WO2019178136A1

WO2019178136A1 - Spectral-temporal lidar

Info

Publication number: WO2019178136A1
Application number: PCT/US2019/021906
Authority: WO
Inventors: Bahram Jalali; Robert R. Rice; Sebastian KARPF; Yunshan JIANG
Original assignee: University of California Berkeley; University of California San Diego UCSD
Current assignee: University of California Berkeley; University of California San Diego UCSD
Priority date: 2018-03-12
Filing date: 2019-03-12
Publication date: 2019-09-19
Anticipated expiration: 2020-09-12

Abstract

Many embodiments of the invention implement LIDAR systems that are designed and configured to measure distance utilizing a spectro-temporal illumination pattern. Such systems can realize ultrafast, inertia-free three-dimensional time-of-flight measurement, with a large field-of-view and depth range, and an adaptive foveated vision. A spectral-temporal LIDAR system can be implemented to include a broadband laser, a spectro-temporal modulator for forming a discrete spectro-temporal pattern, and a diffractive element for illuminating a target with the spectro-temporal pattern. During operation, LIDAR systems can employ an illumination made of a train of wavelength pulses followed by a diffraction element that can create a spectral shower for inertia free scanning of the target. The detection system includes time domain measurements of the return echoes (light reflected from the target), and the spatial location where an echo came from can be identified by the assigned wavelength to each pixel.

Description

Spectral-Temporal LIDAR

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with government support under Grant Numbers N66001 -12-1 -4028 and N00014-14-1 -0505, awarded by the U.S. Navy, Office of Naval Research. The Government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The current application claims the benefit of and priority under 35 U.S.C. § 1 19(e) to U.S. Provisional Patent Application No. 62/641 ,964 entitled“Spectro-Temporal LIDAR,” filed March 12, 2018. The disclosure of U.S. Provisional Patent Application No. 62/641 ,964 is hereby incorporated by reference in its entirety for all purposes.

FIELD OF THE INVENTION

[0003] The present invention generally relates to light detection and ranging methods and apparatuses and, more specifically, to spectral-temporal light detection and ranging methods and apparatuses.

BACKGROUND

[0004] Light detection and ranging (LIDAR) is a remote-sensing technology that creates a 3D map of an environment by illuminating a target with a pulsed, angularly scanned laser and analyzing the reflected "point cloud.” One approach illuminates the target with pulsed light and measures the time-of-flight of the reflected pulses. The advantages of LIDAR over cameras are well known. Since LIDAR uses emitted light, it is robust against interference from ambient light and has much higher resolution than radar. Although cameras provide high resolution, they may be slow and unreliable for certain applications as current computer vision is inadequate for complex scene representation and is susceptible to illumination variation.

[0005] The ability to precisely determine distance to a target is important for many applications from industrial fields, such as largescale manufacturing, and axis control of ultraprecision machine to futuristic space missions, such as formation flying of multiple satellite for synthetic aperture imaging. Since the current SI definition of the meter is based on the path traveled by light in vacuum during a time of 1/299,792,458 second, laser based distance measurement has played a pivotal role for the advance of optical distance metrology and has been steadily developed toward higher precision.

[0006] LIDAR has broad application in other fields, such as autonomous vehicles (for applications such as collision avoidance and cruise control systems), robotic vehicle, UAVs, wearable displays for night vision, mapping of wind for optimization of wind farms, geography, archaeology, forestry, agriculture, atmospheric physics, etc. Recently, LIDAR has come to the forefront of consumer technology for its use in control and navigation for self-driving cars and robotics. LIDAR images are being combined with artificial intelligence for classification for autonomous decision-making and control.

SUMMARY OF THE INVENTION

[0007] One embodiment includes a light detection and ranging apparatus (LIDAR) including a laser scanner including a broadband laser, a spectro-temporal modulator for configuring an output of the broadband light source into a spectro-temporal pattern, wherein the spectro-temporal pattern includes a train of temporally spaced pulses, wherein each pulse includes a unique wavelength, and a diffractive element configured for diffracting the spectro-temporal pattern onto a target.

