Explain about the term step index fibre.

Step index fibre:

Into a step index fibre, the refractive index keeps constant throughout the core and decreases at the core-cladding boundary and after that remains constant during the cladding.

Since the refractive index changes as a “step” at the core-cladding border, the fibre is termed as step index fibre. The light rays travel by the fibre as “meridional” rays which is the rays zigzag by the length of the fibre, by crossing the fibre axis for each reflection.

Single mode Step Index Fibre

Multimode step index fibre