Linear, 1*2 directional coupler modulator with 10 GHz bandwidth

The characteristics are presented of a 1*2 coupler with coplanar stripline, traveling-wave electrodes designed for broadband operation to approximately 10 GHz. Modulators are fabricated by Ti diffusion in Z-cut, Y-propagating LiNbO/sub 3/ to form single-mode guides at the 1.3- mu m wavelength. Electrodes are defined over an approximately 0.3- mu m-thick SiO/sub 2/ buffer layer in approximately 3- mu m electroplated gold, with L=6.5 mm. The waveguide parameters and arm separation are designed with the aim of achieving coupling coefficients corresponding to 0.5