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Published March 11, 2014 | Published
Book Section - Chapter Open

A linearly chirped seed suppresses SBS in high-power fiber amplifiers, allows coherent combination, and enables long delivery fibers

Abstract

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.

Additional Information

© 2014 Society of Photo-optical Instrumentation Engineers (SPIE). This work was supported by the High Energy Laser Joint Technology Office under contract 11-SA-0405 and the U.S. Army Research Office under grant W911NF-11-2-0081.

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