<title>Transversely excited liquid crystal cells</title>

Abstract

The integration of photorefractive liquid crystal beam coupling devices into optical systems is often hampered by the need to tilt the liquid crystal cells to high angles of incidence in order to obtain efficient beam coupling. Owing to poor charge diffusion in most liquid crystal systems, charge migration depends mainly on an externally applied drift field. Conventional cells, with electrodes applied to the surfaces of the windows, therefore need to be tilted with respect to the incident light to enable a component of the applied electric field to appear along the direction of the optical grating k-vector. This paper reports on an alternative design in which the electric field is applied transversely, enabling devices to be presented at normal incidence to the system optical propagation direction. We demonstrate the optical gain from transversely excited homeotropic liquid crystal cells is very similar to that obtainable with conventional homeotropic cells, with the added unexpected advantage of an order of magnitude increase in speed.

Characterization of an inorganic photorefractive liquid crystal hybrid cell

“…For most photorefractive applications an electric field must be applied along the direction of the optical grating k-vector because the charge migration process in LCs is dominated by drift. If this field is applied to the ITO-electrodes, then (unless transverse electrodes are used [10]) the whole cell must be angled with respect to the grating k-vector so that a component of the applied field is parallel to the k-vector (see figure 1). Consequently only a part of the applied field induces charge migration.…”