[0008] In another embodiment, the light detection and ranging apparatus further includes an optical amplifier for amplifying the spectro-temporal pattern.

[0009] In a further embodiment, the diffractive element is configured to diffract different wavelengths at different angles.

[0010] In still another embodiment, the light detection and ranging apparatus further includes a secondary scanner for scanning the spectro-temporal pattern in a second dimension such that the LIDAR apparatus achieves 2D scanning.

[0011] In a still further embodiment, the light detection and ranging apparatus further includes a detector configured to measure light reflected from the target, wherein the light reflected from the target from different angles is identified by a time of arrival. [0012] In yet another embodiment, the detector includes at least one of a high sensitivity avalanche photodiode and a photomultiplier tube.

[0013] In a yet further embodiment, the light detection and ranging apparatus further includes an electronic amplifier.

[0014] In another additional embodiment, the light detection and ranging apparatus further includes a digitizer for converting the light reflected from the target into a digital representation and a digital signal processor for creating a map of the target based on the digital representation.

[0015] In a further additional embodiment, the light detection and ranging apparatus further includes a machine learning stage configured to classify the target.

[0016] In another embodiment again, the broadband laser includes a mode locked laser.

[0017] In a further embodiment again, the broadband laser includes a supercontinuum source.

[0018] In still yet another embodiment, the broadband laser is a frequency domain mode locked laser and the spectro-temporal modulator is an electro-optical modulator configured to modulate the output of the broadband light source into a discrete spectro- temporal pattern.

[0019] In a still yet further embodiment, the spectro-temporal modulator is a wavelength selective delay configured to modulate the output of the broadband light source into a discrete spectro-temporal pattern.

[0020] In still another additional embodiment, the wavelength selective delay is implemented using an arrayed waveguide grating.

[0021] A still further additional embodiment includes a method for light detection and ranging, the method including generating a spectro-temporal pattern, wherein the spectro-temporal pattern includes a train of temporally spaced light pulses, wherein each light pulse includes a unique wavelength, diffracting the spectro-temporal pattern onto a target, measuring light reflected from the target, and determining spatial location of the target based on the measured light.

[0022] In still another embodiment again, the spectro-temporal pattern is generated using a broadband laser and a spectro-temporal modulator. [0023] In a still further embodiment again, the spectro-temporal modulator includes a wavelength selective delay configured to modulate the output of the broadband light source into a discrete spectro-temporal pattern.

[0024] In yet another additional embodiment, the wavelength selective delay is implemented using an arrayed waveguide grating.

[0025] In a yet further additional embodiment, the broadband laser includes a supercontinuum source.

[0026] In yet another embodiment again, the broadband laser is a frequency domain mode locked laser and the spectro-temporal modulator is an electro-optical modulator configured to modulate the output of the broadband light source into a discrete spectro- temporal pattern.

[0027] Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the invention. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The description will be more fully understood with reference to the following figures and data graphs, which are presented as exemplary embodiments of the invention and should not be construed as a complete recitation of the scope of the invention.

[0029] FIGS. 1A and 1 B conceptually illustrate a system implementing a spectral- temporal LIDAR system in operation in accordance with an embodiment of the invention.

[0030] FIG. 2 conceptually illustrates an experimental setup demonstrating the concept of spectro-temporal encoded time-of-flight measurement in accordance with an embodiment of the invention.

[0031] FIG. 3 conceptually illustrates foveated imaging in accordance with an embodiment of the invention.

[0032] FIG. 4A and 4B conceptually illustrate discrete time-stretch for fluorescent lifetime imaging in accordance with an embodiment of the invention. [0033] FIG. 5A and 5B conceptually illustrate a system utilizing spectro-temporal excitation and spectral shower illumination in accordance with an embodiment of the invention.

