Optical Fiber Fabry-Perot Interferometer Refractive Index Sensor Based On Vernier Effect For Silica Colloidal Sol Aging Monitoring

A refractive index (RI) sensor is demonstrated using dual paralleled Fabry-Perot (FP) cavities and applied to silica colloidal sol aging monitoring in situ. Due to the Vernier effect, a 22-fold enhancement of spectral envelope wavelength variation in response to RI change is achieved compared with single FP sensor. The high RI sensitivity (-20811 nm/RIU at RI from 1.3337 to 1.3409) and excellent static stability (envelope wavelength shifts less than +/- 2.5 nm within 7 days) enable the sensors to monitor slow chemical reaction of silica colloidal sol aging in situ in real time. The results show that the RI of silica colloidal sol decreases while aging, and the sol needs at least 4 days to reach stability.