Derive an expression for Acceptance angle or Numerical aperture for fiber optics. Derive an expression for Fractional refractive index change or relative refractive index Answer: The light propagates through the fiber only when its angle of incidence at the launching end is less than or equal to a certain value. This maximum possible angle with the axis of the fibre up to … [Read more...] about Fiber optics: Derivation for acceptance angle or numerical aperture