279 km, 591 Mb/s direct detection transmission experiment usingfour in-line semiconductor optical amplifiers

The authors realized a direct detection intensity-modulation system experiment with four cascaded in-line semiconductor optical amplifiers. Using optical isolators between the amplifiers, they transmitted a NRZ 2²³-1 message over a distance of 279 km at a bit rate of 591.2 Mb/s. A comparison of this result with parallel experiments without optical isolators indicates that for a realistic implementation of long distance systems with semiconductor optical amplifiers, interamplifier optical isolators will be needed unless the residual facet reflectivity of the optical amplifiers is brought to a very low value (<1×10^-4)