As the performance of microprocessors continues to improve, the data flow to and from the processors becomes an increasingly predominant bottleneck for the overall system performance. The situation is quite comparable to an expanding city where the traffic infrastructure is not growing at the same rate as the traffic. Main bottlenecks are the pins and pads of processor packages, long (i.e. off-card) and dense high-speed copper lines, and the connectors at the card edges. Optical data transmission has successfully replaced electronic data transmission in most link classes exceeding 10 meters, profiting from a 100,000 times higher carrier frequency, thus avoiding many of the limitations of electrical interconnects. The most important advantages and promises of optics in this context are a higher bandwidth × length product, higher density, plus potential cost and power savings for cases when repeaters can be avoided. In view of the historical technology progress and the projected link performance requirements, it is safe to predict that optics will also be used for "intra-box" data communication in the future.
At IBM Research, optical solutions for intra-system optical interconnects have been studied, evaluated and developed for several years (see Publications). Our activities aim to provide a generic technology platform for a wide range of applications. Individual building blocks of such a technology platform are illustrated in Figure 1. They range from system and link architecture to CMOS I/O circuitry and optoelectronic packages to the optical channel and optical interfaces. At the Zurich Research Lab, a multidisciplinary effort covers many of these building blocks.
The optics-related work of the I/O Link Technology group is focused on
- system-level opportunities for optical links,
- overall chip-to-chip link architecture,
- CMOS driver and TIA designs with maximum speed at minimal area and power consumption, and
- the interface between the electrical and the optical domain (opto-electronic packaging).
Work pursued by the Photonics team is focused on the interface between the electrical and the optical domain (opto-electronic packaging), the development of integrated optical polymer waveguides, and optical connectors. A passive alignment concept was developed that enables low-cost assembly of the optical and opto-electronic elements on the printed circuit board.
Jointly, the two groups realized a series of system-level demonstrators of increasing complexity. One goal of these demonstrators has been to gain practical experience with the integration of all the involved building blocks to a complete optical interconnect system, and to balance the numerous aspect of this multidisciplinary endeavor. See the downloadable overview presentation (right) for additional information.
Our efforts are performed in collaboration with various internal and external partners such as the IBM Research Labs in the US and in Japan, Varioprint AG (printed circuit board technology), Intexys Photonics (opto-electronic packages) and Rohm & Haas (waveguide material).