Abstract To measure surrounding refractive index (SRI) and temperature simultaneously, this paper presents a long period fiber grating in few-mode fiber fabricated by CO2 laser. The few-mode long period fiber grating (FM-LPFG) fabrication method is introduced in detail. Through the dislocation experiment, the resonant peaks formed by the coupling between the cladding modes and core modes LP01 and LP11 are observed and selected. In the sensing experiment, the SRI and temperature are measured by the shift of the two resonant peaks, further the different sensing characteristics of such peaks are studied. The results show that as the SRI increases, such peaks shift toward the short-wave direction, and as the temperature increases, the peaks shift toward the long-wave direction. The SRI and temperature sensitivities are −263.257 nm/RIU and 0.058 nm/°C, respectively. By the dual-wavelength matrix method, the SRI and temperature simultaneous measurement can be achieved. This FM-LPFG has great potential application in multi-parameter measurement.

中文翻译：

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CO2 激光器写入 FM-LPFG 的同步 SRI 和温度测量

摘要 为了同时测量周围折射率（SRI）和温度，本文提出了一种用CO2激光器制造的少模光纤长周期光纤光栅。详细介绍了少模长周期光纤光栅（FM-LPFG）的制作方法。通过位错实验，观察和选择了包层模式与纤芯模式LP01和LP11之间耦合形成的共振峰。在传感实验中，通过两个共振峰的位移来测量SRI和温度，进一步研究了这些峰的不同传感特性。结果表明，随着 SRI 的增加，这些峰向短波方向移动，随着温度的升高，峰向长波方向移动。SRI 和温度灵敏度为 -263.257 nm/RIU 和 0.058 nm/°C，分别。通过双波长矩阵法，可以实现SRI和温度同时测量。这种FM-LPFG在多参数测量中具有很大的应用潜力。