Dielectric waveguide

In telecommunication, a dielectric waveguide is a waveguide that consists of a dielectric material surrounded by another dielectric material, such as air, glass, or plastic, with a lower refractive index.

Note 1: An example of a dielectric waveguide is an optical fiber.

Note 2: A metallic waveguide filled with a dielectric material is not a dielectric waveguide.

Source: from Federal Standard 1037C