In hierarchical computer systems, conventionally the interconnection is handled via parallel electrical busses. Although the latest high performance structures such as the JIAWG parallel interface bus (PI-bus) can operate over 58 electrical bus lines and handle total data and control rates in excess of 500 Mbits/s (when implemented at full specification), they are physically dense structures which are intrinsically unreliable. The aim of the HOLICS project is to develop optoelectronic technology to alleviate these problems, with a new approach based on board mounted optoelectronic drivers communicating directly over polymer waveguide backplanes. The main focus was to design and assemble a fully functional, high speed, EMC (electromagnetic compatability) tolerant, optically interconnected processor cluster consisting of a set of high speed processors and associated circuitry, interconnected via an optical backplane. Once validated, this cluster system was used in a complete hierarchical computer demonstrator within HOLICS.
Technically, the key development was the design and realization of optoelectronic transceivers, implemented as a multichip module assembly. They are constructed using a silicon substrate housed in an all silicon hermetic package and incorporate a number of novel features, which results in a compact low profile surface mount package. A robust, custom single chip ECL receiver was also specifically designed by ETH Zurich, providing high gain and a wide dynamic range, and capable of operating over a wide range of supply voltages and environmental conditions. These transceiver modules have exceptionally high sensitivity (-29 dBm at 500 Mbits/s for 10E9 bit error rate), low power consumption (700 mW for full transceiver mode) and very low crosstalk (equivalent to -50 dB of internal attenuation) and can replace existing electronic interconnect systems in backplane links, local board to board links and global links.