An optical fibre (μ=1.72) is surrounded by a glass coating (μ=1.50). Find the critical angle for total internal reflection at the fibre-glass interface.
μ1 sin θc=m2 sin 90∘
sin θc=1.501.72
⇒θc=sin−1[7588]
Calculate the critical angle of an optical fibre without cladding if the glass has a refractive index of 1.56.