A voltage sensor based on a singlemode-multimode-singlemode (SMS) fiber structure, attached to a piezoelectric (PZT), used in a ratiometric optical power measurement scheme is proposed. The elongation of the PZT due to an applied voltage induces a strain on the SMS fiber structure and in turn results in a change in the transmission loss response of the SMS fiber structure. It is found that at selected wavelengths, a strong voltage dependence for the transmission loss of the SMS fiber structure can be achieved. The voltage information can be obtained from the power ratio of the system, assuming the system is calibrated. The proposed voltage sensor offers a simpler configuration when compared to other fiber optic voltage sensors. © 2010 Wiley Periodicals, Inc.