Multidimensional Constellations for Power-Efficient and Flexible Optical Networks

Multidimensional constellations and time domain hybrid QAM both realize a non-integer ratio of bits per complex 2D symbol in order to allow for flexibility of spectral efficiency. We compare both approaches in terms of symbol error probability, asymptotic power efficiency, and bit error probability. In order to achieve 400G transmission, as an example for a non-integer ratio, an average number of 3.33 bits per complex 2D symbol was chosen, resulting in a symbol rate of 67.2 GBd including 12% FEC overhead. We show a 0.34-dB gain of multidimensional 16-QAM modulation over a hybrid 8-QAM/16-QAM scheme in terms of asymptotic power efficiency.