Nonlinearly limited saturable-absorber mode locking of an erbium fiber laser

We describe an erbium fiber laser that is passively mode locked by a novel, precision antireflection-coated semiconductor saturable-absorber mirror th at incorporates an additional two-photon absorber. It is shown that passive mode locking evolves from a Q-switching instability. The results are achie ved by use of saturable absorbers that provide a large (15%) nonlinear (sat urable) loss. Exploiting two-photon absorption can substantially reduce the peak power of the Q-switched pulses, which results in improved reliability of the laser. Moreover, two-photon absorption can be used to produce an op timal stability range for saturable-absorber mode locking. (C) 1999 Optical Society of America.