A Display Based On Switchable Zero Order Diffraction Grating Light Valves

Abstract

A flat panel display technology has been conceived which utilizes a matrix of line addressable light valves back lighted with a partially collimated source. The basic pixel element of the display is an optical switch based on the zero order of diffraction by two aligned transmission phase gratings. The transmission of light is modulated by mechanic-ally displacing one grating with respect to the other by one-half of the grating period. The color transmitted by the light valve is controlled by the grating profile. Optical spectra of a large-scale prototype of the switchable light valve element are in good agreement with calculations according to simple diffraction theory. Technology for the construction of an optical switch of the desired size has been developed, with 85% of the area devoted to light transmission. The elements are one millimeter squares made of polyvinylidene fluoride (PVDF), a transparent, piezoelectric plastic. Gratings of nearly square profile with 3.8 micron period are produced in 9 micron films of PVDF by embossing at 4000 bars and 70A‚°C and show the expected optical transmission spectra. Mechanical displacement is produced by applying voltage to two sets of bending arms attached to either side of the movable element. The bending arms amplify motion due to piezoelectric strain. Nickel electrodes are patterned onto the PVDF film by photolithography and liftoff. Perforations around the movable element and the bending arms are etched through the film by reactive ion etching in oxygen, using patterned aluminum as a mask. Motion exceeding 2 microns has been observed, which is sufficient to operate the light valve.