The figure schematically shows a micromachined Fabry-Perot interferometer that, when fully developed, would be part of a two-dimensional array of such interferometers in a flat-panel display device. The interferometers, arrays, and display devices according to this concept would be similar to those described in the preceding article, "Micromachined Interferometric Optoelectronic Display Devices" (NPO-19527). The basic principles of design and operation are the same, but there would be differences in some of the details.

This Micromachined Fabry-Perot Interferometer would pass light at a resonant wavelength equal to 2nd/m, where nis the index of refraction of the medium between the mirrors, d is the gap width shown in the figure, and m is an integer that denotes the order of interference. The voltage applied to the transparent electrodes would be varied to vary d and thus the transmitted color.

The major difference in design would be that a device of this type would contain only one micromachined Fabry-Perot interferometer per pixel instead of three as in the devices of the preceding article. The major difference in operation is that instead of using each micromachined Fabry-Perot interferometer as an on/off modulator for light of a preset wavelength, one would use each such interferometer as a tunable band-pass filter and "off" switch: the voltage applied to the electrostatic-deflection electrodes of the interferometer in each pixel could be varied as a function of time to make light of a chosen wavelength pass through at a given time, or the voltage could be increased to a level sufficient to draw the interferometer mirrors together so that no light would pass through. That is, by controlling the voltage applied to each pixel, one could either make it appear to glow in a chosen color or else go dark.

The feasibility of this concept was demonstrated in an experiment on a prototype. The distance between the mirrors was varied, causing the transmitted color to vary between red and blue.

This work was done by Tony K. T. Tang, Linda M. Miller, and Judith A. Podosek of Caltech for NASA's Jet Propulsion Laboratory. NPO-19528

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Variable-wavelength micromachined Fabry-Perot interferometers

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This article first appeared in the June, 1998 issue of Photonics Tech Briefs Magazine.

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