A sensor employing a single monomode low-birefringence fiber, excited with a 632.8-nm He-Ne laser, has been developed for the simultaneous measurement of current and voltage in an energy system. The piezoelectric effect for the voltage and the magnetic stress for the current are utilized. The current and voltage signals are separated at the detector end by suitable self-tracking tuned filters. Experimental results from a laboratory model demonstrate the feasibility of the sensor for field application in high-voltage systems. © 1993 Optical Society of America.