Birefringence-Induced Trains of High-Rate Pulses in a Mode-Locked Fiber Laser

The output of a mode-locked erbium-doped ring fiber laser incorporating a section of a polarization-maintaining (PM) fiber is investigated in both numerical simulations and experiments. With proper inline polarization control, the laser can be set to emit a train of pulses, separated by the differential group delay of the PM section. Repetition rates as high as 500 GHz are experimentally observed. The results provide an added insight into the role of birefringence in mode-locked lasers based on nonlinear polarization rotation.