Brillouin scattering process
The light backscattered by an optical fiber segment without any defects or abnormal characteristics is spectrally decomposed into three distinct peaks corresponding to three outstanding phenomena:
Rayleigh scattering: The electromagnetic wave propagating in the fiber core interacts with the scattering centers, silica impurities and enhancing additives.
Raman Scattering: The Raman effect is an interaction between light and thermal vibration of silica molecules. As such, this phenomenon is highly dependent on temperature at the spectral level.
Brillouin Scatteing: The Brillouin effect originates from photon-acoustic phonon interaction. It generates light with a Frequency shift of approximately 10th GHz compared to the incident light.
The Brillouin Frequency Shift is called Brillouin Frequency. It is sensitive to both temperatur and strain allowing FEBUS-G1 to measure both parameters.
As light is propagating in optical fiber at a given velocity, it is possible to locate precisely from where backscattered light takes origin. Thus on the detector, at one time, corresponds one backscattering position.
It is a common technique utilized by telecom operators called OTDR (Optical Time-Domain Reflectometer) It was initially created to analyze losses inside optical telecommunication lines. It only measures variation on signal intensity.
FEBUS-G1 performs a full Brillouin Frequency measurement of the signal at each point. That is why it can be categorized as B-OTDR (Brillouin Optical Time-Domain Reflectometer).