First observed by
French mathematical physicist,
Marcel Louis Brillouin. Brillouin scattering is a form of
nonlinear scattering which occurs when intensely modulated
light, such as that from a
laser, is launched into a
crystalline substance, such as a
fibre optic line. If this light is launched with sufficient energy (usually above the lines saturation point) it can cause some of it to be converted into
acoustic waves, known as
phonons. These phonons interfere with the incoming signal and cause them to be reflected away from their initial direction of propagation. This reflected light is usually
red-shifted (by about 11
GHz for a 1550nm signal).
Brillouin scattering can cause problems in fibe optic systems as some of the refracted signal can actually be reflected back to its source, creating heating problems for the signal generating laser, reducing its efficiency