Abstract

The bandwidth of Ti:LiNbO₃ traveling wave (TW) optical modulators may be enhanced by improving the phase match between the microwave and optical signals. This has been accomplished in the coplanar waveguide (CPW) configuration by use of a shielding plane [1] and in the coplanar strips (CPS) configuration % use of thick electrodes [2]. In the phase matched condition, the device bandwidth would be limited by only the resistive electrode loss, provided that there is no power leakage from the fundamental coplanar mode to the dielectric substrate modes of LiNbO₃. We have observed and modeled this leakage that occurs in LiNbO₃ traveling wave modulators. Below we describe our model and demonstrate a 20 GHz bandwidth optical modulator in the CPW configuration with thick electrodes without any power leakage over a 40 GHz span. The V_π for this device was 5 V at an operating wavelength of 1.3 μm.

© 1992 Optical Society of America