A sensitivity-enhanced temperature sensor with end-coated PDMS in few mode fiber based on vernier effect

In this paper, a few mode fiber temperature sensor based on vernier effect is proposed. The sensor consists of two cascaded microcavities and realizes temperature sensing based on vernier effect. The single mode fiber(SMF) and few mode fiber(FMF) are fixed by a capillary glass tube to form an air reference microcavity. The end of the FMF is dipped with an appropriate amount of polydimethylsiloxane(PDMS) to form a sensing microcavity with a certain thickness, which is an air microcavity-FMF-PDMS structure. Due to the different refractive index of each medium, the light is reflected on the four critical surfaces, and the four reflected light beams interfere, the vernier effect is formed by adjusting the microcavity length to a suitable length. When the external temperature changes, the microcavity length and refractive index of PDMS change, which leads to the change of interference spectrum. Therefore, the high sensitivity measurement of temperature can be realized by the change of reflection spectrum. The temperature characteristics of the sensor are studied experimentally. The results show that the temperature sensitivity is significantly improved compared with the traditional single microcavity sensor. In the temperature range of 35 degrees C similar to 45 degrees C, the temperature sensitivity can reach 4.7nm/ degrees C, and the linearity is very good. The sensor has the advantages of compact structure, simple fabrication and high sensitivity, so it has wide application prospects in the field of temperature sensing.