Temperature Sensing Characteristics Based on Up-Taper and Single Mode–Multimode Fiber Structure

A novel temperature sensor based on up-taper and single mode–multimode fiber has been presented and demonstrated in this letter. The sensor is fabricated by fusing an up-taper in a single mode fiber (SMF) and splicing the SMF with a section of multimode fiber. In the taper region, a part of light is propagated from the fiber core into the cladding and a series of high-order modes are excited. The reflected light will be coupled back into the core to interfere with the residual core mode when passing through the taper again. Compared with the conventional single mode–multimode–single mode (SMS) fiber sensor, temperature sensitivity of the sensing probe, which consists of SMS and up-taper structure, is improved greatly. According to the experimental results, the temperature sensitivity of 89.42 pm/°C in the temperature range of 20 $^{\circ }\text{C}\sim 80~^{\circ }\text{C}$ can be achieved. The sensor has a series of advantages, such as high sensitivity, low cost, compact size, and reflective measurement.