The upper limit of the efficiency, Stark and Mitra calculate, is about 3 bits of information per Hertz (the unit of wavelength) per second. Coupled with theoretical maximum bandwidth of a fibre, this means that the ultimate optical fibre could carry approximately 150 terabits of information each second - the equivalent of nearly two billion telephone calls at once. At the moment, commercial networks operate at about 1.6 terabits per second.
