Ultra-High-Resolution Optofluidic Fabry-Perot Interferometric Sensor for Real-Time Biochemical Reaction Monitoring

By integrating the laser frequency-modulated continuous-wave (FMCW) technology, cross-correlation demodulation (DM), and Fabry-Perot (F-P) interferometry, we demonstrate a high-precision optofluidic refractive index (RI) sensing system. A 1312 nm distributed feedback (DFB) laser is current-modulated to generate a continuously swept wavelength source, whose spectral stability is improved through real-time calibration using a hydrogen fluoride (HF) molecular absorption line. An F-P RI sensing probe is theoretically designed and experimentally fabricated, enabling high-resolution demodulation through cross-correlation algorithms, while a counting-based scheme extends the measurement range. In experiments with sodium chloride solutions of varying concentrations, the system achieves wavelength resolution of 0.024 pm and an RI detection limit of 3.2×10⁻⁸ RIU. The platform’s capability for real-time biochemical monitoring is demonstrated via the photochemical reaction of chlorophyll in ethanol. Under 405 nm laser irradiation, the solution exhibits a light-induced RI reduction, primarily attributed to photothermal effects. This optofluidic RI sensor combines the ultra-high precision, broad dynamic range, and robust stability, offering significant potential for liquid refractometry and kinetic studies of chemical and photochemical reactions.