Abstract

One of the obstacles in real-time holography as well as in optical information processing is the lack of a real-time addressable spatial light modulator that can display a complex function with both amplitude and phase information. In this paper, we describe a novel method that uses two identical 90° twisted nematic liquid crystal displays to implement a continuous phase/amplitude level spatial light modulator. Phase and polarization modulation properties of the twisted nematic liquid crystal cell is due to the modulation of the tilt and the molecules in the vertical direction along the liquid crystal cell structure and the twist in the horizontal plane, respectively. By aligning the incident light to be perpendicular to the front director of the liquid crystal molecules, and inserting an analyzer (in the same direction as the incident light) immediately after the first liquid crystal cell, amplitude-only modulation can be achieved. The light amplitude coming from the first cell is then parallel to the molecular director of the second cell, and phase-only modulation can be achieved by limiting the applied voltage to be below the polarization modulation threshold. The combined modulator is then capable of modulating both amplitude and phase parameters independently by two identical spatial light modulators.

© 1991 Optical Society of America