Tunable picosecond frequency-shifted feedback fiber laser at 1550 nm

A novel frequency-shifted feedback (FSF) fiber laser cavity is proposed and experimentally verified. The laser generates stable mode-locked pulses of <2 ps, mainly limited due to chirp induced by the frequency-shifting element (i.e., the acoustooptic modulator) on the pulses. Fourier transform-limited subpicosecond pulses were obtained by compensating this excess chirp using a piece of single-mode fiber SMF-28 outside the laser cavity. The unique cavity design also allow us to tune the pulse wavelength throughout the Er-gain band and the ability of the laser to self-start gives us the opportunity to characterize transient behavior of mode-locked pulses in an FSF fiber laser cavity.