High Sensitivity Refractive Index Sensor Based on Trapezoidal Subwavelength Grating Slot Microring Resonator

High performance refractive index sensors are of important significance in numerous sensing applications including chemical, air and biophotonics. Among them, the ones with high sensitivity and large quality factor are especially critical. Here, we propose a high sensitivity refractive index sensor based on a slotted silicon ring resonator, of which the inner and outer rings are made of a deformed subwavelength grating (SWG) waveguide of trapezoidal dielectric blocks and a standard SWG waveguide of rectangular ones, respectively. By optimizing the geometry of inner silicon blocks, the quality factor is improved by 3 times than traditional subwavelength slot micro-ring resonator. The sensitivity of the single trapezoidal subwavelength grating slot microring resonator (T-SWGSMRR) sensor reaches 823 nm/RIU, with the Q factor of 2.5 × 10⁴ and the limit of detection of 7.53 × 10⁻⁵ RIU are obtained. The sensitivity is further promoted by utilizing two cascaded T-SWGSMRRs on the basis of the Vernier effect, which reaches 12151 nm/RIU. The sensors presented in this work can be fabricated with commercial CMOS process, indicating that it has potential prospects in industrial applications.