提出了一种基于单模-多模-单模拉锥结构的光纤布拉格光栅 (FBG) 传感器,该传感器能有效提高应变的检测灵敏度。多模光纤具有孔径大、易耦合、写制光栅较容易、可承受应变较大等优点,使光栅区域位于拉锥多模光纤处,则该多模拉锥光纤的光栅可使传感器获得更高的应变探测精度和灵敏度。通过控制多模光纤的拉伸长度,制作了多个不同锥度的传感器。先将一段长度为1.7 cm的多模光纤对芯熔接在两段单模光纤中间,然后对多模光纤段分别进行长度为0.8,0.9,1.0 cm的拉锥,在多模光纤锥区一侧写入长度为7 mm的FBG。通过分析反射谱中谐振波长的变化来监测温度、应变的改变。实验结果表明,该传感器的应变检测范围为0~960 με,应变灵敏度最高可达15.5 pm/με,而温度灵敏度为10.5 pm/℃,锥区半径越细则应变灵敏度提升越明显。由于应变灵敏度相对传统FBG有大幅提高,而温度传感特性保持不变,在没有温度补偿的情况下,温度引起的应变误差仅为0.677 με/℃,降低了应变和温度之间的交叉敏感性。

This study proposes a fiber Bragg grating (FBG) sensor based on a singlemode-multimode-singlemode tapered structure that can effectively increase strain sensitivity. The grating is located at the tapered-multimode fiber region. A multimode fiber has the advantages of large aperture, easy coupling, easy writing of gratings, and the ability to withstand large strain. The use of tapered-multimode fiber gratings for strain sensing provides high accuracy and sensitivity. We produce multiple sensors with different tapers by changing the stretched length of the multimode fiber. Firstly, a 1.7-cm-long multimode fiber is welded between two singlemode fibers. Then, the middle multimode fiber section is tapered to 0.8, 0.9, and 1.0 cm, respectively. Subsequently, a 7-mm-long Bragg grating is written on the side of the multimode fiber cone. Changes in external parameters, such as temperature and strain, are monitored by analyzing the change of the resonant wavelength in the reflection spectrum. The experimental results show that the strain detection range of the sensor is 0-960 με,the highest strain sensitivity of the sensor can reach 15.5 pm/με, and the temperature sensitivity is 10.5 pm/℃. Furthermore, the thinner the cone radius is, the more obvious the increase in strain sensitivity is. The strain sensitivity is considerably improved compared with that of the conventional FBG, and the temperature sensing characteristics remain unchanged; hence, the temperature-induced strain error is only 0.677 με/℃ without temperature compensation, which reduces the cross-sensitivity between strain and temperature.