基于严格的相位匹配公式, 在充分考虑材料色散的基础上, 详细研究了镀膜长周期光纤光栅的双峰谐振效应。研究发现, 随着环境折射率的变化, 发生谐振的双峰也发生变化, 且变化趋势相反。给出了镀膜长周期光纤光栅双峰谐振波长之间的距离随环境折射率变化的关系, 并与普通长周期光纤光栅的同等情形进行了比较, 发现镀膜长周期光纤光栅的双峰谐振能够极大提高长周期光纤光栅的折射率灵敏度。但由于发生双峰谐振需要的包层模式次数较高, 故其探测范围比应用低次耦合的单峰探测范围要窄。

Based on the strict phase-matching formula and considering the material dispersion, the refractive index sensing properties of the dual resonant peaks of the coated long-period fiber gratings (LPFG) are studied in detail. The study shows that the dual resonant peaks change with the environmental refractive index, and they change in the opposite direction from that of environmental refractive index. It is given that the distance between two resonant peaks of coated LPFG changes with the environmental refractive index, and the refractive index properties of those uncoated LPFG are put into comparison. It is also found that the dual resonant sensor can effectively increase the sensitivity of the coated long-period fiber gratings, but at the cost of the detection range.