Generation and detection of QAM in digital coherent systems

We summarize several novel schemes to generate multilevel modulation formats for high capacity transmission system with high spectral efficiency. We show that multilevel 8QAM, 16QAM, 32QAM and 64QAM optical signals can be generated by commercial optical and electrical devices. We also show new algorithm to improve the performance of blind polarization de-multiplexing in the intra-dyne receiver. Ultra-high-capacity optical transmission experiment of 64Tb/s over 320km at SE=8b/s/Hz has been demonstrated by high-level QAM signals.