Solid-state laser for lidar system

• US 10,418,776 B2
• Filed: 02/21/2018
• Issued: 09/17/2019
• Est. Priority Date: 03/16/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Welford, David, Jaspan, Martin A., Eichenholz, Jason M., Campbell, Scott R., Martin, Lane A., Weed, Matthew D.
• Primary Examiner(s): Ratcliffe, Luke D
• Application Number:
  US15/901,838
• Publication Number:
  US 20180269646A1
• Time in Patent Office: 573 Days
• 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 17/42 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 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: H01S 3/0092 Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H01S 3/061 with elliptical or circular cross-section and elongated shape, e.g. rod
• CPC Class Codes: H01S 3/0612 Non-homogeneous structure H01S3/07 takes precedence
• CPC Class Codes: H01S 3/0621 Coatings on the end-faces, e.g. input/output surfaces of the laser light
• CPC Class Codes: H01S 3/0627 the resonator being monolithic, e.g. microlaser
• CPC Class Codes: H01S 3/08 Construction or shape of optical resonators or components thereof
• CPC Class Codes: H01S 3/094076 Pulsed or modulated pumping H01S3/1024 takes precedence
• CPC Class Codes: H01S 3/094084 with pump light recycling, i.e. with reinjection of the unused pump light, e.g. by reflectors or circulators
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• CPC Class Codes: H01S 3/1022 by controlling the optical pumping
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/113 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/1611 neodymium
• CPC Class Codes: H01S 3/1643 YAG
• CPC Class Codes: H01S 3/1673 : YVO4 [YVO]
• CPC Class Codes: H01S 3/30 : using scattering effects, e.g. stimulated Brillouin or Raman effects

Abstract

A lidar system can include a solid-state laser to emit pulses of light. The solid-state laser can include a Q-switched laser having a gain medium and a Q-switch. The lidar system can also include a scanner configured to scan the emitted pulses of light across a field of regard and a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system. The lidar system can also include a processor configured to determine the distance from the lidar system to the target based at least in part on a round-trip time of flight for an emitted pulse of light to travel from the lidar system to the target and back to the lidar system.

Claims

1. A lidar system comprising:

a solid-state laser configured to emit pulses of light, wherein the solid-state laser comprises a passively Q-switched laser comprising a gain medium and a saturable absorber, wherein the saturable absorber is bonded to the gain medium;

a scanner configured to scan the emitted pulses of light across a field of regard;

a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system; and

a processor configured to determine the distance from the lidar system to the target based at least in part on a round-trip time of flight for an emitted pulse of light to travel from the lidar system to the target and back to the lidar system.

2. The lidar system of claim 1, wherein the pulses of light are emitted by the Q-switched laser, and the pulses of light have a pulse repetition frequency greater than or equal to 20 kHz.

3. The lidar system of claim 1, wherein the pulses of light are emitted by the Q-switched laser, and the pulses of light have optical characteristics comprising:

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; and

a peak power greater than or equal to 1 watt.

4. The lidar system of claim 1, wherein the saturable absorber comprises vanadium-doped yttrium aluminum garnet (V:

YAG), chromium-doped YAG (Cr;

YAG), cobalt-doped MgAl₂O₄ (Co;

spinel), neodymium-doped strontium fluoride (Nd;

SrF₂), or lithium fluoride with F₂⁻

color centers (LiF;

F₂⁻

).

5. The lidar system of claim 1, wherein the gain medium comprises neodymium-doped yttrium aluminum garnet (Nd:

YAG), ytterbium-doped yttrium aluminum garnet (Yb;

YAG), neodymium-doped yttrium orthovanadate (Nd;

YVO₄), neodymium-doped yttrium scandium gallium garnet (Nd;

YSGG), neodymium-doped gadolinium scandium gallium garnet (Nd;

GSGG), neodymium-doped yttrium aluminum perovskite (Nd;

YAP), or neodymium-doped yttrium lithium fluoride (Nd;

YLF).

6. The lidar system of claim 1, wherein the gain medium comprises a back surface with a dielectric coating having a low reflectivity at a pump-laser wavelength and a high reflectivity at an operating wavelength of the Q-switched laser.

7. The lidar system of claim 1, wherein the gain medium is pumped at a pump wavelength between approximately 800 nm and approximately 1000 nm by an edge-emitter laser diode or a vertical-external-cavity surface-emitting laser.

8. The lidar system of claim 1, wherein the Q-switched laser is an eye-safe laser with an operating wavelength between approximately 1400 nm and approximately 1600 nm.

9. The lidar system of claim 1, wherein an operating wavelength of the Q-switched laser is approximately 1030 nanometers, approximately 1064 nanometers, or between approximately 1400 nanometers and approximately 1480 nanometers.

10. The lidar system of claim 1, wherein the Q-switched laser further comprises an end cap coupled to the gain medium, wherein:

the end cap is substantially free of gain-material dopants; and

the end cap is positioned to receive light from a pump laser so that the pump-laser light propagates through the end cap before entering the gain medium.

11. The lidar system of claim 1, further comprising a splitter configured to receive the pulses of light emitted by the solid-state laser and split each received pulse of light into two or more angularly separated pulses of light which are scanned by the scanner across the field of regard.

