【作者】 陈洸；

【导师】 曹庄琪；

【作者基本信息】 上海交通大学 ， 光学， 2007， 博士

【摘要】 光生化传感器基本的作用是将某种生化参量(如,某种化学物质、生物分子、生化结构或某些微生物的性状变化或浓度变化等)转变为可以定性或定量测量的光信号的变化。这样,通过精确的测量光信号的变化,我们就可以对某一生化反应过程中某些感兴趣的过程或参量进行监测。由于具有高灵敏度、快速响应等特征,光生化传感器广泛应用于现代临床医学的检测、生物化学基础研究、环境监测、现代工业和食品检测等等领域中。导波光学问世以来,一直受到学术界和技术界的高度重视。在其发展的推动下,光生化传感器已经发展出了多种具有较高灵敏度的传感结构。其中,又以表面等离子共振传感器和泄漏模波导传感器最具有代表性和前沿性。但随着科技的进步和人们生活水平的提高,多种应用场合都对光生化传感器的灵敏度提出了更高的要求。本文利用导波光学理论,在介绍一般介质平板波导的基础上,着重分析了对称金属包覆波导的特性。对称金属包覆波导结构由上下金属包覆层和夹在中间的导波层组成。其中,上层金属膜比较薄,入射光一般经过这一层耦合进波导层;而其下层金属膜一般较厚,用以隔绝镀膜衬底材料对波导结构的影响;两层金属薄膜之间的介质层作为导波层,以分立的导模形式存在的导波光主要被限制在这层里传输。由于上下包覆层都是金属薄膜(其介电系数在光频范围内的实部一般是一个绝对值很大的负数),所以对称金属包覆波导中导波层的折射率取值范围可以很大,最小甚至可以为1.0。另外,对称金属包覆波导的导波层厚度还可以扩展至亚毫米甚至毫米量级,并因此能够容纳模序数上千的高阶导模。正因为上述这两个特征,使得气体和常用的生物化学流体样本等低折射率介质都可以作为该种波导结构的导波层,并可以在其中自由的流动。这样,利用对称金属包覆波导结构来制作光生化传感器就成为了可能。除了上述特性之外,对称金属包覆波导中的超高阶导模的有效折射率对于导波层介质的折射率变化非常敏感,而且取值范围比一般介质波导大得多,可以介于零和波导层折射率之间。经过分析,发现其超高阶导模能够通过自由空间耦合来激发,并且具有偏振无关性。根据上述特性,本文提出了对称金属包覆波导结构的光生化传感器。在该传感器中,待测样本被注入夹在两个金属薄膜层之间的样品腔中,两层金属膜和夹在其间的待测样本组成了对称金属包覆波导结构。通过观察该波导结构耦合或传输特性的变化,来探知待测样本折射率的微小变化,并进而得出样本浓度变化的信息。本文同时对该传感器的灵敏度进行了详细的理论分析。通过对现有的传感器的灵敏度的分析和比较,发现本文提出的传感器灵敏度要远远高于现有的表面等离子共振型传感器和泄漏模波导传感器。在分析的基础上,文中还给出了带来这一灵敏度提升的理论解释:入射光能量集中于待测样本层中,很小的有效折射率以及很窄的高阶导模吸收峰,这三个因素的综合使得对称金属包覆波导传感器的灵敏度较现有技术有了明显的提升。为了验证该传感器的性能,本文还通过角度调制法和强度调制法,分别设计了不同的实验方案进行实验验证。两种方法下的实验结果都一致证实了其角度调制法的探测灵敏度要优于现有的光生化传感器结构一到两个数量级;其强度调制法的探测灵敏度则更高。另外,本文还对影响该传感器灵敏度和分辨率的几个关键因素进行了分析。本文通过翔实的理论分析和实验表明,文中提出的基于对称金属包覆波导的光生化传感器具有简单的结构和极高的灵敏度,其在临床医疗、生化基础研究环境和食品检测以及现代工业等诸多领域中具有很高的应用价值。更多还原

【Abstract】 Optical biosensor is a general term for a wide range of device that measures the presence or concentration of biological molecules, biological structures, microorganisms etc., by translating a biochemical interaction into a quantifiable optical signal. The potential application fields of biosensors are very extensive, including medical and health care, biological research, chemical industries, drug development, food and water examine, environment monitoring and protection, etc.The rapid developments of integrated optics and waveguide technologies have boosted the research on optical biosensors. Evolved from the ABBE refractometer, biosensors based on surface plasmon resonance (SPR) and the leaky mode waveguide (LW) have attracted a lot of interest for the simple structure and relatively high sensitivity over previous technologies. Recently, the presence of reverse asymmetric leaky waveguide sensor has further improved the sensitivity. But still, as the technologies evolving, application demands for higher sensitivity have never stopped.By employing the theory on dielectric optical waveguide, characteristics of the symmetric metal-clad optical waveguide (SMCW) have been analyzed in this thesis. This kind of waveguide consists of two metal films and a guiding layer in between. The upper metal film is relatively thin to be around 40nm, the incident light will go through it to be coupled into the waveguide structure. On the contrary, the base metal film is usually thicker to block the light from leaking into the substrates. The dielectric media between the two metal films acts as the guiding layer, the guided light wave is confined to propagate in it.As the real part of the dielectric constants of the metal films is negative, the refractive index, RI, of the guiding layer can be very small. Besides, in the SMCW structure, the thickness of the guiding layer can be enlarged to submillimeter scale and can contain ultrahigh order guided modes with mode index of over 1000. The effective RI of those ultrahigh order modes is very small (near 0), and is extremely sensitive to the RI of the guiding layer. These ultrahigh order modes also behave polarization independence and can be excited thorough free coupling technology.These unique features enable us to fabricate an extremely sensitive biosensor based on the SMCW structure. By putting liquid or even gas samples (with small RI as low as to 1) in the sample cell sealed between two metal films, a typical three layer SMCW sensor is presented. The sample works as the guiding layer. By monitoring the coupling properties of the SMCW sensor structure, minute changes in the sample RI can be captured, and thus to identify sample property changes.Based on the theoretical analysis, sensitivity comparison of the proposed sensor with SPR sensor and LW sensor is conducted. The comparisons show that there is a huge sensitivity improvement of the proposed sensor over previous ones. The concentration of incident energy in the sample layer, the small effective RI and the narrow resonance dip of ultrahigh order modes, all the three factors contribute to the sensitivity enhancement of SMCW sensor.To verify the performance of the proposed SMCW sensor, two SMCW sensors with different coupling methods are fabricated (one with prism coupling, the other with free space coupling). Experiments are carried out using angular interrogation and intensity interrogation, respectively, to test the sensor’s performance. The results reveal that by using angular interrogation, the sensitivity of proposed SMCW sensor is 1 to 2 orders to the magnitude higher than the previous sensor structure. What’s more, by using the intensity interrogation, the sensitivity enhancement is even larger. The causes that have influence on the sensor’s sensitivity and performance are also analyzed in the thesis.Based on the solid theoretical analysis and experimental proof, the SMCW proposed in this thesis is of profound potential in future applications for its extremely high sensitivity and simple configuration.更多还原