Extending the Real Remoteness of Long-Range Brillouin Optical Time-Domain Fiber Analyzers

• Published in: Journal of lightwave technology 2014-01, Vol.32 (1), p.152-162
• Main Authors: Soto, Marcelo A., Angulo-Vinuesa, Xabier, Martin-Lopez, Sonia, Sang-Hoon Chin, Ania-Castanon, Juan Diego, Corredera, Pedro, Rochat, Etienne, Gonzalez-Herraez, Miguel, Thevenaz, Luc
• Format: Article
• Language: English
• Subjects: Applied sciences; Brillouin scattering; Circuit properties; Coding, codes; distributed optic fiber sensor; distributed Raman amplification; Electric, optical and optoelectronic circuits; Electronics; Exact sciences and technology; Fiber-optic instruments; 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 instruments, equipment and techniques; optical pulse coding; Optical pulses; Optical pumping; Optical sensors; Optoelectronic devices; Physics; Probes; Scattering; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Signal and communications theory; Stimulated emission; strain and temperature measurements; Telecommunications and information theory
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2013.2292329

The real remoteness of a distributed optical fiber sensor based on Brillouin optical time-domain analysis is considerably extended in this paper using seeded second-order Raman amplification and optical pulse coding. The presented analysis and the experimental results demonstrate that a proper optimization of both methods combined with a well-equalized two-sideband probe wave provide a suitable solution to enhance the signal-to-noise ratio of the measurements when an ultra-long sensing fiber is used. In particular, the implemented system is based on an extended optical fiber length, in which half of the fiber is used for sensing purposes, and the other half is used to carry the optical signals to the most distant sensing point, providing also a long fiber for distributed Raman amplification. Power levels of all signals launched into the fiber are properly optimized in order to avoid nonlinear effects, pump depletion, and especially any power imbalance between the two sidebands of the probe wave. This last issue turns out to be extremely important in ultra-long Brillouin sensing to provide strong robustness of the system against pump depletion. This way, by employing a 240 km-long optical fiber-loop, sensing from the interrogation unit up to a 120 km remote position (i.e., corresponding to the real sensing distance away from the sensor unit) is experimentally demonstrated with a spatial resolution of 5 m. Furthermore, this implementation requires no powered element in the whole 240 km fiber loop, providing considerable advantages in situations where the sensing cable crosses large unmanned areas.