Fiber optic electric field sensors using polymer-dispersed liquid crystal coatings and evanescent field interactions

We report a simple evanescent field fiber optic electric field sensor const ructed by coating the exposed fiber optic core with a polymer-dispersed liq uid crystal (PDLC). It is well known that the effective refractive index of the liquid-crystal polymers has a large dependence on the direction and th e magnitude of an applied electric field. This dependence was large enough in our devices to enable simple transmission measurements to detect the pre sence of an applied electric field across the fiber optic. The sensors show ed good sensitivity and reproducibility with its response dominated by the RC time constant of the structure rather than the response of the PDLC. Its response time was approximately 3 min with 15-20 min relaxation time. Usin g an electric circuit model of the device, we also discuss how the sensor's response time can be improved by many orders of magnitude. (C) 2000 Elsevi er Science S.A. All rights reserved.