Stimulated Brillouin scattering (SBS) is a nonlinear optical process. Its occurance in optical fibers is characterised by an energy transfer from an input (pump) wave to a backward-traveling frequency-downshifted (Stokes) wave.[1,2] This occurs because the pump light generates an acoustic wave through the process of electrostriction. The acoustic wave causes a periodic modulation of the fibers refractive index creating a Bragg grating from which photons can be scattered. Because both energy and momentum must be conserved, counterpropagating photons are preferentially amplified. The frequency of the photons that are preferentially amplified is slightly less than that of the pump wave, due to the Doppler shift associated with the grating moving at the acoustic velocity. If a wave with the appropriate frequency shift is propagating counter to the pump wave it will be amplified. However, even in the absence of an input signal, SBS generates a Stokes wave from spontaneously scattered photons. Both active and passive methods have been employed to suppress SBS. Active methods involve broadening the spectral width of the input pulse,[2] while passive methods involve modulating the fiber characteristics.[3-20] It is the passive techniques which are discussed here. Section II defines several terms and parameters necessary to understand the approaches described. Section III reviews the suppression techniques, and Section IV provides an experimental example. Finally, Section V summarizes.
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