Adaptive Ladar Receiving Method

• US 20170242105A1
• Filed: 02/10/2017
• Published: 08/24/2017
• Est. Priority Date: 02/18/2016
• Status: Active Grant

• Current Assignee: AEye, Inc.
• Original Assignee: AEye, Inc.
• Inventors: Dussan, Luis Carlos, Steinhardt, Allan, Cook, David
• Granted Patent: US 10,761,196 B2
• Time in Patent Office: Days
• 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 17/26 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 17/66 Tracking 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 7/4813 Housing arrangements
• 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 7/4863 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 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: G01S 7/4876 by removing unwanted signals G01S7/495 takes precedence
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

Disclosed herein are various embodiment of an adaptive ladar receiver and associated method whereby the active pixels in a photodetector array used for reception of ladar pulse returns can be adaptively controlled based at least in part on where the ladar pulses were targeted. Additional embodiments disclose improved imaging optics for use by the receiver and further adaptive control techniques for selecting which pixels of the photodetector array are used for sensing incident light.

Claims

1. A method comprising:

transmitting a ladar pulse toward a targeted range point in a field of view;

selecting a subset of light sensors in an array of light sensors based on a location of the targeted range point in the field of view;

sensing light via the selected subset of light sensors, wherein the sensed light includes a reflection of the transmitted ladar pulse;

generating a signal from the sensed light;

processing the generated signal;

computing range information attributable to the targeted range point based on the processing; and

repeating the transmitting, selecting, sensing, generating, processing, and computing steps for a plurality of different targeted range points in the field of view.

2. The method of claim 1 wherein the processing step includes converting the generated signal into a plurality of digital samples that are representative of the generated signal.

3. The method of claim 2 further comprising:

selecting a subset of range points within the field of view for targeting via compressive sensing; and

wherein the transmitting and repeating steps comprise transmitting a plurality of ladar pulses toward the selected subset of range points.

4. The method of claim 2 wherein the generating step comprises:

amplifying a plurality of read signals from the light sensors using a controlled feedback loop; and

generating the sensed light signal based on the amplified read signals.

5. The method of claim 4 wherein the amplifying step comprises amplifying the read signals from the light sensors using a matching network as part of the controlled feedback loop to increase a signal to noise ratio of the read signals.

6. The method of claim 2 wherein the selecting and repeating steps comprise adaptively adjusting which light sensors are included in the selected subsets based on information derived from the sensed light.

7. The method of claim 6 further comprising:

detecting a malfunctioning light sensor in the array; and

wherein the adaptively adjusting step comprises selecting the subsets of light sensors such that the subsets do not include the light sensor detected to be malfunctioning.

8. The method of claim 6 further comprising:

detecting an oversaturation condition with respect to at least one of a light sensor in the selected subset and the generated signal; and

wherein the adaptively adjusting step comprises selecting the subsets of light sensors to mitigate the detected oversaturation condition.

9. The method of claim 8 wherein the oversaturation condition corresponds to a light sensor that is oversaturated with sensed light.

10. The method of claim 8 wherein the oversaturation condition corresponds to a generated signal that exceeds a defined threshold.

11. The method of claim 6 wherein the adaptively adjusting step comprises adjusting which light sensors are included in the selected subsets to control a dynamic range for the generated signal.

12. The method of claim 6 further comprising:

detecting a light sensor in the selected subset for which its sensed light is corrupted by an interfering ladar pulse; and

wherein the adaptively adjusting step comprises selecting the subsets of light sensors such that the subsets do not include the light sensor corrupted by the interfering ladar pulse.

13. The method of claim 6 further comprising:

detecting a region in the field of view that is a source of noise;

determining a plurality of light sensors in the array that correspond to the detected region; and

wherein the adaptively adjusting step comprises selecting the subsets of light sensors such that the subsets do not include the determined light sensors.

