Abstract: An array of picture elements is disclosed for providing a display having selectivitely light or dark areas. The array includes light valves each comprising a pair of light transmissive elements having facing phase gratings, preferably sinusoidal, of like periodicity and parallel grating lines. The pair of elements are selectively positioned in two positions. In the first position, (the relatively dark transmissive position) the maxima and minima of one of the light transmissive elements are respectively coincident with the maxima and minima of the other light transmissive element. In the second position, (the relatively dark transmissive position) the maxima and minima of one of the light transmissive elements are respectively coincident with the minima and maxima of the other light transmissive element. Preferably the gratings comprise two sets of gratings having lines at right angles to each other, and at 45.degree.

Abstract: A light valve comprises a pair of elements of transparent material each comprising a diffraction grating of like periodicity facing each other with parallel grating lines. Such a light valve is termed herein a bigrate. The transmission of light through the bigrate will depend on the relative position of the pair of gratings in the direction perpendicular to the grating lines and means may be provided for moving the elements relative to each other in that direction. One of the gratings may be embossed on a polyvinylidene fluoride (PVF.sub.2) strip and moved by piezoelectric means, which may be a portion of such a strip. One strip may then be moved relative to the other in response to an electrical signal to control the zero diffraction order light transmission from no transmission to full transmission, or any desired intermediate transmission. Two intersecting sets of polyvinylidene fluoride (PVF.sub.