Surface-plasmon tunable filters (SPTFs) have been proposed for use in generating scrolling colors on the faces of liquid-crystal display (LCD) devices. In comparison with a conventional color LCD device equipped with primary-color filters, a LCD device equipped with SPTFs according to the proposal would utilize a greater proportion of the available luminous flux, generating a display about six times as bright, eliminate the in-pixel dye color filters, and cut number of pixels to one third.

A conventional color LCD device operates with linearly polarized light and is equipped with primary-color filters, there being a complete set of such filters (red, green, and blue) in each pixel. Therefore half the available white illumination is rejected through rejection of one of the polarization components. If one primary color is selected for display in a given pixel at a given time, then no more than about 1/3 of the remaining available illumination is utilized. Thus, only about 1/6 of the initially available illumination is utilized.

All Three Primary-Color and Both Polarization Components of the incident unpolarized white light would be utilized in this scheme. In contrast, a conventional color LCD device wastes about 5/6 of incident unpolarized light because it rejects one polarization component and two of the three color components.

According to the proposal, white illumination for an entire LCD device would be processed through assemblies of SPTFs and prisms. The SPTFs would serve as polarization-sensitive band-pass filters to generate the primary colors, while the prisms would serve as total internal reflectors to change the direction of the light.

Incident unpolarized white light would enter the top assembly which contains three SPTFs. It would allow only p-polarized light to generate scrolling RGB (red, green, blue) colors and would reflect the remainder of the incident light downward to the bottom of the assembly. For example, the very top SPTF would allow red-color pass- through only; the downward-reflected remainder of the incident light would be totally internally reflected toward the middle SPTF of the top assembly, which would only pass p-polarized green light. In a similar manner, the bottom SPTF of the top assembly would be made to pass only the p-polarized blue light and reflect the remaining light downward. At this point, the remaining downward-reflected light would comprise the s-polarized portion of the incident white light.

Using scrolling color, the frame should change three times faster, i.e., a 180-Hz frame rate is needed. For example, at the first 1/3 of the 1/60 second, the image on a black-and-white LCD screen would look like this : the sixth and the third sections are red, the fifth and the second sections are green, and the fourth and the first sections are blue. At the next moment, the second 1/3 of the 1/60 second, the colors scrolling downward, the image on the black-and-white LCD screen would look like this: the sixth and the third sections are blue, the fifth and the second sections are red, and the fourth and the first sections are green. At the last 1/3 of the 1/60 second, the image on the black-and-white LCD screen would look like this: the sixth and the third sections are green, the fifth and the second sections are blue, and the fourth and the first sections are red. Therefore, one sees a full color image at 60 Hz.

The bottom assembly would function similarly to the top assembly, except that it would be configured to receive the remaining downward-reflected light, and its SPTFs would be made perpendicular to those of the top assembly so as to exploit the s polarization of this light. Unlike in a conventional color LCD, the two assemblies would utilize both polarization components and all three color components of the white illumination. Thus, the display would be about 6 times as bright as is a conventional LCD.

During each third of a frame period, the voltage applied to each SPTF could be changed so as to change its pass wavelength band to that of a different primary color. The temporal sequence of voltages applied to the six SPTFs could be chosen to make the colors on the corresponding six subdivisions of the display area scroll downward or upward.

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
Mail Stop 122-116
4800 Oak Grove Drive
Pasadena, CA 91109
(818) 354-2240

Refer to NPO-20110, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).
Using surface-plasmon filters to generate scrolling colors.

(reference NPO-20110) is currently available for download from the TSP library.

Don't have an account? Sign up here.

NASA Tech Briefs Magazine

This article first appeared in the February, 1999 issue of NASA Tech Briefs Magazine.

Read more articles from the archives here.