06-07-2012, 04:41 PM
RAY THEORY AND OPTICAL WAVEGUIDE
b. LECTURE 1 - RAY THEORY AND OPYICAL WAVEGUIDE.ppt (Size: 430.5 KB / Downloads: 40)
Introduction
The transmission of light via dielectric waveguide structure was first proposed and investigated at the beginning of twentieth century.
Initially a waveguide consist of transparent dielectric rod typically of silica glass with a refractive index of around 1.5,surrounded by air was proposed.
Due to excessive losses at any discontinuities of the glass air interface ,clad dielectric was proposed.
In this structure losses were 1000 db/km
These losses were reduced to 4.2 db/km by purification of materials used.
Total Internal Reflection
The refractive index of medium is defined as the ratio of the velocity of light in a vacuum to the velocity of light in the medium.
More the medium is dense, lesser will be the velocity of light.
When a ray is incident on the interface between two dielectric of different refractive index, refraction occurs as shown below.
Snell’s law of refraction
Critical Angle
The incidence angle at which angle of refraction becomes equal to 90 degree i.e. parallel to interface ; is called as critical angle.
As the angle of incidence becomes greater than critical angle, total internal reflection takes place.