FIBER OPTICS THERMO REFRACTOMETER BASED ON A LOOSE CAVITY DESIGN

Abstract

This paper describes the workings of a CFBG-based fiber-optic thermorefractometer, including its design, construction, and experimental analysis. A resonant cavity was created by carefully cleaving a piece of singlemode fiber. This enhances sensitivity to changes in both temperature and refractive index (RI). The resonantwavelength shift showed a linear response of 0.00926 nm/C with a coefficient of determination R² = 0.9962 during temperature calibration from 25C to 80C. We used an intensity-attenuation measure since the wavelength shifts in the RI calibration (5%-15% sucrose by weight, n=1.3477-1.3597) were inconsistent (R² = 0.11). By computing the mean of the filtered power within a 0.5 nm spectral band, we obtained a refractive-index sensitivity of –46.65 dB/RIU (R² = 0.9105). These findings show that in this loose-cavity CFBG setup, RI detection is robust when intensity modulation is used, and wavelength tracking is the best for temperature sensing.