Training symbol based channel estimation for ultrafast polarization demultiplexing in coherent single-carrier transmission systems with M-QAM constellations

We propose a training symbol based algorithm that estimates the Jones channel matrix whose entries are used as the initial center taps of a decision-directed butterfly equalizer. With fewer than 40 training symbols, we experimentally demonstrate ultrafast polarization demultiplexing for 112 Gbps PDM-QPSK and 224 Gbps PDM-16QAM systems.