Influence of UV Light on PECVD Silicon Nitride Waveguide Propagation Loss

A large increase in propagation loss is observed when exposing PECVD silicon nitride photonic waveguides to UV light. Annealing at moderate temperatures of ∼300 °C or high intensity optical exposure at visible wavelengths brings the propagation loss back to the initial value or even lower. We postulate that the origin of this effect can be found in the population and depopulation of optically active defect states in the silicon nitride material. We experimentally demonstrate the importance of defect depopulation when using silicon nitride waveguides and present a cleaning and depopulation procedure that yields reproducible, low-loss waveguide conditions.