Optical vernier effect in interferometric add-drop microring resonator for high-sensitivity sensing

Abstract

This research investigates the integration of interferometric resonances within a compact add-drop microring resonator (MRR) to address the trade-off between size and sensitivity. While smaller MRRs offer miniaturization benefits, they often suffer from higher bending and scattering losses, leading to reduced quality (Q) factor and limited sensitivity. By incorporating interferometric resonances, this study aims to enhance the sensitivity of the MRR without compromising its compactness. The proposed Integrated Add-Drop (IAD) MRR configuration utilizes a pair of partially reflecting air holes within the bus waveguide to generate these resonances. The optical transfer function (OTF) for the IAD-MRR was derived using the scattering transfer matrix equation. Parametric analysis was conducted to evaluate the effects of ring radius and air hole distance on the free spectral range (FSR) and sensitivity. The results demonstrate that the IAD-MRR offers significantly higher sensitivity compared to conventional add-drop (CAD) MRRs. The optimized IAD configuration achieved a maximum sensitivity of 652.17 nm/RIU, surpassing previously reported values. The IAD-MRR demonstrated a high Q factor of 8.25 x 10^4, a low limit of detection (LOD) of 1.84 x 10^-6 RIU, and a high finesse of 7.57 x 10^3, values considered excellent for MRR applications. This research highlights the potential of the IAD-MRR for developing highly sensitive and compact all-optical sensors, addressing the challenges associated with miniaturized MRR designs.