Experimental demonstration of 56 Gb/s 4D-PAM-5 trellis coded modulation for 400G WDM metro-access networks

4D-PAM-5 trellis coded modulation is experimentally demonstrated and compared with PAM-4 for use in 8λ×50 Gb/s metro-access optical networks. Power sensitivity gains of up to 2 dB are shown at bit rates of 56 Gb/s.