Passively Q - Switched Linear Cavity IR Fibre Laser via Nonlinear Polarization Rotation

Setup for self-starting passive Q-switch operation of IR fibre laser via nonlinear polarization rotation (NPR) was demonstrated for the first time for linear cavity. A Q-switched pulse duration of ~ 600 ns, a maximum peak power of ~16 W and an average power of 408 mW have been obtained at 223 kHz repetition rate for 5.1 W pump power from 1319 nm CW Nd: YAG laser launched to ~ 2.78 m unidirectional single-clad Tm-doped silica fibre linear cavity using only flat polarizer and feedback mirror to induce NPR. The dependence of the fibre laser output characteristics on the polarization angle of the polarizer is also reported. However, self induced passive Q-switching in linear fibre laser cavities is only observed in fibres with angled cleaved ends and with lengths that are around the optimum length for CW operation. Keywords: IR fibre laser, Passive Q-switching, Nonlinear polarization rotation, Linear cavity, Ring cavity. PACS: Fiber lasers, 42.55.Wd, Q-switching, 42.60.Gd.