Brillouin Scattering refers to the phenomenon of inelastic scattering of light by acoustic phonons (quanta of vibrational energy) in a material. This scattering process involves the transfer of energy between the incident photons and the acoustic phonons, resulting in a shift in the frequency of the scattered light.

Brillouin scattering has found applications in the field of fiber optics, where it is used in Brillouin Optical Time-Domain Reflectometry (BOTDR) systems. These systems utilize Brillouin scattering to measure temperature and strain along an optical fiber by analyzing the frequency shift of the scattered light caused by acoustic phonons.


Using Global Fiber Networks for Environmental Sensing

We review recent advances in distributed fiber optic sensing (DFOS) and their applications. The scattering mechanisms in glass, which are exploited for reflectometry-based DFOS, are Rayleigh, Brillouin, and Raman scatterings. These are sensitive to either strain and/or temperature, allowing optical fiber cables to monitor their ambient environment in addition to their conventional role as a medium for telecommunications. Recently, DFOS leveraged technologies developed for telecommunications, such as coherent detection, digital signal processing, coding, and spatial/frequency diversity, to achieve improved performance in terms of measurand resolution, reach, spatial resolution, and bandwidth. We review the theory and architecture of commonly used DFOS methods. We provide recent experimental and field trial results where DFOS was used in wide-ranging applications, such as geohazard monitoring, seismic monitoring, traffic monitoring, and infrastructure health monitoring. Events of interest often have unique signatures either in the spatial, temporal, frequency, or wavenumber domains. Based on the temperature and strain raw data obtained from DFOS, downstream postprocessing allows the detection, classification, and localization of events. Combining DFOS with machine learning methods, it is possible to realize complete sensor systems that are compact, low cost, and can operate in harsh environments and difficult-to-access locations, facilitating increased public safety and smarter cities.

Bipolar Cyclic Linear Coding for Brillouin Optical Time Domain Analysis

We demonstrate, for the first time, that cyclic linear pulse coding can be bipolar for BOTDA sensors, breaking the unipolar limitation of linear coding techniques and elevating the coding gain for a given code length.