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

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