Enhanced SNR phase-sensitive OTDR system with active fiber

A simplified approximate theoretical model between phase noise and Rayleigh backscattering (RS) light is introduced to analyze the performance of distributed acoustic sensing, and results show that noise is relative to the static RS amplitude. Er³⁺-doped active fiber is used to increase RS light and compress system noise. The system phase noise reduces more than 14 dB, a noise level of 9×10^-4 rad/√Hz and signal-to-noise ratio of 46.6 dB @ 100 Hz are obtained experimentally.