11 March 2014 Using a linearly chirped seed suppresses SBS in high-power fiber amplifiers, allows coherent combination, and enables long delivery fibers
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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.
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Jeffrey O. White, Eliot Petersen, J. Edgecumbe, George Rakuljic, Naresh Satyan, Arseny Vasilyev, A. Yariv, "Using a linearly chirped seed suppresses SBS in high-power fiber amplifiers, allows coherent combination, and enables long delivery fibers", Proc. SPIE 8961, Fiber Lasers XI: Technology, Systems, and Applications, 896102 (11 March 2014); doi: 10.1117/12.2042919; https://doi.org/10.1117/12.2042919
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