Efficient Optical Engine for 2 LCOS projection display panels
Publication Date: 2002-Jul-29
The IP.com Prior Art Database
To reduce cost of 3 LCOS-Optical Engine for rear-projection TV, systems with only 2 panels was developed. These systems are based on use of a sequential color component like a ColorWheel or a ColorSwitch (a ColorLinkTM color panel selector). During one half frame only 2 colors are displayed whereas during the 2nd half frame the third color is transmitted instead of the 2nd one. It means that a color is still projected. This characteristic allow to compensate color weakness of the systems like the lack of red of the UHP lamp for example if the red is chosen as permanent color or to compensate blue losses in the OE if the blue is chosen. The easier 2 LCOS-OE is a system with 2 LCOS panels and 1 Polarizing Beam Splitter (ColorLink patent WO 00/70376). In addition 2 Colorselects are used to associate a polarization to each projected color. Then the PBS will separate the beam into 2 color beams. After reflection on the LCOS in bright state, the polarizations are rotated of 90° and the beams are recombined by the PBS and will be directed to the output. The output colorselect will give finally the same polarization for all colors to be analyzed by the last polarizer. Due to the non-zero P-Reflection of PBS, a part of the color which should be transmitted by the PBS can be reflected by the PBS to the other LCOS and then color pollution on the screen can occur. The PBS must be wideband and must have good contrast in reflection and transmission. Furthermore the use of a colorselect is quite sensitive to the azimuth of its incident polarization. In the case of the output colorselect the incident polarization that comes out of the PBS in reflection will not be perfect linear due to P-reflection. Thus this polarization could be not well rotated and could decrease the contrast.