[0034] FIG. 6A conceptually illustrates the use of a supercontinuum source and arrayed waveguide gratings for generating a spectro-temporal pattern in accordance with an embodiment of the invention.

[0035] FIG. 6B shows operation of spectro-temporal LIDAR with foveated vision using discrete time-stretch in accordance with various embodiments of the invention.

[0036] FIG. 6C shows four plots depicting linear dispersion, sublinear dispersion, superlinear dispersion, and non-monotonic dispersion in accordance with various embodiments of the invention.

[0037] FIG. 7A conceptually illustrates the use of a frequency domain mode locked laser and pulsed electro-optic modulation for generating a spectro-temporal pattern in accordance with an embodiment of the invention.

[0038] FIG. 7B shows two experimental setups and associated measurements collected using a frequency domain mode locking laser approach in accordance with various embodiments of the invention.

DETAILED DESCRIPTION

[0039] LIDAR typically refers to a remote sensing method that uses light in the form of a pulsed laser to measure distance. LIDAR systems can be configured to calculate distance using the velocity of light in“time-of-flight” measurements - i.e. , how long it takes for light to hit an object or surface and reflect back. Convectional LIDAR systems techniques scan the source and the detector to acquire spatial information to create 3D models and maps of objects and environments. Such methods typically rely on mechanical scanning and rotating optics technology, which are inherently slow, bulky, and non-robust.

[0040] LIDAR designs with no moving parts have been proposed by using surface illumination or beamforming with optical phase array as the sources, and sensor arrays as the detectors. Such non-mechanical technologies have several fundamental limits in channel numbers, power, and speed. Illumination with a spatially broad light beam generated with laser or LED arrays has been employed to avoid mechanical scanning. When using lasers, the number of channels of a laser array is restricted by the heat generated, whereas when using LED arrays, the peak power is limited by the peak power of the LED (which is lower than that of a laser). Another approach for avoiding mechanical scanning is the use of a phased array. While this approach is theoretically promising, practical implementations are hindered by the difficulties in control and stabilization of optical phase. On the detection side, image sensor arrays have been proposed to eliminate the need to scan the detector. However, such implementations are slow due to the long read-out time. Additionally, high-resolution and high-sensitivity arrays that include detectors with an internal gain (avalanche photodiodes or photomultiplier tubes) are not feasible.

[0041] Another issue with current LIDAR technology is in the dynamic range. In typically LIDAR systems, the reflected power decays quadratically with distance. This fundamental aspect can limit the operating range, thus limiting the possible applications. As such, a sensitive, fast, and high-dynamic range detection system is of high importance for long-distance LIDAR.

[0042] Turning now to the drawings, spectral-temporal LIDAR in accordance with various embodiments of the invention are illustrated. Many embodiments of the invention implement LIDAR systems that are designed and configured to address the fundamental problems posed above. In several embodiments, the LIDAR system is a spectral-temporal LIDAR system. Such systems can realize ultrafast, inertia-free three-dimensional time-of- flight measurement, with a large field-of-view and depth range, and an adaptive foveated vision. A LIDAR system in accordance with many embodiments of the invention can be implemented to include a broadband laser, a spectro-temporal modulator for converting the broadband light source into a discrete spectro-temporal pattern, and a diffractive element for illuminating a target with the spectro-temporal pattern. In several embodiments, the diffractive element is configured to different wavelengths of light at different angles. In further embodiments, the LIDAR system includes a secondary scanner for scanning the illumination in the second dimension. The LIDAR system can also include a photodetector followed by a digitizer and a digital signal processor for measuring light reflected from the target. In several embodiments, the LIDAR system includes a machine learning system for target classification. During operation, LIDAR systems in accordance with various embodiments of the invention can employ an illumination made of a train of wavelength pulses followed by a diffraction element that can create a spectral shower for inertia free scanning of the target. The detection system includes time domain measurements of the return echoes (light reflected from the target), and the spatial location where an echo came from can be identified by the assigned wavelength to each pixel. Principally, the light reflected from the target from different angles is identified by a time of arrival.

