Discuss about the term graded index fibre.

Graded index fibre:

A graded index fibre is diverse from the step index fibre not merely in the core refractive index variation but also into the size of fibre. Into a graded index fibre, the refractive index does not stay on constant into core, but in its place, it gradually reduces on either side by the axis of the core in the direction of the core-cladding boundary. At the edge, the refractive index of the core is minimised and equals the refractive index of the cladding. Due to the gradual variation of the refractive index beside the radius of the core, the fibre is termed as graded index fibre.

Since the refractive index variation resembles concentric cylinders of equal refractive indices approx the axis, any ray of light entering any one of the cylindrical layers find trapped by this remains into layer for the rest of the travel. This implies that light does not and will not cross axis of the fibre and only goes in a helical path approx the axis. Hence, the rays of light in a graded index fibre are termed as “helical” rays. As the path of the light rays is skewed, they are also termed as skew rays.