Linewidth narrowing in Brillouin fiber lasers

Summary form only given. Contrary to lasers with population inversion, the Brillouin fiber laser is a light source which is very sensitive to the phase noise of the pump laser. This property is attributable to the strong nonlinear coupling between the two optical waves and the acoustic wave interacting inside the fiber. From the usual three-wave model of stimulated Brillouin scattering, we first derive an expression connecting the phase of the incident pump field to that of the emitted Stokes wave. It shows that the phase noise of the pump laser is transferred to the Stokes wave after being strongly reduced and smoothed under the combined influence of the acoustic damping and the cavity feedback.