Liquid crystal on silicon

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Liquid crystal on silicon (LCOS or LCoS) is a "micro-projection" or "micro-display" technology typically applied in projection televisions. It is a reflective technology similar to DLP projectors, however it uses liquid crystals instead of individual mirrors. This is contrary to LCD projectors which use a transmissive approach. In LCoS, liquid crystals are applied directly to the surface of a silicon chip coated with an aluminized layer making it highly reflective. (There might also be a "polyimide alignment layer".) As the liquid crystals open and close, the light is either reflected from the mirror below, or blocked. This modulates the light and creates the image.

LCOS technology requires less optical-quality glass than do liquid crystal display and plasma display technologies, which makes it less expensive to implement in such devices as televisions.

At the 2004 CES, Intel announced plans for the large scale production of inexpensive LCoS chips for use in flat panel displays. These plans were cancelled in October 2004 [1]. Sony has made it to market [2] (December 2005) with the Sony-VPL-VW100 or Ruby projector, using SXRD, 3 LCoS chips each with a native resolution of 1080p (1920 X 1080), with a stated contrast ratio of 15,000 using a dynamic lens. Before this LCoS has been used in standard sets 50" and above (November 2005).

There are two broad categories of LCOS displays: three-panel and single-panel. In three-panel designs, there is one display chip per color, and the images are combined optically. In single-panel designs, one display chip shows the red, green, and blue components in succession. As each color is presented, a color wheel (or an RGB LED array) illuminates the display with only red, green or blue light. If the frequency of the color fields is lower than about 540 Hz, an effect called color breakup is seen, where false colors are briefly perceived when either the image or the observer's eye is in motion. While less expensive, single-panel projectors require higher-speed display elements to process all three colors during a single frame time, and the need to avoid color breakup makes further demands on the speed of the display technology. Single-panel implementations are also available using Texas Instruments DLP technology.

Commercial implementations of LCOS technology include Sony's SXRD (Silicon X-tal Reflective Display) and JVC's D-ILA (Digital Direct Drive Image Light Amplifier). Another provider of third-party LCOS chips is a Novato based firm, Spatialight. Direct-view LCOS devices such as the single-panel LED-illuminated devices made by Displaytech [3] are also used as electronic viewfinders for digital cameras. These devices are made using ferroelectric liquid crystals, which are inherently faster than other types of liquid crystals.

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Three-panel designs

In a DLP device the light is separated into three components and then combined back: Two beam splitters are needed. In LCOS device the light is additionally polarized and then analyzed: Four beam splitters are needed.

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