Visually clear diffusive light panel with embedded semi-reflective rough-surface planar outcouplers

Abstract

We present a visually transparent light panel that passively emits diffused light. The panel is a light guide with semi-reflective thin-film blades buried in the panel acting as outcouplers. The semi-reflective blades can be tilted relative to the light panel surface and have a rough surface texture to scatter the light incident upon them while the transmitted light retains its incident angle. We show that the texturization of the blades can be done following a simple photolithographic process involving a polymer photomask. The polymer photomask has embedded micron-scale air bubbles that disturb the exposure intensity distribution. The surface topology of a photoresist film exposed using this photomask becomes rough, which is subsequently used as a mold to create the rough-textured outcoupler blades with a well-defined outline. Alternatively, molding can occur from commercially available rough surfaces with limited opportunities for a customized outline. We demonstrate that prototype light panels are indeed visually clear, and we show that by changing the angle between the incident propagating light rays and tilted semi-reflective blades, the ratio between the amount of emitted light through both surfaces of the panel can be biased.