Active-passive modelocking in a single-polarisation erbium fibre laser

Subpicosecond pulses have been generated in an actively modelocked, polarisation-maintaining Er-doped fibre ring laser. A single-polarisation fibre amplifier and an uncompensated polarisation bias section are integrated into the laser. This laser combines the nonlinear pulse-shortening mechanism of polarisation-rotation lasers and the single-polarisation operation, environmental insensitivity, and capacity for active modelocking characteristic of unidirectional single-polarisation ring lasers