Active short-wave infrared four-dimensional camera

• US 10,007,001 B1
• Filed: 10/06/2017
• Issued: 06/26/2018
• Est. Priority Date: 03/28/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: LaChapelle, Joseph G., Eichenholz, Jason M.
• Primary Examiner(s): Gaworecki, Mark R
• Application Number:
  US15/727,073
• Time in Patent Office: 263 Days
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 2001/4466 Avalanche
• 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 17/42 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 17/931 of land vehicles
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/484 Transmitters
• 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 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: H01L 31/03046 including ternary or quaternary compounds, e.g. GaAlAs, InGaAs, InGaAsP
• CPC Class Codes: H01L 31/09 Devices sensitive to infrared, visible or ultraviolet radiation H01L31/101 takes precedence
• CPC Class Codes: H01L 31/1085 the devices being of the Metal-Semiconductor-Metal [MSM] Schottky barrier type
• CPC Class Codes: H01L 31/167 the light sources and the devices sensitive to radiation all being semiconductor devices characterised by potential barriers

Abstract

A lidar system operates as an active short-wave infrared (SWIR) camera system to determine a four-dimensional image at each point in a two-dimensional field of regard. The camera system includes a short-wave infrared spectrum scanner that transmits a pulse of light at a particular position or coordinate in a two-dimensional field of regard and a receiver that detects return pulses scattered from a target in the field of regard coincident with the particular position. The receiver includes a detector that detects the returned pulse, a range determination unit that determines, based on the timing of the returned pulse, a distance to the target at the particular position, and an intensity measurement unit that determines the magnitude, amplitude, or intensity of the returned pulse, which information provides an indication of the relative, or in some cases, absolute reflectivity of the target at the particular point in the field of regard.

Claims

1. An active camera system, comprising:

a light source configured to emit light as a series of one or more light pulses;

a scanner configured to direct the one or more light pulses towards a remote target at a particular position in a two-dimensional field of regard; and

a receiver configured to detect one or more light pulses scattered by the remote target, the receiver including;

a detector element that detects a scattered light pulse at the particular position in the two-dimensional field of regard,

a range determination unit that determines, based on the timing of the receipt of the scattered light pulse, a distance to the target at the particular position in the field of regard,

an intensity measurement unit that (i) determines an intensity profile of the scattered light pulse, and (ii) determines from the intensity profile an indication of the reflectivity of the target at the particular position in the field of regard.

2. The active camera system of claim 1, wherein the receiver further includes a plurality of amplitude detectors coupled to the detector element, 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 a scattered light pulse was received.

3. The active camera system of claim 2, wherein a first one of the Hplurality of amplitude detectors detects a rising edge of the scattered light pulse from the remote target and a second one of the plurality of the amplitude detectors detects a falling edge of the scattered light pulse from the remote target.

4. The active camera system of claim 2, wherein the receiver further comprises an envelope detector coupled to the plurality of amplitude detectors that determines an amplitude envelope of the scattered light pulse based on the time delays determined by the plurality of amplitude detectors.

5. The active camera system of claim 2, wherein the intensity measurement unit determines an intensity of the scattered light pulse based on the time delays determined by three or more of the plurality of amplitude detectors.

6. The active camera system of claim 2, wherein a comparator of a first one of the plurality of amplitude detectors compares an indication of a detected scattered light pulse to a first threshold and a comparator of a second one of the plurality of amplitude detectors compares an indication of the detected scattered light pulse to a second threshold different than the first threshold.

7. The active camera system of claim 2, wherein one or more of the comparators is a rising-edge comparator and one or more other ones of the comparators are falling-edge comparators.

8. The active camera system of claim 2, wherein the plurality of amplitude detectors are electrically connected in parallel to each other.

9. The active camera system of claim 1, wherein the receiver further includes an analog-to-digital converter (ADC) configured to produce a digital representation of the scattered light pulse detected by the detector.

10. The active camera system of claim 1, wherein the detector element includes an avalanche photodiode.

11. The active camera system of claim 10, wherein the avalanche photodiode comprises a linear-mode avalanche photodiode.

12. The active camera system of claim 1, wherein the detector element comprises an indium-gallium-arsenide (InGaAs) or silicon semiconductor material.

13. The active camera system of claim 1, wherein the intensity measurement unit includes calibration information and the intensity measurement determines a reflectivity of the target from the calibration information based on an intensity value of the intensity profile of the scattered light pulse and the detected distance to the target.

14. A method of imaging a remote target, comprising:

generating a light pulse for a position in a two-dimensional scanning field of regard;

emitting the generated light pulse towards a remote target in the position of the two-dimensional field of regard;

receiving a scattered light pulse scattered from the remote target;

detecting a receive time associated with the received scattered light pulse;

determining a range to the target based on the receive time of the received scattered light pulse;

detecting an intensity of the received scattered light pulse; and

determining a reflectivity of the remote target from the determined range to the remote target and the detected intensity of the received scattered light pulse.

