Compact fiber-optic temperature sensing employing microspheres

Fabry-Perot interferometer (FPI) optical fiber temperature sensors were designed based on tapered single-mode fiber (SMF) and miniature glass microspheres. First, the SMF is tapered into microstructures a glass microsphere is bonded or fabricated via fusion discharge on the end face of the tapered SMF. The incident light forms reflected light between the two surfaces of the microsphere that forms an FPI. When the glass microsphere is heated, variations in the refractive index and diameter of the microsphere induce changes in the optical path of the Fabry-Perot cavity. This leads to the changes of the dip wavelength and the dip intensity in the FPI spectrum, thus allowing temperature measurement. Two sensors are fabricated: S1 based on adhesive bonding of a glass microsphere to the tapered SMF end face and S2 based on discharge ablation of a glass microsphere on the tapered SMF end face. For S1, the sensitivity of Dip 1 wavelength and intensity to temperature changes were 36.1 pm/°C and −0.145 dB/°C, respectively. S1 has good reversibility and stability, making it suitable for measuring low temperatures. For S2, the sensitivity of Dip 2 wavelength and intensity to temperature changes were 13.1 pm/°C and −0.0782 dB/°C, respectively. S2 has good reversibility and stability, making it suitable for measuring slightly higher temperatures. The proposed sensor structure is small, stable, suitable for temperature measurements in harsh environments, and suitable for confined spaces.