Fiber lasers with increased output brightness

This paper present three methods for increasing the output brightness from fiber lasers. A highly efficient method for the generation of purely radially or azimuthally polarized light within a single multimode fiber laser is investigated. This method involves the introduction of strong losses to unwanted polarizations inside the fiber laser, by introducing intra-cavity spatially variable retarder and a thin film polarizer. Configurations for efficient phase locking and coherent addition in free space of two fiber lasers, each operating with a high order mode, is also presented. The results revealed that the efficiency of the coherent addition can exceed 90%. Lastly, a configuration is demonstrated in which coherent and spectral addition of a two-dimensional fiber laser array is performed.