Femto/nano-second switchable passively mode-locked fiber laser with analytic modeling by the cubic-quintic Ginzburg-Landau equation.

We report a passively mode-locked erbium-doped fiber laser with pulse widths switchable from 473 fs to 76.8 ns, where the fundamental mode-locking, noise-like pulse, nanosecond mode-locking, and dual-width mode-locking (DML) are obtained by adjusting a polarization controller. Co-existence of femto- and nano-second pulses in DML is attributed to the gain balancing. Analytic modeling of the fiber laser with the cubic-quintic Ginzburg-Landau equation is presented, in which the pulse widths are calculated as functions of dispersion, self-phase modulation (SPM), cubic saturable absorption (SA), and quintic SA. The generation of nanosecond pulses is caused by the weakened intracavity pulse-shortening strength, the reduced effective SPM, and the inclusion of quintic SA in the laser cavity.