Topological ring resonator for refractive index sensing at telecommunication wavelength

Abstract

Ring resonators play an increasingly important role in biomedical sensing. Conventional optical ring resonators based on waveguide structures have some problems, such as large size, limited integrated density, and easily influenced by external factors. Therefore, it is desired to evoke new design principles to achieve ultracompact biomedical sensors with high performance. Here, we demonstrated topological refractive index sensors based on valley photonic crystal (VPC) ring resonator structures working at telecommunication wavelength and whose resonant peaks move in response to the surrounding material's refractive index change. The structure is designed to work in an aqueous solution (refractive index of 1.33), and within the sensing range of 1.33–1.45, it has a phase shift of 4.16π and a detection sensitivity of 208.09 nm/RIU (refractive index unit) with a detectable refractive index difference of 0.0044. In addition to the single-ring resonator structure, we further tune the free spectral range (FSR) by combining ring resonators with different sizes, and the sensitivity is tuned accordingly. The designed structures are suitable for the current mature complementary metal-oxide-semiconductor (CMOS) nanofabrication technique. In addition, the refractive index sensor can also be applied as a mechanism for tuning the resonant peaks for optical modulations.