PDM-Nyquist-32QAM for 450-Gb/s Per-Channel WDM Transmission on the 50 GHz ITU-T Grid

We discuss the generation and transmission of 450 Gb/s wavelength-division multiplexed (WDM) channels over the standard 50 GHz ITU-T grid optical network at a net spectral efficiency of 8.4 b/s/Hz. This result is accomplished by the use of Nyquist-shaped, polarization-division-multiplexed (PDM) 32-quadrature amplitude modulation (QAM) and both pre- and post-transmission digital equalization. To overcome the limitation of available digital-to-analog converter bandwidth, a novel method is introduced for the generation of the five-subcarriers of the 450 Gb/s signal. Nearly ideal Nyquist pulse-shaping (roll-off factor = 0.01) enables guard bands of only 200 MHz between subcarriers. To mitigate the narrow optical filtering effects from the 50 GHz-grid reconfigurable optical add-drop multiplexer (ROADM), a broadband optical pulse-shaping method has been proposed and demonstrated. By combined use of electrical and optical shaping techniques, transmission of 5 × 450 Gb/s PDM-Nyquist 32 QAM on the 50 GHz grid over 800 km and one 50 GHz-grid ROADM has been successfully demonstrated.