An optical fibre has a numerical aperture of 0.20 and a refractive index of cladding is 1.59. Determine the core refractive index and acceptance angle for the fibre in water which has a refractive index 1.33.

STEP INDEX FIBRE

1-The refractive index of the core of step index fibre is constant throughtout the core.

2- Step index fibre is of two types viz; mono mode fibre and multi mode fibre.

3-The light rays propagate in zig-zag manner inside the core.

4- The ray cross the fibre axis for every reflection

5-They can be manufactured easily.

GRADED INDEX FIBRE

1- The refractive index of the core of the graded index fibre is maximum at centre, core and then it decreases towards core-cladding interface.

2- Graded index fibre is of only one type that is multi mode fibre

3- The light rays will not cross the fibre axis.

4- The light rays propagate in the form of skew rays or helical rays

5- They manufacturing process is complex.