Abstract

Spatial light modulators are a key element in coherent signal processing applications, primarily as an incoherent light converter. In this and other applications the sensitivity and spatial resolution as well as speed are important considerations which limit performance. In addition, most devices require operation in the reflection mode due to inadequate transmission of the thick photoconductor layer. Reported here is a liquid crystal modulator using a thin-film (≤1-μm) amorphous silicon photodiode in a PIN configuration. A novel electrode design is used to greatly increase the efficiency of the field switching, allowing the use of photoconductor layers thin enough to achieve good transmission. The electrode design incorporates an additional array element located between the photoconductor and the liquid crystal which enhances a horizontal component of the electric field. Spatial resolution of over 20 Ip/mm has been demonstrated. The white light sensitivity is better than 3 μW/cm². A 2-D ac lumped element device model was developed for characterization of the modulation, spatial resolution, complete field distribution, and temporal performance. The unique electrode design combined with the capability for transmission mode operation using the twist mechanism of the nematic liquid crystal alone results in a much desired insensitivity to thickness nonuniformities.

© 1987 Optical Society of America