Figure 3

The optical spectrum and the constellation diagrams. (a) The optical spectrum after wavelength division multiplexing at the transmitter. (b) The constellation diagrams of the transmitted signals based on 100 Gbit/s PM-QPSK, 200 Gbit/s PM-16QAM, 200 Gbit/s PM-QPSK, and 400 Gbit/s PM-16QAM modulation, respectively.