Automatic Resonance Alignment of High-Order Microring Filters

Automatic resonance alignment tuning is performed in high-order series coupled microring filters using a feedback system. By inputting only a reference wavelength, the filter transmission is maximized on resonance, passband ripples are dramatically reduced, and the passband becomes centered at the reference. The method is tested on fifth-order microring filters fabricated in a standard silicon photonics foundry process. Repeatable tuning is demonstrated for filters on multiple dies from the wafer and for arbitrary reference wavelengths within the free spectral range of the microrings.