Electrode optimization for high-speed traveling-wave integrated optic modulators

Different electrode configurations for LiNbO₃-based Mach-Zehnder traveling-wave electrooptic modulators are analyzed. It is found that the Z-cut coplanar waveguide (CPW) configuration provides the best compromise between the characteristic impedance, the half-wave voltage, and the driving power. To increase the bandwidth and simultaneously reduce the half-wave voltage, an optimum design of multisection phase reversal electrode is proposed. To verify the theoretical predictions experimentally, two modulators, both using the Z-cut LiNbO₃ CPW configuration, were fabricated and characterized, one with an optimized five-section phase reversal electrode and the other with a conventional single-section electrode. By comparing the performances of these two devices, it is confirmed that significant improvements on the bandwidth to half-wave voltage ratio and the flatness of the frequency response can indeed be obtained from using an optimized multisection phase reversal electrode