Non-Linear Interactions With Backscattered Light: A Truly Single-Ended Brillouin Optical Time-Domain Analysis Technique

The non-linear interaction between a Rayleigh-backscattered wave and a forward-traveling optical pump pulse is explored using sources separated by approximately one Brillouin shift. It is shown that the pump pulse modulates the Rayleigh backscatter at those locations where the frequencies of the counter-propagating waves differ by a Brillouin shift. As a result, a new Brillouin optical time-domain analysis technique is demonstrated that measures the spatial distribution of the Brillouin gain spectrum from one end only of the sensing fiber. In our experiments, spectra were acquired at a rate of 40 spectra per second over a sensing range of order 1 km with a spatial resolution of 3 m. The experimental arrangement and data analysis are described and a dataset is processed to extract the real part of the Brillouin gain spectrum and determine the peak of the gain spectrum as a function of location along the fiber. We also show that the new technique detects local changes in the phase due to the Brillouin interaction. The potential and limitations of the new technique are also discussed.