[0043] FIGS. 1A and 1 B conceptually illustrate a system implementing a spectral- temporal LIDAR system in operation in accordance with an embodiment of the invention. Fig. 1A shows a spectro-temporal LIDAR system 100 in operation. As shown, collimated light 101 is spatially dispersed according to wavelength. The dispersed light 101 is directed at a target 102 in a line illumination arrangement. Time encoded echoes 103 can be detected, and the spatial location of the target can be determined. FIG. 1 B illustrates how time-of-flight measurements for the dispersed wavelengths of light can be used to determine the spatial location points of the target. FIG. 2 conceptually illustrates an experimental setup demonstrating the concept of spectro-temporal encoded time-of-flight measurement in accordance with an embodiment of the invention. As shown, the setup 200 includes a fiber collimator 201 and a grating element 202 for outputting an illumination pattern, which illuminates a target 203 using an inertia free scan. The time encoded echoes are then detected by an avalanche photodiode (APD) 204. Although FIGS. 1A, 1 B, and 2 illustrate specific spectro-temporal LIDAR implementations, various configurations can be utilized in accordance with various embodiments of the invention. For example, there are many different systems and configurations capable of generating a spectro-temporal pattern of illumination. Such examples and spectro-temporal LIDAR systems in general are discussed below in further detail.

Spectro-Temporal LIDAR Systems

[0044] Photonic time-stretch can be utilized to enable ultrafast optical sensing. In time- stretch imaging, the target’s spatial information can be encoded in the spectrum of the ultrafast laser pulses through frequency-to-space mapping. The temporal waveform can be stretched in time, recorded by a single-pixel detector, digitized by a real-time ADC, and processed by a CPU, a dedicated FPGA, a GPU, etc. In a number of embodiments, a nonlinear dispersion transform is used to generate a foveated image in order to tackle the big-data problem faced by such high-throughput apparatus. FIG. 3 conceptually illustrates foveated imaging in accordance with an embodiment of the invention. Various methods can be used to realize time-stretch, including single mode fibers, dispersion- compensating fibers, chirped Bragg grating, chromo-modal dispersion (CMD), and grating pairs. Flowever, these methods are often unable to provide chirp with a large time- bandwidth product, which can limit the time-depth range that the LIDAR can measure.

[0045] A LIDAR system in accordance with many embodiments of the invention can be implemented to include laser scanner that is composed of a broadband laser, a spectro-temporal modulator for converting the broadband light source into a discrete spectro-temporal pattern, and a diffractive element for illuminating a target with the spectro-temporal pattern. In further embodiments, the LIDAR system includes a secondary scanner for scanning the illumination in the second dimension. The LIDAR system can also include a photodetector followed by a digitizer and a digital signal processor for measuring light reflected from the target. Various detectors can be utilized. In some embodiments, the detector is an avalanche photodiode. In a number of embodiments, the detector is a photomultiplier tube. In several embodiments, the LIDAR system includes a machine learning system for target classification. In some embodiments, the laser scanner also includes an optical amplifier that boosts the source power. As can readily be appreciated, the systems described above can be configured to omit or include certain components depending on the specific requirements of a given application.

[0046] Various embodiments of the invention are directed towards systems and methods for forming and using a discrete spectro-temporal pattern to acquire spatial information. In further embodiments, such systems are designed to make measurements without the use of mechanical scanning. The system can be configured such that no moving parts are needed to measure spatial information across a three-dimensional space. Various types of light sources and optical components can be used for generating a spectro-temporal pattern. In many embodiments, a broadband laser is utilized to form the spectro-temporal pattern. The broadband laser can include any of a number of different components. In some embodiments, the broadband laser is a mode locked laser. In several embodiments, the broadband laser is a supercontinuum source. In a number of embodiments, the broadband laser is a frequency domain mode locked laser.

