<title>Linear light modulation by polymer-dispersed chiral liquid crystals</title>

Abstract

In general, polymer dispersed liquid crystal (PDLC) devices are based on the principle of field controlled light scattering. The effect utilized so far is quadratic and the characteristic response time is in the millisecond range. However, for many applications, a linear electrooptic response is more attractive. A few effects giving such a response are candidates of practical importance. Here, we presented three different polymer dispersed systems, incorporating short pitch smectic C*, smectic A* or N* as electrooptically active materials. By means of a special alignment technique, polymer dispersed chiral liquid crystal films with high transparency and with their optic axis lying in the film plane are prepared. When an electric field is applied across the films, a linear modulation of the transmitted light is observed, due to the field-induced-in-plane deviation of their optical axes. In all three cases, the induced tilt of the optic axis has been found to be a linear function of the applied field and the response time to be in the microsecond range. This means a fast liquid crystal electro-optic effect with grey scale. The induced tilt of the optic axis can be substantial. In the case of short pitch ferroelectric PDLC it is about 13 degrees on applying an electric field less than 10 V/micrometers and higher values are achievable with this kind of material.