XPM Model-Based Digital Backpropagation for Subcarrier-Multiplexing Systems

An advanced digital backpropagation (ADBP) algorithm is proposed to compensate fiber nonlinearities in subcarrier-multiplexing (SCM) systems. We derive the analytical expression and describe the implementation of the ADBP. In addition, the computational complexity of the ADBP as well as the conventional low-pass-filter-assisted DBP (LDBP) is analyzed and compared. In a 34.94 Gbaud/s single channel SCM transmission experiment, we demonstrate that the proposed ADBP with only two steps (40 spans/step for QPSK at 6400 km and 16 spans/step for 16 QAM at 2560 km) has a comparable performance to the LDBP algorithm with 40 steps (2 spans/step) for QPSK and 8 steps (4 spans/step) for 16 QAM, respectively. Moreover, compared to single carrier (SC) systems using only linear compensation (LC), the ADBP algorithm with 40 spans/step for QPSK and 16 spans/step for 16 QAM can extend the maximum reach by 49.7% and 27.3% for the two formats, respectively. The contribution to the reach extension consists of 19.7% and 23.6% which are attributable to the nonlinear compensation algorithm when compared to SCM systems using LC for QPSK and 16 QAM, respectively. The remainder of the improvements is attributable to the use of the SCM scheme. Finally, simulations of 60 Gbaud/s systems show additional improvements using the ADBP schemes compared to the LDBP schemes, indicating the benefits of ADBP in future high capacity optical transmission systems.