Ultrahigh-speed distributed Brillouin reflectometry

An optical fibre sensing scheme that measures strain with a high spatial resolution and a very high sampling rate has been developed. Optical fibre sensors based on Brillouin scattering are promising for monitoring structural health. The system built by Yosuke Mizuno of Tokyo Institute of Technology and colleagues measures the frequency shift induced in the fibre’s Brillouin gain spectrum on stretching the fibre. This frequency shift is converted into a phase delay of a sinusoidal waveform, which enables the direct detection of the frequency shift. The approach allows single-point strain measurements to be performed at a rate of up to 100 kilohertz at any point along the fibre. Distributed measurements at multiple points along the fibre are also possible, although at lower repetition rates. Importantly, the scheme only requires access from one end of the fibre.