter array 310 and a fly-eye optical element 620. The emitter array 310 can be similar to the above description of Figure 3 The emitter array 310 discussed above is similar or identical to, and thus may represent, the emitter array 130 or 230, and the fly's eye element 620 may represent Figure 1 The fly's eye element 136 discussed.

[0068] The fly's eye element 620 can accept the same light cone as the fly's eye element 320 as an input and generate substantially the same target light beam. However, instead of having two separate lenslet arrays 322, 324 spaced apart from each other, the fly's eye element 620 can be a single optical component having lenslet arrays 622, 624 located on opposite faces of an integral block of optically transparent material. The lenslets in the array 622 can focus the light cone received from the transmitter unit 312 onto the lenslets 624, which can in turn generate a target light beam 640 having desired characteristics in the far field. In some embodiments, the lenslet array 622 can be optically equivalent to the lenslet array 322, and the lenslet array 624 can be optically equivalent to the lenslet array 324. Similar to the other figures in the present application, for ease of illustration, Figure 6 Only the portion of the light cone 330 that is focused by two individual lenslets in the lenslet array 622 onto the lenslet array 624 is illustrated.

[0069] The two lenslet arrays 622, 624 can be spaced apart from each other by the focal length of the lenses in the arrays. However, rather than having an empty space between the two arrays, the fly's eye element 620 can include an optical material 626 between the lenslet arrays 622, 624 that is the same as the lenses are made of. In various embodiments, the optical material 626 can be glass or plastic that is optically transparent to the wavelength of light emitted from the emitter array 310.

[0070] Manufacturing the fly's eye element as a single monolithic optical component can provide efficiency and manufacturing benefits. For example, during the manufacturing process, the lenslet 622 can be registered and aligned with the lenslet 624. Therefore, no additional alignment steps are required. In addition, the single optical component 620 can be cheaper than two separate optical components 322, 324.

[0071] 3. Collimating lens

[0072] To improve efficiency in embodiments where the far field angle is less than the divergence angle of the individual emitters, some embodiments disclosed herein may include a collimating lens array. Figure 7 7 is a simplified cross-sectional view of an optical system 700 according to some embodiments. The optical system 700 includes an emitter array 310 and a fly-eye optical element 720. The emitter array 310 can be similar to the above description of Figure 3 The emitter array 310 discussed above is similar or identical to, and thus may represent, the emitter array 130 or 230, and the fly's eye element 720 may represent Figure 1 The optical system 700 may also include an optical element 750 that can receive the light cone 330 from the emitter array 310 and collimate or reduce the divergence of the received light in at least one dimension (i.e., a dimension having a field of view that is smaller than the field of view of the individual emitter units) before passing the light (beam 735) to the fly's eye element 720. In some embodiments, the optical element 750 may be a collimating lenslet array and may represent the above description of Figure 1 Optical element 134 discussed.

[0073] As a non-limiting example, in one particular embodiment, each emitter unit may be a VCSEL chip having 300-600 individual densely packed VCSELs formed on the chip that together emit a cone of light away from the VCSEL chip having a divergence angle of approximately 17 degrees in the X and Y axes. If a lidar system (e.g., lidar system 100) is designed to have a field of view of 15 degrees along the X axis and 30 degrees along the Y axis, optical element 750 may reduce the divergence angle of the emitted light cone from each emitter unit in the X axis to approximately 15 degrees to improve the efficiency of the lidar system.

[0074] Sensor array

[0075] The sensor array (e.g., sensor array 140) employed in some embodiments may include a large, densely packed SPAD array. The individual SPADs in the SPAD can be coupled to provide an arrangement of a large sensor array, wherein each sensor includes multiple SPADs. The field of view and resolution of the sensor array may depend on several related factors, such as, but not limited to, the focal length of the lens paired with the sensor array, the size of the sensor array, the spacing of the sensors, and the spacing of the SPADs within each individual sensor. Typically, the field of view of the sensor array will match the illumination field of the emitter array. Larger sensor arrays can result in a larger field of view, where the size of the sensor spacing is constant. In addition, where the size of the sensor array is constant, a smaller sensor spacing can produce a higher resolution image, but may result in a smaller field of view for each sensor.

