Patent ID: 7982848
Filing Date: 2011-07-19
Classification: G02F,G03B,H04N

Abstract:
1. A variable light transmission device comprising: a plurality of diffraction gratings each comprising a pair of transparent substrates, a multi-layer grating member, a liquid crystal and a plurality of transparent electrodes, wherein the pair of transparent substrates are placed in parallel to each other, the multi-layer grating member is disposed on one of opposing substrate surfaces of said pair of transparent substrates, has plural transparent members having a multi-layer structure and periodically placed so as to form a diffraction grating, said diffraction grating has a convex and concave section shape, the liquid crystal is interposed between said pair of transparent substrates to bury said multi-layer grating member, the transparent electrodes are provided for applying an electric field to said liquid crystal, said transparent members possessed by said multi-layer grating member have a multi-layer structure in which plural dielectric thin films having different refractive indexes are periodically stacked, the liquid crystal has an extraordinary refractive index which is larger than an average refractive index of the multi-layer grating member, the plurality of diffraction gratings comprises two diffraction gratings placed such that orientation directions of liquid crystal molecules in the two diffraction gratings are perpendicular to each other, and said multi-layer grating member has reflection regions in a wavelength range from 230 nm to 430 nm and a wavelength range from 630 nm to 1030 nm, wherein the effective refractive index in the long wavelength side of the 230 nm-430 nm reflection band is relatively high, while the effective refractive index in the short wavelength side of the 630 nm-1030 nm reflection band is made relatively small.