The Use of Wollaston Prisms for a High-Capacity Digital Light Deflector

A digital light deflcctor was recently proposed by T. J. Nelsonl1in which n optical modulators and n uniaxial crystals were used to provide 2npositions of the beam. Each uniaxial crystal was used to deflect a beam of light into either of two beams, with the light at the output remaining parallel to the input but displaced by an amount proportional to the thickness of the crystal. For a large number of positions it was found that a lens had to be employed in order to focus the beam into a smail spot. The lise of the lens requircs that converging or diverging light must pass through the uni ax ial crystal. In this brief we point out that this converging beam, when passing through the crystal as an extraordinary ray, is subjected to an index of refraction which varies rapidly with angle. The digital light deflector using this type of deflection therefore has appreciable image distortion, and the limiting spot densities that can be achieved are less than would be predicted if only diffraction were important.