Fig. 6: Experimental results of 16λ × 903.2-Gb/s/λ wavelength-division-multiplexed (WDM) transmission enabled by residual carrier modulation.
From: Overcoming laser phase noise for low-cost coherent optical communication
The modulation format is probabilistic-shaped 256-ary quadrature amplitude-modulation (PS-256-QAM) with an entropy of 12.82 bits/4D-symbol. a The measured normalized generalized mutual information (NGMI) as a function of different launch power per channel at the 9th channel. The linewidth of signal and lasers are both 100 kHz or 1 MHz. Tx transmitter, Rx receiver. b The recovered constellations at the optimum launch power for transceiver lasers with different linewidths. c The measured optical spectrum of the transmitted 16-channel WDM signal with a 0.02 nm resolution. d The measured NGMI for all 16 channels. The results are well above the NGMI limit of 0.857.
