Abstract: A data telemetric system consists of a pair of optical fibers, each having an associated electrically conductive member. One of the fibers is a reference fiber and the other fiber constitutes a data transmission fiber. A light beam, from a source such as a laser, is launched from one end into both fibers. A signal transfer sensor is non-invasively coupled to the data fiber and applies forces to that fiber that are related to data signals thereby to modulate the light beam therein. A comparator at the other end of the pair of fibers compares variations in a characteristic of the modulated beam with corresponding characteristics of the reference beam to decipher the transmitted information. Means are provided in the signal transfer sensor for inductively sensing control and power signals transmitted through the electrically conductive member.