摘要
依据包层模有效折射率的概念及包层模场的光功率密度分布,重新审视了镀膜长周期光纤光栅"模式转换"现象,对"模式转换"给出了新的物理图像.通过修正镀膜长周期光纤光栅包层模有效折射率的范围,指出有效折射率呈现的台阶式增长是各次包层模自身属性的反映,不存在高次模式替代低次模式的过程,并将"模式转换区"重命名为"模式垒区".通过分析包层模场的光功率密度分布,指出"模式转换区"较低次包层模式进入薄膜层传输说法的不合理性.研究表明,当薄膜厚度达到一定厚度时,包层模场光功率分布将愈加集中在薄膜层内部,但并非沿着薄膜层传输.讨论了镀膜长周期光纤光栅传感器薄膜参数优化的问题,在修正的包层模有效折射率范围和未修正的包层模有效折射率范围的情况下分别进行优化,并对优化结果进行比较,结果表明两种情况下的优化结果存在较大的偏差.从机理上解释了修正薄层模有效折射率范围后的优化结果的正确性,为设计高灵敏镀膜长周期光纤光栅传感器提供了新的理论指导.
Based on the concept of effective refractive index and the power density distribution of cladding mode,this paper re-survey the phenomenon of ＂ mode conversion＂ of long-period fiber grating（ LPFG）,and gives new physical image for ＂ mode conversion＂. By modifying the range of the effective refractive index of cladding mode of LPFG,it is pointed out that the step-like growth of the effective refractive index is the selfproperty of each cladding mode and there is no replacement between high and low order modes,and we rename the ＂ mode conversion region＂ to ＂ mode barrier region＂. It is pointed out that the incorrectness of the argument that the lower order cladding modes will guided in the overlay in the ＂ mode transition＂ region by analyzing the power density distribution of cladding mode. The research in this paper shows that when the thickness of overlay reaches a certain value,the power distribution of the cladding will be more concentrated in the overlay,but the cladding mode will not be guided in overlay. This paper discusses the optimization of overlay parameters of longperiod fiber grating sensors,and compares the optimization results before and after the modification of effective refractive index of cladding mode,the result shows that there is a large deviation between the optimization results of these two cases. The correctness of the optimization results after modifying the effective refractive index range is explained mechanistically,which provides the new theoretical guidance for designing highsensitivity long-period fiber grating sensors.
作者
顾铮■
冯文斌
GU Zheng-tian;FENG Wen-bin(Laboratory of Opto-Electric Functional Film, College of Science, University of Shanghai for Science and Technology, Shanghai 200093, Chin)
出处
《光子学报》
EI
CAS
CSCD
北大核心
2018年第6期66-74,共9页
Acta Photonica Sinica
基金
国家自然科学基金(No.60777035)
教育部科学研究重点项目(No.208040)
上海市教育委员会科研创新重点项目(No.11ZZ131)
上海市重点学科建设项目(No.S30502)资助~~
关键词
光纤光学
镀膜长周期光纤光栅
模式转换
有效折射率
功率密度分布
灵敏度
Fiber optics
Coated long-period fiber grating
Mode transition
Effective refractive index；Power density distribution
Sensitivity
