Seed source for high power optical fiber amplifier
View Patent ↗Methods and systems are provided to reduce stimulated Brillouin scattering in high power optical fiber amplifiers. In an embodiment, a seed source includes a narrow linewidth semiconductor laser driven with a current ramp that simultaneously sweeps the optical power and the lasing frequency at a rate fast enough to reduce stimulated Brillouin scattering.
1. A method of providing a series of laser pulses, the method comprising:
directly modulating a semiconductor laser to generate a seed signal including a plurality of optical pulses, each of the plurality of optical pulses having a frequency chirp substantially larger than a Brillouin gain bandwidth associated with an optical fiber;
providing the seed signal to a first port of an optical circulator;
time-domain filtering the seed signal a first time with an amplitude modulator optically coupled to the optical circulator;
amplifying the time-domain filtered seed signal in a double-pass optical amplifier optically coupled to the modulator to provide a time-domain filtered seed signal; and
time-domain filtering the amplified time-domain filtered seed signal a second time with the amplitude modulator.
2. The method of claim 1 wherein directly modulating the semiconductor laser comprises driving the semiconductor laser with a time varying current waveform.
3. The method of claim 2 wherein the time varying current waveform comprises a current ramp.
4. The method of claim 3 wherein the current ramp is longer than 200 ns.
5. The method of claim 4 wherein the current ramp imposes a frequency chirp rate larger than 1 GHz/ns.
6. The method of claim 1 wherein time-domain filtering the seed signal comprises modulating a drive signal of the amplitude modulator.
7. The method of claim 1 wherein the frequency chirp is larger than about 1 GHz.
8. The method of claim 7 wherein the frequency chirp is larger than about 10 GHz.
9. The method of claim 1 wherein amplifying the time-domain filtered seed signal comprises passing the time-domain filtered seed signal through an optically pumped optical fiber amplifier including a length of rare-earth-doped optical fiber.
10. The method of claim 9 wherein optically pumping the optical fiber amplifier comprises receiving pump energy from one or a plurality of semiconductor lasers.