The present invention discloses an optical device able to luminesce, whereby the optical device comprises, inter alia, a luminescent source that is directly or indirectly mechanically coupled to a low-order mode waveguide, such that light emitting from the luminescent source is optically coupled into the low-order mode waveguide. In embodiments of the invention, the distance D between point sources of the luminescent source and the waveguide is about equal to or smaller than the decay length of the exponential tails of the modes supported by the waveguide, thereby obtaining an optical coupling efficiency of at least 3%. Additional and alternative embodiments are claimed and disclosed.