Physics · Optical Fibres

For light traveling from a core of higher refractive index to a cladding of lower refractive index, total internal reflection is possible. However, if an input specifies a step-index fiber with a core refractive index n1 = 1.25 and a cladding refractive index n2 = 1.42, light cannot guide via total internal reflection since n1 < n2. If the indices are inverted such that n1 (core) = 1.42 and n2 (cladding) = 1.25, calculate the critical angle θc at the core-cladding interface.