Phase-Coded and Noise-Based Brillouin Optical Correlation-Domain Analysis

Abstract

Correlation-domain analysis has enabled distributed measurements of Brillouin gain spectra along optical fibers with high spatial resolution, up to millimeter-scale. The method relies on the joint modulation of counter-propagating Brillouin pump and signal waves so that their complex envelopes are correlated in select positions only. Brillouin optical correlation-domain analysis was first proposed nearly 20 years ago based on frequency modulation of the two waves. This paper reviews two more recent variants of the concept. In the first, the Brillouin pump and signal waves are co-modulated by high-rate binary phase sequences. The scheme eliminates restricting trade-offs between the spatial resolution and the range of unambiguous measurements, and may also suppress noise due to residual Brillouin interactions outside the correlation peak. Sensor setups based on phase coding addressed 440,000 high-resolution points and showed potential for reaching over 2 million such points. The second approach relies on the amplified spontaneous emission of optical amplifiers, rather than the modulation of an optical carrier, as the source of Brillouin pump and signal waves. Noise-based correlation-domain analysis reaches sub-millimeter spatial resolution. The application of both techniques to tapered micro-fibers and planar waveguides is addressed as well.

Evaluation of Horizontal Stresses in Soil during Direct Simple Shear by High-Resolution Distributed Fiber Optic Sensing

“…New sensing developments, however, allow for higher spatial resolution of a few millimeters to centimeters [28,29,30,31,32]. These developments open the window to new possibilities of smaller-scale applications, such as on-sample measurements [33], high-resolution profiling [34], and key-point characterization methods [35].…”

Distributed cladding mode fiber-optic sensor

“…Distributed sensing, however, requires that the Brillouin interactions be confined to discrete and narrow fiber sections of arbitrary locations. Several schemes for the localization of steady-state SBS have been proposed towards distributed sensing of temperature and strain [58][59][60][61][62]. In those protocols, which came to be known as Brillouin optical correlation domain analysis (B-OCDA), the two input optical waves are jointly modulated in frequency or phase [58][59][60][61][62].…”

“…Several schemes for the localization of steady-state SBS have been proposed towards distributed sensing of temperature and strain [58][59][60][61][62]. In those protocols, which came to be known as Brillouin optical correlation domain analysis (B-OCDA), the two input optical waves are jointly modulated in frequency or phase [58][59][60][61][62]. The concept was successfully carried over to BDGs in polarization-maintaining fibers [44][45][46]52].…”

“…The magnitude of the BDG reaches its steady-state value within the correlation peak and oscillates with zero mean everywhere else [61]. Therefore, time-averaged measurements of coupling spectra may be related to the conditions prevailing at a specific position.…”

Load-Independent Characterization of Plate Foundation Support Using High-Resolution Distributed Fiber-Optic Sensing

“…These interpretation methods are mostly based on analysis of static (slow-occurring) loading scenarios and on relatively low spatial resolutions of the order of one meter. However, new technological developments in this field now allows for a much higher spatial resolution at the order of a few millimeters [23,24,25,26,27,28,29,30]. This technological boost, not only enables new possibilities in structural health monitoring, but also makes the technology well suited for studying fundamental problems in a small-scale laboratory setting [31].…”