Introduction to Data Communications
15d. Optical Fibre (cont'd)

An important characteristic of Fibre Optics is Refraction. Refraction is the characteristic of a material to either pass or reflect light. When light passes through a medium, it "bends" as it passes from one medium to the other. An example of this is when we look into a pond of water.

(See image 1 below)

If the angle of incidence is small, the light rays are reflected and do not pass into the water. If the angle of incident is great, light passes through the media but is bent or refracted.

(See image 2 below)

Optical Fibres work on the principle that the core refracts the light and the cladding reflects the light. The core refracts the light and guides the light along its path. The cladding reflects any light back into the core and stops light from escaping through it - it bounds the media!

Optical Transmission Modes

There are 3 primary types of transmission modes using optical fibre.

They are

a) Step Index
b) Grade Index
c) Single Mode