中红外硅基超波导传感器的研究

Silicon has been the material of choice of the photonics industry over the last decade due to its easy integration with silicon electronics as well as its optical transparency in the near-infrared telecom wavelengths. Besides these, it has very high refractive index, and also a broad optical transparency window over the entire mid-infrared till about 8micron. It has been intensively studied during last decade. Mid-infrared is often referred to as the “molecule fingerprint region”, since many molecules have uniquely identifiable absorption spectra within this wavelength range. However, silicon photonics in mid-infrared is still in its infancy. Some works in this area are based on the traditional designs which have the limited light-matter interaction. Hence how to improve light-matter interaction without introducing extra loss becomes a great scientific problem. In order to solve this problem, we propose to use an all silicon based meta-waveguide structure to enhance mode overlap with outside matters. The relation between parameters of this structure and the mode distribution, especially along the propagation direction, will be studied thoroughly, which determines the integral mode overlap with outside materials and the sensitivity of a sensor, to design a structure with strong light-matter interaction without paying for high loss. We will also explore the meta-waveguide based novel devices, such as resonators, to further improve light-matter interaction. Based on that we will design a chemical sensor to detect a representative chemical using the characteristic absorption peaks in this region. The solutions and devices we will develop in our research will be very useful for people to realize an integrated photonic circuit with enhanced light-matter interaction in the future.

硅基光子学因为具有成熟的微加工工艺，极强的集成能力，以及与微电子器件良好的兼容性的先天优势，被视为理想的集成光学平台，在过去的十年中得到了长足的发展。当前的硅基器件研究还主要集中于通信波段，在号称“分子指纹”区域的中红外波段，相关的研究还很少。仅有的一些研究也大多基于传统设计，存在光与物质相互作用不足的缺点，无法充分发挥这一波段的优势。在此背景下，如何增强光与物质的相互作用，在保持器件小型化的前提下提高器件的灵敏度，就成为了一个重大的科学问题。本项目将紧密围绕这一重大科学问题，拟在中红外硅基平台上引入全介电材料的超波导设计，对超波导的各项参数与传播模式的空间分布之间的关系进行研究，并以超波导为基础探索一些新型的器件，如谐振腔等，来达到增强光与物质相互作用的目的。在此基础上，发挥中红外分子特征吸收峰强且全的优势，研究基于特征吸收谱检测的超波导传感器，并对本波段的代表性化学物质进行检测。

硅基光子器件具有材料损耗低、制造技术成熟、折射率高等优点，是未来集成器件的发展方向。当前硅基光子学的主要研究领域集中在近红外的通信波段。与之相比，中红外硅光子学目前仍处于起步阶段。中红外(波长从2-20微米)波段（包含3–5微米和8–12微米的两个大气窗口）具有许多重要的应用潜力，包括吸收光谱，热成像和自由空间光通信等。基于分子吸收光谱的痕量气体检测在民用和军事领域有着广泛的应用。众所周知，中红外区域被称为“分子指纹”区域，涵盖了几乎所有化学键的基本振动信号。通过检测这些振动信号，可以对待测物质有定性和定量的分析，相比于其他依赖于检测折射率变化的方法，该检测方法具有压倒性优势。尽管分子振动特征的泛音延伸到了近红外和可见波长域，也可以通过发达的吸收光谱技术来检测，但是相较中红外波段的化学吸收截面要小几个数量级，限制了检测的灵敏度。.本项目主要对中红外,尤其是3-5微米波段的集成光子器件展开研究。通过引入亚波长周期性结构来构建超波导，使得其具有低传输损耗和高待测物交叠积分的性质，更加适合气体检测的应用。在3.35至3.45微米波段，我们设计了空气上包层的低损耗超波导，通过设计波导的高度，宽度，占空比和周期，实现了对TM偏振传输光高达38％的高重叠因子。在此基础上，我们也通过使用悬浮式复合超波导结构——蜈蚣型波导，实现了从1.5至6微米波长范围内的传输，充分利用硅材料的透明窗口，拓展了超波导的光学带宽。同时，该波导保持了很强的光-物质相互作用，约34%的传播能量位于空气中，可以与测试物充分作用。除此之外，我们还设计了两种复合型传感器：基于游标效应的跑道型超波导微环结构和基于高阶奇异点的传感器，分别展示了达到1240nm/RIU的灵敏度和对微小变化高达100倍的灵敏度增强。我们的研究成果为进一步提升片上光学传感器性能提供了一种新途径，推动了集成光学器件走向最终的应用。