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

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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.