Refractive Index Sensing Using a Three-Port Interferometer and Comparison With Ring Resonators

In this paper, we compare ring resonator and three-port Mach-Zehnder Interferometer (MZI) devices fabricated on silicon-on-insulator for the purpose of refractive index sensing. Their respective sensitivities and limits of detection (LOD) were determined with NaCl solutions. A sensitivity of 113.07 nm per refractive index unit (RIU) and LOD of 2.47e-6 RIU was reached for the ring resonators. The most sensitive three-port MZI has a sensitivity of 13051 rad/RIU, and an LOD of 2.76e-8 RIU is shown to be attainable. A three-port MZI combines several advantages of both ring resonators and normal MZI devices, including a constant and scalable sensitivity, high-bandwidth readout, no directional ambiguity, and a simple interrogation setup. Such a device is promising for applications such as pressure, gas, and biosensing.