Wavelength dependences of Brillouin frequency shifts of optical fibres in 1.55 mu m wavelength region

The Brillouin frequency shifts of three types of optical fibres are measured by the heterodyne method using an electrical spectrum analyser. Owing to its excellent resolution, a change of 10 MHz in the Brillouin frequency shift, which corresponds to a change of the order of 1 nm in pump wavelength, can be easily measured. The longitudinal acoustic velocities of different fibre types can be deduced. The results also confirm that the frequency shift ( approximately 10 GHz) varies inversely to the wavelength and decreases with an increase of GeO₂ doping concentration.