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

硅基光子器件是一种微米级、高折射率的光子器件，可与电子控制电路集成在超大规模集成电路（VLSI）芯片上。这种器件由于其低功耗、小特征尺寸和大规模生产时的低成本而有望在光通信行业中流行。这些设备对于生物学家和医生来说也很有吸引力，因为它们可以在微米尺寸的芯片上开发具有复杂功能的诊断实验室。TeraXion公司正在研制的超窄线宽微激光器是绝缘体上硅平台上的关键器件之一，它将使硅光子器件得到广泛的应用。这种激光器需要超高品质因数（即超过一亿）的微腔用于反馈控制。由于硅的相对高的材料损耗和使用当前制造技术的粗糙波导边缘的组合限制，超过数万个的微腔尚未被证明。另一方面，在硅基硅晶片上制造的硅微Troids，可以在Lu教授的小组中获得，其品质因数高达5亿。因此，我们建议研究通过混合集成技术将微型环形线圈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品质因数的硅微环，并在绝缘体上硅芯片上设计了一种高效的光耦合结构。然后我们将微型环形线圈转移到绝缘体上硅。一旦证明可行，这种技术可以为我们提供一种新的方法，在SOI平台上添加具有5亿Q的超高品质因数微腔。 这不仅将解决TeraXion在开发超窄线宽激光器方面面临的问题，还将在硅光子器件上开辟一系列新的应用，例如芯片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.