Pulsed laser for lidar system

• US 9,812,838 B2
• Filed: 03/27/2017
• Issued: 11/07/2017
• Est. Priority Date: 11/30/2015
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Villeneuve, Alain, Eichenholz, Jason M.
• Primary Examiner(s): Abraham, Samantha K
• Application Number:
  US15/470,694
• Publication Number:
  US 20170201059A1
• Time in Patent Office: 225 Days
• CPC Class Codes: G01S 17/00 Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
• CPC Class Codes: G01S 17/02 Systems using the reflection of electromagnetic waves other than radio waves G01S17/66 takes precedence
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• 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 17/14 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 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 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4804 Auxiliary means for detecting or identifying lidar signals or the like, e.g. laser illuminators
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• 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 7/483 Details of pulse systems
• CPC Class Codes: G01S 7/484 : Transmitters
• CPC Class Codes: G01S 7/4861 : Circuits for detection, sampling, integration or read-out
• 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 7/4873 : by deriving and controlling a threshold value
• CPC Class Codes: G01S 7/4876 : by removing unwanted signals G01S7/495 takes precedence
• CPC Class Codes: H01S 2301/02 : ASE (amplified spontaneous emission), noise; Reduction thereof
• CPC Class Codes: H01S 3/0007 : Applications not otherwise provided for working metals or other materials by laser beam B23K26/00; using photons to produce a reactive propulsive thrust F03H3/00; optical recording of measured values in general G01D15/14; optics in general G02B; holographic processes or apparatus G03H; optical marking or sensing of data record carriers G06K7/10 - G06K7/14, G06K15/12; injection heating of plasma by laser H05H1/22; acceleration of neutral particles by electromagnetic wave pressure H05H3/04
• CPC Class Codes: H01S 3/0078 : Frequency filtering
• CPC Class Codes: H01S 3/0085 : Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 3/06733 : Fibre having more than one cladding
• CPC Class Codes: H01S 3/0675 : Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/06754 : Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06758 : Tandem amplifiers
• CPC Class Codes: H01S 3/08086 : Multiple-wavelength emission
• CPC Class Codes: H01S 3/094003 : the pumped medium being a fibre
• CPC Class Codes: H01S 3/094042 : of a fibre laser
• CPC Class Codes: H01S 3/094076 : Pulsed or modulated pumping H01S3/1024 takes precedence
• CPC Class Codes: H01S 3/0941 : of a laser diode
• CPC Class Codes: H01S 3/10023 : by functional association of additional optical elements, e.g. filters, gratings, reflectors
• CPC Class Codes: H01S 3/1106 : Mode locking
• CPC Class Codes: H01S 3/1608 : erbium
• CPC Class Codes: H01S 3/2383 : Parallel arrangements
• CPC Class Codes: H01S 5/0057 : for temporal shaping, e.g. pulse compression, frequency chirping
• CPC Class Codes: H01S 5/0085 : for modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 5/4012 : Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms
• CPC Class Codes: H01S 5/4087 : emitting more than one wavelength

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.

Claims

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 amplifier.

23. 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; and

a plurality of third amplifiers respectively disposed in the plurality of sensor heads, wherein the third amplifiers comprise free-space amplifiers or fiber-optic amplifiers.

24. 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 amplifier; and

a plurality of third amplifiers respectively disposed in the plurality of sensor heads, wherein the third amplifiers comprise free-space amplifiers or fiber-optic amplifiers.