Illumination unit for a device having a multi-color reflective liquid crystal display

Abstract

A reflective liquid crystal display ( ) is provided with a front illumination unit. The front illumination unit comprises a flat waveguide ( ), at least one surface of which is provided with a diffraction grating ( ). A period of the diffraction grating ( ) is of the order of the wavelength of the light. A light source ( ) generates light of one or more colors, and the colors of light are sequentially coupled into the flat waveguide ( ). The diffraction grating ( ) is divided into separate areas ( ). Each of these separate areas ( ) is tuned to one particular wavelength of the light generated by the light source ( ). Each separate area ( ) is subdivided into various small areas so that the surface of the flat waveguide is subdivided into a large number of small areas ( - - - - - ). Each small area ( - - - - - ) is bounded by small areas ( - - - - - ) tuned to other light wavelengths. A polarizer ( ) is present above the waveguide ( ) to reflect light polarized in one direction back to the reflective liquid crystal display ( ) and to transmit image-wise polarized light in a direction transverse to the one direction.