Question

Internal critical angle in core at core cladding interface of a step index fiber 78.6. The refractive index of cladding is 1.45 what is refractive index of core

Answer 1

$$\sin\theta_c=\frac{n_2}{n_1}$$

$$n_2=n_1\sin\theta_c\\ =1.45*\sin78.6^\circ=1.42$$