Athermalization design for SOI waveguide Bragg grating photonic blood glucose sensors

Accurate monitoring of the blood glucose concentration is critically important for the diagnosis, treatment, and long-term management of diabetes. In this paper， an optical blood glucose sensing method is proposed on the basis of silicon-based waveguide Bragg grating (WBG). This method involves the reaction between glucose oxidase fixed on the cladding of the waveguide and glucose, which causes a local refractive index change, resulting in a shift in the WBG reflection center wavelength, enabling the quantitative detection of blood glucose concentration. Nevertheless, during measurement, optical blood glucose sensors are susceptible to spectral drifts caused by environmental temperature variations, leading to a decrease in sensing accuracy. To address this issue, a silicon-on-insulator (SOI) WBG sensor for glucose concentration measurement is proposed and implemented. Two types of WBG blood glucose sensors, namely, bilateral and slit sensors, are designed, incorporating an athermalization design to enhance system stability and environmental robustness. By employing a compensating material with a negative thermo-optic coefficient (TOC) and optimizing various waveguide structural parameters, temperature-induced drift is effectively suppressed, which enables the design of bilateral and slit WBG glucose sensors with both glucose sensing and temperature compensation capabilities. The experimental results show that the bilateral WBG glucose sensor exhibits a refractive index sensitivity of 161 nm/refractive index unit (RIU) and a temperature sensitivity of 7.27 pm/°C within a glucose concentration range of 0–2.6 mg/mL. The slit WBG glucose sensor has a refractive index sensitivity of 242.3 nm/RIU and a temperature sensitivity of 2.37 pm/°C within the 0–2.8 mg/mL glucose concentration range.