摘要
针对镀高折射率纳米膜的长周期光栅,建立了传感理论模型,研究了长周期光栅的谐振波长与纳米膜厚度及外界折射率的关系,给出不同纳米膜厚度下长周期光栅不同包层模式重组特性。研究发现,当长周期光栅外面镀上一层沿角向均匀分布的纳米膜时,随着膜厚变化会出现包层模分布的明显调制;适当选择镀膜参数和外界介质折射率,最低次包层模式HE1,2会成为镀膜层中的导模,其他的包层模式将会发生模式转换现象;对于较低次包层模式(如HE1,6),在模式转换的时候存在两步转换,而高次的包层模只有一步转换(如HE1,14)。同时给出了包层模式转换对外界折射率响应的关系:当膜层厚度增加时,长周期光栅模式转换现象移至低折射率区域。
The sensing theoretical model of long-period gratings （LPGs） with high-refractive-index nanometer film coating is built. The influence of overlay thickness and external refractive index on the resonant wavelength of LPG is investigated theoretically. The phenomenon of reorganization of cladding modes at different coating film thicknesses is shown and explained in detail. The theoretical analysis shows that a significant modification of the distribution of cladding modes is seen as an azimuthally symmetric nanoscale high-refractive-index coating deposited on the cladding of LPG. If the parameters of layers （the refractive index and thickness） and the external refractive index are chosen accurately,the lowest cladding mode HE1,2 will become the overlay mode and other cladding modes will experience mode transition. For the lower cladding modes （such as HE1,6）,there is two-step modes transition. For higher cladding modes（such as HE1,14）,there is only the one-step modes transition. The mode transition on the sensitivity of the external refractive index is also analyzed：Modes transition shifts to lower refractive index region with the increase of the overlay thickness.
出处
《光学学报》
EI
CAS
CSCD
北大核心
2009年第10期2665-2672,共8页
Acta Optica Sinica
基金
国家自然科学基金(60629401
10776016)资助项目
关键词
光纤光学
长周期光纤光栅
谐振波长
特征方程
纳米膜
模式转换
fiber optics long-period fiber grating（LPG） resonant wavelength characteristic equation nanometer film mode transition
