Subwavelength Grating Slot Waveguide Micro-ring Resonator with Cosine-type Photonic Crystal for Refractive Index Sensing

We proposed a subwavelength grating slot waveguide (SWGS) micro-ring resonator integrated with a one-dimensional (1D) photonic crystal, which is fabricated on a silicon-on-insulator (SOI) platform, and demonstrate its applicability in bulk refractive index sensing applications. The design of the SWGS enables the electric field to be mostly confined in the cladding, thereby enhancing the sensing sensitivity. The cosine-type 1D photonic crystal is utilized to open a photonic bandgap in the micro-ring resonance spectrum, breaking the limitation imposed by the free spectral range (FSR) on the sensing dynamic range. Experiment on measuring sodium chloride solutions with different concentrations shows that the bulk refractive index sensitivity of the air-band mode reaches 621 nm/RIU.