An optimal design of a fiber optic surface plasmon resonance (SPR) sensor for voltage detection has been presented and theoretically analyzed. The proposed measure of contrast to characterize the performance of sensor permits an efficient and low cost single wavelength measurement. The wavelength of 580 nm is chosen as the optimum wavelength for this detection and the corresponding optimized values of gold film thickness and numerical aperture are revealed to be 50 nm and 03, respectively. For this optimized structure, a linear relationship is established to select the sensing length according to the fiber core diameter. On the basis of this design, the sensor can exhibit good voltage detection performance. (C) 2013 Elsevier B.V. All rights reserved.