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Holographic Reflector Provides Whiter, Brighter LCDs

Photonics Spectra
Oct 1997
Jennifer L. Morey

CAMBRIDGE, Mass. -- Scientists at Polaroid Corp. have developed a holographic reflector that promises to make color LCDs whiter and brighter. The secret lies in a transmission hologram that sits behind an LCD and reflects ambient light to produce a white background.
This development follows the company's introduction of a monochromatic holographic reflector last year, dubbed IMAGIX. Like its new cousin, IMAGIX was touted as being brighter than traditional reflectors, but its green display can be limiting in color LCDs. In addition, some people would simply prefer a display with the brightness of white paper, according to Michael Wenyon, a scientist at Polaroid.

Mechanical embossing
The technology's main component is a hologram mounted in front of a mirror or reflective coating, such as aluminized plastic film. Ambient light reflects off the mirror, passes through the hologram and diffuses into a controlled viewing cone. The result is a white appearance that the company says is up to three times brighter than metallic reflectors, which back traditional LCD screens.
Mechanical embossing created the prototype reflectors: A hologram is embossed onto the surface of an aluminized plastic film, similar to the process that puts security holograms on credit cards.
The company has also manufactured the reflectors by copying a master hologram onto a proprietary photopolymer with a single laser exposure. This process, known as optical copying, results in a volume hologram, one in which the recording medium contains information throughout its depth and on its surface.
Besides the increased brightness, the white reflector is expected to exhibit the same non-Gaussian intensity profiles as IMAGIX, responsible for relatively uniform center-to-corner brightness on the display screen.
Wenyon said that color LCDs represent only a small portion of the market. As the market grows, however, color will become a big selling point. The reflector could be used for displays in watches, personal organizers, cellular telephones and even in Tamagotchis -- the virtual pets that seem to be at the top of every child's wish list.
Wenyon said Polaroid will begin shipping the reflectors in the next few months.

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