LIDAR Transmitter and Detector System Using Pulse Encoding to Reduce Range Ambiguity

• US 20180284279A1
• Filed: 03/10/2018
• Published: 10/04/2018
• Est. Priority Date: 03/28/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Campbell, Scott R., LaChapelle, Joseph G., Eichenholz, Jason M., Russell, Austin K.
• Granted Patent: US 10,545,240 B2
• Time in Patent Office: Days
• 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 17/26 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 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4808 Evaluating distance, position or velocity data
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• 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 7/4865 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 7/497 Means for monitoring or calibrating

Abstract

A lidar system includes a transmitter that encodes successive transmit pulses with different pulse characteristics and a receiver that detects the pulse characteristics of each received (scattered or reflected) pulse and that distinguishes between the received pulses based on the detected pulse characteristics. The lidar system thus resolves range ambiguities by encoding pulses of scan positions in the same or different scan periods to have different pulse characteristics, such as different pulse widths or different pulse envelope shapes. The receiver includes a pulse decoder configured to detect the relevant pulse characteristics of the received pulse and a resolver that determines if the pulse characteristics of the received pulse matches the pulse characteristics of the current scan position or that of a previous scan position.

Claims

1. A system, comprising:

a transmitter including a light source, a pulse encoder, and a controller, the light source configured to emit light pulses, the pulse encoder configured to encode light pulses of the light source with one or more pulse characteristics, and the controller configured to cause the encoder to encode light pulses of different scan position times with at least one different pulse characteristic value of the one or more pulse characteristics to produce encoded light pulses;

a scanner configured to scan across a plurality of scan positions within a two dimensional field of regard, each scan position defined by a different set of vector coordinates, and to transmit one or more encoded light pulses towards a remote target at each of the scan positions; and

a receiver configured to detect a light pulse, scattered by the remote target, the receiver including a light detector element, a pulse decoder, and a resolver, wherein the pulse decoder determines a pulse characteristic value of the detected light pulse and the resolver determines a set of vector coordinates of a scan position for a transmitted light pulse with which the detected light pulse is associated based on the pulse characteristic value of the detected light pulse.

2. The system of claim 1, wherein the at least one different pulse characteristic value comprises a different value of wavelength.

3. The system of claim 2, wherein the receiver further comprises a dichroic filter and the light detector element includes a first photodiode and a second photodiode, and wherein the dichroic filter directs the scattered light pulse to the first photodiode if the scattered light pulse has a first wavelength, and directs the scattered light pulse to the second photodiode if the scattered light pulse has a second wavelength.

4. The system of claim 1, wherein the at least one different pulse characteristic value comprises a different value of pulse width.

5. The system of claim 1, wherein the at least one different pulse characteristic value comprises a different pulse shape.

6. The system of claim 1, wherein the receiver further comprises a plurality of amplitude detectors, and wherein;

each of the plurality of amplitude detectors includes a comparator and a time-to-digital converter coupled to the comparator to produce a representation of a time delay between when one of the light pulses was emitted and the scattered light pulse was detected.

7. The system of claim 6, wherein the pulse decoder determines the pulse characteristic value of the detected light pulse based on the time delays determined by the plurality of amplitude detectors.

8. The system of claim 6, wherein the receiver further comprises an envelope detector coupled to the plurality of amplitude detectors, and wherein;

the envelope detector determines an amplitude envelope of the detected light pulse based on the time delays determined by the plurality of amplitude detectors, and

the pulse decoder uses the amplitude envelope determined by the envelope detector to determine the pulse characteristic value of the detected light pulse.

9. The system of claim 1, wherein the receiver further comprises a plurality of amplitude detectors, and wherein each of the amplitude detectors includes an analog to digital converter.

