Coherent Noise Reduction in High Visibility Phase-Sensitive Optical Time Domain Reflectometer for Distributed Sensing of Ultrasonic Waves

• Published in: Journal of lightwave technology 2013-12, Vol.31 (23), p.3631-3637
• Main Authors: Martins, Hugo F., Martin-Lopez, Sonia, Corredera, Pedro, Filograno, Massimo L., Frazao, Orlando, Gonzalez-Herraez, Miguel
• Format: Article
• Language: English
• Subjects: Applied sciences; Circuit properties; Detection, estimation, filtering, equalization, prediction; Distributed sensor; Electric, optical and optoelectronic circuits; Electronics; Exact sciences and technology; General equipment and techniques; Information, signal and communications theory; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Integrated optics. Optical fibers and wave guides; Optical and optoelectronic circuits; Optical fiber sensors; Optical fibers; Optical pulses; Optical pumping; Optoelectronic devices; phase-sensitive OTDR; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Signal and communications theory; Signal, noise; Telecommunications and information theory; vibration measurements; Vibrations
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2013.2286223

Phase-sensitive optical time domain reflectometry (φOTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, φOTDRs have been used mostly for the measurement of sub-kHz vibrations, normally in the context of intrusion sensing. In this paper, the authors present an experimental and theoretical description of a high-visibility φOTDR and its performance when used for ultrasonic vibration measurements. The use of a semiconductor optical amplifier in the setup allows to suppress coherent noise and also to improve the spectral response of the pump pulses. These two advantages greatly decrease the detected intra-band noise thus allowing frequency measurements in the limits set by the time of flight of the light pulses while maintaining the simplicity of the scheme, as no post-processing, extremely high coherence lasers or coherent detection methods are required. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a fully distributed measurement of ultrasonic waves was achieved. The statistical behavior of the system was also described theoretically and characterized experimentally.