PASSIVE HARMONIC MODE-LOCKING IN SOLITON FIBER LASERS

me present an experimental and theoretical study of passively mode-loc ked fiber soliton lasers. Our theoretical analysis based on perturbati on theory describes the soliton interactions that occur when pulse bun ches form. Our results indicate that the nonsoliton component emitted by the propagating solitons causes small changes of the central freque ncy of individual solitons, and the strength and the sign of this inte raction between the soliton and dispersive waves depend on their mutua l phase as well as on the soliton position within the soliton bunch. F or a certain phase difference between the solitons and the nonsoliton component the distribution of the pulses inside the laser cavity. The pulses an then locked into their temporal positions by acoustic effect s. We also demonstrate that the laser performance could be further imp roved by the use of a multiple-quantum-well saturable absorber in comb ination with a nonlinear amplifying loop mirror. In this instance the multiple-quantum-well sample acts not only as a fast saturable absorbe r but also as a passive phase modulator. We experimentally demonstrate that such a laser is capable of generating 500-fs pulses at repetitio n rates exceeding 2 GHz. (C) 1997 Optical Society of America.