Contents I. Introduction
Integrated optical sensing has captured significant interest as a potent solution for swift and precise detection for many applications, such as biosensing [1], [2], [3], [4], [5], chemical sensing [6] and so forth. Optical microring resonators can be used to create sensors, as the closed-loop structure allows light to resonate at certain periodic frequencies (wavelengths). At these resonance frequencies, light positively interferes every round trip, resulting in an intensity drop in the transmission output. The resonances positions can be shifted by the refractive index change in the surrounding medium or the waveguide itself. By following the resonance positions from scan to scan over time, the refractive index changes caused by temperature [7], pressure [8], buffer solution, or biomolecules [1], [2], [3], [4], [5] can be tracked. With the development of chip design and fabrication processes, a detection limitation of refractive index unit (RIU) [9] has been achieved in microring sensing. Additionally, several ring resonator transducer designs are reported, for example, modular microring laser cavity sensor [9], taji resonator [10], hybrid plasmonic waveguide-based microring sensor [11], improving the sensing performance in various aspects. In these studies, one of the many resonances from a single ring is tracked for sensing applications.
