A highly sensitive temperature sensor based on an isopropanol-sealed optical microfiber coupler (OMC) is proposed and investigated. Isopropanol is a kind of material with high thermo-optic coefficient. By encapsulating the OMC into isopropanol environment, the OMC can be turned to a highly sensitive temperature sensor. Using this approach, we experimentally demonstrate a temperature sensor. By optimizing the waist diameter of the OMC, an ultrahigh temperature sensitivity of -5.89 nm/° has been achieved at the waist diameter of 2.2 μm in the range of 30-40°.
A simple composite cavity fiber tip (CCFT) Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The composite cavity is composed of an air cavity and a silica cavity. The air cavity is an elliptical air hole embedded in the SMF. The silica cavity is a short section of SMF cascaded to the air cavity. The CCFT FPIs were applied for temperature sensing. To take advantage of the FP’s resonant property, a laser whose wavelength is tuned to the steep slope of one of the FP resonances is used to interrogate the CCFT FPI system. With a laser interrogation, a small wavelength shift caused by a small temperature change will then be translated into a large change in output power, which can be easily detected. Therefore, the temperature sensitivity can be enhanced significantly, and the CCFT FPI can routinely resolve much smaller temperature changes.