Injecting Light of High-Power LEDs into Thin Light Guides

摘要

A new method using a thin-film multilayer filter is described to couple light from high-power LEDs into a thin light guide such as an LCD backlight. Light emitted below the critical angle is reflected back to the LED and recycled. Large-angle emitted light passes the filter and is transported by total internal reflection in the light guide. The light guide can be as thin as 0.3mm for an LED of lxlmm2, and the best coupling efficiency is estimated to be around 80%. With this approach, a backlight system can be greatly simplified but also compact collimators can be realized. In this paper the optical design and testing of the filter is described, and a lmm thick, 6.5mm diameter collimator is presented that emits in a cone of 2x13°. Measurements on prototypes show good agreement with the designed characteristics.