从长周期光纤光栅(LPFG)谐振透射光谱随外界环境折射率变化敏感特性的角度, 详细研究了LPFG氨氮降解监测传感器的工作原理, 分析了LPFG谐振峰波长与氨氮溶液浓度之间的对应关系。 采用LPFG透射光谱检测技术, 获得7种不同浓度氨氮溶液所对应的LPFG透射光谱曲线族, 其谐振峰波长随溶液浓度的增大而逐渐向长波方向偏移, 波长变化量从2.707 nm减至0.068 nm, 且变化量与溶液浓度值呈良好的对应关系, 其响应度为52.78 pm·mg-1·L。 通过监测LPFG光谱变化获取氨氮溶液的浓度, 进而判断氨氮溶液的降解过程及程度。 该方法对溶液直接进行监测, 简单易行, 测量及传导光路实现全光纤化, 无需化学试剂标记, 可实现对氨氮溶液降解过程的在线、 精确及远距离遥测。

In the present paper, the principle of a long-period fiber grating (LPFG) ammonia-nitrogen degradation monitoring sensor was discussed in detail firstly based on a sensitive characteristic that the resonance spectrum of long-period fiber grating changes with refractive index in external environment. The relationship between the resonance peaking wavelength of long-period fiber grating and the concentration of ammonia-nitrogen solutions was also analyzed detailedly. Then, the long-period fiber grating spectrum measurement technology was selected to obtain long-period fiber grating spectrum curves corresponding to seven different kinds of concentration of ammonia-nitrogen solutions, and the resonance wavelengths increased with the increase in the concentration of ammonia-nitrogen solutions. The variations of the resonance wavelength decreased from 2.707 to 0.068 nm and had a relatively good corresponding relationship with the concentration values of ammonia-nitrogen solutions. The responsivity of this correlation is 52.78 pm·mg-1·L. The concentration of ammonia-nitrogen solutions was acquired exactly through the way of monitoring the changes of the spectrum attribute, at the same time, the process and the extent of ammonia-nitrogen wastewater degradation were estimated. This method, which can directly monitor the concentration of ammonia-nitrogen solutions, is simple and easy to operate. The measurement and transmission section of the system are completely composed of optical fiber, which can avoid the electronic interference. There is no necessary to use chemic reagent to sign the solutions, which are going to be degraded. In conclusion, the late-model long-period fiber grating ammonia-nitrogen degradation monitoring system could achieve a real time, rapid, accurate and long distance measurement.