Abstract

Because of the bipolar response of ferroelectric liquid crystals (FLCs) and the asymmetric current-voltage characteristic of most photosensors used to drive optically addressed spatial light modulators (OASLMs), the voltage signal that drives the FLC in an OASLM contains a dc component. This dc component causes ion migration within the FLC and, consequently, ionic buildup at the alignment layers. The separation of ionic charge creates an internal electric field across the FLC that opposes the dc component of the applied field. This phenomenon affects device performance by reducing bistability and contrast ratio. We discuss how the presence of ions in FLC OASLMs leads to these problems and present approaches that we and others have suggested or tried to reduce or circumvent them, including using conducting alignment layers, using a balanced drive voltage, removing ions from the FLC, and using a photosensor with a symmetric current–voltage characteristic.

© 1992 Optical Society of America