[0047] In addition to the various choices of light sources, many different spectro- temporal modulators can be used to configure the light source to form a spectro-temporal pattern. In many embodiments, the spectro-temporal modulator is an electro-optical modulator. In some embodiments, the spectro-temporal modulator is a wavelength selective delay component. A wavelength selective delay can be implemented in many different ways, such as but not limited to the use of an arrayed waveguide grating. In some embodiments, a dispersion mechanism is used to produce discrete beams that can illuminate the target surface or cells. In many embodiments, the dispersion mechanism is a static element. Such dispersion mechanisms can include but are not limited to spectral dispersing gratings. Light sources and other optical components for forming a spectro- temporal pattern are discussed in the sections below in further detail. As can readily be appreciated, many different types of light sources can be utilized, the choice of which can depend on the specific requirements of a given application.

[0048] A discrete-temporal pattern can be formed and configured in many different ways. The discrete spectro-temporal source can be composed of a train of pulses of a varying frequency and a fixed time interval. In a number of embodiments, the three- dimensional information of the target is encoded in the spectral-temporal source, where the angular position and the reflection are mapped to the spectrum, and the depth information is recorded as the time-delay of the pulse in each time window. A foveated image can be generated using a source with a non-uniform spectrum in accordance with several embodiments of the invention. In a number of embodiments, the maximum imaging depth is limited to the first non-ambiguous distance of the time-of-flight measurement, which is half of the speed of light over the repetition rate and the channel number, (— -— ). In some embodiments, the maximum imaging depth can be tuned. In

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further embodiments, the maximum imaging depth can be tuned freely from tens of centimeters to hundreds of meters. [0049] In many embodiments, the output waveform of a Fourier domain mode-locked laser can be converted to a frequency swept comb that would enable the spectral dispersing gratings to produce discrete beams to illuminate the target surface or cells. An etalon can be inserted in the loop of the Fourier domain mode-locked laser with appropriate Free Spectral Range (FSR) and Finesse, and the Fourier domain mode- locked laser’s spectrally sweeping output will no longer be uniform in time, but will instead be temporal peaks whose instantaneous frequencies are separated by the FSR of the inline etalon. In other words, a pulse train can be generated in which each pulse is separated in time by 1/FSR and in frequency by the FSR of the etalon. The pulse length would be roughly the pulse separation divided by the finesse. At these sweep rates, the fiber gain can be saturated efficiently. The beams from the gratings can then be discrete with no overlap, providing they can resolve the FSR of the etalon. Such a scheme can be a great source for spectroscopy or pulse compression LIDAR using a chirped grating.

[0050] AWG/RPF (recirculating photonic filter) can be a great match for spectro- temporal processing of FDML output because (using external delays) it can synthesize very large time-bandwidths to match the large time-bandwidth of the FDML (10's of nm / us). Normal dispersion elements cannot. Such systems can be used in a variety of applications, including (but not limited to) imaging, spectroscopy, matched detection, regression, NN computation, and optical computing. FIG. 4A and 4B conceptually illustrate discrete time-stretch for fluorescent lifetime imaging in accordance with an embodiment of the invention. A wavelength multiplexed temporal pulse train can be generated by spectro-temporal carving of broadband optical pulses generated - e.g., using a mode locked laser via a recirculating photonic filter consisting of an arrayed waveguide grating in feedback configuration. Detection can be achieved using a spectrometer for separating the echo from each pixel followed by a photodiode or an avalanche photodiode (APD) array plus an ADC where time of arrival of echo from each pixel is measured. A simpler detection system without the spectrometer and needing only a single photodiode can be employed by ensuring that the incremental pulse delay in the illumination beam is larger than the maximum round trip time of the echo. This can impose a limit on the maximum axial range of the LIDAR. FIG. 5A and 5B conceptually illustrate a system utilizing spectro-temporal excitation and spectral shower illumination in accordance with an embodiment of the invention. As shown, an RPF pulse generator 500 is utilized to form an output waveform that is then redirected and modulated to provide a spectral shower illumination scheme 501 . Although FIGS. 5A and 5B illustrate specific configurations for generating a wavelength multiplexed temporal pulse train, various other methods and configurations can be used depending on the specific requirements of a given application. Methods and systems for generating spectro-temporal patterns in accordance with various embodiments of the invention are discussed below in further detail.

