White noise phase modulation (WNS) and pseudo-random binary sequence phase modulation (PRBS) are effective
techniques for mitigation of nonlinear effects such as stimulated Brillouin scattering (SBS); thereby paving the way for
higher power narrow linewidth fiber amplifiers. However, detailed studies comparing both coherent beam combination
and the SBS suppression of these phase modulation schemes have not been reported. In this study an active fiber cutback
experiment is performed comparing the enhancement factor of a PRBS and WNS broadened seed as a function of
linewidth and fiber length. Furthermore, two WNS and PRBS modulated fiber lasers are coherently combined to measure
and compare the fringe visibility and coherence length as a function of optical path length difference. Notably, the
discrete frequency comb of PRBS modulation provides a beam combining re-coherence effect where the lasers
periodically come back into phase. Significantly, this may reduce path length matching complexity in coherently
combined fiber laser systems.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Brian Anderson ; Angel Flores ; Roger Holten ; Thomas Ehrenreich and Iyad Dajani
Beam combining and SBS suppression in white noise and pseudo-random modulated amplifiers
", Proc. SPIE 9344, Fiber Lasers XII: Technology, Systems, and Applications, 93441U (March 20, 2015); doi:10.1117/12.2082713; http://dx.doi.org/10.1117/12.2082713