Lidar system

• US 10,557,940 B2
• Filed: 11/29/2016
• Issued: 02/11/2020
• Est. Priority Date: 11/30/2015
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Eichenholz, Jason M., Russell, Austin K., Campbell, Scott R., Villeneuve, Alain, Cleye, Rodger W., LaChapelle, Joseph G., Weed, Matthew D., Martin, Lane A., Gaalema, Stephen D.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US15/364,085
• Publication Number:
  US 20180364356A1
• Time in Patent Office: 1,169 Days
• Field of Search: 356 501
• CPC Class Codes: G01S 17/00 Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
• CPC Class Codes: G01S 17/02 Systems using the reflection of electromagnetic waves other than radio waves G01S17/66 takes precedence
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/14 wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
• CPC Class Codes: G01S 17/26 wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4804 Auxiliary means for detecting or identifying lidar signals or the like, e.g. laser illuminators
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/4815 using multiple transmitters
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/483 Details of pulse systems
• CPC Class Codes: G01S 7/484 : Transmitters
• CPC Class Codes: G01S 7/4861 : Circuits for detection, sampling, integration or read-out
• CPC Class Codes: G01S 7/4863 : Detector arrays, e.g. charge-transfer gates
• CPC Class Codes: G01S 7/4865 : Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G01S 7/4873 : by deriving and controlling a threshold value
• CPC Class Codes: G01S 7/4876 : by removing unwanted signals G01S7/495 takes precedence
• CPC Class Codes: H01S 2301/02 : ASE (amplified spontaneous emission), noise; Reduction thereof
• CPC Class Codes: H01S 3/0007 : Applications not otherwise provided for working metals or other materials by laser beam B23K26/00; using photons to produce a reactive propulsive thrust F03H3/00; optical recording of measured values in general G01D15/14; optics in general G02B; holographic processes or apparatus G03H; optical marking or sensing of data record carriers G06K7/10 - G06K7/14, G06K15/12; injection heating of plasma by laser H05H1/22; acceleration of neutral particles by electromagnetic wave pressure H05H3/04
• CPC Class Codes: H01S 3/0078 : Frequency filtering
• CPC Class Codes: H01S 3/0085 : Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 3/06733 : Fibre having more than one cladding
• CPC Class Codes: H01S 3/0675 : Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/06754 : Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06758 : Tandem amplifiers
• CPC Class Codes: H01S 3/08086 : Multiple-wavelength emission
• CPC Class Codes: H01S 3/094003 : the pumped medium being a fibre
• CPC Class Codes: H01S 3/094042 : of a fibre laser
• CPC Class Codes: H01S 3/094076 : Pulsed or modulated pumping H01S3/1024 takes precedence
• CPC Class Codes: H01S 3/0941 : of a laser diode
• CPC Class Codes: H01S 3/10023 : by functional association of additional optical elements, e.g. filters, gratings, reflectors
• CPC Class Codes: H01S 3/1106 : Mode locking
• CPC Class Codes: H01S 3/1608 : erbium
• CPC Class Codes: H01S 3/2383 : Parallel arrangements
• CPC Class Codes: H01S 5/0057 : for temporal shaping, e.g. pulse compression, frequency chirping
• CPC Class Codes: H01S 5/0085 : for modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 5/4012 : Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms
• CPC Class Codes: H01S 5/4087 : emitting more than one wavelength

Abstract

In one embodiment, a lidar system includes a light source configured to emit pulses of light and a scanner configured to scan at least a portion of the emitted pulses of light across a field of regard. The lidar system also includes a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system.

Claims

1. A lidar system comprising:

a light source configured to emit pulses of light;

a scanner configured to scan at least a portion of the emitted pulses of light across a field of regard; and

a receiver comprising an avalanche photodiode (APD), a first comparator, a second comparator, and a time-to-digital converter (TDC), wherein the receiver is configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system by generating, by the APD, an electrical-current signal corresponding to a received pulse of light, the received pulse of light corresponding to a pulse of light emitted by the light source, and wherein;

the first comparator is configured to produce a first electrical-edge signal when a voltage signal corresponding to the electrical-current signal generated by the APD rises above a first predetermined threshold voltage;

the second comparator is configured to produce a second electrical-edge signal when the voltage signal falls below a second predetermined threshold voltage; and

the TDC is configured to;

receive the first and second electrical-edge signals;

determine a first interval of time between emission of the pulse of light by the light source and receipt of the first electrical-edge signal; and

determine a second interval of time between emission of the pulse of light by the light source and receipt of the second electrical-edge signal.

