基于长周期光纤光栅迈克耳孙干涉仪的溶液饱和点测量

Measurement of Saturation Point of Aqueous Solution Based on Long Period Michelson Interferometer

采用掩模法制作周期为400μm的长周期光纤光栅,在其一端6cm处镀制Ag反射膜,制成LPFG-Michelson干涉仪.以NaClO3溶液为例,逐次添加等量溶质,研究基于LPFG-Michelson干涉仪快速标定特定温度下溶液饱和点的实验装置及方法.基于相位差原理,求解纤芯、包层模本征方程,分析了LPFG-Michelson干涉仪谱线移动随外界环境的变化规律,参照理论计算曲线,分析实验测得的损耗谷波长移动量随添加的NaClO3粉末质量的变化曲线,最小二乘法拟合后,再计算未饱和及饱和时的拟合曲线的交点,得出NaClO3水溶液在32℃下的饱和点,与已知文献测定值相差仅1.5%.

A Long Period Fiber Grating（LPFG） whose period is 400μm was fabricated by amplitude mask technique. The end of the fiber, which is 6 cm from the LPFG, was coated with Ag. Taking NaC1O3 aqueous solution for example with same amount of NaC103 powder added into the solution by every time, a new device and method for immediately calibrating saturation point under a specified ambient temperature was studied. Based on the principle of phase difference and solving the eigen equation of core mode and cladding mode of single-mode fiber, the reflectance spectrum variation of LPFG-Michelson interferometer induced by ambient refractive index change was analyzed. By reference to variation tendancy of wavelength shift value with refractive index change, the change curve of the notch wavelength shift induced was obtained by repeatedly add NaC1O3 powder into the solution. The experiment value is fitted by least square method, and the theoretical saturation point of NaC1O3 aqueous solution under 32℃ is obtain by solving intersection point of the fitted curves, which the difference between the result and literature is only 1.5 %.