光学学报, 2013, 33 (7): 0706003, 网络出版: 2013-06-25
镀吸收型膜长周期光纤光栅模式转换与折射率响应特性
Mode Transition in Absorption Film Coated Long-Period Fiber Grating and Response Characteristics of Refractive Index
摘要
基于耦合模理论,研究了镀吸收型薄膜长周期光纤光栅(LPFG)的模式转换及其折射率响应特性。讨论了镀膜LPFG包层模有效折射率随薄膜厚度的响应特性,从模场分布和波导传输本质上统一了模式转换与模式跳变两种表述。在此基础上分析了镀吸收型薄膜情形下LPFG包层模有效折射率实部与虚部随膜厚及薄膜折射率的变化,给出并解释了高阶和低阶包层模发生的一步、二步模式转换情况,进一步考察了薄膜消光系数对模式转换区域的影响。结果表明,薄膜消光系数对模式转换区域变化的影响很小。最后研究了转换区及其附近区域的镀吸收型膜LPFG透射谱的折射率响应特性,发现靠近模式转换区相较于模式转换区,LPFG对薄膜折射率分辨率高出近一个数量级,而模式转换区域采用简易的透射率相对变化进行检测,对薄膜折射率的分辨率也高达10-5以上。
Abstract
Based on the coupled-mode theory, the mode transition in absorption film coated long-period fiber grating (LPFG) and response characteristics of refractive index are studied. The response characteristics of effective index of cladding mode for coated LPFG with overlay thickness are discussed, and the mode jump and mode transition are unified in mode field distribution and the essence of waveguide transmission. Based on this result, the change in absorption film coated of real and imaginary of effective index of cladding mode for LPFG coating absorption film with different overlay thicknesses and overlay refractive indexes is analyzed. The one step and two step of mode transition of the high order and low order cladding mode are given and explained. The effect of film extinction coefficient to mode transition zone is further investigated. The results show that the film extinction coefficient has little influence on the mode transition zone. Finally, the response characteristics of refractive index in LPFG coated absorption film are investigated in the mode transition zone and near the mode transition zone. The results indicate that resolution of film refractive index in mode transition is one order larger than that in vicinity of mode transition, and the resolution can be also available to 10-5 in mode transition detected by transmittance change.
顾铮天, 蓝锦龙. 镀吸收型膜长周期光纤光栅模式转换与折射率响应特性[J]. 光学学报, 2013, 33(7): 0706003. Gu Zhengtian, Lan Jinlong. Mode Transition in Absorption Film Coated Long-Period Fiber Grating and Response Characteristics of Refractive Index[J]. Acta Optica Sinica, 2013, 33(7): 0706003.