When seeding a high power fiber amplifier with a frequency-chirped seed, the backward Brillouin scattering can be kept at the spontaneous level because the coherent laser/Stokes interaction is interrupted. Operating a conventional vertical cavity surface-emitting diode laser in an optoelectronic feedback loop can yield a linear frequency chirp of ~1016 Hz/s at a constant output power. The simple and deterministic variation of phase with time preserves temporal coherence, in the sense that it is straightforward to coherently combine multiple amplifiers despite a large length mismatch. The seed bandwidth as seen by the counter-propagating SBS is large, and also increases linearly with fiber length, resulting in a nearly-length-independent SBS threshold. Experimental results at the 600W level will be presented. The impact of a chirped seed on multimode instability is also addressed theoretically.

Date Published: 11 March 2014
PDF: 7 pages
Proc. SPIE 8961, Fiber Lasers XI: Technology, Systems, and Applications, 896102 (11 March 2014); doi: 10.1117/12.2042919

Published in SPIE Proceedings Vol. 8961:
Fiber Lasers XI: Technology, Systems, and Applications
Siddharth Ramachandran, Editor(s)