Light guidance in an optical fibre can be understood by considering a structure comprising of thin solid glass cylinder of refractive index
n1 surrounded by a medium of lower refractive index
n2.
The light guidance in the structure takes place due to successive total internal reflections at the interface of the media
n1 and
n2 as shown in the figure. All rays with the angle of incidence
i less than a particular value
im are confined in the medium of refractive index
n1. The numerical aperture (NA) of the structure is defined as
sinim.
For two structures namely
S1 with
n1=√45/4 and
n2=3/2, and
S2 with
n1=8/5 and
n2=7/5 and
taking the refractive index of water to be
4/3 and that of air to be
1, the correct option(s) is(are)