Optical parametric oscillator for lidar system

Patent metadata

Field	Value
Publication number	US-9810786-B1
Application number	US-201715461380-A
Country	US
Kind code	B1
Filing date	Mar 16, 2017
Priority date	Mar 16, 2017
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

In one embodiment, a lidar system includes a pump laser configured to produce pulses of light at a pump wavelength. The lidar system further includes an optical parametric oscillator (OPO) with 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. The lidar system also includes 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 also includes a processor configured to determine the distance from the lidar system to the target.

First claim

What is claimed is:

1. A lidar system comprising:
a pump laser configured to produce pulses of light at a pump wavelength;
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;

a scanner configured to scan the emitted signal 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, wherein:
an output beam of the lidar system comprises the emitted signal 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;

an overlap mirror configured to overlap the input and output beams so that they are substantially coaxial, wherein the overlap mirror comprises:
a hole, slot, or aperture which the output beam passes through; and
a reflecting surface that reflects at least a portion of the input beam toward the receiver; 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 pump laser is an actively Q-switched laser comprising a gain medium and an active Q-switch.

3. The lidar system of claim 1 , wherein the pump laser is a passively Q-switched (PQSW) laser comprising a gain medium and a saturable absorber.

4. The lidar system of claim 3 , wherein the gain medium is pumped by an edge-emitter laser diode or a vertical-external-cavity surface-emitting laser with an operating wavelength between approximately 800 nm and approximately 1000 nm.

5. The lidar system of claim 3 , wherein:
the gain medium comprises neodymium-doped yttrium aluminum garnet (Nd:YAG), ytterbium-doped yttrium aluminum garnet (Yb:YAG), neodymium-doped yttrium orthovanadate (Nd:YVO 4 ), 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); and
the saturable absorber comprises vanadium-doped yttrium aluminum garnet (V:YAG), chromium-doped YAG (Cr:YAG), cobalt-doped MgAl 2 O 4 (Co:spinel), neodymium-doped strontium fluoride (Nd:SrF 2 ), or lithium fluoride with F 2 color centers (LiF:F 2 − ).

6. The lidar system of claim 1 , wherein the pump wavelength is approximately 1030 nm or approximately 1064 nm.

7. The lidar system of claim 1 , 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 .

8. The lidar system of claim 1 , 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.

9. The lidar system of claim 1 , 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).

10. The lidar system of claim 1 , 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.

11. The lidar system of claim 10 , 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.

12. The lidar system of claim 1 , wherein the signal pulses of light emitted by the OPO have a pulse repetition frequency greater than or equal to 20 kHz.

13. The lidar system of claim 1 , 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.

14. The lidar system of claim 1 , further comprising a splitter configured to receive the signal pulses of light emitted by the OPO 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.

15. The lidar system of claim 14 , 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.

16. The lidar system of claim 14 , 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.

17. 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.

18. 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.

19. The lidar system of claim 1 , wherein:
scanning the emitted signal pulses of light across the field of regard comprises scanning a field of view of the OPO 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 OPO field of view and the receiver field of view are scanned synchronously with respect to one another.

Assignees

• Luminar Tech Inc

Inventors

• Welford David
• Jaspan Martin A
• Eichenholz Jason M
• Campbell Scott R
• Martin Lane A
• Weed Matthew D

Classifications

• G01S17/10 Primary

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

• G01S7/484

  Transmitters · CPC title

• H01S3/1643

  YAG · CPC title

• H01S3/09415

  the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping · CPC title

• H01S3/113

  using intracavity saturable absorbers · CPC title