Analysis and optimization of acoustic speed profiles with large transverse variations for mitigation of stimulated Brillouin scattering in optical fibers

We derive and numerically verify a simple analytical approximation for the calculation of Brillouin gain spectra (BGS) in acoustically antiguiding optical fibers. We use our approximation to find acoustic speed profiles that minimize the peak Brillouin gain. The optimized BGS are top-hat-shaped, regardless of the optical mode distribution, with peak value inversely proportional to the effective area of the optical mode. We further investigate acoustically guiding speed profiles, in which acoustic waveguide modes lead to peaks in the Brillouin gain spectrum. However, for large cores with diameters down to 50 mu m, and often even smaller, these Brillouin gain peaks are spectrally dense, and can be smeared out due to broadening in many practical systems. The Brillouin gain spectrum is then similar for waveguiding and antiguiding acoustic profiles. (C) 2010 Optical Society of America