Optical fiber strain distribution measurement by a Brillouin frequency shift technique

Brillouin scattering in optical fibers is a nonlinear phenomenon in which monochromatic light undergoes a shift by the frequency characteristic of the medium and is scattered as a result of interaction with a acoustic wave in the optical fiber. This frequency shift is referred to as the Brillouin frequency shift. The Brillouin frequency shift is proportional to the speed of the acoustic wave in the optical fiber. which depends largely on the stress applied to the optical fiber, so that it is highly dependent on the tensile strain induced in the optical fiber. The basic configuration of the measurement system is shown. In this measurement system, which is based upon an end-to-end lightwave measurement technique, the change in probe light waveform with time is continuously measured while varying the relative pump light-probe light frequency difference, and the relative frequency difference. The present measurement system has enabled measurement of optical fiber strains in the longitudinal direction, the time for measurement being successfully reduced to within one minute. This measurement system, which permits real-time strain measurement, promises to find a widespread range of applications in various fields