PASSIVE-MODE LOCKING BY DISSIPATIVE 4-WAVE-MIXING

A nonlinear fiber with a gain that has symmetric lateral frequency ban ds is found to generate a stable train of bright or dark pulses with a well-defined repetition rate. The pulse train is generated from noise ; the pulses are unchirped, and their amplitude and repetition rate ar e determined by the parameters of the system. The underlying mechanism for this pulse formation is recognized as dissipative four-wave mixin g in which only two frequencies are nonnegligible; one near the maximu m gain transmits energy by wave mixing to its third harmonic, which is in the region of negative gain. An implicit analytical expression for the pulse train solution is derived. It is demonstrated that dissipat ive four-wave mixing can be employed to yield passive mode locking in a fiber ring laser consisting of only a filter and an active fiber. Th e resulting train of pulses is shown to have a high soliton content. ( C) 1998 Optical Society of America.