Brillouin scattering for refractive index sensing in non-adiabatic tapers

We demonstrate the use of non-adiabatic tapers for refractive index sensing in optical fibers based on Brillouin scattering. By exciting higher order optical modes along the taper, the Brillouin gain spectrum becomes multipeaked, where each peak exhibits a different sensitivity to the refractive index of the surrounding medium. By this method, we demonstrate a sensitivity enhancement of the Brillouin frequency shift to refractive index changes by a factor of ≈ 4, compared to an adiabatic taper with the same waist diameter. Furthermore, the use of the spectral difference between two Brillouin gain peaks provides a temperature-independent measurement of the external refractive index

LONG-TERM TEMPERATURE MONITORING OF VOLCANIC AREAS BY DISTRIBUTED OPTICAL FIBER SENSORS

We present the first results of long- term monitoring of temperature profiles at the Campi Flegrei caldera. The measurements were carried out along a 76 meters-deep borehole already equipped with a borehole strain-meter. We installed a cable containing a loop of optical fiber in order to use a fiber-optics distributed sensor based on stimulated Brillouin scattering. The obtained data are consistent with results of both deep and surface geothermal explorations and indicate that geothermal gradient can be efficiently measured and monitored by the proposed technique

Brillouin optical time-domain analysis for geotechnical monitoring

AbstractIn this paper, we show some recent experimental applications of Brillouin optical time-domain analysis (BOTDA) based sensors for geotechnical monitoring. In particular, how these sensors can be applied to detecting early movements of soil slopes by the direct embedding of suitable fiber cables in the ground is presented. Furthermore, the same technology can be used to realize innovative inclinometers, as well as smart foundation anchors

A reconstruction technique for long-range stimulated Brillouin scattering distributed fibre-optic sensors: Experimental results

The experimental validation of a numerical technique for temperature/strain profile reconstruction based on Brillouin optical-fibre time-domain analysis (BOTDA) sensors is presented. In this approach, we search directly for the Brillouin frequency shift profile along the fibre that matches the measured data. The algorithm is based on a harmonic expansion of the unknown profile, whose coefficients are determined by means of a multidimensional minimization. Experimental measurements have been carried out in order to reveal the influence of nonlocalities in Brillouin measurements, and to prove the capability of the proposed algorithm to compensate for these effect

Efficient dynamic events discrimination technique for fiber distributed Brillouin sensors

A technique to detect real time variations of temperature or strain in Brillouin based distributed fiber sensors is proposed and is investigated in this paper. The technique is based on anomaly detection methods such as the RX-algorithm. Detection and isolation of dynamic events from the static ones are demonstrated by a proper processing of the Brillouin gain values obtained by using a standard BOTDA system. Results also suggest that better signal to noise ratio, dynamic range and spatial resolution can be obtained. For a pump pulse of 5 ns the spatial resolution is enhanced, (from 0.541 m obtained by direct gain measurement, to 0.418 m obtained with the technique here exposed) since the analysis is concentrated in the variation of the Brillouin gain and not only on the averaging of the signal along the time

Time and frequency pump-probe multiplexing to enhance the signal response of Brillouin optical time-domain analyzers

© 2014 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibitedA technique to enhance the response and performance of Brillouin distributed fiber sensors is proposed and experimentally validated. The method consists in creating a multi-frequency pump pulse interacting with a matching multi-frequency continuous-wave probe. To avoid nonlinear cross-interaction between spectral lines, the method requires that the distinct pump pulse components and temporal traces reaching the photodetector are subject to wavelength-selective delaying. This way the total pump and probe powers launched into the fiber can be incrementally boosted beyond the thresholds imposed by nonlinear effects. As a consequence of the multiplied pump-probe Brillouin interactions occurring along the fiber, the sensor response can be enhanced in exact proportion to the number of spectral components. The method is experimentally validated in a 50 km-long distributed optical fiber sensor augmented to 3 pump-probe spectral pairs, demonstrating a signal-to-noise ratio enhancement of 4.8 dB.The authors would like to thank Mr. Javier Urricelqui from Universidad Publica de Navarra (Spain) for the valuable discussions and help in relation to the noise characteristics of BOTDA sensors. This work was performed in the framework and with the support of the COST Action TD1001 OFSeSa. M. A. Soto and L. Thevenaz acknowledge the support from the Swiss Commission for Technology and Innovation (Project 13122.1), and from the Swiss State Secretariat for Education, Research and Innovation (SERI) through the project COST C10.0093. UPVLC group acknowledges the support from the Spanish MICINN and the Valencia Government through the projects TEC2011-29120-C05-05 and ACOMP/2013/146, respectively. L. Zhang acknowledges the support from the China Scholarship Council during his stay at EPFL in Switzerland.Soto, MA.; Ricchiuti, AL.; Zhang, L.; Barrera Vilar, D.; Sales Maicas, S.; Thevenaz, L. (2014). Time and frequency pump-probe multiplexing to enhance the signal response of Brillouin optical time-domain analyzers. Optics Express. 22(23):28584-28595. https://doi.org/10.1364/OE.22.028584S28584285952223Horiguchi, T., Shimizu, K., Kurashima, T., Tateda, M., & Koyamada, Y. (1995). Development of a distributed sensing technique using Brillouin scattering. Journal of Lightwave Technology, 13(7), 1296-1302. doi:10.1109/50.400684Soto, M. A., & Thévenaz, L. (2013). Modeling and evaluating the performance of Brillouin distributed optical fiber sensors. Optics Express, 21(25), 31347. doi:10.1364/oe.21.031347Foaleng, S. 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