Optical electric field sensors have been used for the measurement of high-voltages found in power substations. Typically, the sensor-heads 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, costly and results in uneccessary optical losses. The work presented here is the design and implementation of an optical electric field sensor that uses an entirely fiber-based sensor-head. D-shaped optical fibers allow access to the evanescent optical field, that penetratres into the cladding of the fiber. Replacement of part of the cladding of the fiber with an external medium allows for modulation of this evanescent field and thus the propagation of the light in the fiber can be affected. We are investigating the use of chiral Smectic A liquid crystals, which respond linearly to electric fields, as the external medium. The propagation characteristics of the D-fiber, with varying cladding thicknesses and varying external medium refractive index are investigated. We present theoretical and experimental results of such a D-fiber sensor. Preliminary experimental results for a prototype electric field sensor are also presented. The sensor responds in a linear fashion to an applied electric field.