An Integrated Photonic Gas Sensor Enhanced by Optimized Fano Effects in Coupled Microring Resonators With an Athermal Waveguide

Microresonator-based photonic gas sensors exhibit unique advantages of building a CMOS-compatible, cost-effective, and portable sensing system fully integrated on a single chip. In this paper, we propose gas sensors featured by nanoscale waveguide layers using titanium dioxide to achieve athermal device operation, at close to visible wavelengths. Sensitivity and limit of detection are enhanced by Fano effects in coupled-microresonator devices (also called photonic molecules). Sharp Fano lineshapes are obtained by optimizing the dual-ring structures in terms of coupling coefficients and resonance offsets, with minimized cavity loss including material absorption, scattering and bending losses, and substrate leakage. Various types of dual-ring resonator configurations have been comprehensively compared. Overall performance of the on-chip sensing systems including integrated light sources and detectors is carefully analyzed by taking into account the imperfections of each component, such as relative intensity noise of laser, laser linewidth and frequency jitter, and detector noise. We outline the similarity and difference of three dual-ring systems and provide design guidelines to optimize the sensor with balanced consideration between device performance and its tolerance to fabrication imperfections.