Mach-Zehnder interferometer assisted ring resonator configuration for refractive index sensing

Over the past decades, several waveguide-based refractive index (RI) sensors have been reported for applications in medical diagnosis, food quality control, and environmental monitoring. In the early developmental stage, RI sensors were based on configurations such as Mach-Zehnder interferometer (MZI), ring resonator (RR), surface plasmon resonance and Bragg grating. Among these configurations, RR is considered as one of the most promising for biological and chemical sensing. The most important advantage of a RR over others is the very small footprint. Moreover, lower limit of detection can be achieved by enhancing the Q-factor. In recent time, several Vernier effect-based RI sensors have been reported to further enhance the sensitivity [1] , [2] . In spite of higher sensitivity, Vernier effect-based RI sensors pose a challenge of limited measurement range. Measurement range of Vernier and RR sensors is constrained by free spectral range (FSR). Conventionally, the measurement range of RR and Vernier RI sensors is enhanced by reducing the ring radius, which in return limits the Q-factor and consequently reduces the limit of detection.