Subwavelength grating waveguide racetrack-based refractive index sensor with improved figure of merit

An all-subwavelength grating waveguide-based sensing structure for figure of merit (FOM) improvement on a silicon-on-insulator platform is proposed and demonstrated. Four racetrack resonators are applied to narrow the spectrum from the drop port of a single racetrack resonator for lower full width at half-maximum, and the FOM is therefore higher through the spectrum-narrowing operation. Numerical simulation and analysis illustrate that the proposed structure is able to raise the FOM more than twice compared to a single racetrack resonator, and a high FOM of 1850.57/refractive index unit is achieved.