Doubled frequency optical two-tone generation and optical single sideband (SSB) modulation by the dual-electrode-type electro-optic (EO) modulator with a single Mach–Zehnder (MZ) interferometer were considered. We theoretically showed that redundant spectrum components in the modulated optical signals, which are caused by the imbalance of light splitting ratio between the two arms of the interferometer, are significantly suppressed by controlling the input power ratio of RF modulation signals applied to each electrode. This effect was confirmed by the experiment, where an optical two-tone with the redundant components 49.8 dB lower than the primary two-tone components in intensity level was obtained. This method is also valid for suppression of undesired frequency components of RF signals that are generated at a photo detector from the optical two-tone waves propagated through a dispersive optical fiber.