Meridional rays and skew rays

An optical fiber can transmit two types of rays- Meridional rays and skew rays. Meridional rays are confined to the meridional planes of the fiber. Meridional planes are planes which contain the axis of symmetry or fiber axis. Meridional rays propagate in a single plane and divided into two categories- bound rates and unbound rays. Bound rays obey Snell’s laws of reflection and refraction. They are trapped in the core. Unbound rays are not trapped in the core but refracted out of the fiber according to Snell’s law of refraction. Skew rays follow helical path and propagate without passing through the core of the fiber. Tracking of skew rays is a difficult task since they do not lie in a single plane. If light input to an optical fiber is not uniform, skew rays exhibits some smoothing effects and makes output light uniform. Nuymerical aperture of the fiber is greater when skew rays are transmitted compared to meridonal rays.