Laser-Based Flat Panel Displays
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Mat. Res. Soc. Symp. Proc. Vol. 597 © 2000 Materials Research Society
Operating Principle The basic operating principle of Gemfire's PSM technology is illustrated in Figure 1. Infrared light from a monolithic linear array of diode lasers is transported across the display field by a network of waveguides embedded in a thin, flexible sheet of transparent polymer. Superimposed on the grid of waveguides is a matrix of switches, each connected to a nearby dot of upconversion phosphor. An image is created by synchronizing the activation of the laser array with the sequencing of the voltage applied to the electrodes connecting the columns of switches. A phosphor dot does not illuminate unless two criteria are met: the column electrode associated with the switch is active and the laser emitter associated with the row is active. Gray scale is controlled by pulse width modulation of each emitter. Color is achieved by using triads of subpixels with different upconversion phosphors for red, green and blue.
Column Controller
Chip Column Electrodes
APixel
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Figure 1. Schematic Illustration of Gemfire's PSM Display Technology. Each row is driven by a separate IR emitter in the laser bar. An optical switch, driven by a column electrode, diverts light from a waveguide into an upconversion phosphor pit (see inset). PSM technology takes advantage of a remarkable serendipity of nature: the chance occurrence of three key optical phenomena near 980 nm (see Figure 2).[2,3] First, polymers exhibit a pronounced transmission window near 980 rnm. The window is, in fact, much better than two more widely known telecommunications windows at 1300 and 1550 nm. Second, beside the fact that laser diodes are highly efficient devices, those operating at 980 nm are extraordinarily reliable.[4] Developed for transoceanic telecommunications applications, 980-nm diodes (due to their optimum crystal structure) have lifetimes exceeding 100 years. Third, with upconversion phosphors, the three primary colors can be produced with a single incident wavelength only at 980 nm.[5] Moreover, they can be obtained at this wavelength with near peak efficiencies and narrow emission bands. What makes this coincidence all the more amazing is the fact that these separate phenomena occur in different materials systems for different physical reasons. The polymer transmission window is due to carbon-hydrogen stretches in an organic materials system; the lasers are due to the favorable lattice properties of indium-gallium-arsenide quantum wells in a semiconductor materials system; and the upconversion phosphors are due to fortuitous energy-level dynamics in related ytterbium/rare-earth materials systems. The effect of this serendipity is that the PSM technology has been able to demonstrate rapid progress in just over three years. Starting in early 1996 with little more than a concept in mind, Gemfire has succeeded in developing the device and processing technology necessary to fabricate full-color test dis
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