Characterization of Instability in Ti-indiffused LiNbO3 Modulators Due to Photorefractive and Non-Optical Sources*

The utility of Ti-indiffused LiNbO3 modulators is limited in some applications by a slow temporal instability due to photorefractive and non-optical sources. In this paper we characterize these effects, separating instabilities which occur with or without an applied voltage due to photoconductive and photovoltaic effects respectively from those caused by non-optical sources. The characterization of optically induced instabilities includes an evaluation of devices fabricated on two different crystallographic orientations as well as a demonstration of a "fixing" technique that dramatically reduces the device susceptibility to the photorefractive effect. A simple RC circuit is used to model instabilities not optically induced that occur when a dc or quasi-dc voltage is applied.