Three-panel LCOS projection systems

Abstract

-Three-panel liquid-crystal-on-silicon (LCOS) projection systems are presented with an emphasis on the commercially successful shared retarder-stack-filter (RSF) polarizing-beam-splitter (PBS) architectures. The design and operation of the specific CQ90 projection core is presented in detail, and its contrast and transmission derived. alternative three-PBS/X-cube LCOS architectures are briefly introduced and their performance is compared to that of the CQ90.Keywords -Liquid crystal on silicon, rear-projection television, ColorQuad, ColorSelect, retarder stack polarization optical filter. IntroductionLiquid-crystal-on-silicon (LCOS) microdisplay technology offers the greatest performance/cost ratio of all display technologies by combining the high resolution and performance of silicon VLSI with controlled liquid-crystal optical modulation. To view directly in the form of a conventional TV-like display, one or more LCOS display panels need to be projected onto a viewable screen, as shown in Fig. 1. 1 LCOS projection is non-trivial since the panels are reflective. Modulated light forms a reflected beam with a spatially varying polarization state, which occupies the same region of space as the uniform input illuminating light. Physically separating these beams while maintaining good polarization integrity required for high contrast is demanding, particularly in multiple-panel systems where color separation is also necessary. One of the first attempts at three-panel LCOS projection used a polarizing beam splitter (PBS) to separate input and output light prior to RGB color separation and recombination. 2 A Philips prism (of the type found in early threecolor TV cameras) was used for the color management but proved unsuccessful due to polarization mixing at oblique "skew" incident angles. 3 A more successful attempt separates color first, such that a single primary-color beam is directed onto and away from its modulating panel before its recombination and projection. Input beams are thus separately incident upon each panel, allowing near-equivalent architectures to the established transmissive LC system 4 to be adopted. This generic approach uses dichroic plates to separate color within the illumination before utilizing PBSs to direct light onto and away from the panels. Recombination of the imaged light is carried out with an X-cube. A variation on this approach uses angular separation of the input and output beams in an off-axis configuration. 5 This last approach has, to date, suffered from low contrast and difficulties with the registration of the individual panel images, making it less mainstream and will not be discussed further here. Of the generic 3xPBS/X-cube on-axis architectures, there are three distinct types differing in the type of PBS used. Conventional systems use MacNeille-type PBS cubes, whereas more recent systems use either wire-grid PBS plates 6 or embedded reflective polarizing films. 7 The former modified PBS system is often termed Ultrex after developments by ADO, 6 whereas the latter i...

Invited Paper: Detailed optical characteristics of multi‐layer optical film polarization beam splitter

“…Robinson et al 3 considered the efficiency of different LCOS engine architectures, including the Vikuiti™ Core, and have found differences similar to but smaller than those we have measured. We believe their results are accurate for the systems they have analyzed, but the analysis was done using a much slower f/2.8 optical system than we consider.…”

Atomic Diffusion Bonding for Optical Devices with High Optical Density

“…Here, T signifies total transmittance, R1 expresses the incident-side surface reflectance, R2 denotes the exit-side reflectance, and t stands for the bonded interface transmittance. The values of t for all samples shown in Figure 6 were converted using equation [1].…”

P-206: Circular Polarization Separation Elements for Display Applications

“…What makes these structures unique as opposed to conventional holographic gratings [1][2], is the ability to diffract right-and lefthanded circularly polarized light in the +1 and -1 orders, respectively. In a perfect polarization grating higher diffraction orders do not exist and can be optimized such that 100% of the light is diffracted to the two first orders.…”

“…Three separate beams with separate LCD panels for each primary color are used with a polarization beam splitter (PBS) instead of just one LCD panel to increase output resolution and luminosity. Robinson and co-workers further showed the brightness can be enhanced by approximately 75% with a larger color gamut by using a fourth LCD color panel for yellow light emitted by ultra high performance (UHP) lamps [2].…”