Proceedings PaperUniform color illumination for scrolling color LCoS projection
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Projection based on the scrolling color single panel reflective liquid crystal on silicon (LCoS) architecture developed within Philips is set to become a competitive technology for high definition rear projection television. The colorimetry of the scrolling color illumination light engine is examined in this paper including the design issues considered in specifying dichroic color filters for uniform color illumination. The scrolling action can be achieved with rotating glass prisms (one for each primary color), which combined with the requirement for compact illumination optics can lead to beamsteering at some of the dichroic filters in the light path. This beamsteering can cause unacceptable color changes of the illuminating stripes as they are scrolled from the top to the bottom of the LCoS panel unless special attention is made to the choice of filter cut-off wavelengths and their sensitivity to angle of incidence variations. One solution involves the design of new dichroic filters that are relatively insensitive to these beamsteering effects. Filters have been designed and fabricated with edge sensitivities < 0.9 nm/deg compared with typical sensitivities of ~ 1.4nm/deg from standard filters; the filter specifications and their system performance will be described. Further system solutions are given that utilize conventional angle-sensitive dichroic filters. The effect of color balancing upon the optical efficiency of the system will also be described.