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°C$\sim$45°C, the temperature sensitivity can reach 4.7nm/°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.

本文提出了一种基于游标效应的多模光纤温度传感器。该传感器由两个级联的微腔组成，实现基于游标效应的温度传感。单模光纤（SMF）和少模光纤（FMF）通过玻璃毛细管固定形成空气参考微腔。FMF的末端浸入适量的聚二甲基硅氧烷（PDMS），形成一定厚度的传感微腔，即空气微腔-FMF-PDMS结构。由于每种介质的折射率不同，光线在四个临界面上反射，四个反射光束发生干涉，通过将微腔长度调整到合适的长度形成游标效应。当外界温度变化时，PDMS的微腔长度和折射率发生变化，从而导致干扰频谱的变化。因此，可以通过反射光谱的变化来实现对温度的高灵敏度测量。通过实验研究了传感器的温度特性。结果表明，与传统的单微腔传感器相比，温度灵敏度有显着提高。在 35°C 的温度范围内$～$45°C，温度灵敏度可达4.7nm/°C，线性度非常好。该传感器具有结构紧凑、制作简单、灵敏度高等优点，在温度传感领域具有广阔的应用前景。