NOTE 1 – Acceptance angle is a function of position on the entrance face of the core when the refractive index is a function of radius in the core. In that case, it is:

$\text{arcsin}{\left[n^2\left(r\right)-n_2^2\right]}^{1/2}$

where n (r) is the refractive index and n₂ is the minimum refractive index of the cladding.

NOTE 2 – Power may be coupled into leaky modes at angles exceeding the acceptance angle.