LCD projector and wave guide transmission system

                    The invention relates to a projection system for displaying image information comprising a light source, an illumination system for providing three sub beams of red, green and blue light respectively and three transmissive LCD light valves for modulating said light beams, an X-cube for recombining the modulated sub beams in a single beam, and a projection lens to image the modulated beam on a screen. It is known to provide the illumination system with a waveguide. The purpose of the waveguide in such a projector is to provide a uniform illumination of the LCD panels.             Fig. 1 shows an example of a projection system 1 comprising a lamp 2 for generating light, a waveguide 3 for equalizing the light beam from the lamp, dichroic mirrors 4,5,6 for transmitting the red, green and blue sub beam respectively, reflective polarizer 7,8,9 for transmitting only a portion of the light beam having a first polarization direction of the respective beams and reflecting the other portion of the beam having a second polarization direction perpendicular to the first polarization direction. The three LCD panels 14,15,16 modulate the polarization direction of the beam with the image information. The analysers 17 convert the polarization modulation in an intensity modulation of the respective sub beams. The prisms 10, 11 direct the red and blue sub beams towards the X-cube. The X-cube 12 recombines the respective sub beams in a single modulated light beam. The projection lens images the modulated light beam on a screen (not shown).

            In order to achieve a sufficient homogenous illumination of the LCD panels, a predetermined length of the wave-guide is required. Simulations indicate that a length of at least 5 times the largest of height H or width W of the wave-guide is required. In this example the projection system is provided with three LCD panels with a 0.55” diameter and a 4:3 aspect ratio. These panels have a horizontal size of 1.15 cm, and vertical size of 0.84 cm. The three panels are positioned side by side at their shortest side. Furthermore, some space in between is required because angular spread in the light beams. The total width W of the wave-...