Applied‐voltage induced fatigue of lithium niobate waveguide

z‐cut lithium niobate optical modulator devices were ac (Vp‐p=20 V) operated at 130 °C with an accumulated dc bias voltage of 4 and 8 V. A consequent dc drift phenomenon was larger for the 8 V bias application. After the operation, inversed domains were found along the Mach–Zehnder waveguides, particularly on the waveguide placed under the hot electrode. The results suggested that the device operation at higher voltage and temperature led to an accelerated dc drift and a fatiguelike deterioration of the lithium niobate material.