A stable narrow linewidth Q-switched Er-doped fibre laser

Summary form only given. Compact sources with high peak powers and short pulsewidths are required for applications such as distributed sensing and laser range finding. Previously reported Q-switched erbium-doped fibre lasers consisting of Fabry-Perot or ring cavities are suitable for many applications in the operation wavelength around 1550 nm, but for distributed strain sensing based on spontaneous Brillouin scattering, a stable ultra-narrow linewidth pulsed source with sufficient peak powers is required to resolve the spectral information of the Brillouin signals.