Tunable mode-locked fiber laser with a highly dispersive cavity

Abstract

We describe theoretical and experimental investigations on the spectral and temporal control of an actively mode-locked erbium-doped fiber laser equipped with a highly dispersive cavity. The laser design is based on a unidirectional ring cavity in which a pair of diffraction gratings is inserted. A direct outcome of the dispersion due to the diffraction gratings resides in the fact that the duration of a complete roundtrip in the laser cavity becomes sensitively dependent upon laser wavelength. Tuning of laser emission is then achieved by controlling the modulation frequency of the waveform applied to the loss modulator that produces mode-locked operation. Such a fiber laser enables the generation of picosecond pulses with a rapid tuning over a large bandwidth. We also incorporated a Gires-Tournois interferometer (GTI) in the laser setup in order to investigate how perturbations such as group delay ripple affect the temporal shape of the laser pulses and their spectral content, as well as the stability of the selected laser wavelength. Variation of pulse duration between 40 to100 picoseconds and continuous tuning of laser wavelength will be described.