PHASE SENSITIVE COHERENT OTDR WITH MULTI-FREQUENCY INTERROGATION

摘要

A fiber optic sensor system includes a coherent-detection optical time domain reflectometry system to extract phase information from optical signals returned from a fiber optic sensor arrangement in response to a plurality of interrogating pulses. The system includes a frequency-shifting circuit to repeatedly translate the frequency of an optical pulse generated by a narrowband source to generate a train of interrogating pulses of multiple frequencies. The optical signals returned from the sensor arrangement in response to the pulse train is mixed on a photodetector with light from the narrowband source that has not been shifted to generate mixed output signals. The mixed output signals are filtered into frequency bands, and the phase for each frequency band is extracted.