[0076] Multiple LiDAR units

[0077] Depending on their intended purpose or application, lidar sensors can be designed to meet different fields of view and different range requirements. For example, a car (e.g., a passenger car) equipped with lidar for autonomous driving can be equipped with multiple individual lidar sensors, including a long-range lidar sensor facing forward, a short-range lidar sensor facing rearward, and one or more short-range lidar sensors along each side of the car. Figure 8 is a simplified diagram of a car 800 in which four solid-state lidar sensors 810a-d are included at different locations along the car. The number of lidar sensors, the placement of the lidar sensors, and the field of view of each individual lidar sensor can be selected to obtain most, if not all, of a 360-degree field of view of the vehicle's surroundings, portions of which can be optimized for different ranges. For example, in Figure 8 The lidar sensor 810a shown positioned along the front bumper of the car 800 may be a long-range (200-meter) narrow field-of-view unit, while the lidar sensor 810b positioned along the rear bumper and the lidar systems 810c, 810d positioned at the side-view mirrors are short-range (50-meter) wide field-of-view systems.

[0078] Although designed for different ranges and different fields of view, each of the laser radar sensors 810a-810d can be a laser radar system according to the embodiments disclosed herein. In fact, in some embodiments, the only difference between each of each of the laser radar sensors 810a-810d is the nature of the fly eye element (e.g., fly eye element 136). For example, in the long-range narrow field of view laser radar sensor 810a, the fly eye element 136 can be designed to focus the light emitted by the emitter array of the laser radar system on a relatively narrow range, so that the sensor can operate over a long range. In the short-range, wide field of view laser radar sensor 810b, the fly eye element 136 can be designed to spread the light emitted by the emitter array over a wide angle (e.g., 180 degrees). In each of the laser radar sensors 810a and 810b, the same emitter array, the same sensor array, the same controller, etc. can be used, thereby simplifying the manufacture of multiple different laser radar sensors customized for different purposes.

[0079] Additional Implementation

[0080] In the above detailed description, many specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the present disclosure may be practiced without these specific details. For example, although the various embodiments set forth above describe the emission of laser pulses, the embodiments described herein may be used with a laser radar device that uses continuous wave technology, such as frequency modulated continuous wave (FMCW) technology, to measure distance. As another example, although various embodiments of the optical system are described above with respect to a solid-state laser radar system, in other embodiments, the described optical system may be incorporated into a rotating laser radar system. It should be understood that these embodiments are for illustrative purposes only, and the embodiments are not limited to any particular number of columns or rows of transmitter units.

[0081] In addition, in some instances, well-known methods, procedures, components and circuits are not described in detail to avoid confusing the present disclosure. All embodiments disclosed herein are intended to be implemented individually or combined in any manner and / or combination. Aspects described with respect to an embodiment may be incorporated into different embodiments, although not specifically described with respect to them. That is, all embodiments and / or the features of any embodiment may be combined in any manner and / or combination.

[0082] Although the disclosure has been described with respect to specific embodiments, it should be understood that the disclosure is intended to cover all modifications and equivalents within the scope of the following claims.

Claims

1. An optical system, comprising: A sensor array having a field of view; an emitter array comprising a plurality of emitter units mounted on a surface of a common substrate and arranged in a two-dimensional array, wherein each of the plurality of emitter units is spaced apart from its adjacent emitter unit by a first spacing and emits light pulses having a predetermined beam divergence; and A fly's eye element, which is spaced apart from the emitter array and is configured to spread light received from each of the plurality of emitter units into the entire field of view of the sensor array, the fly's eye element comprising a first lenslet array and a second lenslet array spaced apart from each other, wherein individual lenslets in the first lenslet array and the second lenslet array are spaced apart from each other in at least one dimension by a second spacing different from the first spacing, and wherein each individual lenslet in the first lenslet array is aligned with a corresponding lenslet in the second lenslet array.

2. The optical system according to claim 1, wherein: The light cone generated by each emitter unit in the emitter array has a lower divergence angle in the X-axis than the light beam generated by the fly's eye element.

3. The optical system according to claim 1, wherein: The individual lenslets in the first array and the second array are spaced apart from each other by the second pitch along the X-axis and spaced apart from each other by a third pitch different from the first pitch and the second pitch along the Y-axis.

4. The optical system according to claim 1 further comprises a collimating lenslet array arranged between the emitter array and the fly's eye element, wherein each lenslet in the collimating lenslet array is aligned with a corresponding emitter unit in the emitter array and is spaced apart from an adjacent lenslet in the collimating lenslet array by the first spacing.