15. The method of imaging a remote target of claim 14, wherein detecting a receive time associated with the received scattered light pulse includes detecting an amplitude of the received scattered light pulse at a plurality of temporal positions along the received scattered light pulse, including, at each of the plurality of temporal positions along the received scattered light pulse, comparing the amplitude of the received scattered light pulse at the temporal position along the received scattered light pulse to a plurality of thresholds and time-to-digital converting the received scattered light pulse when the amplitude of the received scattered light pulse at the temporal position matches one of the plurality of thresholds to produce a time delay signal representing a time delay between when the generated light pulse was emitted and when the temporal position along the received scattered light pulse was received.

16. The method of imaging a remote target of claim 15, further including determining a time delay associated with a peak or center of the received scattered light pulse based on one or more of the time delay signals and determining the range to the target based on the time delay associated with the peak or center of the received scattered light pulse.

17. The method of imaging a remote target of claim 14, wherein detecting an intensity of the received scattered light pulse includes determining an amplitude envelope of the received scattered light pulse and determining an intensity of the received scattered light pulse from the amplitude envelope of the received scattered light pulse.

18. The method of imaging a remote target of claim 17, wherein determining an intensity of the received scattered light pulse from the amplitude envelope of the received scattered light pulse includes determining a width of the received scattered light pulse and determining the intensity of the received scattered light pulse from the width of the received scattered light pulse.

19. The method of imaging a remote target of claim 17, wherein determining an intensity of the received scattered light pulse from the amplitude envelope of the received scattered light pulse includes determining a maximum amplitude of the received scattered light pulse and determining the intensity of the received scattered light pulse from the maximum amplitude of the received scattered light pulse.

20. The method of imaging a remote target of claim 17, wherein determining an amplitude envelope of the received scattered light pulse includes comparing a detected amplitude of the received scattered light pulse at each of a plurality of temporal positions along the received scattered light pulse to each of a plurality of amplitude thresholds and producing a representation of a time delay between when a light pulse was emitted and when the temporal position of the received scattered light pulse was received based on the comparisons.

21. The method of imaging a remote target of claim 20, wherein comparing a detected amplitude of the received scattered light pulse includes detecting when a rising edge of the received scattered light pulse meets a particular threshold and detecting when a falling edge of the received scattered light pulse meets the particular threshold.

22. The method of imaging a remote target of claim 14, wherein determining a reflectivity of the remote target includes determining a maximum intensity of a scattered light pulse at the detected range to the remote target and determining the reflectivity of the remote target by comparing the maximum intensity of a scattered light pulse at the detected range to the remote target to the detected intensity of the received scattered light pulse.

23. The method of imaging a remote target of claim 22, wherein determining the reflectivity of the remote target includes determining a ratio of the detected intensity of the received scattered light pulse to the maximum intensity of a scattered light pulse at the detected range to the remote target.

24. The method of imaging a remote target of claim 14, wherein determining a reflectivity of the remote target includes determining a reflectivity of the remote target from a look-up table based on the determined intensity of the received scattered light pulse and the detected range to the target.

25. The method of imaging a remote target of claim 14, further comprising:

determining that the reflectivity of the target is greater than 100%; and

associating the greater-than-100% reflectivity value with light received from an external light source.

26. An imaging system, comprising:

a laser light source that emits light as a series one or more light pulses;

a controller that controls the laser light source to emit one or more light pulses towards a remote target;

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

a pulse detector that detects an envelope of the scattered light pulse from the electronic signals;

a range processor that determines, based on a timing of the receipt of the scattered light pulse, a range to the target; and

an intensity measurement unit that (i) determines an intensity indication of the scattered light pulse from the envelope of the scattered light pulse, and (ii) determines the reflectivity of the target from the intensity indication and the determined range to the target.

27. The imaging system of claim 26, wherein the pulse detector includes a plurality of amplitude detectors coupled to the light detector, 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 the light pulse was emitted and a portion of the scattered light pulse was received.

28. The imaging system of claim 27, wherein a first one of the plurality of amplitude detectors detects a rising edge of the scattered light pulse from the remote target and a second one of the plurality of the amplitude detectors detects a falling edge of the scattered light pulse from the remote target.

29. The imaging system of claim 27, wherein the comparator of the first one of the plurality of amplitude detectors compares an electronic signal indicative of the scattered light pulse to a first threshold and a comparator of the second one of the plurality of amplitude detectors compares an electronic signal indicative of the scattered light pulse to a second threshold different than the first threshold.

30. The imaging system of claim 27, wherein one or more of the comparators is a rising-edge comparator and one or more other ones of the comparators are falling-edge comparators.