Distributed Vibration Sensing Over 125 km With Enhanced SNR Using Phi-OTDR Over a URFL Cavity

• Published in: Journal of lightwave technology 2015-06, Vol.33 (12), p.2628-2632
• Main Authors: Martins, Hugo F., Martin-Lopez, Sonia, Corredera, Pedro, Ania-Castanon, Juan Diego, Frazao, Orlando, Gonzalez-Herraez, Miguel
• Format: Article
• Language: English
• Subjects: Amplification; Distributed sensor; Frequency ranges; Holes; Noise; Optical fiber amplifiers; Optical fiber sensors; phasesensitive OTDR; Raman lasers; Raman scattering; Reflectometers; Signal to noise ratio; Stimulated emission; Vibration; Vibration measurement; vibration sensor; Vibrations
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2015.2396359

We describe the use of a phase-sensitive optical time domain reflectometer (ΦOTDR) over an ultra-long Raman fiber laser cavity allowing fully distributed detection of vibrations over 125 km. Compared to a first-order Raman-assisted ΦOTDR, this scheme shows an enhanced signal-to-noise ratio (SNR). This is due to the fact that the relative intensity noise introduced by the Raman amplification is mostly transferred to a lower frequency range, where the balanced detection implemented in the setup provides better suppression of the common-mode noise. The sensor was able to measure vibrations of up to 380 Hz (limit set by the time of flight of light pulses) in a distance of 125 km with a resolution of 10 m and an average SNR of 8 dB with no postprocessing. This implies a >3 dB improvement in SNR over a first-order Raman-assisted setup with similar characteristics.