Going beyond limits in Brillouin distributed fibre sensors: Challenges and possible approaches

Abstract

Abstract-Brillouin distributed optical fibre sensing has been a subject of intense research and industrial development for more than twenty years, demonstrating its capabilities to be an effective and powerful measurement tool for a wide range of applications. Making use of sophisticated implementations, remarkable progresses on the sensing performance have been reported in the last decade, allowing significant improvements in spatial resolution and sensing range. However, the demand for distributed sensors with more performing features is steadily growing, imposing new and more challenging requirements to the sensor design. This paper presents a brief overview of the fundamentals of Brillouin distributed fibre sensing and reviews the main current limitations and challenges faced when the sensing capabilities are pushed beyond the state-of-the-art. Different possible approaches and methods to enhance and compare the sensing performance are also discussed.

Novel Concepts and Recent Progress in Distributed Optical Fiber Sensing

“…The solution to increase the activating energy is to spread the energy over several pulses by forming a sequence which can be identified to a binary word: a "1" corresponds to the pulse "on" and a "0" to the pulse "off", as shown in Fig.1. Instead of averaging N temporal traces obtained by an isolated pulse, N non-averaged traces are acquired, each with a different bit sequence arrangement [4,12]. Then by a linear combination of all traces a trace equivalent to a N-times averaged single-pulse trace is obtained, but with an equivalent pulse energy N/2 times larger, since the sequences nominally contain the same number of 0 and 1.…”

“…The most promising techniques are those based on stimulated Brillouin scattering and on coherent Rayleigh scattering, which can today commonly reach a distance range of 50 km with a spatial resolution of 1 m and an acquisition time below 1 minute, for a typical temperature accuracy of 1 K. In addition, Brillouin-based distributed sensors can be implemented in sophisticated configurations to obtain a very sharp spatial resolution down to the centimeter range [1][2][3][4] or to realize efficient signal enhancement by combining gain and loss Brillouin processes [5][6][7].…”

“…It has been clearly demonstrated that the signal-to-noise ratio (SNR) on the sensor response actually scales any sensor performance [8]: the maximum distance range, since the response decays exponentially with distance; the spatial resolution, since the signal is proportional to the interaction length; the acquisition time, because a higher SNR requires less averaging, and finally, the uncertainty on the measured quantity [4]. So it can be easy concluded that any action resulting in an improved SNR will automatically lead to a better performing sensor.…”