Forming Spectro-Temporal Patterns

[0051] As mentioned above, a discrete spectro-temporal pattern can be generated in many different ways. In many embodiments, a broadband light source can be modulated to form the spectro-temporal pattern. Supercontinuum sources can be an attractive candidate for the broadband light source. They can easily cover octaves in the near- infrared (NIR), and highly coherent operation is achievable (from pulse to pulse, the spectrum and temporal waveform are highly regular); moreover, the power can be scaled up to tens of Watts or greater for long-range applications. In numerous embodiments, the supercontinuum sources use high pulse rates to integrate a large number of echoes in order to greatly improve image signal-to-noise ratio (SNR). Systems in accordance with some embodiments of the invention measure individual pixel delays to realize a 3-D imaging LIDAR. The benefits of such a system can include scalability and flexibility in wavelength band selection.

[0052] In some embodiments, the system is configured to form a spectro-temporal pattern of light using a broadband pulse laser and a spectro-temporal modulator based on a recirculating photonic filter. The system can reshape the spectrum and provide a true time delay that is a function of wavelength. In certain embodiments, the input signal from the broadband pulse laser is optically demultiplexed (DeMUX) into a plurality of wavelengths. The various wavelengths can then be delayed by fibers with varying length, modified by the variable optical attenuators (VOA), and fed to a multiplexer (MUX). The generated pulse train can be amplified by a fiber based optical amplifier for the sensing stage. The maximum imaging depth in accordance with several embodiments of the invention can be determined by the increment in the fiber delays. In several embodiments, the system performs non-uniform sampling of the input broadband spectrum with an arbitrary waveform generator (AWG) to achieve foveated (warped) spatial illumination in order to allocate more data to the region of interest.

[0053] FIG. 6A conceptually illustrates the use of a supercontinuum source 600 and arrayed waveguide gratings 601 for generating a spectro-temporal pattern in accordance with an embodiment of the invention. As shown, discrete time-stretch is performed on a spectrally separated, collimated light source 602 from a supercontinuum laser 600. Spatial dispersion 603 is then performed on the output wave 604. FIG. 6B shows operation of spectro-temporal LIDAR with foveated vision using discrete time-stretch in accordance with various embodiments of the invention. The graphs in FIG. 6B show measurements depicting various dispersion transforms for spectro-temporal illumination in accordance with many embodiments of the invention. In FIG. 6C, four plots showing linear dispersion, sublinear dispersion, superlinear dispersion, and non-monotonic dispersion are depicted.

[0054] In certain embodiments, the system uses a frequency domain mode locking laser (FDML) to produce the chirped source with a giant time-bandwidth product, which is then temporally coded by an electro-optical modulator (EOM). The maximum imaging depth in accordance with some embodiments of the invention can be determined by the sampling rate of the EOM. The foveated vision in accordance with numerous embodiments of the invention can be programmed by employing a varying sampling rate along the chirp. FIG. 7A conceptually illustrates the use of a frequency domain mode locked laser and pulsed electro-optic modulation for generating a spectro-temporal pattern in accordance with an embodiment of the invention. FIG. 7B shows two experimental setups and associated measurements collected using a frequency domain mode locking laser approach in accordance with various embodiments of the invention.

