Hello Aashiah
In general, in order to measure "ordinary" refractive index and film
thickness, you have to induce TE modes light into your film through a
prism and observe light pattern which is emitted from your thin film
(waveguide).

In other words, you want to know two values in experiment.
1) An incident angle of laser (TE0) into a prism when there is the
strongest intensity of the emitted light from your thin film
2)An incident angle of laser (TE1) into a prism when there is the
strongest intensity of the emitted light from your thin film

After getting two incident angles, you can calculate film thickness
and ordinary refractive index at the same time using Goos-Haensen
shift relation.

Sometimes, to make sure the values you have obtained by above method,
the extraordinary refractive index and film thickness can be measured
using same method because the film thickness is constant regardless of
the kinds of refractive indices.

If you want, you can contact me directly through an email.

Good luck

Sung