ABSTRACT
It is becoming evident to the builders of large digital routing and crossconnect systems that optical links provide the most efficient and scalable intra-system interconnect to the boards, shelves and bays of their equipment. In such systems, the interconnect technology typically represents a performance bottleneck, as electrical interconnect technologies struggle to keep pace with increasing demand for more connectivity and bandwidth. To address this, a number of parallel optical fibre interconnect modules have been developed and several have recently appeared in the marketplace (figure D4.4.1). Several system vendors of routers and crossconnects have adopted parallel optical links due to their performance (size, weight, power), their span (up to 600 m with graded-index multi-mode fibre),scalability (up to 120 Gbit s−1 in a single module) and relatively low cost when compared to alternative telecommunications optical components. In addition to the transport issue, equipment makers have transitioned from bus-based architectures to switched interconnection networks, wherein line-cards residing in a particular shelf or rack of equipment communicate with other line-cards on the same or separate shelf via a non-blocking switch. For systems that favour optical transparency at very high line rates and need relatively infrequent reconfiguration of the switch (i.e. certain optical crossconnects), all-optical switches provide a scalable alternative to electrical crossbar switches. However, for applications that require fast reconfiguration (e.g. packet switching and routing) or aggregation of multiple lower-speed lines, a scalable alternative to electrical switch technology has not yet emerged. Instead, a hybrid approach with optical links and electrical switching appears to be best suited for this application. In this paradigm, it is important to reduce the power and cost of the optical-to-electrical interface, which inevitably calls for the integration of microlasers and detectors to the electrical interface and switching circuits (figure D4.4.2). Such technology will ultimately allow low-power, high-bandwidth systems that are based on fibre and surfacenormal optical interconnects for data-transport and silicon VLSI for switching (figure D4.4.3). This chapter will focus on the key integration technologies, with an emphasis on the design and fabrication of vertical cavity surface emitting lasers (VCSELs) that are suitable for intimate integration with VLSI electronics.
