Refractive Index Sensing Based on Mode Splitting in Subwavelength Grating Metamaterial Microring Resonators

Microscale cavities have been extensively studied for ultrasensitive sensing in recent years. However, highly sensitive sensors are generally accompanied by high noise level. In this paper, we propose to use mode splitting in subwavelength grating metamaterial ring resonators (SGMRRs) for self-referenced refractive index sensing. Due to the reflection in the subwavelength grating, the clockwise and counter clockwise propagating modes mutually couple to each other, leading to the lift of degeneracy. The wavelength difference between the split modes, which is sensitive to refractive index perturbation, forms an ultra-sensitive self-referenced architecture. We theoretically demonstrated that a self-referenced surface sensitivity of 21 pm/nm can be achieved with an effective suppression of thermal noise.