US Patent 7145614 - Nanocrystal Color Filter

http://www.freepatentsonline.com/7145614.pdf

Conventional reflective color displays can suffer from inefficiency of light reflection due to light passing through color filters twice (once on entry and once on exit). This patent from Samsung proposes the use of nanoparticles of varying sizes to regulate the reflected color and avoid the use of a separate filter. Claim 1 reads:

1. A reflective display device using photonic crystals, comprising: a plurality of reflective color filters, each reflective color filter reflects a predetermined wavelength range of an incident visible light, each of the plurality of reflective color filters including three-dimensional photonic crystals of inverse opal structure having colloids of varying sizes; and a plurality of optical switches disposed adjacent to and facing a corresponding one of the plurality of reflective color filters, each of the plurality of optical switches extracts a predetermined color by adjusting an intensity or on/off-frequency of light reflected from the corresponding one of the plurality of reflective color filters.