A Novel Technique for Measuring Group Velocity Dispersion of an Installed Ultralong Fiber by Using Erbium-Doped Fiber Amplifiers

Abstract
A new technique is presented for measuring the group velocity dispersion (GVD) of optical fibers. It makes it possible to measure the GVD of an already installed ultralong dispersion-shifted fiber. The method is based on phase rotation measurement, but it includes erbium amplifiers and an optical circulator or a 100% reflector. This allows round-trip propagation of the modulated signal and the GVD was successfully measured at one terminal. The maximum measurable length is as long as 125 km.