Cross-talk mitigation using wavelength switching

• US 10,663,564 B2
• Filed: 05/18/2018
• Issued: 05/26/2020
• Est. Priority Date: 03/30/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: LaChapelle, Joseph G.
• Primary Examiner(s): Ratcliffe, Luke D
• Application Number:
  US15/983,545
• Publication Number:
  US 20180284228A1
• Time in Patent Office: 739 Days
• 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 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/4865 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: G05D 1/0088 characterized by the autonomous decision making process, e.g. artificial intelligence, predefined behaviours using knowledge based models G06N5/00
• CPC Class Codes: G05D 1/0238 using obstacle or wall sensors G05D1/0246 and G05D1/0289 take precedence; lidar systems designed for anti-collision purposes G01S17/93

Abstract

A lidar system includes a lighting module configured to (i) select a wavelength from among a plurality of wavelength values, for a particular time period, and (ii) emit light at the selected wavelength. The lighting module emits light at different wavelengths during at least two adjacent periods of time. The lidar system further includes a scanner configured to direct the pulse of light to illuminate a respective region within a field of regard of the lidar system and a receiver module configured to (i) receive a light signal and (ii) determine whether the received light signal includes the light emitted by the lighting module and scattered by a remote target, based at least in part on the wavelength selected by the lighting module.

Claims

1. A lidar system comprising:

a lighting module configured to (i) select a wavelength from among a plurality of wavelength values, for a particular time period, and (ii) emit a pulse of light at the selected wavelength, wherein the lighting module emits pulses of light at different wavelengths during at least two adjacent periods of time;

a scanner configured to direct the emitted pulses of light to illuminate different regions within a field of regard of the lidar system, to scan the field of regard of the lidar system; and

a receiver module configured to (i) receive a light signal and (ii) determine whether the received light signal includes a portion of the pulse of light emitted by the lighting module and scattered by a remote target, based at least in part on the wavelength selected by the lighting module, wherein the receiver module includes;

an avalanche photodiode (APD) configured to produce an electrical-current signal corresponding to the received light signal;

a transimpedance amplifier (TIA) configured to receive the electrical-current signal from the APD and produce a voltage signal corresponding to the received electrical-current signal;

a gain circuit configured to amplify the voltage signal;

a comparator configured to produce an electrical-edge signal when the amplified voltage signal rises above or falls below a particular threshold voltage; and

a time-to-digital converter (TDC) configured to determine an interval of time between emission of the pulse of light and receipt of the electrical-edge signal.

2. The lidar system of claim 1, wherein the APD is a single-photon avalanche diode (SPAD).

3. The lidar system of claim 2, wherein:

the receiver includes a plurality of SPADs, each SPAD configured to generate a respective row of pixels, and

the lighting module is configured to concurrently emit a plurality of beams of light, each for detection by a respective one of the plurality of SPADs.

4. The lidar system of claim 1, wherein the APD is a linear-mode APD configured to operate with an applied reverse bias voltage that is less than a breakdown voltage of the APD.

5. The lidar system of claim 1, further comprising a controller configured to determine a distance from the lidar system to the remote target based at least in part on the interval of time determined by the TDC.

6. The lidar system of claim 1, wherein the lighting module comprises a plurality of laser diodes corresponding, respectively, to the plurality of wavelength values, wherein each laser diode is configured to produce light at a particular wavelength of the plurality of wavelength values.

7. The lidar system of claim 1, wherein the receiver module further includes a wavelength filter adjustable to transmit the wavelength selected by the lighting module.

8. The lidar system of claim 7, wherein the wavelength filter is electronically tunable to the wavelength selected by the lighting module.

9. The lidar system of claim 7, wherein the wavelength filter includes one or more passive filters mechanically adjusted to the wavelength selected by the lighting module.

10. The lidar system of claim 1, further comprising a controller to control wavelength selection at the lighting module and the receiver.

11. The lidar system of claim 10, wherein the controller is configured to select a new wavelength according to a predefined schedule.

12. The lidar system of claim 10, wherein the controller is configured to select a new wavelength in response to detecting a cross-talk event.

