This study presents a novel high-efficiency electro-optic (EO) light modulator whose operation is based on the attenuated total reflection effect, in which the surface plasmon wave is excited by an incident waveguide light wave. The EO light modulator is fabricated using a nonlinear optical polymer material that is a side-chain EO polyimide with 2-[N-ethyl-4-(tricyanovinyl)anilino]ethanol chromophore. The modulator is characterized, and its performance tested, in terms of the thickness and dielectric constant of the polymer thin film, the EO coefficient, the insertion loss, and the modulation index. Additionally, the dynamic response of the EO light modulator is fully investigated and discussed. © 2005 Society of Photo-Optical Instrumentation Engineers.