The optical phenomenon that is responsible for the propagation of ligh

The optical phenomenon that is responsible for the propagation of light signal through an optical fibre is

interference
scattering
total internal reflection
refraction
This question was previously asked in
UPSC CAPF – 2018
The correct answer is C) total internal reflection.
Optical fibres work by guiding light along a core made of a material with a higher refractive index, surrounded by a cladding material with a lower refractive index. Light rays entering the core at appropriate angles strike the interface between the core and the cladding at an angle greater than the critical angle. When this condition is met, the light is completely reflected back into the core, a phenomenon called total internal reflection (TIR). This process repeats along the length of the fibre, allowing the light signal to propagate with minimal loss.
Refraction is the bending of light as it passes from one medium to another with a different refractive index, which is involved when light *enters* the fibre but not for its propagation *within* the fibre. Interference and scattering are optical phenomena but are not the primary principle responsible for guiding light in optical fibres; scattering, in fact, is a cause of signal loss.