A Temperature Sensor Based on Composite Optical Waveguide

We propose a temperature sensor, which consists of a composite optical waveguide (COW) sandwiched between two single mode fibers (SMFs). The COW is formed by side polishing a capillary optical fiber (COF) and filling with polydimethylsiloxane (PDMS). Unlike the conventional fixed sensing structure, the Mach-Zehnder interferometer (MZI) and multimode interferometer (MMI) can be selectively formed by adjusting different fusion splicing parameters, so as to produce a blunt or sharp tapered fusion structure between the SMF and the COF. Because of the high thermo-optic coefficient of PDMS and the high-order modes excited by the tapered fusion structure, the MZI and MMI sensors are very sensitive to temperature. The experimental results show that within the temperature measurement range from 16 °C to 80 °C, several resonance wavelengths of the MZI and MMI sensors exhibit a remarkable blue shift with the increase of temperature. The maximum temperature sensitivities of the MZI and MMI sensors can reach −0.50 nm/ °C and −0.88 nm/ °C, respectively. The humidity sensitivity of the sensor is −0.10 nm/%RH. However, in the process of temperature measurement, humidity has little influence on the sensitivity of the sensor. Due to the advantages of compact size, flexible structure, and high sensitivity, the sensor has great application potential in monitoring the changes of environment and living temperature.