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Proceedings Paper

1 kW cw Yb-fiber-amplifier with <0.5GHz linewidth and near-diffraction limited beam-quality for coherent combining application
Author(s): Doruk Engin; Wei Lu; Mehmetcan Akbulut; Bruce McIntosh; Horacio Verdun; Shantanu Gupta
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Paper Abstract

In this paper, we present results on a master-oscillator Yb-doped fiber amplifier with 1 kW cw output power (at 1064nm), and near-diffraction limited beam quality (M2<1.4), with internal quantum efficiency >83%. The final amplifier stage uses a very high Yb-doped 35-um core LMA fiber, using a new process recipe that virtually eliminates photo-darkening. As a result, high efficiency, SBS-free operation to 1 kW cw power level is obtained, with a phase modulation bandwidth of only 450MHz, well below other reported results. To enable single-frequency cw power scaling to kW levels, we investigate LMA fiber waveguide designs exploiting gain-discrimination, using partially Yb-doped LMA fiber cores, with various diameters up to 80-um. SBS-free, singlefrequency (few kHz) operation is demonstrated up to 0.9kW cw power. At the lower cw powers (<200W) neardiffraction limited beam-quality is obtained, but is observed to deteriorate at higher cw powers. We discuss potential causes, and present a detailed simulation model of kW large-core fiber-amplifiers, that includes all guided modes, fiber bend, transverse spatial hole burning, gain-tailoring, mode-scattering, SBS nonlinearity, and various thermal effects. This model shows good agreement with the observed single-frequency power scaling and beam-quality characteristics.

Paper Details

Date Published: 21 February 2011
PDF: 7 pages
Proc. SPIE 7914, Fiber Lasers VIII: Technology, Systems, and Applications, 791407 (21 February 2011); doi: 10.1117/12.875701
Show Author Affiliations
Doruk Engin, Fibertek, Inc. (United States)
Wei Lu, Fibertek, Inc. (United States)
Mehmetcan Akbulut, Fibertek, Inc. (United States)
Bruce McIntosh, Fibertek, Inc. (United States)
Horacio Verdun, Fibertek, Inc. (United States)
Shantanu Gupta, Fibertek, Inc. (United States)

Published in SPIE Proceedings Vol. 7914:
Fiber Lasers VIII: Technology, Systems, and Applications
Jay W. Dawson, Editor(s)

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