Pulsed laser for lidar system

Patent metadata

Field	Value
Publication number	US-9812838-B2
Application number	US-201715470694-A
Country	US
Kind code	B2
Filing date	Mar 27, 2017
Priority date	Nov 30, 2015
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

A lidar system with a seed laser to produce seed pulses with wavelengths between approximately 1400 nm and 2050 nm. A first amplifier amplifies the seed pulses to produce amplified seed pulses and amplified spontaneous emission (ASE). An optical filter removes at least a portion of the ASE. A second amplifier amplifies the seed pulses to produce output pulses having a repetition frequency less than or equal to 100 MHz, a duration less than or equal to 20 nanoseconds, a duty cycle less than or equal to 1%, an energy greater than or equal to 10 nanojoules, a peak power greater than or equal to 1 watt, and an average power less than or equal to 50 watts, the ASE comprising less than or equal to 25% of the average power. A sensor head directs the output pulses into a field of view and detects reflected light therefrom.

First claim

What is claimed is:

1. A lidar system comprising:
a seed laser configured to produce optical seed pulses at one or more operating wavelengths between approximately 1400 nm and 2050 nm, wherein the seed laser comprises:
a plurality of laser diodes; and
an optical multiplexer configured to combine light produced by the plurality of laser diodes into a single optical fiber;

a first fiber-optic amplifier configured to amplify the optical seed pulses with a first gain to produce a first amplifier output that comprises amplified seed pulses and amplified spontaneous emission (ASE);
a first optical filter configured to remove from the first-amplifier output at least a portion of the ASE by transmitting light at the one or more operating wavelengths and attenuating light at other wavelengths by at least 20 dB;
a second fiber-optic amplifier configured to receive the amplified seed pulses from the first optical filter and to amplify them with a second gain to produce output pulses having a pulse repetition frequency less than or equal to 100 MHz, a pulse duration less than or equal to 20 nanoseconds, a duty cycle less than or equal to 1%, a pulse energy greater than or equal to 10 nanojoules, a peak power greater than or equal to 1 watt, and an average power less than or equal to 50 watts, the ASE comprising less than or equal to 25% of the average power; and
a plurality of sensor heads to direct at least a portion of the output pulses into a plurality of fields of view and to detect reflected or scattered light therefrom.

2. The lidar system of claim 1 , wherein:
the optical seed pulses have an average power greater than or equal to 1 microwatt;
the output pulses have an average power greater than or equal to 1 milliwatt; and
the first gain and the second gain are together greater than or equal to 40 dB.

3. The lidar system of claim 1 , wherein:
one or more of the laser diodes are configured to produce continuous-wave (CW) light; and
the seed laser further comprises an optical modulator configured to produce the optical seed pulses from the CW light.

4. The lidar system of claim 1 , wherein:
one or more of the laser diodes are configured to produce optical pulses; and
the seed laser further comprises an optical modulator configured to selectively transmit a sub-portion of each of the optical pulses to produce the optical seed pulses.

5. The lidar system of claim 1 , further comprising a wavelength-dependent delay line configured to receive light comprising a plurality of portions, each portion corresponding to at least one of the one or more operating wavelengths, and to delay each portion in time by an amount based on its corresponding operating wavelength.

6. The lidar system of claim 5 , wherein the delay line comprises:
a circulator; and
a plurality of fiber Bragg gratings (FBGs) corresponding to the one or more operating wavelengths, wherein:
the FBGs are arranged in series and separated from one another by a length of optical fiber; and
each FBG is configured to reflect at least one of the operating wavelengths.

7. The lidar system of claim 1 , wherein the seed laser comprises a wavelength-tunable laser configured to produce light at the one or more operating wavelengths.

8. The lidar system of claim 1 , wherein the seed laser comprises a mode-locked fiber laser and a pulse picker configured to extract optical pulses produced by the mode-locked fiber laser.

