Module 2 : Ray Model
Lecture : Ray Model
1.2 SIMPLE RAY MODEL
 


Figure 2 (optical fiber with core, cladding and total internally reflected ray)

   
  For propagation of light inside the core there are two possibilities.
   
1.
 A light ray is launched in a plane containing the axis of the fiber. We can then see the light ray after total internal
  reflection travels in the same plane i.e., the ray is confined to the plane in which it was launched and never leave the plane. In this situation the rays will always cross the axis of the fiber. These are called the Meridional rays. (Fig. 2)
   
2.
The other possibility is that the ray is not launched in a plane containing the axis of the fiber.
 

For example if the ray is launched at some angle such that it does not intersect the axis of the fiber, then after total internal reflection it will go to some other plane. We can see that in this situation the ray will never intersect the axis of the fiber. The ray essentially will spiral around the axis of fiber. These rays are called the Skew rays.

So it can be concluded that if the light is to propagate inside an optical fiber it could be through two types of rays

   
a)
 Meridional rays: The rays which always pass through the axis of fiber giving high optical intensity at the center of the core
  of the fiber.
   
b)

Skew Rays : The rays which never intersect the axis of the fiber, giving low optical intensity at the center and high intensity
  towards the rim of the fiber.
   
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