5. The optical system according to claim 1, wherein: The fly's eye element is a single monolithic optical component having the first lenslet array formed on a first side of the optical component and the second lenslet array formed on a second side of the optical component opposite the first side.

6. The optical system according to claim 1, wherein: The optical system is part of a solid-state LiDAR system that does not include any moving parts.

7. The optical system of claim 6, further comprising a timing generator and driver circuit operably coupled to control the emitter array to emit radiation pulses at a desired time and frequency.

8. The optical system according to claim 7, wherein: The emitter array comprises a plurality of individual VCSEL chips mounted on a common substrate, the driver circuit is mounted on the common substrate in close proximity to the VCSEL chips, and the fly's eye element is mounted to the common substrate.

9. The optical system according to claim 1, wherein: The first lenslet array and the second lenslet array in the fly's eye element are spaced apart from each other by a focal length (f) of the lenslets.

10. The optical system according to claim 1, wherein: The sensor array includes a plurality of single photon avalanche diodes (SPADs).

11. The optical system according to claim 10, wherein: The fly's eye element is designed to produce a flood illumination distribution that macroscopically matches the field of view of the sensor array.

12. The optical system according to claim 1, wherein: The sensor array includes a plurality of sensors arranged in a two-dimensional array.

13. The optical system according to claim 12, wherein: Each sensor includes an array of single photon avalanche diodes (SPADs).

14. The optical system according to claim 13, wherein: Each sensor of the plurality of sensors is coupled to a memory circuit configured to accumulate histogram data for the sensor.

15. An optical system according to any one of the preceding claims, wherein: The second interval is smaller than the first interval.

16. An optical system for measuring distance, the optical system comprising: a sensor array having a field of view, the sensor array comprising a plurality of single photon avalanche diodes (SPADs); an emitter array comprising a plurality of emitter units mounted on a surface of a common substrate and arranged in a two-dimensional array, wherein each of the plurality of emitter units is spaced apart from its adjacent emitter unit by a first spacing and emits light pulses having a predetermined beam divergence; a fly's eye element, the fly's eye element being spaced apart from the emitter array, the fly's eye element being positioned to receive light from the emitter array and being configured to generate a flood illumination distribution macroscopically matching the field of view of the sensor array, the fly's eye element comprising a first lens array and a second lenslet array spaced apart from each other, wherein individual lenslets in the first lenslet array and the second lenslet array are spaced apart from each other in at least one dimension by a second pitch different from the first pitch, and wherein each individual lenslet in the first lenslet array is aligned with a corresponding lenslet in the second lenslet array; and A timing generator and driver circuit operatively coupled to control the transmitter array to transmit radiation pulses at a desired time and frequency.

17. The optical system of claim 16, further comprising a collimating lenslet array disposed between the emitter array and the fly-eye element, wherein each lenslet in the collimating lenslet array is aligned with a corresponding emitter unit in the emitter array and is spaced apart from adjacent lenslets in the plurality of collimating lenslets by the first spacing.

18. An optical system according to claim 16 or 17, wherein: The emitter array comprises a plurality of individual VCSEL chips mounted on a common substrate, the driver circuit is mounted on the common substrate in close proximity to the VCSEL chips, and the fly's eye element is mounted to the common substrate.

19. A solid-state laser radar system, comprising: A sensor array having a field of view; an emitter array comprising a plurality of emitter units mounted on a surface of a common substrate and arranged in a two-dimensional array, wherein each emitter unit of the plurality of emitter units is spaced apart from its adjacent emitter unit by a first spacing and emits light having a predetermined beam divergence; and A fly's eye element, the fly's eye element is spaced apart from the emitter array, the fly's eye element is positioned to receive light from the emitter array, and is configured to generate a flood illumination distribution that macroscopically matches the field of view of the sensor array, the fly's eye element comprising a first lenslet array and a second lenslet array spaced apart from each other, wherein individual lenslets in the first lenslet array and the second lenslet array are spaced apart from each other in at least one dimension by a second pitch different from the first pitch, and wherein each individual lenslet in the first lenslet array is aligned with a corresponding lenslet in the second lenslet array.

20. The solid-state laser radar system according to claim 19, wherein: Each sensor in the sensor array includes a single photon avalanche diode (SPAD) array and is coupled to a memory circuit configured to accumulate histogram data for the sensor.

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