The four generations of fiber-optic systems

The first generations of fiber-optic systems - the ones in widest use today-are digital systems using multimode fibers and either light-emitting diodes or laser diodes of gallium arsenide (GaAs), a binary material, or aluminum gallium arsenide (AlGaAs), a ternary material. Such systems operate at a wayelength of 0.8 or 0.9 micrometer and are well suited to short-distance communications. However, they have fundamental limits to the distance a signal can travel and to their information-carrying capacity.