Page "Numerical aperture" Paragraph 27
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A multi-mode optical fiber will only propagate light that enters the fiber within a certain cone, known as the acceptance cone of the fiber.
The half-angle of this cone is called the acceptance angle, θ < sub > max </ sub >.
For step-index multimode fiber, the acceptance angle is determined only by the indices of refraction of the core and the cladding:
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