Wave Model

Module 3 : Wave Model

Lecture : Wave Model

	MODAL PROPAGATION INSIDE AN OPTICAL FIBER (WAVE MODEL-I)
1.	Basics
1.	There are certain limitations to ray model.
2.	The ray model does not predict correctly that even after total internal reflection there will be some field in the cladding
	Also it does not predict that rays can be launched at only discrete angles in an optical fiber.
3.	For an accurate and complete description of light propagation inside an optical fiber we have to go in for a more
	rigorous model, called the WAVE MODEL. Here we shall discuss the propagation of light inside an optical fiber, treating light as an electromagnetic wave.
4.	Inside a fiber core the optical energy gets guided i.e. the energy propagates along the axis of the core and the fields
	exponentially decay in the cladding away from the core-cladding interface.
5.	In a practical fiber the cladding is surrounded by a protective layer. Generally, by the time the field reaches that layer, it
	dies down significantly so that the protecting layer does not affect the propagation of the wave significantly. That is, the whole propagation of light is governed by the core cladding interface and the interface between the cladding and other protecting layers does not affect the propagation. In other words, we can take the cladding to be of infinite size in our analysis, without incurring significant error.

2.	Analysis of cylindrical waveguides (Optical Fiber)
	Figure (1)