Silicon hybrids for better optics and electronics
Photonic networks (those relying on the passing of light) are widely used in telecommunications, electronics and many emerging technologies. A key priority in these areas is the demand for greater functionality in ever-smaller devices. This means that optical components must be able to combine increasing complexity and compactness. Lowering costs of production is another over-riding concern in these highly competitive markets. A group of European researchers collaborated on the project 'Merger of electronics and photonics using silicon based technologies' (Mephisto) to help meet these requirements. During the four-year project which ended in 2008, they developed new silicon-on-insulator (SOI) hybrid integration platform concepts that can cover optical, optoelectronic and electronic functions. SOI is suitable for these types of applications as it can accommodate optical waveguides and related devices of widely varying dimensions and it is suitable for use with high-speed electro-optical modulators. Another advantage is compatibility with complementary metal-oxide-semiconductor (CMOS) technologies widely used in integrated circuits. The work continued the rapid progress made in recent years in using compound semiconductors for telecommunication applications. These materials enable active and passive optical functions for components and electronic devices - compared to traditional 'monolithic' approaches which use one common material for different devices to be integrated. With hybrid integration, different device chips are attached to an optical waveguide board using micro- and nano-assembly techniques, combining different material technologies to optimise performance and versatility. The project team created and demonstrated a new distributed feedback (DFB) laser structure using these material technologies that achieved lower device costs and easier mounting possibilities. Their design offers several advantages over conventional approaches including low beam divergence, high slope efficiency, high single mode yield, high stability and superior feedback sensitivity. The laser system has been granted European and German patents and is being used in various research and development projects. Project coordinator the Henrich Hertz Institut (HHI) in Munich, Germany is using the Mephisto device as its preferred laser source for polymer PLC based hybrid integration technology. Project partners Freescale also developed 10Gb/s laser driver circuits based on low impedience silicon-germanium (SiGe ) BICMOS integrated circuit technologies. This innovation has the potential for future commercial exploitation. The project has enhanced the cost-effectiveness of SOI products and proved their viability, opening up their adoption by new customers and applications.
