中文摘要：

实现了一种基于光纤布拉格光栅（FBG）及其末端镀膜的高灵敏度Ni（2＋）浓度光纤传感器。壳聚糖和聚丙烯酸（PAA）通过自组装,以聚合物膜的形式直接聚合沉积在光纤末端。当Ni^（2＋）因螯合作用而被膜吸附时,膜的折射率发生变化,从而使光纤末端的菲涅尔反射发生改变。通过测量菲涅尔反射光谱中信噪比（SNR）的变化,就可以得到Ni^（2＋）的浓度。实验测得传感器的最大线性灵敏度可达35.52dB/mM。利用SNR解调的方法不仅可以消除光源功率波动对测量精度的影响,同时可以利用FBG谐振波长的漂移测量温度变化。本文实现的Ni^（2＋）浓度光纤传感器,具有良好的灵敏度、成本低和结构简单等优点。

英文摘要：

Nickel ions （Ni^2＋ ） probe with enhanced sensitivity is experimentally demonstrated by using a normal fiber Bragg grating （FBG） cascaded with coating-functionalized fiber tip. The coating of chitosan/ poly acrylic acid （PAA） is formed directly onto the cleaved fiber tip via layer by layer assembly. When the Ni^2＋ is absorbed by the chitosan/PAA coating,the Fresnel reflectivity of the fiber tip,which forms the noise background in the FBG＇s reflection spectrum, can be modulated due to Ni^2＋ -caused refractive index variation of the coating. Therefore, bv tracing the variation of the signal to-noise ratio （SNR）.measurement of Ni^2＋ concentration is achieved successfully with maximum sensitivity of 35.52 dB/mM. By using the SNR demodulation method,we can not only eliminate the influence of power fluctuation of the light source on the demodulation accuracy and stability, but also allow independent temperature measurement through Bragg wavelength shift of the FBG. The heavy metal ions sensor based on SNR measurement of fiber Bragg grating has the advantages of low cost,miniature size, light weight and im munity to electromagnetic, which demonstrates a promising potential in the field of measurement of heav- y metal ions.