(G). Light guide image transmission:
Fig.26 is an optical fibre. Fig.27 shows the longitudinal cross section of a fibre. For a ray entering the fibre, if the angle of incidence F[at the core-cladding interface] is greater than the critical angle [=Sin-1(n2/n1)],then the ray will undergo total internal reflection at the interface. Further , because of the cylindrical symmetry in the fibre structure, this ray will suffer total internal reflection at the lower interface also, and therefore get guided through the core by repeated total internal reflections. Thus an optical fibre acts as a 'light guide'.
If a coherent bundle of parallel fibres (i.e., the relative positions of the fibres in the input and output ends are the same) is used to construct an optical transmission line, images can be transferred from one place to other (Fig.28).
The most important application of the coherent bundle is a fibre optic endoscope. Optic endoscope is used to inspect internal organs - like interior of lungs and other passages in the human body (Fig.29).
