TUNABLE FIBER SOURCE FOR PICOSECOND PULSES AROUND 1.55-MU-M WITH REPETITION RATES UP TO 20-GHZ

We report on the generation of picosecond optical pulses around 1.55 mum using a tuneable actively mode-locked erbium-doped fibre ring laser. Pulse widths of less than 10 ps have been achieved within the wavelength range 1518 to 1570 nm at a pulse repetition rate of 20 GHz. Pulse trains with lower repetition rates have been generated using electrical square-wave signals for driving the electrooptic modulator, resulting in <20 ps pulse widths. The implementation of an all polarization-preserving fibre ring cavity enabled stable and reproducible operation of the laser. Minimization of the overall ring dispersion offers tuneability at nearly constant repetition rate throughout the whole wavelength range. Simple analytic expressions are given that allow for optimization of the ring laser performance with respect to output power, relaxation oscillations and wavelength tuneability at constant repetition rate.