A passively mode-locked fiber laser with an enhanced repetition rate characteristic

Passively mode-locked erbium-doped fiber lasers (EDFLs) have gathered much attention as ultrashort optical pulse sources. Successful demonstrations of generating passively mode-locked pulses shorter than 100 fs of pulse width have been reported by using a figure-8 laser with a nonlinear amplifying loop mirror (NALM) and a ring laser with stretched-pulse additive pulses. One of the most significant disadvantages of the passively mode-locked lasers is that the repetition rate of the output pulses is usually limited to the cavity round trip frequency. In order to overcome this shortcoming of passively mode-locked EDFLs a few schemes, such as ones using a sub-ring cavity and extracavity feedback at linear loop of the figure-8 geometry, were demonstrated. We propose a new passively mode-locked EDFL scheme with a delayed optical path (DOP) coupled to the linear loop of figure-8 laser to enhance the pulse repetition rate.