Dual-Carrier-Paired Point-to-Multipoint Transmission Over ROADM Systems: Frequency-Polarization Coding and Frequency Collaborative Control

In dual-carrier (DC)-paired fiber optic long-reach transmission, which extends a point-to-multipoint coherent system to a cascaded reconfigurable optical add-drop multiplexing (ROADM) system, a narrow passband causes severe performance degradation of the edge subcarriers. In this study, we proposed two-dimensional frequency and polarization domain coding and multicarrier-frequency control for cascaded ROADM filtering of robust multicarrier transmissions at a single wavelength. The proposed coding scheme reduced fiber nonlinearity, polarization-dependent loss (PDL), and passband narrowing (PBN) simultaneously. The multicarrier frequency control algorithm, which feeds back the received signal quality at multiple points, reduced PBN owing to long-term laser frequency drifts. With the proposed coding, the Q value of 56 Gbit&#x002F;s &#x00D7; DC-paired dual-polarized (DP)-4QAM and 112 Gbit&#x002F;s &#x00D7; DC-paired DP-16QAM signals improved by 1 dB and 0.2 dB, respectively, compared to that when no coding was used. Furthermore, the long-term frequency control emulated through the emulation model of laser frequency drifts and the performance degradation of average Q value were less than 0.4 dB and 0.1 dB, respectively. To the best of our knowledge, no other study has evaluated point-to-multipoint transmission over ROADM-induced optical filtering systems that apply frequency and polarization domain coding and multicarrier frequency control for DC-paired DP-<italic>M</italic>-QAM signals. The proposed methods enable stable operation while suppressing the effects of PDL and PBN, which are problems in multicarrier transmission, in long-reach optical fiber transmission systems that integrate access and metro networks.