Envelope Spectrum of the Subwavelength Grating Slot Waveguide Microring Resonator for High-Sensitivity and Wide-Range Refractive Index Sensing Applications

The silicon-based platform is highly competitive in developing next-generation on-chip chemical, biological, and medical sensing systems. Improving the sensitivity and expanding the detectable range of silicon-based integrated sensors attract great attention. We experimentally demonstrate a high-sensitivity and wide-range refractive index (RI) sensing relied on tracking the envelope spectrum of a subwavelength grating slot waveguide microring resonator (SWGS-MRR). Owing to the exceptional releasing field performance of the SWGS waveguide, the SWGS-MRR allows for high sensitivity of the RI sensing. Furthermore, monitoring the envelope spectrum can remove the limitation of the free spectral range (FSR) on the detectable range of the RI sensing. By combining the merits of the releasing field mechanism and the envelope spectrum tracking approach of the SWGS-MRR, we demonstrate the wide-range RI sensing with a sensitivity of up to 1420 nm/RIU and a detection limit of 1.2×10-3 RIU. In addition, the SWGS-MRR exhibits thermally stability with a low-temperature sensitivity of 10 pm/°C. This work represents a highly effective strategy for enhancing sensitivity and extending the detectable range of MRR sensors and, thus, is promising for lab-on-chip sensing systems.