High sensitivity and submillimeter resolution optical time-domain reflectometry based on low-coherence interference

Characteristics of the low-coherence optical time-domain reflectometer (OTDR) are presented, and optical waveguide diagnosis using the OTDR is demonstrated. Ultrahigh sensitivity in the shot noise limited operation is discussed, and jagged-shaped Rayleigh-backscatter signals are predicted and observed experimentally. Signal smoothing by widening the resolution from 14 to 400 mu m can drastically reduce the jagging. In the experiment, polarization-sensitive and insensitive OTDRs using a fiber-coiled piezoelectric phase modulator are proposed. Measurements of beat length and bending loss, quality characterization of low-loss waveguides by polarization-sensitive OTDR, and cancellations of polarization fading in discrete backreflection and polarization jagging in Rayleigh backscattering by polarization-insensitive OTDR are successfully demonstrated.>