Fiber laser with free-space components

• US 10,211,592 B1
• Filed: 05/21/2018
• Issued: 02/19/2019
• Est. Priority Date: 10/18/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Villeneuve, Alain, Eichenholz, Jason M., Lingvay, Laurance S.
• Primary Examiner(s): Rodriguez, Armando
• Application Number:
  US15/985,486
• Time in Patent Office: 274 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 17/931 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 7/4815 using multiple transmitters
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/484 Transmitters
• 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 7/497 Means for monitoring or calibrating
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 27/0927 Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
• CPC Class Codes: G02B 27/10 Beam splitting or combining systems polarising systems G02B27/28; mixing and splitting light signals using optical waveguides G02B6/28; beam shaping, e.g. changing the cross-sectional area, by dividing or superposing multiple light beams G02B27/0905
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H01S 3/0064 Anti-reflection devices, e.g. optical isolaters absorbing layers for marking or protecting purposes in laser working B23K26/50; magneto-optical non-reciprocal devices G02F1/093, G02F1/0955
• CPC Class Codes: H01S 3/0078 Frequency filtering
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/06733 Fibre having more than one cladding
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/08077 Pump induced waveguiding, i.e. the pump induces refractive index change in the laser medium to guide the amplified light, e.g. gain- or loss- guiding or thermally induced refractive index change
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094007 : Cladding pumping, i.e. pump light propagating in a clad surrounding the active core
• CPC Class Codes: H01S 3/094042 : of a fibre laser
• CPC Class Codes: H01S 3/094053 : Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle
• CPC Class Codes: H01S 3/094096 : Multi-wavelength pumping
• 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 3/1608 : erbium
• CPC Class Codes: H01S 3/1618 : ytterbium
• CPC Class Codes: H01S 3/2333 : Double-pass amplifiers
• CPC Class Codes: H01S 3/2375 : Hybrid lasers H01S3/07 takes precedence
• CPC Class Codes: H01S 5/0057 : for temporal shaping, e.g. pulse compression, frequency chirping
• CPC Class Codes: H01S 5/02469 : Passive cooling, e.g. where heat is removed by the housing as a whole or by a heat pipe without any active cooling element like a TEC
• CPC Class Codes: H01S 5/0287 : Facet reflectivity
• CPC Class Codes: H01S 5/06216 : Pulse modulation or generation
• CPC Class Codes: H01S 5/0683 : by monitoring the optical output parameters
• 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

In one embodiment, a laser system includes a seed laser diode configured to produce a free-space seed-laser beam. The laser system also includes a pump laser diode configured to produce a free-space pump-laser beam. The laser system further includes an optical-beam combiner configured to combine the seed-laser and pump-laser beams into a combined free-space beam and a focusing lens configured to focus the combined beam. The laser system also includes an optical gain fiber that includes an input end configured to receive the focused beam. The laser system also includes a mounting platform, where one or more of the optical-beam combiner, the focusing lens, and the input end of the gain fiber are mechanically attached to the platform.

Claims

1. A laser system comprising:

a seed laser diode configured to produce a free-space seed-laser beam, wherein the seed laser diode is thermally coupled to a thermoelectric cooler configured to stabilize a temperature of the seed laser diode;

a pump laser diode configured to produce a free-space pump-laser beam;

an optical-beam combiner configured to combine the seed-laser and pump-laser beams into a combined free-space beam;

a focusing lens configured to focus the combined beam;

an optical gain fiber comprising an input end configured to receive the focused beam; and

a mounting platform, wherein one or more of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform.

2. The laser system of claim 1, wherein:

the pump laser diode is a first pump laser diode; and

the laser system further comprises;

a second pump laser diode; and

a pump-laser optical-beam combiner configured to combine light from the first pump laser diode and light from the second pump laser diode to form the free-space pump-laser beam.

