Abstract
Optical-time-domain-reflectometer (OTDR) suffers from the existence of dead-zones along a deployed fiber under test (FUT). Within a dead-zone, OTDR typically fails to provide any reliable diagnostic information. We here use a few-mode fiber (FMF) to completely cancel the OTDR dead-zone produced by the front facet reflection of the FUT. In particular, we launch the optical pulses in the form of the LP01 mode into the FMF, and meanwhile we record the Rayleigh signal from the higher-order modes. The developed system successfully monitors the amplitude and frequency of a vibration event produced by a piezoelectric transducer (PZT) located within the dead-zone.