Cascaded ring resonator and Mach-Zehnder interferometer with a Sagnac loop for Vernier-effect refractive index sensing

tIn this paper, we propose a novel photonic integrated sensor characterized by the cascade of a ringresonator (RR) and a Mach-Zehnder interferometer (MZI) architecture with a Sagnac loop (i.e., RR-MZI-Sagnac). We present the modelling and detailed guidelines for the design of such devices that are assumedto be fabricated on complementary metal-oxide semiconductor (CMOS) compatible silicon-on-insulator(SOI) platforms. Ultra-high refractive index (RI) sensing performance such as wavelength sensitivitieslarger than 2.5 × 103m/RIU (RI unit) and limits of detection (LOD) of 1 × 10−8RIU can be achieved byemploying the Vernier effect in the near-infrared (NIR), around the wavelength of 1.55 m. Furthermore,we theoretically demonstrate that the novel RR-MZI-Sagnac Vernier devices can operate better than themost performing state-of-the-art Vernier sensors characterized by cascaded RR and MZI (RR-MZI). Infact, an operating bandwidth that is half than that requested by the RR-MZI devices is exhibited whenbalanced MZIs are designed in both configurations, still preserving similar RI sensing performance. Alter-natively, double RI sensing performance can be achieved by RR-MZI-Sagnac Vernier sensors with respectto RR-MZI devices when unbalanced MZIs are considered in both the Vernier configurations, exhibitingthe same operating bandwidths. Finally, simulations reveal that ammonia (NH3) concentrations in the0–30,000 ppm range and carbon dioxide (CO2) traces lower than 5,000 ppm can be detected in deionizedwater and air, respectively.