Decision-directed CPR-assisted IQ imbalance-multiplexing for coherent PON downlink system with access-span length difference

Abstract In the 10 GSymbol/s/ λ coherent PON downlink system with I- and Q-axis mapping for different optical node units (ONUs), an extra power transmission happens because of the transmission difference between the ONUs. An adaptive IQ imbalance modulation with optimum IQ power loading for two ONUs is introduced at the transmitter-side digital signal processing (DSP). For scaling of the IQ power ratio setting range, DD-CPR with PADE scheme as an accurate frequency offset compensation is used at the receiver-side DSP. We numerically and experimentally show 2.8 dB power saving compared to a conventional balanced QPSK signal using the adaptive IQ imbalanced QPSK signal ( θ = π /12) in the case of the 57 km downlink transmission difference between two ONUs.

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