In-line D-fiber electric field sensor using chiral liquid crystals

Optical electric field sensors have been used for the measurement of high-voltages found in power substations. Typical sensors are based on electro-optic crystals and hence require the coupling of light into and out of the crystals from optical fibers. This coupling is difficult and costly. The objective of the work presented here is the design and implementation of an optical electric field sensor that uses an entirely fiber-based sensor-head. The sensor-head is comprised of a D-shaped optical fiber with its flat side coated with liquid crystals. D-fibers allow easy access to the evanescent optical field and replacement of part of the cladding with an external medium allows for modulation of this optical field. We are investigating the use of chiral Smectic A liquid crystals, which respond linearly to electric fields through the electroclinic effect. The propagation characteristics of the D-fiber for various distances between the fiber core edge and flat and for various refractive indices of the external medium are theoretically investigated and experimentally verified. Preliminary experimental results for a prototype electric field sensor are presented. The sensor responds in a linear fashion to an applied electric field.