Marko Parikka

Coupling of light from an LED into a thin light guide by diffractive gratings.

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 SiO2 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.

Deterministic diffractive diffusers for displays

A LCD backlighting device that uses a diffractive light extractor has been developed for applications in which pointlike light sources are employed. The novel system eliminates the images of light sources, which appear as bright lines emanating from each source in the conventional diffractive approach. In addition, the system illuminates the LCD uniformly: Modulation of the diffractive structure as a function of position is used to control the output field of this extended planar light source.

LED light coupling into a lightguide with gratings

Two grating couplers are designed with rigorous diffraction theory to couple LED light into a thin lightguide through the bottom side. Designed couplers can be mass replicated with Ni-shim technology by injection molding.