Seed source for high power optical fiber amplifier

Abstract

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 generating laser pulses, the method comprising:
 directly modulating a semiconductor laser to generate a plurality of optical pulses, each of the plurality of pulses having a frequency chirp substantially larger than a Brillouin gain bandwidth associated with an optical fiber; and   externally modulating each of the plurality of optical pulses to reduce a duration of each of the plurality of optical pulses.   
     
     
         2 . The method of  claim 1  wherein externally modulating each of the plurality of optical pulses is performed at a first time as each of the plurality of optical pulses passes through a modulator a first time and at a second time as each of the plurality of optical pulses passes through a modulator a second time. 
     
     
         3 . The method of  claim 1  wherein each of the plurality of optical pulses are characterized by a single frequency. 
     
     
         4 . The method of  claim 1  wherein each of the plurality of optical pulses are characterized by a plurality of frequencies. 
     
     
         5 . The method of  claim 4  wherein a linewidth of each of the plurality of frequencies is less than a Brillouin gain bandwidth of about 30 MHz. 
     
     
         6 . The method of  claim 1  wherein the frequency chirp is larger than 1 GHz. 
     
     
         7 . The method of  claim 6  wherein the frequency chirp is larger than about 10 GHz. 
     
     
         8 . A method of generating laser pulses, the method comprising:
 directly modulating a semiconductor laser to generate a plurality of optical pulses, each of the plurality of pulses having a frequency chirp substantially larger than a Brillouin gain bandwidth associated with an optical fiber;   amplifying the plurality of optical pulses to generate a plurality of amplified optical pulses; and   externally modulating the plurality of amplified optical pulses to reduce a temporal length of each of the plurality of amplified optical pulses.   
     
     
         9 . The method of  claim 8  wherein each of the plurality of optical pulses are characterized by a single frequency. 
     
     
         10 . The method of  claim 8  wherein each of the plurality of optical pulses are characterized by a plurality of frequencies. 
     
     
         11 . The method of  claim 10  wherein a linewidth of each of the plurality of frequencies is less than a Brillouin gain bandwidth. 
     
     
         12 . The method of  claim 8  wherein externally modulating each of the plurality of optical pulses is performed at a first time as each of the plurality of optical pulses passes through a modulator a first time and at a second time as each of the plurality of optical pulses passes through a modulator a second time. 
     
     
         13 . The method of  claim 8  wherein the frequency chirp is larger than about 1 GHz. 
     
     
         14 . The method of  claim 13  wherein the frequency chirp is larger than about 10 GHz. 
     
     
         15 . The method of  claim 8  wherein amplifying the plurality of optical pulses comprises passing the plurality of optical pulses through an optically pumped optical fiber amplifier including a length of rare-earth-doped optical fiber.