Acceptance Angle
The maximum angle relative to the fiber axis at which incident light can enter the fiber core and undergo total internal reflection.
Governing formula
θ_a = arcsin(NA) = arcsin(√(n1² - n2²))
SI unit
Degrees (°)
In depth
Rays entering at angles larger than $θ_a$ strike the core-cladding boundary at less than the critical angle and leak out into the cladding.
Examples in the real world
Coupling laser light efficiently into an optical fiber by focusing the beam within the fiber's acceptance cone.