Picosecond SESAM-Based Ytterbium Mode-Locked Fiber Lasers

Abstract

Using semiconductor saturable absorber mirrors and a grating-pair dispersion compensator, we obtain reliable self-starting mode locking of a ytterbium (Yb) fiber laser tunable over 125 nm. The 980-1105-nm tuning range is achieved by optimization of nonlinear reflection and bandgap characteristics of the multiple-quantum-well saturable absorber and by proper engineering of the laser cavity. A short-length Yb-doped double-clad amplifier seeded with mode-locked Yb-fiber laser produces picosecond pulses with energy of 30 nJ (700 mW of average power). A compact version of the fiber laser was built using a Gires-Tournois compensator and short length (1-cm long) of highly doped Yb fiber. Using a novel semiconductor saturable abserver mirror based on GaInNAs structure, self-started 1.5-ps pulse mode-locked operation was obtained at 1023 nm with a repetition rate of 95 MHz. A mode-locked Yb-doped fiber laser was also developed without using any dispersion compensation technique. Overall group-velocity dispersion was minimized by using highly doped Yb fiber in a compact amplifying loop cavity. Self-started mode-locked operation was obtained in 980-1030-nm wavelength range with a fundamental repetition rate of 140 MHz. Without using dispersion compensation, the lasers produced pulses in a range from 15 to 26 ps.