Coherent LIDAR method and apparatus

Patent metadata

Field	Value
Publication number	US-10901089-B2
Application number	US-201815936240-A
Country	US
Kind code	B2
Filing date	Mar 26, 2018
Priority date	Mar 26, 2018
Publication date	Jan 26, 2021
Grant date	Jan 26, 2021

Abstract

A coherent LIDAR method and apparatus are provided, in which two optical signals having a first frequency difference are reflected by an object. A difference in frequency between the corresponding received and reflected signals is determined. The frequency difference between the reflected signals differs from the first frequency difference due to Doppler effects. The object velocity is determined based on a comparison between the first frequency difference and the frequency difference in the reflected signals. The emitted signals can be produced by modulating a common light source. The reflected signals are inherently mixed at the receiver and further processed. Distance to the object can be determined by pulsing the emitted signals and measuring a time of flight by detecting corresponding pulse edges in the reflected signals, or by using phase sweeping. The emitter can be implemented using an optical phased array.

First claim

We claim:

1. A light detection and ranging (LIDAR) apparatus comprising:
an emitter configured to emit a first optical signal and a second optical signal in a common direction for reflection by an object, wherein an optical frequency of the first optical signal differs from an optical frequency of the second optical signal by a first frequency difference; and
a receiver configured to receive a first received optical signal due to reflection of the first optical signal by the object, receive a second received optical signal due to reflection of the second optical signal by the object, perform a first mixing operation using said first received optical signal and said second received optical signal to form an optical mixed signal having a component at a detection frequency, wherein said detection frequency is equal to a difference between a frequency of the first received optical signal and a frequency of the second received optical signal, and convert said optical mixed signal into an electronic signal using an optical detector;
the apparatus further configured to
extract the detection frequency using a first filter;
perform a second mixing operation using the detection frequency and an indication of the first frequency difference to obtain a resultant signal;
apply a second filter on said resultant signal to provide a filtered resultant signal;
use a frequency detector to obtain a resultant frequency of the filtered resultant signal;

and
measure a component of velocity of the object toward or away from the apparatus based on the resultant frequency.

2. The apparatus of claim 1 , wherein the optical detector receives the first received optical signal and the second received optical signal and forms the optical mixed signal, thereby performing the first mixing operation, and wherein the optical detector has a response bandwidth sufficient to output said detection frequency.

3. The apparatus of claim 1 , wherein the indication of the first frequency difference is a reference signal having a major component at a reference frequency equal to the first frequency difference.

4. The apparatus of claim 3 , wherein the emitter comprises one or more modulators configured to generate the first optical signal and the second optical signal by modulating input light using a modulation signal, and wherein the reference signal is obtained from, or is a portion of, the modulation signal.

5. The apparatus of claim 1 , wherein the indication of the first frequency difference is a numerical indication of the first frequency difference, the apparatus further configured to:
measure the detection frequency by measuring a beat frequency present in the mixed signal;
numerically determine the resultant frequency equal to a difference between the measured detection frequency and the numerical indication of the first frequency difference; and
compute the component of velocity based on the numerically determined resultant frequency.

6. The apparatus of claim 1 , further comprising generating the indication of the first frequency difference using another optical detector configured to receive a portion of the first optical signal and a portion of the second optical signal prior to emission from the apparatus.

7. The apparatus of claim 1 , wherein the receiver further comprises an amplifier, a filter, or both an amplifier and a filter, configured to receive and process the electronic mixed signal.

8. The apparatus of claim 1 , wherein measuring the component of velocity comprises computing a difference between the first frequency difference and the detection frequency, and multiplying the computed difference by a scaling factor that is inversely proportional to the first frequency difference.

9. The apparatus of claim 1 , wherein measuring the component of velocity of the object does not directly use a local copy or local portion of the first optical signal or the second optical signal, or a local copy or local portion of an optical signal used in generating the first optical signal or the second optical signal.

10. The apparatus of claim 1 , wherein the emitter is further configured to emit the first optical signal as a pulsed signal having a first pulse edge emitted at a first time, and wherein the receiver is configured to detect a corresponding pulse edge in the first received optical signal and register a second time at which the corresponding pulse edge is detected, the apparatus further configured to measure a distance to the object based on a comparison of the first time and the second time.

11. The apparatus of claim 1 , wherein the emitter is configured to vary frequency of one or both of the first optical signal and the second optical signal over time, and wherein the apparatus is further configured to measure a distance to the object based on a comparison of frequency of one or both of the first received optical signal and the second received optical signal at time of detection with frequency of a respective one or both of the first optical signal and the second optical signal at time of emission.

12. The apparatus of claim 1 , further comprising adjusting the common direction over time to measure components of velocities of one or more further objects, or further portions of the same object, relative to the apparatus.

13. The apparatus of claim 1 , wherein the emitter comprises an emitter beam scanner (EBS), and wherein the first optical signal and the second optical signal are emitted by the EBS as a combined beam directed in the common direction or as separate respective beams directed in the common direction.

14. The apparatus of claim 13 , wherein the emitter further comprises a modulator configured to receive and modulate narrowband input light to generate a first pre-transmission signal having the optical frequency of the first optical signal and a second pre-transmission signal having the optical frequency of the second optical signal, the first optical signal based on the first pre-transmission signal and the second optical signal based on the second pre-transmission signal.

15. The apparatus of claim 14 , wherein the modulator is a double sideband suppressed carrier (DSB-SC) modulator.

16. The apparatus of claim 1 , wherein the emitter comprises:
a first emitter beam scanner (EBS) configured to emit the first optical signal according to a first radiation pattern having a first major lobe directed in the common direction; and
a second emitter beam scanner (EBS) configured to concurrently emit the second optical signal according to a second radiation pattern having a second major lobe directed in the common direction.

17. The apparatus of claim 16 , wherein the emitter further comprises:
an optical splitter configured to receive and split narrowband input light into a first input light and a second input light;
a first modulator configured to receive and modulate the first input light to generate a first pre-transmission signal having the optical frequency of the first optical signal, the first pre-transmission signal provided to the first EBS for use in generating the first optical signal; and
a second modulator configured to receive and modulate the second input light to generate a second pre-transmission signal having the optical frequency of the second optical signal, the second pre-transmission signal provided to the second EBS for use in generating the second optical signal.

18. The apparatus of claim 1 , wherein the receiver comprises an optical phased array (OPA), a grating coupler, or an edge coupler, the OPA, grating coupler or edge coupler operati

Assignees

• Zhang Chunshu
• Dumais Patrick
• Goodwill Dominic John
• Huawei Tech Co Ltd

Inventors

• Zhang Chunshu
• Dumais Patrick
• Goodwill Dominic John

Classifications

• G01S7/4815

  using multiple transmitters · CPC title

• G01S7/4817

  relating to scanning · CPC title

• G01S17/10

  using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) · CPC title

• G01S17/58 Primary

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

• G01S7/4861

  Circuits for detection, sampling, integration or read-out · CPC title