Illumination by subwavelength grating with antireflection effect

摘要

This research concerns a thin illumination device to be used by mounting between a Reflection-type liquid crystal display device (LCD) and a viewer. Because, the brightness of display is highly dependent on the surrounding environment, an auxiliary illumination is needed to provide against cases when surrounding light is insufficient. We investigated theoretically and experimentally into a grating for monochromatic illumination. First, the requirements of illumination were calculated and a grating shape for illumination was developed. The antireflection effect of the grating was confirmed. In this paper, the diffraction efficiency of the grating was calculated by a rigorous analysis method. It is structured the right triangular profile with the subwavelength period to project light onto the display object by using diffraction effect. Therefore, the light guide of length/thickness = 50, with the grating, gets an illumination efficiency of 90%. Not occurring reflected light from the illumination device by an antireflection effect prevents that the contrast of display becomes low. Next, the fabrication method by using a reactive ion etching (RIE) that makes the grating of high precision was developed.