14. The method of claim 6 further comprising:

detecting a light sensor in the selected subset for which its sensed light is corrupted by a scattering ladar pulse; and

wherein the adaptively adjusting step comprises selecting the subsets of light sensors such that the subsets do not include the light sensor corrupted by the scattering ladar pulse.

15. The method of claim 2 wherein the repeating step comprises adjusting which range points are targeted by the transmitted ladar pulses based on information derived from the sensed light.

16. The method of claim 2 wherein the repeating step comprises transmitting ladar pulses at a reduced power level based on information derived from the sensed light.

17. The method of claim 2 wherein the transmitting and repeating steps comprise (1) transmitting the ladar pulses toward the targeted range points via a plurality of scanning mirrors, and (2) transmitting a reference light at a frequency different than the transmitted ladar pulses, the method further comprising:

a photodetector that is optically downstream from the scanning mirrors receiving the transmitted ladar pulses and the transmitted reference light;

the photodetector passing the received transmitted ladar pulses toward the range points;

the photodetector absorbing the received transmitted reference light and converting the absorbed reference light into a tracking signal; and

tracking where the scanning mirrors are targeted when the ladar pulses were transmitted based on the tracking signal.

18. The method of claim 17 wherein the selecting and repeating steps comprise controlling which light sensors are included in the selected subsets based on the tracking.

19. The method of claim 2 further comprising:

directing a reference light onto the array via an optical path that is distinct from a path taken by (1) the transmitted ladar pulse to the targeted range point and (2) the ladar pulse reflection back to the array such that the sensed light includes a portion attributable to the reflection of the transmitted ladar pulse and a portion attributable to the reference light;

wherein the processing step comprises determining a timing relationship between the reflection of the transmitted ladar pulse and the reference light based on the generated signal.

20. The method of claim 19 wherein the computing step comprises computing the range information attributable to the targeted range point based on the determined timing relationship.

21. The method of claim 19 wherein the reference light and the transmitted ladar pulse share a common pulse shape, and wherein the step of determining the timing relationship comprises correlating a delayed version of the generated signal against the generated signal to determine the timing relationship.

22. The method of claim 21 wherein the timing relationship determining step further comprises interpolating at least one of the delayed version of the generated signal and the generated signal to facilitate the timing relationship determination.

23. The method of claim 21 wherein the distinct optical path comprises a direct optical path between (1) a transmitter that transmits the ladar pulse and the reference light and (2) the array.

24. The method of claim 21 wherein the reference light and the transmitted ladar pulse are the same pulse.

25. The method of claim 2 wherein the transmitted ladar pulse comprises a pulse that exhibits a Gaussian pulse shape.

26. The method of claim 2 wherein the light sensors in the array correspond to a plurality of pixels, wherein a plurality of the pixels exhibit a hexagonal shape.

27. The method of claim 2 wherein the light sensors in the array correspond to a plurality of pixels, wherein a plurality of the pixels exhibit different sizes.

28. The method of claim 2 wherein at least one of selected subsets of light sensors is a single light sensor in the array.

29. The method of claim 2 wherein the selecting step comprises selecting a plurality of the light sensors for inclusion in the subset.

30. The method of claim 2 wherein each of a plurality of the selected subsets of light sensors includes different numbers of light sensors.

31. The method of claim 2 wherein the processing step comprises processing the generated signal in a single channel.

32. The method of claim 2 wherein the processing step comprises:

processing the generated signal in a plurality of channels;

coherently combining the channels using filtering to reduce a spatially directional noise component in the generated signal.

33. The method of claim 2 wherein a ladar system performs the method steps while the ladar system is in motion, and wherein the processing step comprises:

reducing a noise component of the generated signal based on a signal derived from the motion of the ladar system relative to fixed surroundings or another moving object.

