1. Step index fiber is of two types viz; mono mode fiber and multi mode fiber.

Graded index fiber is of only of one type that is multi mode fiber.

2. The refractive index of the core of the step index fiber is constant through out the core.

The refractive index of the core of the graded index fiber is maximum at the center of the core and then it decreases towards core-cladding interface.

3. Number of modes for step index fiber N = V2/2, where V is cut off frequency or normalized frequency or V- number

Number of modes for graded index fiber is N = V2/ 4.

4. V number can be less that 2.405 or more that 2.405 for step index fiber

V number is always more than 2.405 for graded index fiber.

5. Step Index Fiber is a fiber in which the core is of a uniform refractive index and there is a sharp decrease in the index of refraction at the cladding.

Graded Index Fiber is a type of fiber where the refractive index of the core is lower toward the outside of the fiber. It bends the rays inward and also allows them to travel faster in the lower index of refraction region. This type of fiber provides high bandwidth capabilities.

A graded index multimode fiber will transmit 800 modes, and has a varying refractive index. A step index multimode will transmit 228 modes.

The single step fiber mode tolerates high powered laser use and a high bandwidth in comparison to the multi-step which only allows for non-coherent light sources and lower bandwidth.

If V is less than 2.405 then the fiber is mono mode but if V is greater than 2.405 then fiber is multimode.

V number is also related with the number of modes is the fiber as:

N = V2/ 2 for step index fiber and

Number of modes for graded index fiber is N = V2/ 4.

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