Optically active diffractive device

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred diffractive liquid crystal phase gratings according to the invention are shown in the drawings.
Referring to FIG.
1, the liquid crystal cells for use as a diffractive light valve according to the invention include a pair of opposing substrates 2, 4 that are sealed around their edges and separated by spacers (not shown) to accommodate a liquid crystal material 16 therebetween as is known in the art.
As shown, the cell 10 includes continuous transparent electrodes 6, 8 disposed on opposing substrates 2, 4, and alignment layers 12, 14 disposed on the electrodes.
The alignment layers 12 and/or 14 are prepared so as to create a series of alternating stripes on one or both of the substrates 2, 4 to create alternating domains A, B within the cell in which the liquid crystal exhibits different orientations in adjacent domains.
It is to be understood that although as shown, the domains are depicted as being rather large with respect to the substrate, in practice they are quite small.
Preferably, each domain will be on the order of about 0.
5 to 500 .
mu.
m wide, and still more preferably about 20 to 75 .
mu.
m wide.
By coupling the electrodes or other addressing means overlying portions of two or more stripes, to suitable drive electronics, pixels can be selectively actuated to produce images in a diffractive light valve projection system.
One advantage of the invention is that a plurality of generally continuous pixel sized transparent electrodes may be used, rather than high resolution patterned electrodes that must be processed to correspond precisely to each stripe.
Alignment layers 12, 14 are designed to provide for different liquid crystal orientations in adjacent domains or stripes such that the liquid crystal in one domain A will cause light passing therethrough to exit the cell .
pi.
radians, or 180.
degree.
, out of phase with light exiting an adjacent domain B.
In the practice of the invention there are essentially two principal liquid crystal properties that may be relied upon to accomplish this