【作者】 顾江华；

【导师】 曹庄琪；

【作者基本信息】 上海交通大学 ， 光学， 2008， 博士

【摘要】 随着现代科学技术的发展,特别是生命科学、临床医学等新兴科学的发展,生物探测和传感所面临的挑战越来越大,对光学生物传感器的灵敏度要求也越来越高。在研究了传统的基于迅衰场探测的光学传感器的特点之后,我们提出了一种基于振荡场探测的对称金属包覆波导(SMCW)结构的传感器。与普通的介质光波导不同的是,SMCW采用金属薄膜作为波导的包覆层,金属薄膜的厚度和光学常数的测量也成为一个重要的课题。厚度在几十个纳米范围内的金属薄膜的厚度和光学常数通常采用衰减全反射(ATR)法进行测量。从表面等离子共振吸收峰的三个参数共振角θSPR,半峰宽Wθ和反射率最小值Rm in出发会得到两组关于金属薄膜光学常数与厚度的解。传统的测量方法认为,必须改变探测条件进行二次测量才能对这两组解进行验算,找出真解。我们利用扩展的ATR谱,即包括全反射(TIR)部分的ATR谱,使用最基本的棱镜-金属薄膜结构,只用一次测量就可以完全定金属薄膜的厚度和光学常数。其原理是引入一个新的参数—全反射时的反射率阶越变化ΔR,根据ΔR是金属薄膜厚度的敏感函数的性质,就可以确定所得到的两组解中的真解。金属薄膜的特殊光学性质使得SMCW具有普通的介质光波导所不同的特点,如波导层厚度可以扩展到毫米量级,所激发的超高阶导模对波导参数的变化非常灵敏以及模式无关等特性。基于SMCW的以上特点,我们提出了将样品注入到SMCW的波导层中,利用激发的超高阶导模进行测量,实现了振荡场光学传感器的构造。其特征是,处于波导层中的样品由功率较大振荡场进行探测;另外,作为探针的超高阶导模比普通波导中的低阶模具有更高的灵敏度。理论分析表明,与现有的光学迅衰场传感器相比, SMCW振荡场传感器的灵敏度有一到两个量级的提升。我们通过实验对SMCW传感器的性能作了验证。用不同浓度的NaCl水溶液作为样品,在采用角度调制法时达到了424o/RIU的灵敏度和7.3×10-6RIU的分辨率;在采用强度调制法时,实现了0.88×10-6RIU的分辨率。在测量样品的吸收时,我们使用了亚甲蓝溶液作为样品,探测分辨率达到5×10-6,并且避免了亚甲蓝分子在波导表面的吸附效应所产生的影响。研究结果表明,SMCW振荡场光学传感器具有简单的结构和极高的灵敏度,在迅速发展的生物探测领域将有广阔的应用前景。更多还原

【Abstract】 With the development of modern science and technology, especially the development of emerging science such as life sciences and clinical medicine, the biological survey and the sensing face growing challenge, the need for more sensitive biosensor has increased rapidly as well. After studying the conventional biosensors based on evanescent-field sensing, a symmetrical metal-clad waveguide (SMCW) sensor based on oscillating-field sensing is proposed.Different from the common dielectric waveguide, the cladding layer of SMCW is constructed by two thin metal films. Measurement of thickness and optical constants of thin metal films is also a research subject of our article. An extended attenuated total reflection (ATR) spectrum, which consists of a surface plasmon resonance (SPR) dip and a total internal reflection (TIR) step, is used to determine the optical constant and the thickness of a thin metal film at a given frequency in the conventional Kretschmann configuration. Previous research has shown that two sets of solutions for the optical constant and thickness can be obtained from a SPR dip, and the ambiguity should be removed by carrying out another angular scan process or employing a more complicated structure. However, we find that the true solution can be simply selected by a new parameter that denotes the TIR step change. Our method can avoid not only the troubles caused by the double-scan techniques, but also the increased difficulties due to the existence of an additional polymer film in a single-scan method.Due to the special optical properties of the metal film, the characteristic of SMCW is greatly different from the common dielectric waveguide in many aspects, such as the waveguide layer can be enlarged to millimeter scale, the ultra-high order modes in SMCW is very sensitive to refractive change of the waveguide, and present polarization independence. These unique features enable us to fabricate an oscillating-filed sensor based on SMCW. The samples are introduced into the waveguide layer and probed by the ultra-high order modes. Owing to the concentrated power in the sensing region and the use of very sensitive ultra-high order modes, the SMCW sensor gains a sensitivity enhancement of 1 to 2 orders of magnitude than that of the previous sensor structure.To verify the performance of the proposed SMCW sensor, several experiments with different measurement interrogation are carried out. Using the NaCl water solutions as samples, we obtain a sensitivity of 424o/RIU and resolution of 7.3×10-6RIU by applying an angular interrogation, and a resolution of 0.88×10-6RIU by applying an intensity interrogation. When employed as an absorption sensor, with the methylene blue solutions as samples, the SMCW structure achieves a resolution of 5×10-6, and avoides the surface adsorption effect of methylene blue solutions.It is demonstrated both theoretically and experimentally that the SMCW senor based on oscillating-filed sensing is more sensitive and easy fabricated, and has the potential applications in high sensitivity, low cost and accurate bio-sensing science.更多还原