Guided longitudinal acoustic modes in spontaneous and stimulated Brillouin scattering in optical fibers

We investigate the Brillouin gain spectrum in the spontaneous and stimulated regimes in AllWave/sup TM/, TrueWave/sup TM/ and dispersion compensating fibers. It is found that several longitudinal modes, depending on the core diameters, exist in the spontaneous regime but decay as the process becomes stimulated. Also, our results on the linewidth narrowing are in an agreement with the theory in undepleted-pump regime.