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  • Light-Shaping Diffuser Enables Miniature High-Resolution Display

Photonics Spectra
Dec 1997
Ruth A. Mendonsa

When engineers at Kopin Corp. began development of a flat panel display that would allow portable electronic devices such as pagers and cell phones to display text, video and graphics, their goals were simple construction with high-yield and low-cost manufacturing. The result of their efforts is CyberDisplay, what Kopin says is the world's smallest high-performance, high-resolution, low-cost active-matrix liquid crystal display. Their success was due in part to Physical Optics Corp.'s Holographic Light Shaping Diffuser.

CyberDisplay allows the user to view information such as e-mail while using a cellular phone.

First, Kopin needed a power-conservative backlight to complement these unique displays, but finding one small enough was a problem. The display is only 0.24 in. diagonally, and the smallest backlight available was 0.5 in. Second, the displays were to be installed in lightweight, portable personal electronic devices, and extending battery power lifetime was critical. They decided that the ideal solution would be a brightly and uniformly illuminated light-emitting diode (LED). For color they would need a red, a green and a blue LED.

The next hurdle was to take the light from the LED point source and diffuse it evenly over the 0.24-in. diagonal area -- and they needed to do it in a few millimeters. The engineers found backlights designed with milky white Plexiglas to be inefficient because they scattered light in all directions. After Kopin heard about a product from Physical Optics that had solved a similar problem for a military application, engineers from the two companies worked together to solve the problem.

Physical Optics' lightweight, holographic light-shaping diffuser uses nonperiodic randomly positioned surface-relief microstructures to homogenize otherwise nonuniform light sources. Physical Optics also can control the distribution of incident light from circular to extremely elliptical so that light is placed exactly where it is needed. Because these optics are refractive, efficiency is high and throughputs are typically 88 to 92 percent.

"Physical Optics Corporation's light-shaping diffuser was not only more efficient and brighter, it was incredibly uniform," said Jeff Jacobsen, senior vice president in charge of product development at Kopin Corp.

Soon you may pick up your cellular phone and be able to save or view information such as e-mail or a map to your next client's office. Kopin recently announced a business relationship with Siemens Corp. in Germany, which plans to place the displays in "docking stations" for cellular phones.

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