9. The lidar system of claim 1 , wherein the first optical filter is configured to remove at least 80% of the ASE from the first amplifier output.

10. The lidar system of claim 1 , wherein the first optical filter comprises a temporal filter configured to be in a transmitting state when an amplified seed pulse is present and to be in a non-transmitting state otherwise.

11. The lidar system of claim 1 , further comprising a second optical filter configured to reduce an amount of ASE produced by the second amplifier.

12. The lidar system of claim 1 , further comprising an optical demultiplexer configured to distribute the output pulses amongst the plurality of sensor heads.

13. The lidar system of claim 1 , further comprising an output collimator configured to produce a free-space optical beam comprising at least a portion of the output pulses.

14. The lidar system of claim 1 , wherein:
the first fiber-optic amplifier comprises a double-pass amplifier comprising:
a circulator;
an erbium-doped or erbium/ytterbium-doped gain fiber with a first end coupled to the circulator; and
a fiber Bragg grating (FBG) coupled to a second end of the gain fiber, wherein the FBG is configured to reflect light corresponding to at least one of the one or more operating wavelengths; and

the second fiber-optic amplifier comprises a booster amplifier with a double-clad gain fiber having erbium dopants or erbium and ytterbium dopants.

15. The lidar system of claim 1 , wherein:
the first fiber-optic amplifier comprises a first single-pass amplifier with a first gain fiber having erbium dopants or erbium and ytterbium dopants;
the second fiber-optic amplifier comprises a second single-pass amplifier with a second gain fiber having erbium dopants or erbium and ytterbium dopants; and
further comprising a third fiber-optic amplifier, wherein the third amplifier comprises a booster amplifier with a double-clad gain fiber having erbium dopants or erbium and ytterbium dopants.

16. The lidar system of claim 1 , wherein:
the first fiber-optic amplifier comprises a double-pass amplifier comprising:
a circulator;
an erbium-doped or erbium/ytterbium-doped gain fiber with a first end coupled to the circulator; and
a fiber Bragg grating (FBG) coupled to a second end of the gain fiber, wherein the FBG is configured to reflect light corresponding to at least one of the one or more operating wavelengths;

the second fiber-optic amplifier comprises a single-pass amplifier with an erbium-doped or erbium/ytterbium-doped gain fiber; and
further comprising a third fiber-optic amplifier, wherein the third amplifier comprises a booster amplifier with a double-clad gain fiber having erbium dopants or erbium and ytterbium dopants.

17. The lidar system of claim 1 , wherein the second fiber-optic amplifier comprises a booster amplifier with a double-clad gain fiber having erbium dopants or erbium and ytterbium dopants.

18. The lidar system of claim 17 , wherein the booster amplifier further comprises a cladding mode stripper.

19. The lidar system of claim 1 , wherein the seed laser, the first amplifier, the first optical filter, and the second amplifier are packaged together within a single housing.

20. The lidar system of claim 1 , further comprising a third fiber-optic amplifier configured to amplify the portion of the output pulses by a third amplifier gain prior to the portion of the output pulses being directed into the plurality of fields of view, wherein the third amplifier comprises a booster amplifier with a double-clad gain fiber having erbium dopants or erbium and ytterbium dopants.

21. The lidar system of claim 1 , further comprising a plurality of optical links to transmit the portion of the output pulses to the plurality of sensor heads, each optical link comprising a gain fiber of a third fiber-optic amplifier.

22. The lidar system of claim 1 , further comprising a plurality of optical links to transmit the amplified seed pulses to the plurality of sensor heads, each optical link comprising a gain fiber of the second

Assignees

• Luminar Tech Inc

Inventors

• Villeneuve Alain
• Eichenholz Jason M

Classifications

• G01S17/14 Primary

  wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters · CPC title

• G01S17/26

  wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals · CPC title

• G01S17/89

  for mapping or imaging · CPC title

• G01S7/4861

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

• G01S17/931

  of land vehicles · CPC title