Analysis of a silicon subwavelength grating ring resonator as a refractometric sensor

Silicon sub-wavelength grating ring resonators (SGRRs), based on the combination of gratings and ring resonators, enable to engineer the light guidance in a finer manner. These structures can be used as the building blocks in integrated optics and sensing platforms. In this work, we consider a SGRR operating at a wavelength of 1550 nm made with a Si core layer, with index 3.47, positioned on a SiO2 substrate with index 1.46. For the application as refractometric sensor, the air top cladding of the structure is replaced with aqueous solutions with refractive index values in the range 1.332-1.350. The described devices have been numerically studied using an axis-symmetric model, employing the eigenfrequency analysis of the COMSOL Multiphysics software. The refractive index (RI) sensitivity is calculated by taking into account the wavelength shift of four guided modes in the mentioned range of RI values. Results have demonstrated that the highest sensitivity of 12920 nm/RIU is found for the third mode of the device with an initial effective index of 1.7707. This demonstrates the excellent potential of the proposed SGRR in the early detection of the small amount of bio/chemical analytes in medicine, biology, and chemical applications.