We have proposed and demonstrated highly efficient coherent beam combining of N fiber lasers by Y-shaped array coupled with fused fiber couplers. 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 scaling limit and the complementary bandwidth narrowing property will be discussed. By threshold control of the supermodes, high-speed (>1 kHz), high-contrast-ratio (>100) coherent control of beam direction has been demonstrated. No requirements of complicated phase-control optics/electronics, perfect single beam formation without side lobes, and mass-free and reaction-free properties are unique advantages.

© 2005 Optical Society of America

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