PHASE VOLUME HOLOGRAPHIC OPTICAL-COMPONENTS FOR HIGH-BRIGHTNESS SINGLE-LCD PROJECTORS

Projection systems based on liquid-crystal displays (LCD's) offer new opportunities to display high-definition and large-size TV images. The re are two types of LCD projector architectures: the 3-LCD architectur e uses one LCD for each primary color, red, green, and blue, whereas a single-LCD configuration employs only one LCD paved with color filter s. The single-LCD projector is simple and compact but suffers from a p oor luminous efficiency because of losses in the color filters: each f ilter transmits only similar to 1/3 of the flux emitted by the lamp. T o increase this optical efficiency, we propose to introduce volume hol ographic elements in the architecture of a single-LCD projector. Innov ative systems are presented in which volume holographic elements reali ze the spatiochromatic illumination of the LCD. This illumination cons ists of selectively directing all the Light that corresponds to a prim ary color, red, green, or blue, in the pixel addressed with the corres ponding video composite signal and exploits the spectral selectivity a nd dispersion properties of volume holographic gratings and lenses. Th e two main advantages of such illumination are the suppression of the color filters and the recovery of the Light lost in a classical archit ecture by absorption of the color filters. A complete luminous efficie ncy analysis of spatiochromatic illumination with volume holographic e lements is presented. The achieved performances are compared with clas sical single-LCD projectors. (C) 1997 Optical Society of America.