An effective graded index profile optical fiber waveguide comprises alternating regions of high and low indexes of refraction of controlled thickness. The effective refractive index of the fiber has a graded profile of decreasing refractive index when the regions of high index have either a constant...http://www.google.se/patents/US4265515?utm_source=gb-gplus-sharePatent US4265515 - Optical fiber waveguide with effective refractive index profile
