Repetition rate enhancement and mode shaping in dual-cavity stretched pulse fiber laser

A novel orthogonally polarized coupled-cavities configuration for stretched pulse fiber lasers, based on tunable birefringence, is presented. By alignment of the birefringence, we achieve envelope modulated mode patterns, which in turn are used to increase the repetition rate of the laser while maintaining the well-profiled femtosecond pulses. Experimental results and a supporting theoretical model are presented.