A fiber optic sensor for measuring voltage in direct current and alternating current systems is disclosed. The sensor may include an optical fiber probe containing transmitting and receiving fibers, fixed conductor elements, and a dynamic conductor element with a reflective surface or material. The reflector may be attached to a dynamic conductor. The two fixed conductors may be placed parallel to one another and coupled to a static voltage source. The dynamic conductor may bisect the fixed conductors and be coupled to a voltage source. The dynamic conductor may be spaced apart from the ends of the fibers in the fiber probe, and positioned so that light transmitted through the transmitting fiber is reflected by that surface into a receiving fiber. A light sensing means may be coupled to the receiving fiber, so light from a light reflected by the reflector body back into the receiving fibers is detected.