Journal of lightwave technology, Vol. 29, No. 4, February 15, 2011.Abstract — We discuss the generation, wavelength-division-multiplexed (WDM) long-haul transmission, and coherent detection of 224-Gb/s polarization-division-multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) at a line rate of 28 Gbaud. We measure a required optical signal-to-noise ratio of 23.4 dB
(0.1-nm reference bandwidth; 10^-3 bit-error ratio), 3.4-dB off the theoretical limit. Using ultra-large-area fiber, we achieve 2000-km single-channel transmission. We also demonstrate 1200-km WDM transmission on a 50-GHz grid (4-b/s/Hz spectral efficiency),including three passes through a wavelength-selective switch.Index Terms — Coherent detection, optical networking, quadrature amplitude modulation (QAM), wavelength-division multiplexing (WDM), transmission, 100 G Ethernet.
