Measuring optical fiber diameter variations with few nanometers resolution

Accurate measurement of optical fiber diameter variations with a detection limit of a few nanometers using forwardstimulated Brillouin scattering (FSBS) is reported. Torsional-radial acoustic modes were characterized in short sections of optical fibers of different diameters. Based on the sensitivity, i.e., frequency shift versus fiber diameter, and linewidth, both measured for more than 20 acoustic modes, it is shown that a fiber diameter variation of the order of a few nm can readily be detected.