Channel Impairment-Insensitive Monitoring of Multi-Dimensional Transceiver Imbalance for Dual-Polarization Coherent DSCM System

In digital subcarrier multiplexing (DSCM) systems, imperfections in transceiver hardware lead to mismatches between the in-phase (I) and quadrature (Q) components of the signal, causing inter-subcarrier interference and significantly degrading overall system performance. This paper proposes a channel impairment-insensitive scheme for online monitoring of multi-dimensional transceiver impairments tailored for dual-polarization coherent DSCM systems. The proposed scheme enables simultaneous and comprehensive monitoring of transceiver impairments originating from both the transmitter and receiver, including amplitude imbalance, phase imbalance, and skew between the I and Q components, as well as amplitude imbalance and skew between the X and Y polarizations. The key aspect of the monitoring scheme is the insertion of frequency-domain pilot tones (FPTs) into the guard bands between adjacent subcarriers of the I and Q components of the transmitter signals. The inserted FPTs in each branch are extracted using low-pass filters for comprehensive multi-dimensional monitoring of transceiver imbalances. Unlike conventional techniques relying on intricate DSP algorithms to sequentially compensate for individual impairments, our proposed scheme exhibits remarkable resilience against channel impairments. By utilizing FPTs, the scheme effectively mitigates the influences of chromatic dispersion, polarization variations, and carrier phase noise, enabling transceiver impairment monitoring without the need for DSP algorithms to compensate for channel impairments. Furthermore, the scheme enables the decoupling of impairments between the transmitter and receiver, as well as the separation of impairments within each. The effectiveness of the proposed scheme is validated through experiments conducted on a 48 Gbaud (12 Gbaud/SC) dual-polarization 16QAM DSCM system. The experimental results demonstrate that the proposed scheme achieves accurate and wide-range estimation for multi-dimensional transceiver impairments. Notably, even in scenarios with coexisting transceiver and link impairments, the scheme achieves simultaneous and precise estimation of each transceiver impairment.