Reflective flat-panel color display devices based on surface plasmons are undergoing development. Heretofore, no reflective flat-panel color display devices have been available. The active matrix liquid-crystal devices now used to provide flat-panel color displays must be lit internally, are power-hungry (typically consuming about 80 percent of the power of a laptop computer), and cannot be read in bright ambient light. In contrast, the surface-plasmon display devices would be operated without internal lighting, would consume much less power, and would be readable in bright ambient light (including sunlight).
This development is based on voltage-induced color-selective absorption of light in surface plasmons: When a surface-plasmon wave is excited at a metal/liquid-crystal interface, the absorption spectrum of surface-plasmon resonance can be shifted across the visible range by altering a voltage applied to the liquid crystal. This effect can be exploited to make a tunable notch filter -- more specifically, a filter that absorbs most of the incident light in a voltage-adjustable wavelength range (the "notch") and reflects most of the incident light outside that range. If incident white light can be reflected from two tunable notch filters in succession and if the absorption wavelength range of each filter can be made to span about 2/3 of the visible spectrum, then by suitable choice of the notch wavelengths, the resulting display can be made to appear black (most of the incident light absorbed), white (most of the incident light reflected), or any primary color at a selectable level of brightness.
Figure 1. A Surface-Plasmon Optoelectronic Device of this general configuration would exhibit the desired voltage-tunable notch-filter characteristic, according to theoretical calculations.
The problem then becomes one of how to implement a voltage-tunable notch filter and to combine a number of such filters into an array of pixels to construct a flat-panel display device. Figure 1 illustrates such a filter, which includes two high-index-of-refraction prisms for coupling, plus four silver films interspersed with three liquid-crystal layers. Surface-plasmon waves are excited at the six liquid-crystal/metal-film interfaces, and the layers are made sufficiently thin that the surface-plasmon waves are coupled together. When a voltage is applied between the two outermost silver films, the device acts electrically like three capacitors in series, and the electric field affects the indices of refraction of the liquid-crystal layers, causing a wavelength shift of the absorption spectrum. A theoretical calculation shows that this filter would exhibit the desired notch characteristic, that with no voltage applied, it would absorb primarily in blue-green light, and that its absorption wavelength region could be shifted to red or beyond by applying increasing voltage.
Figure 2. A Reflective Flat-Panel Color Display Device would contain two surface-plasmon notch filters, similar to that shown in Figure 1, in each pixel.
Figure 2 shows part of a proposed flat-panel display device, wherein each pixel would contain two notch filters. The prisms -- now microscopic to fit the pixels -- would be molded into sheets of high-index-of-refraction plastic. A polarizer sheet would be mounted on the front surface to select p-polarized light. After polarization, the incident light would be reflected from one notch filter, then from the other notch filter. By choice of the voltages applied to the two notch filters in each pixel, one could obtain a desired color combination as described above.
This work was done by Yu Wang of Caltech for NASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Technology Reporting Office
JPL
Mail Stop 122-116
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Pasadena, CA 91109
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Overview
The document discusses the development of surface-plasmon reflective flat-panel color displays by NASA's Jet Propulsion Laboratory (JPL). These innovative displays aim to address significant limitations of current active matrix liquid crystal displays (AMLCDs), which are power-hungry and often unreadable in bright ambient light. The new technology leverages voltage-induced color-selective absorption of light through surface plasmons, allowing for a more efficient and versatile display solution.
The core concept involves using tunable notch filters that can absorb light in a specific wavelength range while reflecting light outside that range. Each filter can cover approximately two-thirds of the visible spectrum, enabling the generation of various colors and grayscale images by adjusting the overlap of the absorption curves of two filters. This mechanism allows the display to appear black, white, or any primary color at different brightness levels, depending on the applied voltage.
The structure of the display includes multiple layers, such as liquid crystals and silver films, arranged to create a reflective surface that can manipulate light effectively. The design incorporates high-index-of-refraction prisms and polarizers to enhance light reflection and color generation. The document also mentions the potential use of microlens arrays to improve the viewing angle, ensuring that the display remains effective from various perspectives.
The advantages of these surface-plasmon displays are significant: they do not require internal lighting, consume much less power, and can be easily read in bright sunlight, making them ideal for outdoor use. This technology represents a substantial step forward in display technology, promising to deliver high-quality color images while being environmentally friendly and energy-efficient.
In summary, the document outlines a promising new approach to flat-panel displays that could transform how we interact with screens, particularly in environments where traditional displays struggle. The combination of tunable filters, efficient light manipulation, and reduced power consumption positions these surface-plasmon reflective displays as a leading solution for future display technologies.
