Concentric silicon micro-ring resonators with enhanced transmission notch depth

ABSTRACT In this work, we have analyzed, fabricated and demonstrated concentric micro-ring resonators in silicon-on-insulator (SOI) structure for enhanced transmission notches. The operation principles of the concentric ring resonators are studied by time-domain coupled-mode theory. Directional coupling between concentric rings offers another freedom in designing deep notch optical filters and ultra-sensitiv e biosensors. The finite-difference-time-domain (FDTD) simulations have shown the improvement of the notch depth, evenly distributed mode field and the effect of the resonance shift. The device is demonstrated in silicon-on-in sulator structure. Transmission notch depth improvement of ~ 15dB is demonstrated for the 21-20.02-µm-radius double-ring structure comparing with the single 21-µm-radius ring. Keywords: concentric micro-ring resonators, silicon-on-insulator 1. INTRODUCTION Micro-ring resonators based on silicon- on-insulator (SOI) structure are promising building-blocks for ultra-compact and highly integrated photonic circuits. The fabrication technology is mostly CMOS-compatible. Potential applications include optical filtering, switching, signal processing and bio-se nsing [1]. Micro-ring resonators with high quality factors (Q) and deep transmission notches are desired in most cases. However, it is practically challenging to achieve deep notches in the transmission spectra for the single-waveguide-single-ring structure. To reach the conventional critical coupling, the resonator intrinsic factor (Q