We demonstrate the fabrication of long-period fiber gratings (LPFGs) in an elliptical core few-mode fiber (e-FMF) by CO2 laser. The mode conversion from fundamental mode to high-order modes (LP11a, LP11b, and LP21a mode) can be realized by the LPFGs with high efficiency of more than 95%. The effect of bending, torsion, temperature, and strain on the resonance wavelength of the e-FMF based LPFG mode converters are experimentally investigated. The temperature and strain sensitivities of the LPFGs are characterized to be -36 pm/°C and -4.9 pm/με, and the LPFGs are found to be insensitive to the bending and torsion. Due to the existence of trench in the e-FMF, the higher-order LP02 and LP31a mode can also be stimulated by the e-FMF based LPFGs with a grating period of 515 μm and 400 μm, respectively. The proposed e-FMF based LPFGs could have a promising prospect in the application of fiber sensing and mode division multiplexing optical communication system.

中文翻译：

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刻在椭圆纤芯少模光纤中的长周期光栅实现模式选择性转换


我们演示了通过 CO2 激光器在椭圆芯少模光纤 (e-FMF) 中制造长周期光纤光栅 (LPFG)。 LPFG可实现从基模到高阶模（LP11a、LP11b和LP21a模）的模式转换，效率高达95%以上。通过实验研究了弯曲、扭转、温度和应变对基于 e-FMF 的 LPFG 模式转换器谐振波长的影响。 LPFG 的温度和应变灵敏度分别为 -36 pm/°C 和 -4.9 pm/με，并且发现 LPFG 对弯曲和扭转不敏感。由于e-FMF中沟槽的存在，基于e-FMF的长周期光栅也可以分别激发高阶LP02和LP31a模式，其光栅周期分别为515μm和400μm。所提出的基于e-FMF的LPFG在光纤传感和模分复用光通信系统的应用中具有广阔的前景。