Ultralong single-span lines with remote pumping of optical amplifiers

Methods for estimation of the maximum transmission length of the DWDM signals in single-span lines with different configurations are proposed. A transponder that works at a bit rate of 100 Gb/s using the dual-polarization quadrature phase-shift keying (DP-QPSK) is used as an example to present the maximum lengths of the single-span lines with different configurations. The estimations are used to experimentally demonstrate that a transceiver with the above modulation and coherent detection and soft-decision forward error correction (SoftFEC) and an ultralow-loss fiber make it possible to reach a transmission length of greater than 500 km for the DWDM signals at a channel bit rate of 100 Gb/s.