2. The lidar system of claim 1, further comprising a sensor head located remotely from the light source, wherein:

the sensor head comprises the scanner and the receiver; and

the sensor head is coupled to the light source by an optical link, wherein the optical link conveys the portion of the emitted pulses of light from the light source to the sensor head.

3. The lidar system of claim 2, wherein the lidar system further comprises one or more additional sensor heads, wherein:

each of the additional sensor heads comprises a respective scanner and receiver; and

the light source is coupled to each of the additional sensor heads by a respective optical link which conveys a respective portion of the emitted pulses of light from the light source to each of the additional sensor heads.

4. The lidar system of claim 2, wherein the lidar system is incorporated into a vehicle wherein the sensor head and one or more additional sensor heads of the lidar system are positioned to provide a greater than or equal to 30-degree view of an environment around the vehicle.

5. The lidar system of claim 1, wherein the lidar system has a maximum range of greater than or equal to 50 meters.

6. The lidar system of claim 1, wherein the field of regard comprises:

a horizontal field of regard greater than or equal to 25 degrees; and

a vertical field of regard greater than or equal to 5 degrees.

7. The lidar system of claim 1, wherein the lidar system has a horizontal resolution of greater than or equal to 100 pixels and a vertical resolution of greater than or equal to 4 pixels.

8. The lidar system of claim 1, wherein the lidar system is configured to generate point clouds at a rate between approximately 0.1 frames per second and approximately 1,000 frames per second.

9. The lidar system of claim 1, wherein the light source comprises a pulsed laser diode.

10. The lidar system of claim 1, wherein the light source comprises:

a seed laser configured to produce optical seed pulses; and

one or more optical amplifiers configured to amplify the optical seed pulses to produce the pulses of light emitted by the light source.

11. The lidar system of claim 10, wherein the seed laser comprises a distributed-feedback (DFB) laser or a distributed-Bragg reflector (DBR) laser.

12. The lidar system of claim 1, wherein the light source comprises a booster amplifier comprising a double-clad gain fiber comprising erbium dopants or erbium and ytterbium dopants.

13. The lidar system of claim 1, wherein the light source comprises:

a plurality of laser diodes, wherein each laser diode is configured to produce light at a different operating wavelength; and

an optical multiplexer configured to combine the light produced by each laser diode into a single optical fiber.

14. The lidar system of claim 1, wherein the light source is an eye-safe laser with an operating wavelength between approximately 1400 nm and approximately 1600 nm.

15. The lidar system of claim 1, wherein the pulses of light emitted by the light source have pulse characteristics comprising:

an operating wavelength between approximately 1400 nm and approximately 1600 nm;

a pulse repetition frequency of less than or equal to 100 MHz;

a pulse duration of less than or equal to 20 nanoseconds; and

a duty cycle of less than or equal to 1%.

16. The lidar system of claim 15, wherein the pulse characteristics further comprise:

a pulse energy of greater than or equal to 10 nanojoules;

a peak power of greater than or equal to 1 watt; and

an average power of less than or equal to 50 watts.

17. The lidar system of claim 1, wherein the light source comprises an optical filter configured to transmit light at one or more operating wavelengths of the light source and attenuate light away from the transmitted wavelengths by at least 10 dB.

18. The lidar system of claim 1, wherein the light source comprises an optical filter configured to reduce an amount of amplified spontaneous emission light produced by one or more optical amplifiers of the light source.

19. The lidar system of claim 1, wherein the light source comprises a diode-pumped solid-state (DP S S) laser.

20. The lidar system of claim 1, wherein the scanner comprises one or more mirrors, wherein each mirror is mechanically driven by a galvanometer scanner, a resonant scanner, a microelectromechanical systems (MEMS) device, or a voice coil motor.

21. The lidar system of claim 20, wherein the scanner comprises:

a first mirror driven by a first galvanometer scanner that scans the first mirror along a first direction; and

a second mirror driven by a second galvanometer scanner that scans the second mirror along a second direction substantially orthogonal to the first direction.

22. The lidar system of claim 20, wherein the scanner comprises:

a first mirror driven by a resonant scanner that scans the first mirror along a first direction; and

a second mirror driven by a galvanometer scanner that scans the second mirror along a second direction substantially orthogonal to the first direction.

23. The lidar system of claim 1, wherein the scanner comprises two mirrors driven synchronously, wherein the synchronously driven mirrors trace out a scan pattern that comprises substantially straight lines.

24. The lidar system of claim 1, wherein the scanner comprises a mirror driven by two actuators configured to scan the mirror along two substantially orthogonal directions.

25. The lidar system of claim 1, wherein the scanner comprises a mirror configured to be scanned along two axes, wherein motion along each axis is provided by two actuators arranged in a push-pull configuration.

