Unrepeatered 256 Gb/s PM-16QAM transmission over up to 304 km with simple system configurations

We study unrepeatered transmission of 40x256 Gb/s systems with polarization-multiplexed 16-quadrature amplitude modulation (PM-16QAM) channels using simple coherent optical system configurations. Three systems are investigated with either a homogeneous fiber span, or simple two-segment hybrid fiber designs. Each system relies primarily on ultra-low loss, very large effective area fiber, while making use of only first-order backward pumped Raman amplification and no remote optically pumped amplifier (ROPA). For the longest span studied, we demonstrate unrepeatered 256 Gb/s transmission over 304 km with the additional aid of nonlinear compensation using digital backpropagation. We find an average performance improvement in terms of the Q-factor of 0.45 dB by using digital backpropagation compared to the case of using chromatic dispersion compensation alone for an unrepeatered span system. (C)2014 Optical Society of America