Phase tuning in optical directional coupler

Abstract
A new phase‐tuning method for an optical directional coupler fabricated in a c‐plate LiNbO3 by TiO2 diffusion is presented. The method consists of applying a bias voltage to an additional electrode set closely outside the modulation electrodes. The propagation constants of the two waveguides could be made equal by a bias voltage of 5 V. The modulation voltage of 8 V was unaffected by the bias voltage.