Brillouin spectrum of single-mode optical fibers

Experimental and theoretical results are presented for the Brillouin spectrum of single-mode optical fibers in the 180° scattering geometry. It is shown that for core diameters less than 10 μm both the Brillouin frequency shift and spontaneous linewidth are influenced by the nature of the normal acoustic-mode spectrum and wave-vector nonconservation in the acousto-optic interaction. The velocity and lifetime of longitudinal phonon excitations in the core are evaluated, and the consequences to stimulated Brillouin scattering assessed.