二维环形光子晶体的敏感能带特性及生物传感应用研究

To satisfy the detection requirements of tiny and ultramicro biological molecules, extensive attention has been paid by scholars both at home and abroad to developing new biosensing technologies based on the photonic band gap and localized enhancement effects in two-dimensional photonic crystals. Since the structure of unit cell in current widely used two-dimensional photonic crystals is composed of simple air holes, this may restrict the improvement of sensing performance of two-dimensional photonic crystals due to relatively low shifting sensitivity of photonic band gaps and resonant peaks as the refractive index of ambient changes. In the present project, we will carry out the study of biosensing technologies based on a new type of structure, i.e., two-dimensional photonic crystal slabs with annular unit cell. The working mechanisms and corresponding adjusting rules of such annular structure in improving the sensing properties of two-dimensional photonic crystals will be investigated. Particularly, considering different structures and refractive indexes of ambient, we will study the sensitive band properties of two-dimensional annular photonic crystal waveguides and microcavities by using the plane wave expansion and the finite difference time domain methods. The detailed studies include analyzing the properties of band gaps and defect modes when different lattice types, filling factors of the annular unit cell, and defect structures are considered, as well as exploring the sensing properties when filling materials with different refractive indexes are used. Furthermore, we will fabricate high-precision samples of two-dimensional annular photonic crystals on SOI materials by employing the electron beam lithography (EBL) and inductively coupled plasma (ICP) etching techniques. The sensing parameters of these samples for the solution, such as sensitivity and detection limit will also be verified by using the wavelength scanning approach. It is believed that the present project can provide new theoretical basis and technical support for the improvement of sensing performance of two-dimensional photonic crystals.

为满足超微量生物小分子的探测应用需求，利用二维光子晶体的光子禁带和局域化增强效应来发展新型生物传感技术引起了国内外学者的广泛关注。目前普遍采用的二维光子晶体为单一空气孔单元结构，光子带隙和缺陷谐振峰对折射率变化的移动灵敏度较低，制约了传感性能的提高。本项目围绕一种新型的二维环形光子晶体平板来开展生物传感技术研究，采用平面波展开法和时域有限差分法研究二维环形光子晶体波导和微腔在结构变化以及环境折射率变化时的敏感能带特性，即在不同晶格类型﹑环形单元填充率和缺陷结构条件下对应的带隙和缺陷模特性，以及在不同折射率材料填充时的能带变化特性，探寻环形结构在提高二维光子晶体传感性能上的作用机理和调节规律，通过进一步采用光刻和离子束刻蚀技术基于SOI材料制备出高精度的二维环形光子晶体样品，以及采用波长扫描法验证其对溶液的传感灵敏度和探测极限等参数，为提高二维光子晶体的传感性能提供新的理论依据和技术支持。

目前普遍采用的二维光子晶体为单一空气孔单元结构，光子带隙和缺陷谐振峰对折射率变化的移动灵敏度较低，制约了传感性能的提高。本项目围绕一种新型的二维环形光子晶体平板来开展生物传感技术研究，理论上采用平面波展开法和时域有限差分法探寻二维环形光子晶体传感器的工作机理和优化设计，即研究二维环形光子晶体在环形单元填充率和环境折射率变化时的敏感能带特性并设计不同的二维环形光子晶体波导和微腔生物传感器；实验上基于“自上而下”的微纳加工手段来探索高精度的二维环形光子晶体样品的制备并验证器件对溶液的传感特性。主要理论研究结果包括：（1）发现了二维环形光子晶体能够获得比普通空气孔光子晶体2到3倍的折射率传感灵敏度，这归功于空气环单元的引入后光子晶体将具有更低的上禁带边频率。与此同时，普通空气孔光子晶体的灵敏度随着折射率增加出现“饱和现象”，而二维环形光子晶体会出现“灵敏度反转”现象，即灵敏度随着折射率增加而下降，这主要是因为二维环形光子晶体的上禁带边频率会更快的靠近下禁带边频率，从而导致光子带隙的快速闭合。（2）发展了多种典型的二维环形光子晶体波导以及微腔折射率传感器模型，特别是将空气槽波导和二维环形光子晶体结合得到的传感器模型（申请了中国发明专利）同时具备高灵敏度、单模截止响应、以及大探测面积的优点，是一种应用性很强的新型生物传感器。（3）首次提出一种具有超高灵敏度的“交叉偏振式”光子晶体折射率传感器工作方式（申请了中国发明专利），其灵敏度是两种偏振波灵敏度之和，特别适用于二维环形光子晶体工作。（4）首次报道了二维环形光子晶体的双偏振慢光和自准直现象，对未来开发基于慢光和自准直波导的新型生物传感器提供了重要的理论基础。主要实验研究结果包括：（1）基于电子束曝光（EBL）和感应耦合等离子体刻蚀（ICP）技术研究了近红外及可见光波段二维环形光子晶体微腔的微纳加工工艺，制备得到了双偏振量子点发光器件（申请了中国发明专利），可用于低温条件下的生物分子探测。（2）基于聚焦离子束刻蚀（FIB）技术制备了可见光波段高质量二维环形光子晶体微腔，光致发光谱验证了其对溶液的高灵敏度传感性能。本项目的研究成果为提高二维光子晶体的传感性能提供了新的理论依据和技术支持，在超微量生物分子的探测中具有潜在应用价值。

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