利用长周期光纤光栅（LPFG）中的双峰谐振效应，结合表面等离子体共振（SPR）传感器的高灵敏度，提出了一种新型镀金属光纤光栅液体浓度传感器。采用双包层结构模型和耦合模理论，分析了镀金属长周期光纤光栅双峰效应的谐振特性，环境折射率的传感特性以及金属膜厚对双峰LPFG灵敏度的影响。实验上制作了具有双峰效应的镀银膜长周期光纤光栅，并进行了NaCl盐溶液浓度的监测实验。结果表明，随着盐溶液浓度的增大，双峰谐振峰相互远离，各自向短波和长波方向偏移。选择银膜厚为103 nm的光纤光栅传感器，对溶液折射率分辨率可达1.8×10-5。进一步通过与基于双峰效应的无镀膜光纤光栅和普通单峰光纤光栅的盐溶液传感实验的比较，表明基于双峰效应镀金属长周期光纤光栅传感器对溶液浓度的监测灵敏度明显高于前两者。

A novel metal-coated long period fiber grating (LPFG) liquid concentration sensor is presented, which is based on dual-peak resonance combined with high sensitivity of surface plasmon resonance (SPR). On the basis of double-clad structural model and coupled-mode theory of LPFG, the dual-peak resonant characteristics and refractive index sensing properties of metal-coated LPFG are analyzed, and the influence of metal film thickness on sensitivity of dual-peak based LPFG is discussed. Experimentally, the dual-peak resonance-based LPFG with silver film coating has been fabricated, and the salt solution concentration monitoring test was performed. The results show that dual resonant peaks are far away from each other, and shift in opposite directions with increase of salt solution concentrations. The resolution of liquid refractive index is available to 1.8×10-5 for a LPFG with silver film thickness of 103 nm. Furthermore, compared with the dual-peak based non-coated LPFG and general single peak based LPFG, the metal-coated LPFG based on dual-peak resonance has higher refractive index sensitivity.