Abstract :
Over the past 20 years, principally enabled by wavelength-division multiplexing (WDM), fiber-optic transport capacities have been growing exponentially. As a result of world-wide R&D in the optical communications field, the capacity per fiber has increased at a rate of 100 every 10 years reaching 32 Terabits/second in recent research demonstrations and several Terabits/second in commercial systems. Associated with this remarkable growth was an important reduction in the cost per transmitted bit and also in the power consumption per bit. Because the transmission capacity of optical fibers was seemingly limitless, the unabated exponential growth of demand was viewed as lucrative business opportunities by carriers, service providers, and equipment manufacturers alike. However recent information-theoretic studies have concluded that the capacity of conventional fiber optic systems is not as limitless as had been thought, and in fact that the "end" could be in sight. Scientists and engineers are now struggling to squeeze the last few doublings of capacity out of optical fibers using a variety of techniques, in particular by implementing complex modulation formats. But what then?
