Microring-resonator-based add-drop filters in SiN: fabrication and analysis

Third-order add-drop filters based on series-coupled microring resonators were fabricated in silicon-rich silicon nitride with accurate dimensional control and negligible sidewall roughness. For the first time, a low 3 dB drop loss is demonstrated with a wide 24 nm free-spectral-range in a high-order microring filter without using the Vernier effect. The spectral response is matched by rigorous numerical simulation, and non-idealities in the drop- and through-port responses are shown to be of design origin and to be correctable.