Electro-optical phase shift in polymer dispersed liquid crystals

An anisotropic version of the Maxwell Garnett approximation is applied for studying the electrooptical phase modulation by polymer dispersed liquid cr ystals (PDLC). The PDLC contain bipolar liquid crystal droplets that can be reoriented by an external field causing a change in the optical birefringe nce. This approach provides an explicit link between the droplet orientatio n distribution and the electro-optical phase shift. For aligned droplets we find that the sharpness of the change in the birefringence may be controll ed by selecting the initial orientation. For a planar distribution me find sharp transitions with a hysteresis loop whose width depends on the droplet concentration. For a random distribution, the droplet orientation and the optical phase shift change more gradually with the applied field. These res ults demonstrate that PDLC may be suitable for a wide range of electro-opti c applications based on their field-induced phase modulation properties. In addition, it is apparent that the optical phase shift is quite sensitive t o changes in droplet orientation. It should therefore be useful for studyin g reorientation phenomena in PDLC, overcoming the problems due to light sca ttering in these materials.