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利用镀自组装薄膜的双峰谐振长周期光纤光栅(LPFG)实现了高灵敏的折射率传感,给出了提高镀膜双峰谐振光纤光栅对环境折射率(SRI)灵敏度的途径。确定最佳镀膜厚度,使光纤包层模位于模式转换区附近;调整光纤半径,使镀膜后光栅的双峰位于相位匹配转折点(PMTP)附近,给出了确定最优膜厚和光纤半径的方法。将不同半径的双峰光栅镀自组装聚丙烯胺盐酸盐(PAH)/聚丙烯酸(PAA)薄膜后,放入不同浓度的葡萄糖溶液中进行折射率传感实验。结果表明:通过优化光纤半径和薄膜厚度,镀膜后工作于模式转换区附近和PMTP附近的双峰光栅对1.333~1.372范围内折射率的灵敏度高达3985nm/RIU(RIU为单位折射率),明显高于不在模式转换区或PMTP附近的光栅,亦高于已报道的非双峰镀膜长周期光纤光栅。
Highly sensitive refractive index sensing is achieved by using bimodal resonant long period fiber grating (LPFG) coated with a self-assembled thin film, and a method to increase the sensitivity of the bimodal resonant fiber grating to the ambient refractive index (SRI) is proposed. The optimal coating thickness is determined so that the cladding mode of the optical fiber is located near the mode transition area. The radius of the optical fiber is adjusted so that the double peak of the coated grating is located near the phase matching point (PMTP), and the method of determining the optimal film thickness and the radius of the optical fiber . The bimodal gratings with different diameters were self-assembled with polyacrylamide hydrochloride (PAH) / polyacrylic acid (PAA) film, and then put into different concentrations of glucose solution for refractive index sensing experiment. The results show that by optimizing the fiber radius and film thickness, the sensitivity of the bimodal grating operating in the vicinity of the mode transition region and near the PMTP after coating to the refractive index in the range of 1.333 to 1.372 is as high as 3985 nm / RIU (RIU is the unit refractive index) Gratings not in the mode transition region or in the vicinity of PMTP are also higher than the reported non-bimodal coated long-period fiber gratings.