3. The laser system of claim 2, wherein:

the laser system further comprises a half-wave plate configured to rotate a polarization of the light from the second pump laser diode to be approximately orthogonal to a polarization of the light from the first pump laser diode; and

the pump-laser optical-beam combiner is a polarization combiner configured to combine the orthogonally polarized light from the first and second pump laser diodes.

4. The laser system of claim 1, wherein the pump laser diode is thermally coupled to a thermoelectric cooler configured to stabilize a temperature of the pump laser diode.

5. The laser system of claim 1, wherein the pump laser diode is mechanically attached to the platform, wherein the pump laser diode is passively cooled by being thermally coupled to the platform.

6. The laser system of claim 1, wherein the platform is in thermal contact with a thermally conductive object configured to receive or dissipate heat from the platform.

7. The laser system of claim 1, wherein the platform is thermally coupled to a thermoelectric cooler configured to remove excess heat from the platform or maintain the platform at a substantially constant temperature.

8. The laser system of claim 1, wherein the platform is thermally coupled to a thermoelectric cooler (TEC), wherein when a temperature of the platform reaches or exceeds a particular maximum temperature, the TEC is activated to keep the temperature of the platform at or below the particular maximum temperature.

9. The laser system of claim 1, wherein the platform is thermally coupled to a heating element, wherein when a temperature of the platform reaches or goes below a particular minimum temperature, the heating element is activated to keep the temperature of the platform at or above the particular minimum temperature.

10. The laser system of claim 1, wherein the optical gain fiber comprises a section of relay fiber and a gain-fiber section, wherein the relay fiber is configured to receive the focused beam and convey light from the seed-laser beam and pump-laser beam to the gain-fiber section.

11. The laser system of claim 10, wherein the relay fiber comprises a fiber Bragg grating configured to reflect a portion of the light from the pump-laser beam back to the pump laser diode.

12. The laser system of claim 1, further comprising a seed-laser detector configured to receive light emitted from a back facet of the seed laser diode.

13. The laser system of claim 1, further comprising a pump-laser detector configured to receive light emitted from a back facet of the pump laser diode.

14. The laser system of claim 1, wherein:

the seed laser diode is mechanically attached to the mounting platform;

the pump laser diode is mechanically attached to the mounting platform; and

the laser system further comprises;

a seed-laser lens configured to collimate the seed-laser beam; and

a pump-laser lens configured to collimate the pump-laser beam.

15. The laser system of claim 1, wherein the mounting platform comprises a glass, ceramic, semiconductor, or metal material having a relatively low coefficient of thermal expansion or a relatively high thermal conductivity.

16. The laser system of claim 1, wherein the mounting platform comprises one or more mechanical registration features configured to define a fixed position on the mounting platform for each of one or more of the seed laser diode, the pump laser diode, the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber.

17. The laser system of claim 1, wherein each of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform using either a passive-alignment technique or an active-alignment technique.

18. The laser system of claim 1, wherein one or more of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform by epoxy, solder, or one or more mechanical fasteners.

19. The laser system of claim 1, wherein:

the seed laser diode is configured to produce light at a wavelength between approximately 1400 nm and approximately 1600 nm; and

the pump laser diode is configured to produce light at a wavelength between approximately 900 nm and approximately 1000 nm.

20. The laser system of claim 1, wherein the seed laser diode is configured to be operated in a pulsed mode wherein the seed-laser beam comprises optical pulses having a pulse duration less than or equal to 100 nanoseconds and a duty cycle less than or equal to 10%.

21. The laser system of claim 1, wherein the optical gain fiber is configured to:

absorb, by a gain material of the optical gain fiber, at least part of the pump-laser portion of the received beam; and

amplify, by the gain material, the seed-laser portion of the received beam.

22. The laser system of claim 1, wherein the input end of the optical gain fiber comprises an input face with an anti-reflection coating having a low optical reflectivity at a wavelength of the seed laser diode or a wavelength of the pump laser diode.

