Skewless multimode fiber parallel optical interconnection for the parallel processor RWC-1

A calibration-free 64-Gbps/board parallel optical interconnection subsystem was mounted directly on the 4-CPU processor board of the optically connected parallel-processing machine RWC-1/ON (Real World Computer-i, Optical- interconnection-NEC version). The subsystem was composed of eight pairs of an array optical transceiver module and aone-chip link LSI. Even though it used multimode fiber parallel optical modules, parallel data could be transmitted over 1km because of the de-skewing and synchronization action of the link LSI.Keywords: optical interconnection, array, parallel, computer, skew, multimode fiber 1. INTRODUCTION Optical interconnections are in high demand for connecting nodes of parallel processors because high-speed and high-capacity electrical interconnections suffer from various problems (Fig. 1). Inside the ISIs, these problems are (a) highpower consumption, (b) simultaneous on/off of the output line driver block, and (c) restricted number of pins. At the boardlevel, problems are (d) cross-talk, (e) electromagnetic interference, and (f) degradation of the high-speed signal linewaveform. At the inter-board level, problems are (f) waveform degradation, (g) skew, (h) ground-level discontinuity, and( i) large and heavy connectors and cable&5. Some parallel machines used optical interconnection to solve these problems6.However, some problems still remain even when optical interconnections are used.Calibration is necessary for the link length to synchronize the data and the clock at each node. Optical interconnections arenot compact enough to mount on the processor board. So many electrical connections between the processor board andoptical interconnection board will still be needed even when optical interconnections are used. Special skills are needed tohandle optical interconnection, i.e. the system designers must learn about the characteristics of opto-electronic devices (LD5and PDs), fibers, and high-speed analog signals. The biggest problem, however, may be cost.