Yang Jian, Yang Li, Xu Chang-Qing, Xu Chenglin, Huang Weiping, Li Yingfu
McMaster University, Hamilton, Ontario L8R 4K1, Canada.
Appl Opt. 2006 Aug 20;45(24):6142-7. doi: 10.1364/ao.45.006142.
What is believed to be a novel long-period grating (LPG) refractive index sensor with a modified cladding structure is proposed and studied. In the proposed structure, the cladding of the fiber has a two-layer structure, i.e., a cladding layer of low refractive index with a reduced radius and an overlay of high refractive index. The sensitivity of the structure-modified LPG sensor to the ambient refractive index change as a function of the cladding layer and overlay parameters is investigated by way of modeling. It is found that an increase of the ambient refractive index causes a field redistribution of the cladding mode into the overlay when the parameters of the overlay are properly selected. It is shown that by reducing the radius of the cladding layer, the operational range of the LPG refractive index sensor can be as large as 0.195 (from 1.244 to 1.440) with a minimum sensitivity of 660 nm/refractive index, which represents a 31% increase of operational range in comparison with the operational range obtained from the reported structure. The design guidelines for achieving this large operation range and high sensitivity are explained by investigating the dependence of the cladding modes on the radius of the cladding layer.
本文提出并研究了一种据信具有改进包层结构的新型长周期光栅（LPG）折射率传感器。在所提出的结构中，光纤包层具有两层结构，即半径减小的低折射率包层和高折射率覆盖层。通过建模研究了结构改进型LPG传感器对环境折射率变化的灵敏度与包层和覆盖层参数的函数关系。研究发现，当覆盖层参数选择适当时，环境折射率的增加会导致包层模场重新分布到覆盖层中。结果表明，通过减小包层半径，LPG折射率传感器的工作范围可达0.195（从1.244到1.440），最小灵敏度为660 nm/折射率，与报道结构相比，工作范围增加了31%。通过研究包层模对包层半径的依赖性，解释了实现这种大工作范围和高灵敏度的设计准则。
