Feasibility investigation on silica microtoroid integration on silicon-on-insulator platform

建立在绝缘体上硅晶圆上的硅光子器件是一种微米级、高折射率的对比光子器件，真正实现了与超大规模集成（VLSI）芯片上电子控制电路的集成。这种器件具有功耗低、特征尺寸小、批量生产成本低等优点，有望在光通信行业占据主导地位。生物学家和医生也对这些设备感兴趣，因为它们可以在微米大小的芯片上开发具有复杂功能的诊断实验室。目前正在开发的超窄微激光器TeraXion是导致硅光子器件广泛应用的绝缘体上硅平台的关键部件之一。这种激光器需要一个超高质量因子（即超过一亿）的微腔进行反馈控制。由于目前的制造技术存在硅材料损耗相对较高和波导边缘粗糙的综合限制，超过数万个的微腔尚未被证明。另一方面，卢教授的团队已经证明，建立在硅上硅晶片上的硅微晶片具有高达5亿的质量因子。因此，我们建议研究通过混合集成技术将微环面转移到绝缘体上硅芯片的可行性。为了实现这一目标，我们首先制造了超高质量因子二氧化硅微环，并在绝缘体上的硅芯片上设计了一种高效的光耦合结构。然后我们把微环形转移到绝缘体上的硅上。一旦被证明是可行的，这种技术可以为我们提供一种新的方法，在SOI平台上添加5亿Q的超高品质因子微腔。这不仅将解决TeraXion在开发超窄线宽激光器时面临的问题，还将在硅光子器件上开辟一系列新的应用，如芯片上的实验室单分子传感器，其中超高Q微腔是必须的。

Silicon photonic devices built on silicon-on-insulator wafer are micron scale, high refractive index contrast photonic devices truly integrable with electronic control circuits on a very-large-scale integration (VLSI) chip. Such devices are promised to prevail in the optical communication industry for their low power consumption, small feature size, and low cost upon mass production. These devices are also attractive to biologists and doctors for developing a diagnosis lab with complex functions on a micron sized chip. One of the critical components on silicon-on-insulator platform that leads to wide applications of silicon photonic devices is the ultra-narrow microlaser TeraXion is currently developing. Such a laser requires an ultra-high quality factor (i.e. exceeding one hundred million) microcavity for feedback control. Due to the combined limitation of relatively high material loss of silicon and rough waveguide edges using current fabrication technology, microcavities exceeding more than several tens of thousands have not yet been demonstrated. On the other hand, silica microtroids built on a silica-on-silicon wafer and available at Prof. Lu's group have a quality factor as high as five hundred million, as has been demonstrated. Therefore, we propose to study the feasibility of transferring a microtoroid to silicon-on-insulator chip through hybrid integration techniques. To achieve this, we first fabricate the ultra-high quality factor silica microtoroid and design an efficient light coupling structure on a silion-on-insulator chip. We then transfer the microtoroid to the silicon-on-insulator. Once proven feasible, such technology can provide us with a new approach for adding an ultra-high quality factor microcavity with 500 million Q onto a SOI platform. This will not only solve the problem TeraXion is facing on developing their ultra-narrow linewidth laser, it will also open a series of new applications on silicon photonic devices such as a lab-on-a-chip single molecule sensor, where an ultra-high Q microcavity is a must.