High-performance silicon photonic filters based on all-passive tenth-order adiabatic elliptical-microrings

Ultra-compact silicon photonic filters with box-like responses and high extinction ratios are proposed and demonstrated by introducing tenth-order adiabatic elliptical-microrings (AEMs) with bent directional couplers. For the AEMs, the waveguides in the non-coupling regions are wide and have a minimal bending radius, while the waveguides in the coupling regions are narrowed and have a maximal bending radius. The present silicon photonic filters based on tenth-order AEMs show a free spectral range as large as 37 nm for the first time. Even fabricated with commercial complementary metal–oxide–semiconductor-compatible 248 nm deep-ultraviolet lithography processes, the present devices show high performances with excess losses as low as ∼1 dB and extinction ratios as high as >60 dB. More importantly, the present silicon photonic filters work very well all-passively without any thermal control for calibration.