Comparison of mode-locking regimes based on nonlinear rotation of the polarization plane in erbium-doped fibre lasers with dumbbell-shaped and ring cavities

Stable generation regimes of both single ultrashort pulses and pulse trains in the spectral range 1540–1600 nm are demonstrated for two configurations of dumbbell-shaped and ring fibre laser cavities. In both configurations, mode-locking is ensured by a nonlinear rotation of the polarisation plane. An advantage of using a dumbbell-shaped cavity with a circulator in an erbium-doped fibre laser to obtain single-pulse lasing is demonstrated in comparison with a classical ring cavity assembled on similar elements.