Ray Model

Module 2 : Ray Model

Lecture : Ray Model

	The ratio then lies between 1 and 1.5 only. The time difference per unit length therefore is more or less proportional to . per km ( ) The time difference essentially is the measure of pulse broadening on the optical fiber. This phenomenon is called DISPERSION of an optical fiber. The dispersion (pulse broadening) has to be small since the data rate is inversely proportional to the pulse broadening. For high speed communication (high speed does not refer to the time taken by data to reach the destination but it refers to the number of bits per sec) the pulse broadening and hence the dispersion should be minimal.
(f)	For low dispersion ( ) should be as small as possible. So for an optical fiber the refractive index of core has to
	be made as close to the refractive index of cladding as possible.

3.	Contradictory Requirement:
(a)	For higher launching efficiency (higher NA), should be as large as possible .
(b)	For high data rate (bandwidth), should be as small as possible .
	The two are contradictory requirements.
	Since data transfer rate is rather more important in communication, is made as small as the fabrication technology permits. So for all practical fibers, Refractive index of the cladding differs from that of the core by only 0.1 to 1%.