薄膜消光系数对镀膜长周期光纤光栅传输谱的影响  

Impact of Thin Film Extinction Coefficient on Coated Long-Period Fiber Grating Transmission Spectrum

作　　者：蒋秀丽[1,2] 顾铮■ 

机构地区：[1]上海理工大学光电功能薄膜实验室,上海200093 [2]上海电力学院数理系,上海200090

出　　处：《光学学报》2010年第8期2189-2195,共7页Acta Optica Sinica

基　　金：国家自然科学基金(60777035);教育部科学技术研究重点项目(208040);上海市教育委员会科研项目(07ZZ87);上海市重点学科建设项目(T0501)资助课题

摘　　要：在长周期光纤光栅外镀折射率随环境变化而改变的敏感薄膜,其谐振波长随薄膜折射率的变化而改变。对无吸收薄膜,光栅耦合强度为π/2时,其传输谱中谐振波长对应的损耗峰峰值为零。镀复折射率薄膜的长周期光纤光栅,耦合强度为π/2时,损耗峰不为零,在谐振波长对薄膜折射率变化响应灵敏的区域,包层模传输常数的虚部较大,损耗峰幅值减小,甚至消失,不利于谐振波长的测量。通过求解镀复折射率薄膜长周期光纤光栅的耦合模方程,得到了损耗峰峰值的解析解。找到了损耗峰为零的条件。在此条件下设计光栅,可以有效地避免损耗峰减小带来的不利因素。The resonant wavelength of long-period fiber grating（LPFG）coated with sensitive film,whose refractive index varies with the surrounding medium,changes with the film refractive index.When the coupling strength of LPFG with non-absorbing film coating is π/2,the loss peak corresponding to the resonance wavelength gets to zero.However,it is not the case for the LPFG coated with complex refractive index film.When the coupling strength of LPFG with complex refractive index film is π/2,the loss peak is not zero.While the resonant wavelength is sensitive to the film refractive index,imaginary part of propagation constant of clad mode becomes larger,which causes reduction or even disappearance of the loss peak.It is not conducive to the measurement of resonant wavelength.Analytical solution of the value of the loss peak is obtained by solving the coupled-mode equations for LPFG with complex refractive index film.The condition under which loss peak gets to zero is found.Designing LPFG according this principle,the unfavorable factor mentioned above can be effectively avoided.

关 键 词：光纤光学 长周期光纤光栅 薄膜消光系数 损耗峰 光栅长度 

分 类 号：TP212.14[自动化与计算机技术—检测技术与自动化装置]