Traveling-wave electrodes for an optical waveguide modulator are characterized and designed. The characteristic impedance and the microwave effective index are calculated by varying the traveling-wave electrode thickness, the buffer layer thickness, and the overlaid layer thickness using the second-order triangular-element quasi-TEM finite element method(FEM). The measured characteristics of the fabricated electrodes confirm the calculation results. Effects of pad, taper, and bending parts constituting the non-active section in the electrode are investigated. The performance of the optical waveguide modulator with the designed electrode is estimated using the measured mode size of the optical single-mode waveguide at 1.5㎛ that we have fabricated. For modulation bandwidth of 10 GHz, the estimated driving voltages($V_π$) are 9.3 volts and 7.4 volts in the conventional structure and the shielded velocity matched structure, respectively.
