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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。
Based on the bimodal resonance effect in long period fiber grating (LPFG) and the high sensitivity of surface plasmon resonance (SPR) sensor, a new type of metallized fiber grating liquid concentration sensor is proposed. Based on the double-clad structure model and the coupled-mode theory, the resonance characteristics of the bimodal metallization and the sensing properties of the environmental refractive index and the influence of the metal film thickness on the sensitivity of the bimodal LPFG are analyzed. Experimentally, a long-period silver-plated fiber grating with bimodal effect was fabricated and the NaCl salt solution concentration was monitored. The results show that as the concentration of salt solution increases, the bimodal resonance peaks move away from each other and shift to shortwave and longwave respectively. Select the silver film thickness of 103 nm FBG sensor, the refractive index of the solution resolution of up to 1.8 × 10-5. By comparing with the salt solution sensing experiment of uncoated fiber grating and ordinary unimodal FBG based on bimodal effect, it is shown that the monitoring sensitivity of the long-period fiber grating sensor based on bimodal effect on solution concentration is obviously higher than that of the first two By.