Optical amplifier with multi-wavelength pumping

• US 10,211,593 B1
• Filed: 11/30/2017
• Issued: 02/19/2019
• Est. Priority Date: 10/18/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Lingvay, Laurance S., Villeneuve, Alain, Eichenholz, Jason M.
• Primary Examiner(s): Abraham, Samantha K
• Application Number:
  US15/828,415
• Time in Patent Office: 446 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, an optical amplifier includes a first pump laser diode and a second pump laser diode. The first pump laser diode is configured to produce pump light that includes a first amount of optical power at a first wavelength, and the second pump laser diode is configured to produce pump light that includes a second amount of optical power at a second wavelength different from the first wavelength. The optical amplifier also includes an optical gain fiber configured to receive the pump light from the first and second pump laser diodes and provide optical gain for an optical signal propagating through the optical gain fiber. The optical amplifier further includes a controller configured to adjust the first amount of optical power produced by the first pump laser diode and the second amount of optical power produced by the second pump laser diode.

Claims

1. An optical amplifier comprising:

a first pump laser diode configured to produce pump light comprising a first amount of optical power at a first wavelength;

a second pump laser diode configured to produce pump light comprising a second amount of optical power at a second wavelength different from the first wavelength;

an optical gain fiber configured to receive the pump light from the first and second pump laser diodes and provide optical gain for an optical signal propagating through the optical gain fiber; and

a controller configured to adjust, in response to a temperature change, the first amount of optical power produced by the first pump laser diode and the second amount of optical power produced by the second pump laser diode, wherein the adjustment of the first and second amounts of optical power is based at least in part on an absorption spectrum of the optical gain fiber.

2. The optical amplifier of claim 1, wherein:

the temperature change corresponds to a respective change in a temperature of the first or second pump laser diode, and wherein the temperature change is associated with a shift in the first or second wavelength;

the shift in the first or second wavelength is associated with a change in absorption by the optical gain fiber of the pump light from the first or second pump laser diode, the change in absorption being related to the absorption spectrum of the optical gain fiber; and

the adjustment of the first and second amounts of optical power is configured to compensate for the change in absorption.

3. The optical amplifier of claim 1, further comprising one or more temperature sensors configured to measure a temperature of the first pump laser diode, a temperature of the second pump laser diode, or a temperature of a part of the optical amplifier, wherein the temperature change corresponds to a change in the temperature of the first pump laser diode, the second pump laser diode, or the part of the optical amplifier.

4. The optical amplifier of claim 1, wherein:

if the temperature change corresponds to an increase in temperature, then in response to the increase in the temperature, the controller increases the first amount of optical power and decreases the second amount of optical power.

5. The optical amplifier of claim 1, wherein the first and second wavelengths vary with a temperature change of the first and second pump laser diodes, respectively, by approximately +0.3 nanometers per degree Celsius.

6. The optical amplifier of claim 1, wherein the first and second pump laser diodes are each passively cooled by being thermally coupled to a heat sink.

7. The optical amplifier of claim 1, wherein:

the first wavelength is between approximately 900 nanometers and approximately 950 nanometers;

the second wavelength is between approximately 940 nanometers and approximately 990 nanometers; and

the optical signal has a wavelength between approximately 1400 nanometers and approximately 1600 nanometers.

8. The optical amplifier of claim 1, wherein:

adjusting the first amount of optical power comprises adjusting a first electrical current supplied to the first pump laser diode; and

adjusting the second amount of optical power comprises adjusting a second electrical current supplied to the second pump laser diode.

9. The optical amplifier of claim 1, wherein:

adjusting the first amount of optical power produced by the first pump laser comprises adjusting the first amount of optical power to a value between approximately 0 watts and approximately 20 watts; and

adjusting the second amount of optical power produced by the second pump laser comprises adjusting the second amount of optical power to another value between approximately 0 watts and approximately 20 watts.

10. The optical amplifier of claim 1, wherein:

adjusting the first amount of optical power produced by the first pump laser comprises increasing the first amount of optical power; and

adjusting the second amount of optical power produced by the second pump laser comprises decreasing the second amount of optical power or leaving the second amount of optical power unchanged.

11. The optical amplifier of claim 1, wherein the first and second amounts of optical power are adjusted in a reverse manner wherein:

if the first amount of optical power is increased, then the second amount of optical power is decreased; and

if the first amount of optical power is decreased, then the second amount of optical power is increased.

12. The optical amplifier of claim 1, wherein the controller is further configured to adjust the first and second amounts of optical power in response to a change in an amount of residual pump light detected at or near an output end of the optical gain fiber.

13. The optical amplifier of claim 12, wherein adjusting the first and second amounts of optical power in response to the change in the amount of residual pump light comprises:

if the amount of residual pump light associated with the first pump laser diode increases, then decreasing the first amount of optical power; and

if the amount of residual pump light associated with the first pump laser diode decreases, then increasing the first amount of optical power.

14. The optical amplifier of claim 1, wherein the controller is further configured to adjust the first and second amounts of optical power in response to a change in an amount of power of the optical signal after propagating through the optical gain fiber.

