提出了一种折射率不敏感的级联型单模-少模-单模光纤温度传感器。 在制作传感器的过程中, 设置熔接电流为100 mA, 通过将少模光纤与单模光纤进行无错位熔接, 以激发稳定的传输模式, 形成光纤马赫-曾德尔干涉仪。 由于外界环境的改变会引起少模光纤中不同模式之间相位差的改变, 从而导致干涉条纹的漂移, 因此通过检测干涉条纹的漂移量就可以实现待测参数的检测。 少模光纤可以传输LP01, LP11, LP21, LP02共四种模式的光。 实验中对长度为81.5 mm的传感器光谱进行分析可知, 发生干涉的两个模式主要是LP01模和LP11模。 利用该长度的级联型单模-少模-单模光纤传感器进行折射率和温度传感实验, 结果表明, 随着传感器温度不断的增加, 其传输光谱出现了明显的蓝移现象, 在27.6~93.8 ℃的温度变化范围内, 灵敏度高达-85.9 pm·℃-1, 且具有较好的线性度; 在甘油折射率为1.347 1~1.443 9变化范围内, 其传输光谱没有出现明显的漂移现象, 灵敏度仅为3.697 34 nm·RIU-1, 具有折射率不敏感特性。 因此, 相对于传统的包层模干涉型与多模干涉型光纤传感器, 所提出的基于FMF的传感器更易于实现对传输模式的控制与分析, 且具有结构简单、 易于制备、 灵敏度高等优点, 能够避免温度与折射率同测的交叉敏感问题, 可用于电力系统、 生物医学、 航空航天等领域的温度检测。

A refractive index insensitive temperature sensor is proposed base on cascading single mode fiber with few mode fiber(FMF). During the sensor preparation, the splicing current is set to 100 mA, and a section of FMF is no core-offset splicing between two single-mode fibers. Therefore, it can motivate the transmission mode preferably and form optical fiber Mach-Zehnder interferometer. The mode phase difference in FMF will be changed according to the outside environment. It will cause interference fringe shift. The parameter to be measured can be achieved by detecting the amount shift of interference spectrum. The FMF can transmit four modes with LP01, LP11, LP21, LP02. The transmission spectrum is also analyzed, which shows that they have two modes of LP01 and LP11 in sensor with the length of 81.5 mm. In the refractive index and temperature sensing experiment, the cascading FMF sensor with the length of 81.5 mm is used. The results show that the transmission spectrum of sensor appears obvious blue shift as temperature is increasing, the temperature sensitivity can be up to -85.9 pm·℃-1 within the range of 27.6~93.8 ℃ with good linearity. The refractive index sensitivity is 3.697 34 nm·RIU-1 within the range of 1.347 1~1.443 9. There is no obvious shift phenomenon in the transmission spectrum with the feature of refractive index insensitive. Therefore, compared with the traditional cladding mode and multimode interferometric fiber-optic sensor, the proposed sensor based on FMF is easier to control and analyze transmission mode has the advantages of simple structure, easy process and high sensitivity. It can avoid cross-sensitivity between temperature and refractive index measurement. Thus, it can be used for temperature detection of power system, biomedicine, aerospace and other fields.