<P>This book covers the basics of band structure of silicon and germanium and their influence on photonic properties and discusses system layout and key device components with the application background in mind. Special focus is given to SOI-based interconnects and passive waveguide devices and to germanium-on-silicon heterostructure devices for light detection, modulation, and emission. The high index contrast of SOI shows great promise for submicron waveguide structures suited to integration on chip scale. The Ge/Si heterostructures have already proved the expansion of the spectral range, high-speed operation of detection, efficient modulation and switching of optical signals, and enhanced emission properties. In the research focus are chip systems with more than 100 GHz speed. The book also contains an overview of the technological and material science challenges associated with the integration on Si.</P>