22 April 2005 Fiber laser coherent array for power scaling, bandwidth narrowing, and coherent beam direction control
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Coherent beam combining of many fiber lasers realizes power and brightness scaling. We have proposed and demonstrated highly efficient coherent beam combining of N fiber lasers by Y-shaped array coupled with fused fiber couplers. Power-summed single beam output is obtained from one of the N fiber ports with the lowest loss by selective excitation of one of the N constructive-interference supermodes. The basic characteristics of the coherent array, scalability of power summation, and bandwidth narrowing property will be presented. A 2.65-W fiber laser with only a 12-MHz bandwidth has been obtained by arraying eight 10-nm-bandwidth erbium-doped fiber lasers with an 85% addition efficiency. The characteristic bandwidth narrowing by the Vernier effect can be applied to high-power, narrowband fiber laser beyond nonlinearity limitations. By threshold control of the supermodes, high-speed (>1 kHz), high-contrast-ratio (>100) coherent control of beam direction has been demonstrated in the N=8 coherent array. An electro-optically-driven, 8-channel variable optical attenuator array was implemented in the output ports, and the thresholds were controlled electrically. No requirements of complicated phase-control optics/electronics and perfect single beam formation without side lobes are unique advantages. Mass-free and reaction-free properties will be quite useful in material processing and space communications.
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Akira Shirakawa, Akira Shirakawa, Keigo Matsuo, Keigo Matsuo, Ken-ichi Ueda, Ken-ichi Ueda, } "Fiber laser coherent array for power scaling, bandwidth narrowing, and coherent beam direction control", Proc. SPIE 5709, Fiber Lasers II: Technology, Systems, and Applications, (22 April 2005); doi: 10.1117/12.590328; https://doi.org/10.1117/12.590328

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