Step Index Fibre Vs Graded Index Fibre

Step Index Fibre	Graded Index Fibre
The refractive index of the core is uniform and step or abrupt change in refractive index takes place at the interface of core and cladding in step index fibres.	The refractive index of core is non-uniform, the refractive index of core decreases parabolically from the axis of the fibre to its surface.
The light rays propagate in zig-zag manner inside the core. The rays travel in the fibre as meridional rays and they cross the fibre axis for every reflection.	The light rays propagate in the form of skew rays or helical rays. They will not cross the fibre axis.
The index profile formed is in the shape of a step.	The index profile formed is in the shape of parabola (in core) and straight line (in clad).
The refractive index of the core is constant throughout the core.	The refractive index of the core is maximum at center and then it decreases towards core-clad interface.
Rays suffer from multiple total internal reflections (T.I.R’s).	Rays suffer from both multiple total internal reflections as well as multiple total internal refractions (T.I.R’s).
There is a straight line between two successive total internal reflections.	There is a no straight line between two successive total internal reflections.
There is transient time dispersion or inter modal dispersion because different modes of light entering with different angles takes different time to travel through the length of optical fibre.	No transient time dispersion or inter modal dispersion because refractive index is inversely proportional to speed.
T.I.R. take place at core clad interface.	T.I.R. can take place before core-clad interface.
It is of two types: mono mode fibre and multi mode fibre.	It is of only one type i.e. multi mode fibre.
Number of modes for step index fibre, MS = V2/2. V <= 2.405 for single mode fibre and V > 2.405 for multi mode fibre.	Number of modes for graded index fibre, MG = V2/4.