Ultra-long graded-index multimode optical-fiber fault location using Raman optical time-domain reflectometry

Ultra-long graded-index (GI) multimode fiber fault location has been carried out using Raman optical time-domain reflectometry (ROTDR), where the Stokes\´ light pulses generated by the stimulated Raman scattering effect in a measured fiber are used as probe pulses. For basic investigation, spectral power distributions of the Stokes\´ pulses in a multimode fiber pumped by a 1.06-μm -switched Nd:YAG laser have been measured. Maximum locatable distance for a fiber break using the ROTDR technique has been estimated by the measurement results, and it has been shown that a more-than-100-km-long multimode fiber break is locatable. On the basis of these results, a 86-km-long multimode fiber fault-location experiment has been carried out, and the break without Fresnel reflection has been located.