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 constructed by coating the exposed fiber optic core with a polymer-dispersed liquid crystal (PDLC). It is well known that the effective refractive index of the liquid-crystal polymers has a large dependence on the direction and the magnitude of an applied electric field. This dependence was large enough in our devices to enable simple transmission measurements to detect the presence of an applied electric field across the fiber optic. The sensors showed 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. Using 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 Elsevier Science S.A. All rights reserved.