Effect of acoustic waveguide properties on the Brillouin gain spectrum in multi-mode fibers

With a recent developed mode-coupling model, the Brillouin gain spectra (BGS) of multi-mode fibers (MMF) are investigated and compared with the corresponding experiment. It is found that the calculation results are coincident well with the experiment data. Furthermore, the BGS are found to be very sensitive to the index fluctuation. Such phenomenon is demonstrated by introducing a small index hump or dip in the center of the fiber core. And it can be explained by that the index fluctuation may influence the acoustic mode greatly.