When voltage is applied to a basal section of uniaxial crystal of the type XH2PO4, the crystal becomes biaxial. Between crossed polarizers it can be considered, then, to act as a light valve. The angular field of view is limited by the natural retardation of the crystal. This paper discusses methods by which this natural retardation can be minimized or effectively canceled so that the retardation with no voltage is essentially zero over a large angular field. In the first method a basal section of uniaxial crystal of opposite sign is placed in series with the slab to be excited. Another technique uses two slabs of similar crystal with a 90-degree optical rotator placed between them. Both these techniques are treated theoretically and experimental measurements are given to show the resulting angular polarization pattern. This pattern is shown both for the electrically excited case and the unexcited case.
BRUCE H. BILLINGS, "The Electro-Optic Effect in Uniaxial Crystals of the Dihydrogen Phosphate (XH2PO4) Type. IV. Angular Field of the Electro-Optic Shutter," J. Opt. Soc. Am. 42, 12-18 (1952)