If we take a look at the light returned back from the
optical fiber we can see that almost every power is returned
with the same wavelength which was launched into the
fiber (the Rayleigh scattering). However a small amount of
power returns with a changed wavelength. This effect has
been predicted by the Austrian scientist Smekal in 1923
and has been studied theoretically in 1925 - 1927 by
Heisenberg, Dirac, Kramers and Schrödinger. In 1928 this
effect has been proved experimentally by the Indian scientist
Chandrasekhara Venkata Raman after whom this effect
took its name [1], [5].