Measurement of acoustic noise in field-deployed fiber optic cables

In the paper we are presenting the results of the measurements of the phase noise occurring in the optical fiber because of mechanical (acoustic) vibrations. The system used for these measurements, based on a dual-mixer time-difference method, is also presented. We tested two different fiber spans, one running along the motorway and the second one running along the railroad tracks. After analyzing more than 100 h of recorded acoustic noise signals we found substantial differences depending not only on the route of the fiber but even on the time of the day.