An all-dielectric Waveguide in which electromagnetic waves are guided by a Refractive Index gradient SO that the waves are confined to the guide by Refraction or Reflection from the outer surface of the guide or from surfaces within the guide.

Note 1: In an open waveguide, the electromagnetic waves propagate, without radiation, within the waveguide, although evanescent waves coupled to internal waves may travel in the space immediately outside the waveguide. Note 2: Examples of open waveguides are (a) optical fibers and (b) Planar Waveguides in integrated optical circuits.