3. Non-linear sources of distortion

If optical systems were limited only by the aforementioned linear effects, we could imagine connecting every point on the globe without any difficulty other than the availability of sufficient optical power. Unfortunately, there are physical phenomena that stand in the way of an increase in power in the fiber, and therefore of an unlimited increase in distance. These are non-linear optical effects. These effects are unique in that they are distributed along fiber cables. As such, they are specific to optical systems and are the main obstacle to the introduction of many tried-and-tested recipes in other fields of telecommunications. Because the optical beam in a fiber is guided in a core with a very small surface area (50 to 100 μm ² ), and the distances involved can reach several hundred kilometers, the fiber's refractive index becomes significantly...