On-Chip Biological and Chemical Sensing With Reversed Fano Lineshape Enabled by Embedded Microring Resonators

High- Q microresonators play an important role in developing fully integrated, highly sensitive, and cost-effective bio/chemical sensors. The Fano effect in doubly resonant physical systems may be used to improve sensing performance. In this paper, we show that coupled optical resonators (sometimes termed photonic molecules) in an embedded configuration can significantly enhance the sensitivity and limit of detection (LOD) of on-chip sensors by producing a reversed Fano effect. Improvement of one order in sensitivity, as compared to a sensor based on conventional Fano effect, can be achieved using embedded high- Q resonators on a CMOS-compatible platform. We estimate the LOD by taking into account thermal drift, optical losses (material absorption, scattering, substrate leakage and bending loss), laser intensity noise, linewidth and frequency jitter, and link and detector signal-to-noise ratio (SNR). The overall LOD is found to be as low as 3.24 × 10^-8 RIU. Moreover, in the proposed sensor based on embedded rings, intensity SNR is no longer the limiting factor of the LOD, which could be further lowered with better thermal control and laser frequency stability.