为了实现被测折射率范围可调, 提高检测灵敏度, 将双波长差分检测技术应用于平面波导激励的金属-介质-金属组成的对称型表面等离子体共振传感结构中.通过对对称结构的模式特性分析, 研究了该结构中激发等离子体表面波时, 介质厚度与被测折射率的关系及双波长差分检测的原理.采用离子交换法制备平面波导, 用费米函数拟合其渐变折射率分布.用光强调制方式, 分别进行单波长和双波长差分检测, 对折射率为1.33~1.428之间的甘油溶液进行测试, 实验结果表明, 该结构可激发等离子体表面波, 与传统平面波导激励的表面等离子体共振传感结构相比, 通过改变被测介质的厚度可以改变共振条件, 进而改变折射率的测量范围.若被测范围选择合适, 检测的线性较好, 采用差分检测方法比单波长检测方法的灵敏度提高近一倍.

In order to improve the detection sensitivity, the method of dual-wavelength differential detection is used. To realize the measured refractive index range being adjustable, a novel surface plasmon resonance sensing structure is described, which consists of a planar waveguide and a symmetric structure with metal-sample-metal layer. The mode characteristic of the symmetric structure is analyzed. When the surface plasmon wave is excited, the relationship between the tested refractive index and the dielectric thickness, and the dual-wavelength differential method are researched. Planar waveguides are prepared by the ion-exchange and the graded-index distribution can be fitted by the Fermi function. In experiments Glycerin solutions with the refractive index range of 1.33-1.428 are used for detection by intensity method. Methods of single wavelength and dual-wavelength based on the symmetric structure are used respectively, then the plasmon surface wave can be excited. The refractive index matching condition of this structure can be adjusted through the thickness of the sample, so the tested range is adjustable. If the measured range is appropriate, a linear relationship between normalized intensity and refractive index can be obtained. Theoretical analysis and experimental results show that the sensitivity of the differential detection method is nearly doubled compared with the single-wavelength method.