DC Drift Phenomena in LiNbO₃ Optical Waveguide Devices

Abstract

DC drift phenomena in LiNbO 3 optical waveguide devices are investigated. From low speed switching experiments of a directional coupler modulator, two kinds of dc drift are found to exist in this device. One is a short time dc drift with several seconds relaxation time and the other is a long time one whose relaxation time is several hours. It is shown analytically that the former originates from current leakage through a buffer layer, and it is successfully suppressed by a separation of the layer. For the latter problem, photocurrents measuring experiments were carried out for various LiNbO 3 samples. We may consider from the results that the main origin of the long time dc drift is a photorefractive effect due to the guided light itself. Some solutions for overcoming these effects are also given.