Brillouin Distributed Fiber Sensors: An Overview and Applications <s> Introduction <s> We present and demonstrate a technique for remote sensing of fiber Bragg gratings (FBGs) beyond 150 km. The system combines Raman, Brillouin, and erbium gain in a linear cavity fiber laser and deploys a novel heterodyne detection technique to avoid the signal-to-noise ratio limitations produced by Rayleigh scattering. Two FBGs located in series were interrogated at 155 km away from the processing unit using 0.6 W of Raman pump and less than 2 mW of Brillouin pump provided by a tunable wavelength-swept laser. Heterodyne detection brings forth a signal-to-noise ratio of approximately 10 dB in our measurements. <s> BIB001 </s> Brillouin Distributed Fiber Sensors: An Overview and Applications <s> Introduction <s> PART ONE: PRELIMINARY OVERVIEW Introduction to Fibre Optic Sensing Technology (J.M. Lopez--Higuera) The Commercialisation of Fibre Optic Sensors (S.D. Crossley) PART TWO: FUNDAMENTALS OF PHOTONICS AND COMPONENTS FOR SENSING Light and Waveguiding (J.L. Arce--Diego) Optical Waveguides and their Manufacture (J. Zubia and M. Lomer) Passive Bulk Optical Components for Sensing (C. Gomez--Reino, V. Perez and C. Bao) Fibre and Integrated Optic Components for Sensing (R. Willsch and W. Ecke) Semiconductor Optical Sources for Sensing Technology (I. Esquivias and J. Arias) Photodetectors for Sensing (J.M. Lopez--Higuera and J. Madruga) Optical Amplifiers (M.A. Rebolledo and M. Lopez--Amo) Superfluorescent Fibre Optic Sources (J.M. Lopez--Higuera) PART THREE: PRINCIPLES AND TECHNIQUES FOR SENSING Transduction Techniques based on Intensity Modulation of Light (A.C. Garcia and J. Echevarria Cuenca) Interferometry and Polarimetry for Optical Sensing (DC. Jones) Gas Spectroscopy Techniques for Optical Fibre Sensors (B. Culshaw) Distributed Optical--fibre Sensing (A. Rogers) Principles of Laser Doppler Velocimetry (D.A. Jackson and C.N. Pannell) Fibre Gyroscope Principles (S. Merlo, M. Norgia and S. Donati) Fibre Grating Technology: Theory, Photosensitivity, Fabrication and Characterization (R. Khasyap and J.M. Lopez--Higuera) Fibre Bragg Grating Interrogation Techniques (J.L. Santos and W.N. MacPherson) Discrimination Techniques for Optical Sensors (J.D.C. Jones and W.N. MacPherson) Optical Reliability of Fibre Gratings (S. Kannan and P. Lemaire) Passive Fibre Optic Sensor Networks (A. Dandridge and C. Kirkendall) Active Fibre Optic Sensor Networks (S. Abad, M. Lopez--Amo and I.R. Matias) PART FOUR: APPLICATIONS Optical Fibre Gratings Applications (S.T. Vohra) Laser Doppler Velocimetry Applications (D.A. Jackson and C.N. Pannell) Phototonic Sensing Technology in Civil Engineering Applications (D. Inaudi) Applications of Optical Fibre Sensors for the Nuclear Power Industry (P. Ferdinand and S. Magne) Optical Fibre Current and Voltage Sensors for the Electric Power Industry (A.H. Rose and G.W. Day) Fibre Optic Gyroscope for Industrial Applications (T. Kumagai and H. Kajioka) Optical Fibre Sensors for Fly--By--Light Aircraft (M. Kobayashi and K. Toyama) Optical Fibre Sensing of Electrical Discharges and Plasmas (G. Woolsey) Fibre Optic Sensors for Oilfield Services (R.J. Schroeder, R.T. Ramos, T. Yamate and E. Udd) Fibre Optic Biosensors (C.A. Rowe--Taitt and F.S. Ligler) Biomedical Fibre Optic Sensors (F. Baldini and A.G. Mignani) Fibre Optic Sensors for Environmental Applications (G. Holst and B. Mizaikoff) The Optical Nose (D. Walt and S. Stitzel) A New Approach to optical Fibre Sensing Techniques based on the Sensory Systems of Living Bodies (J.A. Martin--Pereda and A.P. Gonzalez--Marcos) Acronyms. Index. <s> BIB002
Optical fibers have commonly used as communication channels where light waves propagate along haul distances. In this situation the fibers are isolated from the external perturbations by means of cabling techniques. However, by enhancing the environment influences on the properties of the light that travels into the waveguide, the fibers can be used to detect, to monitor, and even to measure external perturbations (measurands) in an integral or distributed format BIB002 . When the optical power overpass a given power threshold, nonlinear phenomena such as Brillouin scattering can be forced inside the core fiber. Furthermore, Brillouin scattering of light in optical fibers can be used as a basis to develop optical devices such as fiber lasers BIB001 , optical filters  , and due to its strong dependence on environmental variables (strain and temperature), it is successfully employed in distributed fiber sensor systems  . In these cases, the optical fiber constitutes the medium where the interaction takes place, acting at the same time as distributed transducer and optical channel. These sensors are capable of measuring the change of a specific parameter (measurand) along the entire fiber transducer. Hence, the dynamic range (correlated with the maximum fiber-length of the transducer) and the spatial resolution (minimum fiberlength required to measure to consecutive perturbations or events) are key factors, whose values still remain as challenges (they must be improved).