Light in a vacuum, a refractive index of 1, which is the speed of light is c = 30 million km / s;
when light other medium to propagate in the surface, which is the medium refractive rate from n, in which the light speed is reduced to v = c / n;
The material of the optical fiber is silica, and its refractive index n is about 1.44. When calculating the delay, it can be approximated as 1.5;
the optical transmission speed in the optical fiber is approximately v = c / 1.5 = 200,000 km / s.
