Method and system using phase modulation to reduce spectral broadening

1. A laser system comprising:

a seed laser operable to output a seed laser signal along an optical path;

a phase modulator disposed along the optical path and operable to receive the seed laser signal;

a phase modulator driver coupled to the phase modulator, wherein a drive signal from the phase modulator driver is operable to produce, as an output from the phase modulator, an unmodulated seed laser signal when the drive signal is associated with a first state and a modulated seed laser signal when the drive signal is associated with a second state;

a fiber amplifier disposed along the optical path and operable to receive the output of the phase modulator, wherein a spectral bandwidth of an output of the fiber amplifier associated with the second state is less than a spectral bandwidth of the output of the fiber amplifier associated with the first state.

2. The laser system of claim 1 wherein the seed laser comprises a semiconductor laser.

3. The laser system of claim 1 wherein the phase modulator comprises a LiNbO3 phase modulator.

4. The laser system of claim 1 wherein the modulated seed laser signal comprises a signal including temporal phase modulation.

5. The laser system of claim 4 wherein the temporal phase modulation comprises a Gaussian waveform.

6. The laser system of claim 1 further comprising a seed laser driver.

7. The laser system of claim 6 wherein the phase modulator driver and the seed laser driver comprise a single driver.

8. The laser system of claim 1 wherein a power spectrum of the output of the fiber amplifier associated with the first state is characterized by a plurality of peaks.

9. A method of operating a laser system, the method comprising:

providing a seed signal having an initial power spectrum;

applying a voltage to a phase modulator;

transmitting the seed signal through the phase modulator;

modulating the seed signal to provide a modulated signal having a modulated power spectrum;

injecting the modulated signal into a fiber amplifier; and

amplifying the modulated signal to provide an output signal having an output power spectrum substantially equal to the initial power spectrum.

10. The method of claim 9 further comprising pulse modulating the seed signal to provide a series of laser pulses to the phase modulator.

11. The method of claim 9 wherein the seed laser is characterized by an initial temporal power profile comprising a function having a rising edge, a peak at a first time after the rising edge, and a trailing edge after the peak.

12. The method of claim 11 wherein the trailing edge is characterized by a fall time greater than a rise time associated with the rising edge.

13. The method of claim 9 wherein the seed signal is characterized by a seed wavelength and wherein the modulated power spectrum comprises a plurality of peaks including peaks associated with larger wavelength variations from the seed wavelength having a larger amplitude than peaks associated with smaller wavelength variations from the seed wavelength.

14. The method of claim 9 further comprising determining a level of SPM broadening associated with the fiber amplifier prior to transmitting the seed signal through the phase modulator.

15. The method of claim 9 wherein a spectral bandwidth associated with the modulated power spectrum is greater than a spectral bandwidth associated with the initial power spectrum.

16. The method of claim 9 wherein the output power spectrum is characterized by a spectral bandwidth less than twice a bandwidth associated with the initial power spectrum.

17. The method of claim 9 wherein the voltage applied to the phase modulator comprises a time varying voltage.