Recent progress in amplified undersea systems

The advent of the optical amplifiers has removed the loss limitation of the fiber in the conventional undersea systems using 3R (retiming, reshaping, regenerating) repeaters, and it has introduced new design criteria for the undersea lightwave systems. The accumulation of the small impairment factors that was negligible in the conventional system becomes significant to determine the transmission performances of the amplified system. The fiber nonlinearity is a distinctive limitation factor that dominates the transmission performance of the amplified system, although it was not a limitation factor in the conventional system. This paper describes the recent progress of the undersea lightwave cable systems employing optical amplifier repeaters. The limitation factors and the polarization dependent characteristics of the amplified system are described. The system demonstrations with conventional IM-DD technology are presented using both recirculating loop and straight fiber transmission line. The system maintenance method is also explained briefly. Future technologies adopting the WDM or the optical solitons are also discussed