在含涂覆层的标准通信光纤中，用红外飞秒激光直接写入长周期光纤光栅(long period fiber gratings，LPFGs)，并通过理论和实验分析，研究含涂覆层LPFGs的轴向应变特性.分析结果表明，与去除涂覆层的LPFGs相比，涂覆层的存在不仅增强了LPFGs的机械强度，同时有效地抑制了LPFGs由外加应变引起的谐振波长偏移.基于以上优点，含涂覆层的LPFGs若作为带阻滤波器或增益平坦器，将有良好的机械可靠性和波长应变稳定性.

This paper proposes a direct, pointbypoint inscription of long period fiber gratings (LPFGs) in standard communication coated fibers using an infrared femtosecond laser. The characteristics of axial strain of the coated LPFGs are investigated theoretically and experimentally. The results show that the presence of coating not only strengthens the mechanical robustness but also effectively reduces the shift of the resonant wavelength caused by an applied strain. The coated LPFGs can be modified as bandreject filter and gain equalizer, which show good mechanical reliability and strain stability of resonant wavelength