A coherent approach to stationary stimulated Brillouin fiber amplifiers

An analytical stationary solution is proposed for the collinear Brillouin fiber mirror in the frame of the 1-D-coherent 3-wave model, in which decoupled phases allow side-resonance interaction, the conservation of the impulsion being insured by a nonlinear phase gradient. The Lorentzian shape of the gain curve of low efficiency stationary SBS amplifiers is then justified, even when the interaction is strong enough to stimulate an acoustic wave with a narrow spectral width. It is shown that, when SBS efficiency increases, the gain curve first exhibits some gain narrowing, then saturates, yielding for high pump powers a spectral band larger than the spontaneous Brillouin bandwidth.