Optimized signal constellations for ultra-high-speed optical transport

The joint optimization of coding and modulation formats would provide significant receiver sensitivity improvement due to the increased Hamming distance of codes. By applying Arimoto-Blahut algorithm to maximize mutual information, optimized coded-modulation has been found out together with optimized bit-mapping rule. Simulated channel capacity shows that optimized coded modulation could outperform its counterparts, such as regular qaudrature-amplitude modulation, by around 0.3dB up to about 0.9 coding rate. The improvement is found to be larger in higher modulation formats. Optimal coded-8QAM modulation has been further verified in experiment, where 40Tb/s over 6787km is demonstrated by transmitting 200G per wavelength thanks to the better receiver sensitivity of optimal coded modulation.