High-sensitivity complex refractive index sensing based on Fano resonance in the subwavelength grating waveguide micro-ring resonator.

High-sensitivity complex refractive index sensing is proposed and experimentally demonstrated, favoring with sharp Fano resonance at 1550 nm wavelength based on subwavelength grating waveguide (SWG) micro-ring resonator. The micro-ring is composed by trapezoidal silicon pillars with subwavelength period to enhance the light-analyte overlap and get high quality factor as well. One straight SWG waveguide is side coupled with the micro-ring, which is specially designed to produce partial Fabry-Perot (FP) effect. Due to the interaction of resonant state of micro-ring and partial FP effect in straight waveguide, a sharp asymmetrical Fano resonance is formed at 1550 nm wavelength. Benefit from the large light-analyte overlap of the SWG waveguide structure and the sharp asymmetrical Fano resonance in spectrum, high theoretical sensitivities of 366 nm/RIU and 9700/RIU can be realized for the real part (n) and the imaginary part (κ) of refractive index respectively. We also experimentally demonstrate the sensing for glucose solution concentrations, and high experimental sensitivity of 363nm/RIU is obtained for n, and for κ the experimental results are also in well agreement with the simulation results.