Abstract
We discuss the generation, wavelength-division-multiplexed (WDM) long-haul
transmission, and coherent detection of 112-Gb/s
polarization-division-multiplexed (PDM) 16-ary quadrature amplitude
modulation (16-QAM) at a line rate of 14 Gbaud and spectral efficiencies
beyond 4 b/s/Hz. We describe the (off-line) digital signal processing and
blind filter adaptation algorithms used in our intradyne receiver and
characterize its performance using both simulated and measured 16-QAM
waveforms. We measure a required optical signal-to-noise ratio of 20.2 dB
(0.1-nm reference bandwidth; $10^{-3}$ bit-error ratio), 3.2-dB off the theoretical limit. We study the
effects of finite analog-to-digital converter resolution, laser frequency
offset, laser phase noise, and narrowband optical filtering. Our experiments
on a 25-GHz WDM grid (4.1-b/s/Hz spectral efficiency) reveal a 1-dB penalty
after 7 passes though reconfigurable optical add/drop multiplexers (ROADMs)
and an achievable transmission reach of 1022 km of uncompensated standard
single-mode fiber. At a spectral efficiency of 6.2 b/s/Hz (16.67-GHz WDM
channel spacing) a transmission reach of 630 km is attained.
© 2010 IEEE
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