Microwaves Photonic Links: Components and Circuits

Chapter 3

Optical Fibers andAmplifiers

3.1. Optical fibers

3.1.1. General

If a transparent material has a refraction index greater than the environment, all penetrating light is trapped in this material. This is this principle jewelers use when cutting precious stones to capture the environmental light. The total reflection principle was demonstrated by an Irish physicist named John Tyndal in front of the British Royal Society in 1854. His demonstration consisted of showing that a light wave guided by a water jet was able to follow curved trajectories contrary to the thought that light could only travel in a straight line. It is this principle that is used to create illuminated water fountains in which the light seems to come from inside the water jets [WIK 09].

Glass optical fibers have been used to create lighting in special locations and to enable image transmission from inaccessible (human endoscopy) or dangerous (ionizing radiation or toxic) places.

As recalled in [GOW 93], regarding telecommunications, the first optical links were laser based and the beam propagated in air (attenuation of 1 dB/km). The first to propose travel through an optical wave guide was Kao and his collaborators in 1966 [KAO 66]. At that time the attenuation in glass for visible optical wavelengths was 1,000 dB/km, due to impurities in glass. Actions were taken to reduce these impurities, leading to a reduction in the optical attenuation, both in the visible and the near infrared. This development ...