Silicon Photonics: Fundamentals and Devices

13.9 Materials Systems for Waveguide Formation

Earlier chapters of this volume described the general principle of guiding light in a planar structure, and the earlier sections of the present chapter discussed the techniques used in forming planar waveguides and Bragg gratings. The basic requirement for having light guiding is to introduce a RI variation along one or two directions. Different techniques employed to bring about the changes have been outlined there. The other characteristics of the waveguide, that is, loss and various sources contributing to it, have been mentioned. The treatment in the earlier sections is general and applicable to most of the optical integrated circuits (OICs), irrespective of the substrate, be it LiNbO₃, III–V compounds, or Si.

In the present section, we shall consider waveguiding light in structures grown with Si as the substrate. After giving a general survey of the various methods, we shall consider specific materials systems consisting of Si and related materials that guide light. Then, the methods of fabrication of the waveguides will be introduced. The chapter is concluded by presenting a comparative study of the systems considered.

13.9.1 General Considerations

The structures considered in this section are thin or epitaxial layers grown on silicon substrates. Furthermore, the thin layers that serve as the guide and are considered in this work are all derived from silicon. It may be mentioned that layers of III–V compound semiconductors have ...