All-optical switching in a nematic liquid crystal twist cell

Continuous wave photorefractive-like all-optical switching was demonstrated using a twisted nematic liquid crystal cell composed of the liquid crystal 5CB (4-pentyl-4'-cyanobiphenyl) with polyvinyl alcohol (PVA) aligning layers. The nonlinear optical effect involved is due to optical control of surface charge on the polyvinyl alcohol alignment layer. The cell exhibits strong optical control of the Friedericksz transition by an argon ion laser. A mechanism is proposed involving the modulation of the charge double layer by photoinduced charge. Optical limiting in the milliwatt range was observed.