Coherent addition of fiber lasers by use of a fiber coupler

Coherent addition of fiber lasers coupled with an intracavity fiber coupler is reported. Almost a single output is obtained from one of the fiber ports, which one can switch simply by unbalancing the losses in the ports. We show that the constructive supermodes, each of which has a single output in a different port, build up automatically because of the dense longitudinal-mode, length-unbalanced laser array with unbalanced port loss. High addition efficiencies of 93.6% for two fiber lasers and 95.6% for four fiber lasers have been obtained.