[0055] Although FIGS. 6A - 7B illustrate specific arrangements for generating a spectro-temporal patterns, various configurations can be utilized in accordance with various embodiments of the invention. For example, many embodiments include an optical amplifier. In some embodiments, other diffractive elements are used. As can readily be appreciated, the specific configurations of such systems can depend on the specific requirements of a given application.

DOCTRINE OF EQUIVALENTS

[0056] While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as an example of one embodiment thereof. It is therefore to be understood that the present invention may be practiced in ways other than specifically described, without departing from the scope and spirit of the present invention. Thus, embodiments of the present invention should be considered in all respects as illustrative and not restrictive. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1 . A light detection and ranging apparatus (LIDAR) comprising:

a laser scanner comprising:

a broadband laser;

a spectro-temporal modulator for configuring an output of the broadband light source into a spectro-temporal pattern, wherein the spectro- temporal pattern comprises a train of temporally spaced pulses, wherein each pulse comprises a unique wavelength; and

a diffractive element configured for diffracting the spectro-temporal pattern onto a target.

2. The light detection and ranging apparatus of claim 1 , further comprising an optical amplifier for amplifying the spectro-temporal pattern.

3. The light detection and ranging apparatus of claim 1 , wherein the diffractive element is configured to diffract different wavelengths at different angles.

4. The light detection and ranging apparatus of claim 1 , further comprising a secondary scanner for scanning the spectro-temporal pattern in a second dimension such that the LIDAR apparatus achieves 2D scanning.

5. The light detection and ranging apparatus of claim 1 , further comprising a detector configured to measure light reflected from the target, wherein the light reflected from the target from different angles is identified by a time of arrival.

6. The light detection and ranging apparatus of claim 5, wherein the detector comprises an instrument selected from the group consisting of: a high sensitivity avalanche photodiode and a photomultiplier tube.

7. The light detection and ranging apparatus of claim 5, further comprising an electronic amplifier.

8. The light detection and ranging apparatus of claim 5, further comprising: a digitizer for converting the light reflected from the target into a digital representation; and

a digital signal processor for creating a map of the target based on the digital representation.

9. The light detection and ranging apparatus of claim 5, further comprising a machine learning stage configured to classify the target.

10. The light detection and ranging apparatus of claim 1 , wherein the broadband laser comprises a mode locked laser.

11. The light detection and ranging apparatus of claim 1 , wherein the broadband laser comprises a supercontinuum source.

12. The light detection and ranging apparatus of claim 1 , wherein the broadband laser is a frequency domain mode locked laser and the spectro-temporal modulator is an electro-optical modulator configured to modulate the output of the broadband light source into a discrete spectro-temporal pattern.

13. The light detection and ranging apparatus of claim 1 , wherein the spectro- temporal modulator is a wavelength selective delay configured to modulate the output of the broadband light source into a discrete spectro-temporal pattern.

14. The light detection and ranging apparatus of claim 13, wherein the wavelength selective delay is implemented using an arrayed waveguide grating.

15. A method for light detection and ranging, the method comprising: generating a spectro-temporal pattern, wherein the spectro-temporal pattern comprises a train of temporally spaced light pulses, wherein each light pulse comprises a unique wavelength;

diffracting the spectro-temporal pattern onto a target;

measuring light reflected from the target; and

determining spatial location of the target based on the measured light.

16. The method of claim 15, wherein the spectro-temporal pattern is generated using a broadband laser and a spectro-temporal modulator.

17. The method of claim 16, wherein the spectro-temporal modulator comprises a wavelength selective delay configured to modulate the output of the broadband light source into a discrete spectro-temporal pattern.

18. The method of claim 17, wherein the wavelength selective delay is implemented using an arrayed waveguide grating.

19. The method of claim 16, wherein the broadband laser comprises a supercontinuum source.

20. The method of claim 16, wherein the broadband laser is a frequency domain mode locked laser and the spectro-temporal modulator is an electro-optical modulator configured to modulate the output of the broadband light source into a discrete spectro- temporal pattern.