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Engineering Physics by S. Mani Naidu

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11.2 Principle of optical fibre, acceptance angle and acceptance cone

Principle: Once light rays enter into core, they propagate by means of multiple total internal reflections at the core-cladding interface, so that the rays travel from one end of the optical fibre to the other. The phenomenon of total internal reflection in a straight optical fibre is explained in the following way. Let the refractive index of the core is n1 and that of the cladding is n2 such that n1 > n2. As shown in Fig. 11.2, a ray of light AO is incident at ‘O’ on the end face of core; let this ray makes an angle of incidence θ0 with the axis of the fibre. This ray is refracted into the core and passes along OB, the angle of refraction in the core is, say θ1. The ray OB ...

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