12. The lidar system of claim 11, wherein:

the angularly separated pulses of light are scanned along a scanning direction; and

the angularly separated pulses of light are split along a direction that is approximately orthogonal to the scanning direction.

13. The lidar system of claim 11, wherein the receiver comprises an array of two or more detector elements, wherein each detector element is configured to detect scattered light from a respective pulse of the two or more angularly separated pulses of light which are scanned across the field of regard.

14. The lidar system of claim 1, wherein the field of regard comprises:

a horizontal field of regard greater than or equal to 25 degrees; and

a vertical field of regard greater than or equal to 5 degrees.

15. The lidar system of claim 1, wherein the scanner comprises one or more mirrors, wherein each mirror is mechanically driven by a galvanometer scanner, a resonant scanner, a microelectromechanical systems (MEMS) device, or a voice coil motor.

16. The lidar system of claim 1, wherein:

an output beam of the lidar system comprises the emitted pulses of light which are scanned across the field of regard;

an input beam of the lidar system comprises the portion of the scanned pulses of light detected by the receiver; and

the input and output beams are substantially coaxial.

17. The lidar system of claim 1, wherein:

scanning the emitted pulses of light across the field of regard comprises scanning a field of view of the solid-state laser across the field of regard; and

the scanner is further configured to scan a field of view of the receiver across the field of regard, wherein the solid-state laser field of view and the receiver field of view are scanned synchronously with respect to one another.

18. A lidar system comprising:

a solid-state laser configured to emit pulses of light, wherein the solid-state laser comprises;

a Q-switched laser comprising a gain medium and a Q-switch, wherein the Q-switched laser is configured to produce pump pulses of light at a pump wavelength; and

an optical parametric oscillator (OPO) comprising an OPO medium configured to;

receive the pump pulses from the pump laser;

convert at least part of the received pump pulses into pulses of light at a signal wavelength and pulses of light at an idler wavelength; and

emit at least a portion of the signal pulses, wherein the pulses of light emitted by the solid-state laser comprise the signal pulses emitted by the OPO;

a scanner configured to scan the emitted pulses of light across a field of regard;

a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system; and

a processor configured to determine the distance from the lidar system to the target based at least in part on a round-trip time of flight for an emitted pulse of light to travel from the lidar system to the target and back to the lidar system.

19. The lidar system of claim 18, wherein the signal pulses of light emitted by the OPO have a pulse repetition frequency greater than or equal to 20 kHz.

20. The lidar system of claim 18, wherein the signal pulses of light emitted by the OPO have optical characteristics comprising:

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; and

a peak power greater than or equal to 1 watt.

21. The lidar system of claim 18, wherein the pump wavelength is approximately 1030 nm or approximately 1064 nm.

22. The lidar system of claim 18, wherein the pump wavelength (λ

_p), signal wavelength (λ

_s), and idler wavelength (λ

_i) are at least approximately related by an expression 1/λ

_p=1/λ

_s+1/λ

_i, wherein;

λ

_p is less than λ

_s and λ

_i; and

λ

_s is less than λ

_i.

23. The lidar system of claim 18, wherein the OPO is an eye-safe light source and the signal wavelength of the signal pulses emitted by the OPO is between approximately 1400 nm and approximately 1600 nm.

24. The lidar system of claim 18, wherein the OPO medium comprises periodically poled potassium titanyl phosphate (PPKTP), periodically poled potassium titanyl arsenate (PPKTA), periodically poled rubidium titanyl arsenate (PPRTA), periodically poled lithium niobate (PPLN), periodically poled lithium tantalate (PPLT), or periodically poled stoichiometric lithium tantalate (PPSLT).

25. The lidar system of claim 18, wherein the OPO medium comprises a back surface and an output surface, wherein:

the back surface comprises a dielectric coating with low reflectivity for the pump wavelength and high reflectivity for the signal wavelength; and

the output surface comprises a dielectric coating with high reflectivity for the pump wavelength and low or partial reflectivity for the signal wavelength.

26. The lidar system of claim 25, wherein:

the coating of the back surface additionally has high reflectivity or low reflectivity for the idler wavelength; and

the coating of the output surface additionally has high reflectivity or low reflectivity for the idler wavelength.

27. A lidar system comprising:

a solid-state laser configured to emit pulses of light, wherein the solid-state laser comprises a Q-switched laser comprising a gain medium and a Q-switch, wherein the pulses of light are emitted by the Q-switched laser, and the pulses of light have optical characteristics comprising;

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; and

a peak power greater than or equal to 1 watt;

a scanner configured to scan the emitted pulses of light across a field of regard;

a receiver configured to detect at least a portion of the scanned pulses of light scattered by a target located a distance from the lidar system; and

a processor configured to determine the distance from the lidar system to the target based at least in part on a round-trip time of flight for an emitted pulse of light to travel from the lidar system to the target and back to the lidar system.

28. The lidar system of claim 27, wherein the pulses of light have a pulse repetition frequency greater than or equal to 20 kHz.

29. The lidar system of claim 27, wherein the Q-switched laser is an actively Q-switched laser and the Q-switch is an active Q-switch.

30. The lidar system of claim 27, wherein the Q-switched laser is a passively Q-switched (PQSW) laser and the Q-switch is a saturable absorber.