A waveguide electro‐optic grating coupler modulator based on a single straight channel waveguide and an interdigital modulation electrode structure on an electro‐optic substrate, has been reported. Both single‐mode and multimode operations are possible. Preliminary experiments have demonstrated the modulation on a proton exchanged LiNbO3waveguide device. Modulation performed on other electro‐optic waveguides, such as GaAs, LiTaO3, and EO polymers, are also possible. ©1995 American Institute of Physics.