10. The system of claim 1, wherein the pulse encoder comprises an optical modulator external to the light source.

11. The system of claim 1, wherein the light source and the pulse encoder are integrated together as a common unit.

12. The system of claim 11, wherein the light source and pulse encoder comprise a pulse-encoding light source.

13. The system of claim 12, wherein the pulse-encoding light source comprises a current-modulated seed diode laser.

14. The system of claim 1, wherein the scanning system further comprises a range detector, and wherein

the resolver allows the range detector to use the detected light pulse for range detection for a current scan position when the scan position with which the detected light pulse is associated matches a pulse characteristic value of an encoded light pulse for the current scan position.

15. The system of claim 14, wherein the resolver allows the range detector to use the detected pulse for range detection for a scan position other than the current scan position when the scan position with which the detected light pulse is associated matches a pulse characteristic value of an encoded light pulse of a scan position other than the current scan position.

16. The system of claim 1, wherein the light source is a laser.

17. The system of claim 1, wherein the light source includes a laser diode.

18. The system of claim 1, wherein the light source includes a photodiode.

19. The system of claim 18, wherein the light detector element comprises an avalanche photodiode.

20. The system of claim 18, wherein the light detector element comprises a single-photon avalanche photodiode.

21. The system of claim 1, wherein the light source, scanner, and receiver are packaged together within a single housing, and wherein the single housing includes a window with an exterior surface and an interior surface.

22. The system of claim 21, wherein the window includes a dielectric coating on at least one of the interior surface and the exterior surface.

23. The system of claim 22, wherein the dielectric coating is anti-reflecting at an operating wavelength of the light source.

24. A method for transmitting and receiving light pulses, the method comprising:

transmitting one or more light pulses at each of a plurality of scan positions within a two dimensional field of regard, each scan position defined by a different set of vector coordinates;

encoding light pulses of different scan positions with at least one different pulse characteristic value;

receiving light pulses scattered by a remote target;

detecting a scattered light pulse;

identifying a pulse characteristic value of the detected light pulse;

determining from the pulse characteristic value of the detected light pulse a set of vector coordinates of the scan position for a transmitted light pulse with which the detected light pulse is associated.

25. The method of claim 24, wherein encoding light pulses of different scan positions with at least one different pulse characteristic value includes encoding light pulses with a different value of pulse width.

26. The method of claim 24, wherein encoding light pulses of different scan positions with at least one different pulse characteristic value includes encoding light pulses with a different pulse shape.

27. The method of claim 24, wherein identifying the pulse characteristic value of the detected light pulse includes determining an amplitude of the detected light pulse at a plurality of positions along the detected light pulse and producing an amplitude envelope of the detected light pulse.

28. The method of claim 24, wherein encoding light pulses of different scan positions with a least one different pulse characteristic value includes encoding light pulses with a different value of wavelength.

30. The method of claim 24, further comprising calculating a range to the remote target based on the scan position of the transmitted light pulse with which the detected light pulse is associated.

29. (canceled)

31. (canceled)

32. A range detection system, comprising:

a light source capable of emitting light pulses;

a controller configured to direct a pulse encoder to encode a first emitted light pulse with a first set of pulse characteristic values and a second emitted light pulse with a second set of pulse characteristic values, wherein the first set and second set of pulse characteristic values are different;

a scanner configured to direct the first emitted light pulse at a first scan position within a two dimensional field of regard and to direct the second emitted light pulse at a second scan position within the two dimensional field of regard, each scan position defined by a different set of vector coordinates;

a detector configured to detect a light pulse scattered by a remote target and to produce electric signals indicative of the scattered light pulse;

a pulse decoder coupled to the detector that detects one or more pulse characteristic values of the scattered light pulse using the electric signals a resolver that determines if the detected one or more pulse characteristic values match the first set of pulse characteristic values of the first emitted pulse or the second set of pulse characteristic values of the second emitted pulse, and

a range detector that calculates a range to the remote target based on the first emitted light pulse if the detected pulse characteristic values match the first set of pulse characteristic values or on the second emitted light pulse if the detected pulse characteristic values match the second set of pulse characteristic values.

33-36. -36. (canceled)