Mitigation of UV-Induced Propagation Loss in PECVD Silicon Nitride Photonic Waveguides

We observe a drastic increase in propagation loss at visible wavelengths in PECVD silicon nitride waveguides after exposure to ultraviolet (UV) light. Low temperature annealing or high intensity optical exposure at visible wavelengths brings the propagation loss back toward the original value before UV exposure or even lower. We postulate that these effects can be explained by the population and depopulation of defect centers in the silicon nitride. We demonstrate the importance of defect depopulation before using waveguides in any silicon nitride based visible photonic application and provide a cleaning procedure that yields reproducible, low-loss, initial waveguide conditions.