In view of the problem that the sensing characteristics of the multi-mode interferometric fiber sensors cannot be accurately analyzed, an analysis method based on the fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) is proposed and demonstrated theoretically and experimentally. The suitabilities of the rectangular window function with the narrow main lobe (high spectrum resolution) and low side lobe (high main mode energy leakage) and the Hanning window function with the wide main lobe (low spectrum resolution) and high side lobe (high energy concentration) in this kind of sensor analysis are discussed, respectively. This method can not only realize the sensing performance analysis of the various modes, but also overcome the inconsistency of the different interference wavelength (dip) sensing characteristics in the conventional analysis methods. At the same time, this method is also beneficial to solve the repetitive problem of such sensors.

为了在测量NaCl溶液浓度的同时实现对温度的监测, 提出了一种基于马赫-曾德干涉仪(Mach-Zehnder Interferometer, MZI)级联法布里-珀罗干涉仪(Fabry-Perot Interferometer, FPI)的干涉型传感器。在单模光纤上通过熔融放电制作出一对腰锥直径155 ?滋m、间隔1.5 cm的MZI, 其对比度为10 dB、周期29.85 nm; 在MZI尾纤的一端与光子晶体光纤(Photonic Crystal Fiber, PCF)相对熔接并在距熔接点176 ?滋m处将PCF切平, 形成对比度为8 dB、周期为5.71 nm的FPI。实验选取1 535~1 555 nm波段MZI和FPI的干涉波谷特征波长, 在0~150 ℃的温度和0%~24%的NaCl溶液浓度变化范围内测得MZI的温度和折射率灵敏度分别为50 pm/℃和9.97 nm/RIU, 线性度均大于0.97; 而FPI的波谷特征波长对折射率不敏感, 温度灵敏度约为8.3 pm/℃, 线性度为0.98。最后, 通过构建温度-浓度函数关系矩阵得出了对温度和NaCl溶液浓度的灵敏度矩阵。该干涉型传感器对温度和NaCl溶液浓度表现出良好的灵敏度和线性度, 可实现上述双参数的同时测量。