Initial bias dependency in dc drift of z-cut LiNbO<sub>3</sub> optical intensity modulators

Abstract

Estimation of a long-term dc drift behavior is essential for the application of LiNbO3 optical intensity modulators to fiber communication systems. Therefore temperatureaccelerated tests are carried out using a feedback-biascontrol operation system, and the results are converted into a duration at ordinary device operation temperatures, e.g., 50°C. The activation energy Ea for the data conversion was reported to be about 1 eV for z-cut LiNbO3 modulators. 1–3 In the feedback-bias-controlled operation, a certain dc voltage is applied to the ac-driven modulator sample as the initial dc bias, and this applied dc voltage is varied continuously to keep the state of the optical output modulation at the initial state. Furthermore, the initial bias voltage set to be the same for all samples is effective in simplifying the device qualification process. However, there is a possibility that the initial dc bias will change, sample by sample, because the bias voltage required to adjust the initial output modulation state depends not only on a device design but also on an initial temperature for the system operation. The output modulation states are strongly affected by mechanical fluctuation introduced into devices during the fabrication, and a complete equalization of them is difficult. To provide practical information on the longterm drift performance of z-cut LiNbO3 modulators, we carried out experiments to show a relationship between the initial dc bias and the resulting dc drift. Because the z-cut