Optical Fiber,Propagation Phenomenon, Numerical Aperture, Acceptance angle, Fractional index

ENGINEERING PHYSICS-OPTICAL PHYSICS-
The Numerical Aperture (NA) of a fiber is defined as the sine of the largest angle an incident ray can have for total internal reflectance in the core. Rays launched outside the angle specified by a fiber's NA will excite radiation modes of the fiber.
The Acceptance angle of a optical fiber is the maximum incidence angle of a light ray which can be used for injecting light into a fiber core or waveguide
The fractional difference Δ between the refractive indices of the core and the cladding is known as the fractional refractive index change. It is given by. The value of Δ is always positive because n1 must be greater than n2 for the total internal reflection condition.