Experimental study of SBS suppression via white noise phase modulation

Power scaling of single-frequency high power optical fiber lasers is limited due to the stimulated-Brillouin scattering (SBS). Towards that end, line broadening through white noise phase modulation can be used to suppress SBS. Theoretical models predict the SBS threshold enhancement factor as a function of linewidth and fiber length, but have yet to be experimentally verified. A radio frequency (RF) white noise source (WNS), in conjunction with RF low pass filters, is used to randomly modulate an optical signal through an electro-optic modulator (EOM). The optical signal is broadened, with optical bandwidth controlled through RF filtering. Subsequently, this modulated signal is used in a cutback experiment with a passive fiber. Studies describing SBS enhancement factors as a function of linewidth and fiber length are investigated. Results indicate a reduction in the SBS threshold enhancement factor at shorter fiber lengths, which is in reasonable agreement with the theoretical predictions. Finally, we compare these results with cutback experiments conducted using phase modulation through pseudo random bit sequence (PRBS).