15. The optical amplifier of claim 1, further comprising:

a first back-facet detector configured to receive light emitted from a back facet of the first pump laser diode, wherein the controller is further configured to adjust the first amount of optical power based at least in part on a first electrical signal received from the first back-facet detector; and

a second back-facet detector configured to receive light emitted from a back facet of the second pump laser diode, wherein the controller is further configured to adjust the second amount of optical power based at least in part on a second electrical signal received from the second back-facet detector.

16. The optical amplifier of claim 1, wherein the controller is further configured to:

determine that the first pump laser diode is beginning to fail; and

increase the second amount of optical power produced by the second pump laser diode to compensate for the failing first pump laser diode.

17. The optical amplifier of claim 16, wherein increasing the second amount of optical power comprises operating the second pump laser diode above a recommended maximum operating current or power.

18. The optical amplifier of claim 16, wherein the controller is further configured to send a notification that the first pump laser diode is beginning to fail.

19. The optical amplifier of claim 1, wherein:

the pump light from the first pump laser diode is configured to co-propagate or counter-propagate with the optical signal; and

the pump light from the second pump laser diode is configured to co-propagate or counter-propagate with the optical signal.

20. The optical amplifier of claim 1, further comprising:

a first optical filter that transmits light at the first wavelength and blocks light at the second wavelength, wherein the first optical filter is configured to prevent light from the second pump laser from damaging or destabilizing the first pump laser; and

a second optical filter that transmits light at the second wavelength and blocks light at the first wavelength, wherein the second optical filter is configured to prevent light from the first pump laser from damaging or destabilizing the second pump laser.

21. The optical amplifier of claim 1, further comprising a third pump laser diode configured to produce pump light comprising a third amount of optical power at a third wavelength different from the first and second wavelengths, wherein the optical gain fiber is further configured to receive the pump light from the third pump laser diode.

22. The optical amplifier of claim 1, wherein:

the optical amplifier is part of a laser system comprising a seed laser configured to produce at least part of the optical signal that is amplified by the optical amplifier, wherein the optical signal comprises pulses of light having a wavelength between approximately 1400 nanometers and approximately 1600 nanometers, a pulse duration less than or equal to 100 nanoseconds, and a duty cycle less than or equal to 10%; and

the optical gain fiber comprises a gain material configured to;

absorb the pump light from the first and second pump laser diodes; and

provide the optical gain for the pulses of light.

23. The optical amplifier of claim 22, wherein the laser system is part of a lidar system comprising a scanner, a receiver, and a temperature sensor attached to or located near the lidar system, wherein:

the laser system provides the pulses of light to the scanner;

the scanner scans at least a portion of the pulses of light across a field of regard of the lidar system;

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

the temperature change is determined from a signal from the temperature sensor.

24. The optical amplifier of claim 1, wherein the optical gain fiber is an erbium-doped gain fiber or an erbium/ytterbium-doped gain fiber.

25. The optical amplifier of claim 1, wherein:

the pump light from the first pump laser diode is contained in a first free-space pump-laser beam;

the pump light from the second pump laser diode is contained in a second free-space pump-laser beam; and

the optical amplifier further comprises;

a first pump-laser lens configured to collimate the first free-space pump-laser beam;

a second pump-laser lens configured to collimate the second free-space pump-laser beam;

one or more optical-beam combiners configured to combine the collimated first and second pump-laser beams into a combined free-space beam;

a focusing lens configured to focus the combined beam into an input end of the optical gain fiber; and

a mounting platform, wherein one or more of the first pump laser diode, the second pump laser diode, the first pump-laser lens, the second pump-laser lens, the one or more optical-beam combiners, the focusing lens, and the input end of the optical gain fiber are mechanically attached to the mounting platform.

26. The optical amplifier of claim 25, wherein each of the optical-beam combiners is a dichroic combiner or a polarization combiner.

27. The optical amplifier of claim 1, wherein the temperature change is determined from one or more temperature sensors attached to or located near a part of the optical amplifier.

28. The optical amplifier of claim 1, wherein the absorption spectrum represents a wavelength dependence of absorption by the optical gain fiber of the pump light from the first pump laser diode and the pump light from the second laser diode.

29. A method comprising:

producing, by a first pump laser diode, pump light comprising a first amount of optical power at a first wavelength;

producing, by a second pump laser diode, pump light comprising a second amount of optical power at a second wavelength different from the first wavelength;

receiving, by an optical gain fiber, the pump light from the first and second pump laser diodes;

providing, by the optical gain fiber, optical gain for an optical signal propagating through the optical gain fiber; and

adjusting, by a controller, in response to a temperature change, the first amount of optical power produced by the first pump laser diode and the second amount of optical power produced by the second pump laser diode, wherein the adjustment of the first and second amounts of optical power is based at least in part on an absorption spectrum of the optical gain fiber.

30. The method of claim 29, wherein adjusting the first and second amounts of optical power comprises:

measuring a change in an ambient temperature, a temperature of the first pump laser diode, or a temperature of the second pump laser diode; and

in response to the measured temperature change;

if the measured temperature change corresponds to a temperature increase, then increasing the first amount of optical power and decreasing the second amount of optical power; and

if the measured temperature change corresponds to a temperature decrease, then decreasing the first amount of optical power and increasing the second amount of optical power.