Rayleigh-Based Distributed Optical Fiber Sensing

Abstract

Distributed optical fiber sensing is a unique technology that offers unprecedented advantages and performance, especially in those experimental fields where requirements such as high spatial resolution, the large spatial extension of the monitored area, and the harshness of the environment limit the applicability of standard sensors. In this paper, we focus on one of the scattering mechanisms, which take place in fibers, upon which distributed sensing may rely, i.e., the Rayleigh scattering. One of the main advantages of Rayleigh scattering is its higher efficiency, which leads to higher SNR in the measurement; this enables measurements on long ranges, higher spatial resolution, and, most importantly, relatively high measurement rates. The first part of the paper describes a comprehensive theoretical model of Rayleigh scattering, accounting for both multimode propagation and double scattering. The second part reviews the main application of this class of sensors.

High resolution seafloor thermometry for internal wave and upwelling monitoring using Distributed Acoustic Sensing

“…The possibility of using Rayleigh-scattering systems to measure temperature had been recognized decades ago [32,33].…”

Coherent combination method applied to distributed acoustic sensing over deployed multicore fiber

“…The cores of the MCF are subject to the same perturbations and have distinct and uncorrelated Rayleigh fading signatures 7 ; therefore, they act as independent measurement channels whose information can be combined to reduce signal fading. The information gathered by the cores needs to be optimally combined, or averaged, into a single result.…”

Numerical modeling of a novel athermal fiber optic cable

“…4 Eqs. (2) shows that a compliant coating can be used to drive, via its thermal and mechanical properties, the temperature sensitivity of the fiber. In particular, assuming ∂n/∂T = 9.5 × 10 −6 K −1 , 5 a fully athermal behavior, in terms of phase shift, can be obtained with a coating capable of inducing a negative thermal expansion (NTE), such that:…”

“…On the contrary, among Brillouin-and Rayleigh based distributed sensors', whose response depends on strain and temperature simultaneously, only phase-based Rayleigh-ones are directly affected by the phase delay. 2 In this regard, the capability of tuning the temperature dependency of phase delay is therefore relevant in the development of sensing cables, either to achieve high-temperature sensitivity or, on the contrary, and up-to-know quite unexplored, to implement athermal cables. For example, athermal cables are of great interest for all those applications where the temperature compensation is critical, such as in low-frequency distributed acoustic sensing applications.…”