A method and apparatus is described for multimode electro-optic multiplexing which provides high interchannel isolation. This isolation is achieved by utilizing voltage induced optical barriers to channelize optical signals and may be increased by positioning spoiler electrodes, which are energized with the channel barrier electrode, in each channel. These spoiler electrodes establish a varying refractive index in the median which deflects optical signals from the output port of the channel, thus providing the increased isolation. The spoiler electrode concept is also employed to provide a non-guided optical multiplexer/demultiplexer.