2. Fundamental physical effects and optical solitons

The propagation of light waves in transparent (low-loss) media is governed by linear phenomena, such as chromatic dispersion or fiber losses, and non-linear phenomena, such as the Kerr effect. These two effects are linked to the variation of light velocity in the medium, as a function of wavelength (linear effect) and light intensity (non-linear effect).

The ratio of the speed c of light in a vacuum to its speed in the medium is called the refractive index of the medium. This index, as its name suggests, governs the refraction of a light wave as it passes from one medium to another. Snell's law is applied. The angle relative to the normal of the light beam in the new medium depends on the ratio of the refractive indices of the two media to the wavelength λ of the light beam. If the indices vary with wavelength (chromatic dispersion), the different colors of a light...