26. The lidar system of claim 1, wherein the receiver further comprises a transimpedance amplifier (TIA) and a voltage-gain circuit, wherein the TIA and voltage-gain circuit are configured to receive the electrical-current signal from the APD and produce the voltage signal that corresponds to the electrical-current signal.

27. The lidar system of claim 1, wherein determining the first or second interval of time comprises determining a time associated with the emission of the pulse of light by the light source, wherein the time associated with the emission of the pulse of light is determined based at least in part on detection by the receiver of a portion of light from the emitted pulse of light.

28. The lidar system of claim 1, further comprising a processor configured to determine the distance from the lidar system to the target based at least in part on the first and second intervals of time.

29. The lidar system of claim 1, further comprising an optical filter located in front of the receiver, wherein the optical filter is configured to transmit light at one or more operating wavelengths of the light source and attenuate light at surrounding wavelengths by at least 10 dB.

30. The lidar system of claim 1, wherein the receiver comprises an array of two or more avalanche photodiodes (APDs), wherein the APD is part of the array of APDs.

31. The lidar system of claim 1, further comprising a processor configured to determine the distance from the lidar system to the target based at least in part on a round-trip time of flight for the pulse of light emitted by the light source to travel from the lidar system to the target and back to the lidar system.

32. The lidar system of claim 31, wherein the round-trip time of flight is determined based at least in part on the first or second interval of time.

33. The lidar system of claim 1, wherein:

the receiver comprises three or more comparators, the three or more comparators comprising the first and second comparators; and

each of the three or more comparators is associated with a respective threshold voltage, the threshold voltages comprising the first and second predetermined threshold voltages, wherein;

each of the threshold voltages has a different value; and

each comparator is configured to provide a rising or falling electrical-edge signal to the TDC when the voltage signal rises above or falls below the threshold voltage associated with the comparator.

34. The lidar system of claim 1, further comprising a processor configured to determine a duration of the received pulse of light based at least in part on a time difference between receipt of the first and second electrical-edge signals.

35. The lidar system of claim 1, further comprising a processor configured to determine a time associated with a peak of the received pulse of light based at least in part on the first and second intervals of time.

36. The lidar system of claim 35, wherein the processor is further configured to determine the distance from the lidar system to the target based at least in part on the time associated with the peak of the received pulse of light.

37. A lidar system comprising:

a light source configured to emit pulses of light;

a scanner configured to scan an output beam comprising at least a portion of the emitted pulses of light across a field of regard;

an overlap mirror configured to overlap an input beam and the output beam so that the input and output beams are substantially coaxial, wherein;

the input beam comprises at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system; and

the overlap mirror comprises;

a hole, slot, or aperture through which the output beam is configured to pass; and

a reflecting surface configured to reflect at least a portion of the input beam toward the receiver; and

a receiver configured to detect the portion of the scanned pulses of light scattered by the target.

38. The lidar system of claim 37, wherein:

scanning the portion of the emitted pulses of light across the field of regard comprises scanning a field of view of the light source across the field of regard; and

the scanner is further configured to scan a field of view of the receiver across the field of regard, wherein the light-source field of view and the receiver field of view are scanned synchronously with respect to one another.

39. The lidar system of claim 38, wherein the light-source field of view and the receiver field of view are at least partially overlapped during scanning.

40. The lidar system of claim 38, wherein:

the light-source field of view and the receiver field of view are scanned along a scanning direction; and

the receiver field of view is offset from the light-source field of view in a direction opposite the scanning direction.

41. The lidar system of claim 38, wherein an angular extent of the light-source field of view is approximately equal to an angular extent of the receiver field of view.

42. The lidar system of claim 38, wherein:

the light-source field of view has an angular extent of less than or equal to 50 milliradians; and

the receiver field of view has an angular extent of less than or equal to 50 milliradians.

43. A lidar system comprising:

a light source configured to emit pulses of light;

a scanner configured to scan at least a portion of the emitted pulses of light across a field of regard; and

a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system, wherein the receiver comprises;

an avalanche photodiode (APD) configured to operate as a single-photon avalanche diode (SPAD); and

a quenching circuit configured to reduce a reverse-bias voltage applied to the SPAD when an avalanche event occurs in the SPAD.

44. A lidar system comprising:

a light source configured to emit pulses of light;

a scanner configured to scan at least a portion of the emitted pulses of light across a field of regard; and

a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system, wherein the receiver comprises;

two or more avalanche photodiodes (APDs); and

one or more logic gates coupled to the APDs, wherein the logic gates are configured to produce an output indicating that the receiver has detected an optical pulse only if each of the APDs produces an electrical signal corresponding to detection of the optical pulse.