High spatial resolution: an integrative review of its developments on the Brillouin optical time- and correlation-domain analysis

Abstract

In the past two decades, Brillouin-based optical fiber sensors have gained significant ground for distributed temperature and strain measurements in the real world. Among these sensors, Brillouin optical time-domain analysis (BOTDA) and Brillouin optical correlation-domain analysis (BOCDA) are good candidates to realize a high spatial resolution, which is of great importance to distinguish small-size events in practical applications. In this paper, high-spatial-resolution BOTDA and BOCDA are introduced and summarized. For the BOTDA, simulation experiments are made for further comprehension of the dark-pulse technique, pulse pre-pump (PPP) technique, differential pulse-width pair (DPP) technique and Brillouin echo technique. The dark-pulse and PPP techniques utilize the DC portion of the pulse signal, which brings the cross talk of the surrounding information. It is known as the non-local information in the Brillouin spectrum, which limits the minimum temperature and strain detection accuracy. The DPP and Brillouin echo techniques, utilizing differential measurement with two pump pulses, are free from this problem. The Brillouin echo-based sensor has a good signal-to-noise ratio, while the DPP-BOTDA owns the advantages of simple installation and easy implementation. For the BOCDA, its operating principle allows it to circumvent the pulse-based limit on the spatial resolution and two specific implementations are introduced, which are enabled by the frequency and phase modulation techniques. A brief overview of the developments and improvements on these two types of BOCDA sensor are introduced and summarized.