23. The laser system of claim 1, wherein the laser system is part of a lidar system comprising a scanner and a receiver, wherein:

the laser system provides pulses of light to the scanner;

the scanner is configured to scan at least a portion of the pulses of light across a field of regard of the lidar system; and

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

24. A laser system comprising:

a seed laser diode configured to produce a free-space seed-laser beam;

a pump laser diode configured to produce a free-space pump-laser beam;

an optical-beam combiner configured to combine the seed-laser and pump-laser beams into a combined free-space beam;

a focusing lens configured to focus the combined beam;

an optical gain fiber comprising an input end configured to receive the focused beam;

a mounting platform, wherein one or more of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform, wherein the seed laser diode is located remotely from the platform, and wherein light from the seed laser diode is delivered to the platform by an optical fiber, and an end of the optical fiber is mechanically attached to the platform; and

a seed-laser lens configured to collect the seed-laser light from the end of the optical fiber and produce the free-space seed-laser beam.

25. A laser system comprising:

a seed laser diode configured to produce a free-space seed-laser beam;

a pump laser diode configured to produce a free-space pump-laser beam;

an optical-beam combiner configured to combine the seed-laser and pump-laser beams into a combined free-space beam;

a focusing lens configured to focus the combined beam;

an optical gain fiber comprising an input end configured to receive the focused beam;

a mounting platform, wherein one or more of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform, wherein the pump laser diode is located remotely from the platform, and wherein light from the pump laser diode is delivered to the platform by an optical fiber, and an end of the optical fiber is mechanically attached to the platform; and

a pump-laser lens configured to collect the pump-laser light from the end of the optical fiber and produce the free-space pump-laser beam.

26. A laser system comprising:

a first seed laser diode configured to produce light at a first seed-laser wavelength;

a second seed laser diode configured to produce light at a second seed-laser wavelength different from the first seed-laser wavelength;

a seed-laser optical-beam combiner configured to combine the light from the first seed laser diode and the light from the second seed laser diode to form a free-space seed-laser beam;

a pump laser diode configured to produce a free-space pump-laser beam;

an optical-beam combiner configured to combine the seed-laser and pump-laser beams into a combined free-space beam;

a focusing lens configured to focus the combined beam;

an optical gain fiber comprising an input end configured to receive the focused beam; and

a mounting platform, wherein one or more of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform.

27. A laser system comprising:

a seed laser diode configured to produce a free-space seed-laser beam;

a pump laser diode configured to produce a free-space pump-laser beam;

an optical-beam combiner configured to combine the seed-laser and pump-laser beams into a combined free-space beam;

an optical filter located between the seed laser diode and the optical-beam combiner, wherein the optical filter is configured to transmit light at one or more wavelengths of the free-space seed-laser beam and reflect or attenuate light at one or more other wavelengths;

a focusing lens configured to focus the combined beam;

an optical gain fiber comprising an input end configured to receive the focused beam; and

a mounting platform, wherein one or more of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform.

28. A laser system comprising:

a seed laser diode configured to produce a free-space seed-laser beam;

a pump laser diode configured to produce a free-space pump-laser beam;

a pump-laser detector configured to receive light emitted from a back facet of the pump laser diode;

a pump-laser driver configured to;

supply an amount of electrical current to the pump laser diode; and

in response to detecting a decrease in a signal produced by the pump-laser detector, increase the amount of electrical current supplied to the pump laser diode;

an optical-beam combiner configured to combine the seed-laser and pump-laser beams into a combined free-space beam;

a focusing lens configured to focus the combined beam;

an optical gain fiber comprising an input end configured to receive the focused beam; and

a mounting platform, wherein one or more of the optical-beam combiner, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform.

29. The laser system of claim 28, wherein the pump-laser driver is further configured to send a notification indicating that the pump laser diode is degrading or is close to failure when the amount of electrical current supplied to the pump laser diode exceeds a particular threshold current.