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Compare step- index and graded-index fiber.
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Sr. No.
Step index fiber
Graded Index Fiber
1 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 fibers. The refractive index of core is non-uniform, the refractive index of core decreases parabolically from the axis of the fiber to its surface.
2 The light rays propagate in zig-zag manner inside the core. The rays travel in the fiber as meridional rays and they cross the fiber axis for every reflection. The light rays,propagate in the form of skew rays or helical rays. They will not cross the,fiber axis.
3 Step index fiber is of two types viz; mono mode fiber and multi mode fiber. Graded index fiber is of only one type,that is multi mode fiber.
4 The refractive index of the core of step index fiber is constant throughout the core. The refractive index of the core of the graded index fiber is maximum at center,core and then it decreases towards core-Cladding interface.
5 The refractive index profile may be defined as: enter image description here The refractive index profile may be defined as: enter image description here
6 Number of modes for step index fiber $M_s=\frac{V^2}2$. V number can be less that 2.405 or more that 2.405 for step index Number of modes for graded index fiber is $M_g=\frac{v^2}4$.
7 Modal dispersion affects signal quality in step index fiber. Graded index fiber,provides zero dispersion as the velocity of modes is changed by changing R.I,such that time taken by all modes is same.

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