How can we calculate the acceptance angle of Graded index multimode fibre?
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Dear Maryam
Thanks for your question.
The Numerical Aperture (acceptance angle): The Numerical Aperture (NA) of an optical fiber is a measure of its acceptance angle and refers to the angle over which an optical fiber accepts light. Graded-index (GRIN) multimode fibers have acceptance angles that vary with radial distance (rho) from the center of the fiber axis. In contrast to the traditional step-index multimode fibers that provide the same maximum acceptance angle at every position across the fiber’s core. GRIN multimode fibers, accept rays with the largest range of acceptance angles only at the core’s center. Then, the the acceptance angle decreases with increasing distance from the center and approaches 0° near the interface with the cladding. For GRIN fibers, the acceptance angle is calculated taking into according to the refractive indices of the core and cladding and the distance (rho) from the centre of the core according to:
where n is the refractive index of the fiber’s core, θ is the maximum half-angle of the light cone that can be accepted by the fiber and rho is the radial distance of the fiber.
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