refracted ray

A ray that undergoes a change of velocity, or in the general case, both velocity and direction, as a result of interaction with the material medium in which it travels. 2. In an optical fiber, a ray that is refracted from the core into the cladding. Specifically a ray having direction such that
where r is the radial distance from the fiber axis, Φ(r) is the azimuthal angle of projection of the ray at r on the transverse plane, θ(r) is the angle the ray makes with the fiber axis, n(r) is the refractive index at r, n(a) is the refractive index at the core radius, a. Refracted rays correspond to radiation modes in the terminology of mode descriptors.