Linearization of chirp in coherent lidar systems

Patent metadata

Field	Value
Publication number	US-12436245-B2
Application number	US-202117318441-A
Country	US
Kind code	B2
Filing date	May 12, 2021
Priority date	May 12, 2021
Publication date	Oct 7, 2025
Grant date	Oct 7, 2025

Abstract

Disclosed herein are systems and methods for linearizing frequency chirp in a frequency-modulated continuous wave (FMCW) coherent LiDAR system. Exemplary methods can include generating a continuous wave laser signal having a frequency characteristic, in which the frequency characteristic can include a frequency chirp over a frequency band in at least one period; and receiving a signal based on the generated laser signal. The methods can further include mixing the received signal with a local oscillator signal, the local oscillator signal having the frequency characteristic; determining at least one beat frequency based on the mixed signal; sampling the mixed signal at a rate equal to at least two times the beat frequency; determining a correction signal based on the sampled signal; and applying the correction signal to the laser signal.

First claim

What is claimed is:

1. A method for linearizing frequency chirp in a frequency-modulated continuous wave (FMCW) coherent LiDAR system, the method comprising:
generating a continuous wave laser signal having a frequency characteristic, the frequency characteristic comprising a frequency chirp over a frequency band in at least one period;
receiving a signal based on the generated laser signal;
mixing the received signal with a local oscillator signal, the local oscillator signal having the frequency characteristic;
determining at least one beat frequency based on the mixed signal;
sampling the mixed signal at a rate equal to at least two times the beat frequency;
determining a correction signal based on the sampled signal; and
providing the correction signal to a modulator coupled to a laser, the laser configured to generate the continuous wave laser signal, wherein an ideal signal has an ideal frequency characteristic, the ideal frequency characteristic comprising a linear frequency chirp over the frequency band in the at least one period, and for a given sample in the sampled signal, the correction signal indicates a difference between the frequency characteristic of the laser signal and the ideal frequency characteristic.

2. The method of claim 1 , wherein determining at least one beat frequency of the mixed signal comprises determining a maximum beat frequency, and wherein sampling the mixed signal is at a rate equal to at least two times the maximum beat frequency.

3. The method of claim 1 , further comprising scanning a reference reflector with the generated laser signal.

4. The method of claim 1 , wherein the linear frequency chirp comprises a first linear chirp having a positive slope and a second linear chirp having a negative slope.

5. The method of claim 1 , wherein determining the correction signal based on the sampled signal comprises:
determining an average frequency of the sampled signal; and
determining the ideal signal based on the average frequency.

6. The method of claim 1 , wherein the received signal is a reflected signal from a target.

7. The method of claim 6 , further comprising:
determining at least one of a range or a velocity of the target based on the reflected signal.

8. The method of claim 1 , further comprising applying the correction signal to the laser signal.

9. A system for linearizing frequency chirp in a frequency-modulated continuous wave (FMCW) coherent LiDAR system, the system comprising:
a laser configured to generate a continuous wave laser signal having a frequency characteristic, the frequency characteristic comprising a frequency chirp over a frequency band in at least one period;
a mixer coupled to an output of the laser and configured to mix:
a received signal based on the generated laser signal; and
a local oscillator signal having the frequency characteristic;

an analog-to-digital converter coupled to an output of the mixer and configured to sample the mixed signal at a rate equal to at least two times a beat frequency of the mixed signal;
a processor coupled to an output of the converter and configured to determine a correction signal based on the sampled signal; and
a modulator coupled to the laser and configured to apply the correction signal to the laser signal, wherein an ideal signal has an ideal frequency characteristic, the ideal frequency characteristic comprising a linear frequency chirp over the frequency band in the at least one period, and for a given sample in the sampled signal, the correction signal indicates a difference between the frequency characteristic of the laser signal and the ideal frequency characteristic.

10. The system of claim 9 , wherein the beat frequency is a maximum beat frequency and wherein the converter is configured to sample the mixed signal at a rate equal to at least two times the maximum beat frequency.

11. The system of claim 9 , further comprising:
a scanner coupled to the output of the laser and configured to scan at least one of a reference reflector or a target with the generated laser signal.

12. The system of claim 11 , wherein the mixer is configured to receive a reflection signal from the scanner, and wherein the signal is the reflection signal based on the scan of the reference reflector.

13. The system of claim 9 , wherein the linear frequency chirp comprises a first linear chirp having a positive slope and a second linear chirp having a negative slope.

14. The system of claim 9 , wherein the processor is further configured to:
determine an average frequency of the sampled signal; and
determine the ideal signal based on the average frequency.

Assignees

• Velodyne Lidar Usa Inc

Inventors

• Khatana Sunil
• Banas Tyler

Classifications

• G01S17/34

  using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal · CPC title

• G01S17/58

  Velocity or trajectory determination systems; Sense-of-movement determination systems · CPC title

• G01S7/4911 Primary

  Transmitters · CPC title

• G01S7/4917

  superposing optical signals in a photodetector, e.g. optical heterodyne detection · CPC title

• G01S7/497 Primary

  Means for monitoring or calibrating · CPC title