Fibernet: Multimode Optical Fibers for Local Computer Networks

Local computer networks which communicate over copper conductors have been developed both to promote resource sharing and provide increased performance. Such networks typically operate at bandwidth-length (
Bw \circ L
) products up to a few
MHz \circ km
. In this paper we consider the use of fiber optics in such networks, and give a status report on a star-configured fiber optic network experiment called Fibernet which operates at a
Bw \circ L
product of
\sim 100 MHz\circ km
at a data rate of 150 Mbits/s and which in its final phases will connect up to 19 stations. We compare the merits and problems of linear, ring and several star configurations, and of active versus passive networks. The packet communication protocol is discussed and network efficiency is calculated as a function of the packet length, channel capacity and network propagation time. We describe the system performance of the present Fibernet experiment, which uses a 19-port transmissive star coupler, GaAIAs injection lasers and avalanche photodiodes, and incorporates bi-phase data encoding. Power distribution inhomogeneities, observed in the output of the transmissive star coupler's mixer rod, are explained geometric-optically.