Light-valve technologies for high-definition television projection displays

Abstract

For proper viewing, high-definition television (HDTV) images should be bright as well as large. Light-valve projection, whose feasibility is proven by several existing commercial devices (e.g. the Gretag Eidophor, the GE Talaria, the Sodern Titus, the Hughes LCLV and several Japanese liquid-crystal light-valve (LCLV) projectors), offers high resolution with large image areas and high brightness, and it thus appears to be most suitable for HDTV displays. The increasing availability of active-matrix-addressed liquid-crystal light-valve projectors for standard television, and the continuing dominance of ‘classical’ electron-beam-addressed light-valve projectors for the most demanding professional applications, are the starting points of a survey on the state of the art. After the two groups of light-valve projectors have been briefly reviewed, the major light-valve technologies are explained in some detail. Transmissive and reflective liquid-crystal light valves with various types of addressing are described first; the trend toward active-matrix addressing and high resolution is demonstrated. Commercial light-valve projectors with electrooptic and oil-film control layers are briefly introduced, and more recently developed technologies, such as metallized viscoelastic layers, deformable micromechanical mirrors, and polymer-encapsulated liquid crystals, are discussed. The author's research on deformable viscoelastic light-valve control layers for use in schlieren optical systems and on Si-Mosfet active matrices for addressing these is reported in some detail. The deformation behaviour of thin metallized elastomer layers has been analysed by the combination of the theories of electrostatics, linear viscoelasticity and thin plates; the calculated time behaviour and spatial-frequency response are found to be, at least in principle, sufficient for HDTV projection displays. Viscoelastic and metal layers have been manufactured by spin coating and vacuum evaporation, respectively; the deformation has been determined experimentally, mainly by phase-shift interferometry, and it is found to be in reasonable agreement with theoretical predictions. Sample Mosfet active matrices with picture-element densities suitable for HDTV have been designed and fabricated. In addition, the concept of a full-colour schlieren optical projection system for the above reflective VSLMs is briefly described. Finally, in view of its importance for the field, some general aspects of active-matrix addressing are briefly examined.