34. A method comprising:

transmitting a plurality of ladar pulses toward a plurality of targeted range points within a scan area; and

for a photodetector array comprising a plurality of detector pixels and while the ladar pulses are being transmitted, adaptively controlling which of the detector pixels are activated at a given time to sense light for use in range processing based a relationship between locations of the detector pixels in the photodetector array and locations of the targeted range points in the scan area.

35. A method comprising:

sensing light via an array, the array including a plurality of light sensors, each light sensor generating a signal indicative of the sensed light, wherein the sensed light includes a plurality of ladar pulses reflected from a plurality of range points;

selecting a light sensor within the array via a multiplexer;

passing the signal generated by the selected light sensor to a signal processing circuit via the multiplexer; and

amplifying the passed signal via the signal processing circuit, the amplified signal for processing to compute range information with respect to a range point; and

repeating the selecting, passing, and amplifying steps with respect to a plurality of light sensors over time to support a computation of range information with respect to a plurality of the range points.

36. The method of claim 35 further comprising:

transmitting the ladar pulses toward the range points via a scanning ladar transmitter in accordance with a shot list;

controlling the multiplexer to selectively switch between the light sensors in a pattern that follows the shot list.

37. The method of claim 36 wherein the shot list targets a subset of range points

38. The method of claim 35 wherein the selecting step comprises concurrently selecting a plurality of light sensors within the array via the multiplexer, the method further comprising combining the signals generated by the concurrently selected light sensors, and wherein the providing the combined signals to input lines of the multiplexer to thereby define a plurality of composite pixels for the array.

39. The method of claim 35 further comprising:

interpolating a plurality of samples of the amplified signal to compute range information for the range points.

40. The method of claim 39 wherein the interpolating step is performed by a field programmable gate array (FPGA).

41. The method of claim 35 further comprising:

collecting light onto the array via a coherent fiber taper collector.

42. The method of claim 41 further comprising:

focusing light onto an entrance pupil of the coherent fiber taper collector via a lens that includes an imaging system.

43. The method of claim 35 further comprising:

focusing light directly onto the array via a lens that includes an imaging system.

44. The method of claim 36 wherein the selected light sensor comprises a plurality of selected light sensors, the selected light sensors forming a subset of the light sensors of the array.

45. The method of claim 44 wherein the selecting and repeating steps comprise adaptively adjusting which light sensors are selected for inclusion in the subset based on information derived from the sensed light.

46. The method of claim 44 further comprising:

directing a reference light onto the array via an optical path that is distinct from an optical path traveled by the ladar pulse to the array such that the sensed light further includes a component attributable to the reference light, wherein the reference light and the transmitted ladar pulses share a common pulse shape;

determining a timing relationship between the transmitted ladar pulses and the reflected ladar pulses based on information derived from the sensed light.

47. The method of claim 44 wherein the scanning ladar transmitter comprises a plurality of scanning mirrors, wherein the transmitting step comprises scanning ladar transmitter transmitting the ladar pulses toward the range points via the scanning mirrors, the method further comprising:

the scanning ladar transmitter outputting a reference light via the scanning mirrors, wherein the reference light exhibits a frequency different than the ladar pulses;

a dichroic photodetector positioned optically downstream from the scanning ladar transmitter receiving the ladar pulses and the reference light;

the dichroic photodetector passing the ladar pulses toward the range points;

the dichroic photodetector converting the reference light into a tracking signal; and

tracking where the scanning ladar transmitter is targeted when the ladar pulses are transmitted based on the tracking signal.

48. A method comprising:

for each of a plurality of frames, selecting a subset of range points within a frame per frame;

selectively scanning a plurality of mirrors to target the selected range points for each frame;

transmitting a plurality of ladar pulses toward the targeted range points via the scanning mirrors, whereupon the ladar pulses are reflected from the range points;

sensing light that includes the reflected ladar pulses;

generated a signal indicative of the sensed light;

digitizing the signal into a plurality of digital samples; and

an FPGA interpolating the digital samples to compute range information for the range points.