应用镀膜长周期光纤光栅实现微折射率变化的测量

Application of coated long period fiber grating to measure the change of mic ro-refractive index

摘要:

基于长周期光纤光栅(LPFG)4层镀膜模型,详细研 究了耦合的包层模式、薄膜厚度、薄膜折 射率和环境折射率等因素对镀膜LPFG折射率灵敏度的影响。研究发现,薄膜材料 折射率越高、薄膜厚度越接近最优薄膜厚度和耦合的包层模式越接近转折模式,镀膜LPFG的 折射率灵敏度越高。应用这类LPFG可对诸如乳化液、蔗糖溶液等在 浓度较小时浓度的微小变化引起的折射率微变化进行有效测量。以浓度为0～8%(对应的折 射率变化为1.3316~1.340,远离LPFG折射率敏 感区域)的乳化液为例进行了测量数值分析,结果表明,应用这类镀膜LPFG可以实现对远离 折射率敏感区的溶液浓度的微变化进行有效测量。

Abstract:

Based on the strict four-layer model,the influence of some factors,inclu ding cladding modes,film thickness,film refractive index and the environment r efractive index,on the refractive index sensitivity of coated long period fiber grating (LPFG) is studied in detail.It is found that the higher the re fractive index of the film material,the closer the thickness of the film is to the optim al film thickness,the closer the coupled modes are to the transition mode and th e h igher the refractive index sensitivity of the coated long period fiber grating. Eve n the micro-change of refractive index caused by a little change in the small concentrations of emulsion,sucrose solution,and something like that can be measu red by the se gratings.The emulsion with 0% to 8% concentration (corresponding to the refra c tive index change of 1.3316－1.3405,away f rom the the sensitive areas of the long period fiber grating refractive index is taken as an example to carry out numer ical analysis.The results indicate that the application of coated long period fiber grating can achieve the effective measurement of the micro-changes in co ncentration away from the sensitive area of the refractive index.