Transmissive light valves based on voltage-tunable color-selective absorption of light in surface plasmons are undergoing development. Like other surface-plasmon-based devices reported in a number of recent articles in NASA Tech Briefs, these light valves could be constructed in many different configurations and concatenated with other optical and electronic components to produce a variety of display and color-filtering devices. These devices would be compatible with, and could be incorporated into, monolithic integrated circuits for use in display, addressing, and interface applications.
As shown in Figure 1, a basic transmissive surface-plasmon light valve would include a substrate made of glass or other suitable transparent material, a metal film (e.g., a thin layer of metal or of indium tin oxide), a layer of electro-optical material (typically a liquid crystal), and another metal film as top electrode. White light would be introduced from the bottom; some of this light would pass through the bottom electrode and impinge on the top electrode, where it would excite surface plasmons at the interface between the metal films and the liquid crystal.
The surface plasmons would absorb some light in a resonance wavelength band determined partly by the index of refraction of the electro-optical material. The light not absorbed in the surface plasmons would pass through the top metal film. The color of this transmitted light would be complementary to that of the reflected light. As in the previously reported surface-plasmon devices, the index of refraction of the electro-optical material, and thus the absorption wavelength band, would depend on the electric field imposed by applying an electric potential between the electrodes. Therefore, one could control the transmitted complementary color by controlling the applied voltage.
Figure 2 illustrates part of a flat-panel display device comprising one of the many different possible combinations of surface-plasmon light valves. This device would be similar to that of Figure 1, except that the lower electrode would be divided into segments that could, for example, correspond to pixels of a display. The colors in each segment could be controlled, independently of the other segments, by applying a distinct voltage between the common upper electrode and the lower electrode for that segment. The electronic circuitry for controlling the voltages on the lower electrode segments could be fabricated on the transparent substrate.
This work was done by Yu Wang, Randy Shimabukuro, and Stephen Russell of Caltech for NASA's Jet Propulsion Laboratory.
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