Frequency Doubling of Femtosecond Erbium-Fiber Soliton Lasers in Periodically Poled Lithium Niobate

We report efficient frequency doubling of passively mode-locked femtosecond erbium-fiber lasers. Quasi- phase-matched second-harmonic generation in periodically poled lithium niobate is used to generate 8.1 mW of 190-fs (FWHM), 90-pJ pulses at 777 nm with a conversion efficiency greater than can be obtained with existing birefringently phase-matched nonlinear materials. A dispersion-compensation-free soliton oscillator generating transform-limited 230-fs (FWHM) pulses at 1554 nm is used as a pump laser.