title: White LED light coupling into light guides with diffraction gratings.
abstract: Radial diffractive gratings are used to couple light of a white LED into a light guide. Theoretical coupling efficiencies are evaluated with rigorous diffraction theory in a pure conical mounting. It is shown that when the refractive index of the grating increases from 1.46 to 2.05 the incoupling efficiency increases from 42% to 63%. Also, with the increasing refractive index the incoupling efficiency is shown to become more nearly uniform over the visible spectrum. Experimental results for the incoupled efficiencies and the color coordinates of the incoupled spectra are introduced for refractive indices n=1.46 and n=1.56.
authors.affiliation: Department of Physics, University of Joensuu, Finland. samuli.siitonen@joensuu.fi
authors.forename: Samuli
authors.initials: S
authors.lastname: Siitonen
authors.forename: Pasi
authors.initials: P
authors.lastname: Laakkonen
authors.forename: Pasi
authors.initials: P
authors.lastname: Vahimaa
authors.forename: Markku
authors.initials: M
authors.lastname: Kuittinen
authors.forename: Noora
authors.initials: N
authors.lastname: Tossavainen