Ring-shaped and radial diffractive gratings are designed with rigorous diffraction theory to couple light of a nearly monochromatic LED into a thin planar light guide on the bottom side. The theoretical coupling efficiencies for ring-shaped and radial gratings are 41% and 66%, respectively. Optimized diffractive elements are manufactured with direct electron-beam lithography and reactive-ion-etching into SiO<sub>2</sub> substrates. Good agreement between experimental and theoretical results for selected radial gratings is reached. Furthermore, the mass production tests using injection molding are carried out with good replicability.
© 2004 Optical Society of America
Samuli Siitonen, Pasi Laakkonen, Pasi Vahimaa, Konstantins Jefimovs, Markku Kuittinen, Marko Parikka, Kari Mönkkönen, and Ahti Orpana, "Coupling of Light from an LED into a Thin Light Guide by Diffractive Gratings," Appl. Opt. 43, 5631-5636 (2004)