A lidar system with a pulsed laser diode to produce a plurality of optical seed pulses of light at one or more operating wavelengths between approximately 1400 nm and approximately 1600 nm. The lidar system may also include one or more optical amplifiers to amplify the optical seed pulses to produce a plurality of output optical pulses. Each optical amplifier may produce an amount of amplified spontaneous emission (ASE), and the output optical pulses may have characteristics comprising: a pulse repetition frequency of less than or equal to 100 MHz; a pulse duration of less than or equal to 20 nanoseconds; and a duty cycle of less than or equal to 1%. The lidar system may also include one or more optical filters to attenuate the ASE and a receiver to detect at least a portion of the output optical pulses scattered by a target located a distance.
1. A lidar system comprising:
a pulsed laser diode configured to produce a plurality of optical seed pulses of light at one or more operating wavelengths between approximately 1400 nm and approximately 1600 nm;
one or more optical amplifiers configured to amplify the optical seed pulses to produce a plurality of output optical pulses, wherein each optical amplifier produces an amount of amplified spontaneous emission (ASE), and the output optical pulses have characteristics comprising:
a pulse repetition frequency of less than or equal to 100 MHz;
a pulse duration of less than or equal to 20 nanoseconds; and
a duty cycle of less than or equal to 1%;
one or more optical filters, wherein each optical filter is configured to transmit light at the one or more operating wavelengths and attenuate the ASE produced by one or more of the optical amplifiers; and
a receiver configured to detect at least a portion of the output optical pulses scattered by a target located a distance from the lidar system.
2. The lidar system of claim 1 , wherein:
the optical amplifiers comprise a first optical amplifier configured to amplify the optical seed pulses and a second optical amplifier configured to receive and further amplify the optical pulses from the first amplifier; and
the optical filters comprise a first optical filter located between the first and second optical amplifiers and configured to transmit the optical pulses from the first amplifier and attenuate the ASE produced by the first optical amplifier.
3. The lidar system of claim 2 , wherein:
the optical amplifiers further comprise a third optical amplifier configured to receive and further amplify the optical pulses from the second amplifier; and
the optical filters further comprise a second optical filter located between the second and third optical amplifiers and configured to transmit the optical pulses from the second amplifier and attenuate the ASE produced by the second optical amplifier.
4. The lidar system of claim 1 , wherein the optical amplifiers comprise an optical amplifier configured to be disabled when an amount of light coming into the optical amplifier drops below a particular threshold level.
5. The lidar system of claim 4 , wherein disabling the optical amplifier comprises reducing an amount of light produced by a pump laser of the optical amplifier.
6. The lidar system of claim 4 , further comprising a photodiode configured to monitor the amount of light coming into the optical amplifier, wherein the amount of light dropping below the particular threshold level comprises an electrical signal produced by the photodiode dropping below a particular threshold voltage or current, wherein the electrical signal corresponds to the amount of light coming into the optical amplifier.
7. The lidar system of claim 1 , further comprising a controller configured to:
detect a fault condition indicating a problem with the lidar system; and
in response to detecting the fault condition, shut down the optical amplifiers or reduce an amount of power of the output optical pulses.
8. The lidar system of claim 7 , wherein the fault condition comprises:
a failure of a scanner of the lidar system;
a failure of the receiver; or
a person or object coming within a threshold distance of the lidar system.
9. The lidar system of claim 1 , wherein each of the optical filters is configured to attenuate the ASE produced by one of the optical amplifiers by at least 10 dB.
10. The lidar system of claim 1 , wherein the characteristics of the output optical pulses further comprise:
a pulse energy of greater than or equal to 10 nanojoules;
a peak power of greater than or equal to 1 watt; and
an average power of less than or equal to 50 watts, wherein less than 25% of the average power comprises ASE from one or more of the optical amplifiers.
11. The lidar system of claim 1 , wherein the pulsed laser diode is configured to be electrically driven by a pulse generator to produce the optical seed pulses of light.
12. The lidar system of claim 1 , further comprising a scanner configured to scan the output optical pulses across a field of regard of the lidar system.
13. The lidar system of claim 12 , wherein the scanner comprises:
a first mirror driven by a first galvanometer scanner that scans the output optical pulses along a first direction; and
a polygonal scanner that scans the output optical pulses along a second direction substantially orthogonal to the first direction.
14. The lidar system of claim 1 , further comprising 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 one of the output optical pulses to travel from the lidar system to the target and back to the lidar system.
15. The lidar system of claim 1 , wherein the lidar system is configured to generate point clouds of distance measurements at a rate between approximately 0.1 frames per second and approximately 1,000 frames per second.
16. The lidar system of claim 1 , further comprising an output collimator configured to receive the output optical pulses from the optical amplifiers and produce a free-space optical beam comprising the output optical pulses.
17. The lidar system of claim 1 , wherein each optical amplifier comprises a gain fiber and one or more pump lasers, wherein each pump laser has an operating wavelength of approximately 908 nm, 915 nm, 940 nm, 960 nm, 976 nm, 980 nm, 1050 nm, 1064 nm, 1450 nm, or 1480 nm.
18. The lidar system of claim 1 , wherein the optical amplifiers comprise a single-pass amplifier comprising a gain fiber with erbium dopants or erbium and ytterbium dopants.
19. The lidar system of claim 1 , wherein the optical amplifiers comprise a double-pass amplifier comprising:
a circulator;
an erbium-doped or erbium/ytterbium-doped gain fiber comprising a first end and a second end, wherein the first end is coupled to the circulator; and
a fiber Bragg grating (FBG) coupled to the second end of the gain fiber, wherein the FBG is configured to reflect light corresponding to the one or more operating wavelengths and transmit or attenuate light that is away from the reflected wavelengths.
20. The lidar system of claim 1 , wherein the optical amplifiers comprise a booster amplifier comprising a double-clad gain fiber having erbium dopants or erbium and ytterbium dopants.