13. A method for scanning a field of regard of a lidar system, the method comprising:

selecting a first wavelength from among a plurality of wavelength values;

emitting, by a lighting module, a first pulse of light at the selected first wavelength during a first time period;

detecting a triggering event for changing the first wavelength;

in response to detecting the triggering event, selecting a second wavelength from among the plurality of wavelength values;

emitting, by the lighting module, a second pulse of light at the selected second wavelength during a second time period;

receiving, by a receiver module, light signals during the first time period and the second time period, wherein the receiver module includes;

an avalanche photodiode (APD) configured to produce an electrical-current signal corresponding to a received light signal of the received light signals;

a transimpedance amplifier (TIA) configured to receive the electrical-current signal from the APD and produce a voltage signal corresponding to the received electrical-current signal;

a gain circuit configured to amplify the voltage signal;

a comparator configured to produce an electrical-edge signal when the amplified voltage signal rises above or falls below a particular threshold voltage; and

a time-to-digital converter (TDC) configured to determine an interval of time between emission of the first or second pulse of light and receipt of the electrical-edge signal;

determining whether the received light signal includes a portion of the first or second pulse of light emitted by the lighting module and scattered by a remote target, based at least in part on the wavelength used by the lighting module during the corresponding time period; and

using the received light signal to generate pixels only if it is determined that the received light signal includes the portion of the first or second pulse of light emitted by the lighting module during the corresponding time period.

14. The method of claim 13, wherein detecting the triggering event includes detecting an expiration of a periodic timer.

15. The method of claim 13, wherein detecting the triggering event includes detecting a cross-talk event.

16. The method of claim 13, wherein detecting the triggering event includes detecting that a scan of the entire field of regard of the lidar system, corresponding to one frame of pixels, has been completed.

17. The method of claim 13, wherein detecting the triggering event includes detecting that a scan of one horizontal scan line has been completed.

18. The method of claim 13, wherein the second wavelength is selected from among the plurality of wavelength values randomly.

19. The method of claim 13, wherein the second wavelength is selected from among the plurality of wavelength values in accordance with an order assigned to wavelength values in the plurality of wavelength values.

20. The method of claim 13, wherein emitting the first pulse of light at the selected first wavelength includes using a light source and a filter electronically tuned to the first wavelength, and emitting the second pulse of light at the selected second wavelength includes using the light source and the filter electronically tuned to the second wavelength.

21. The method of claim 13, wherein emitting the first pulse of light at the selected first wavelength and the second pulse of light at the selected second wavelength includes using a first laser diode configured to produce light at the first wavelength and a second laser diode configured to produce light at the second wavelength, respectively.

22. The method of claim 13, wherein determining whether the received light signal includes the portion of the first or second pulse of light emitted by the lighting module includes electronically tuning a wavelength filter to transmit the wavelength selected by the lighting module.

23. The method of claim 13, wherein determining whether the received light signal includes the portion of the first or second pulse of light emitted by the lighting module includes mechanically adjusting a wavelength filter to transmit the wavelength selected by the lighting module.

24. An autonomous vehicle comprising:

one or more components configured to maneuver the autonomous vehicle;

a lidar system configured to generate a point cloud representing objects within a field of regard of the lidar system, the lidar system including;

a lighting module configured to emit pulses of light at different wavelengths during different respective periods of time;

a scanner configured to direct the emitted pulses of light to illuminate respective regions within the field of regard of the lidar system; and

a receiver module configured to receive light signals and generate pixels for the point cloud based on the received light signals only when a received light signal includes a wavelength at which the lighting module emitted a pulse of light during a corresponding period of time, wherein the receiver module includes;

an avalanche photodiode (APD) configured to produce an electrical-current signal corresponding to one of the received light signals;

a transimpedance amplifier (TIA) configured to receive the electrical-current signal from the APD and produce a voltage signal corresponding to the received electrical-current signal;

a gain circuit configured to amplify the voltage signal;

a comparator configured to produce an electrical-edge signal when the amplified voltage signal rises above or falls below a particular threshold voltage; and

a time-to-digital converter (TDC) configured to determine an interval of time between emission of the pulse of light and receipt of the electrical-edge signal; and

a vehicle controller configured to provide control signals to the one or more components to maneuver the autonomous vehicle, based at least in part on the point cloud generated from the lidar system.

25. The autonomous vehicle of claim 24, wherein the vehicle controller is configured to detect a cross-talk event and, in response to detecting the cross-talk event, provide a command to the lidar system to switch to a different wavelength.

26. The autonomous vehicle of claim 25, wherein the vehicle controller is configured to detect the cross-talk event based on analyzing the point cloud.