Constellation Expansion for 100G Transmission

In this letter, we focus on coherently detected, non differentially encoded, polarisation division multiplexed 100G communication systems; through incorporating phase noise in the channel model, we assess the net coding gain achievable by various constellations that can be used in lieu of the conventional quadrature phase-shift keying (QPSK). Whereas the optical community put much effort into the optimization of the forward error correction codes for QPSK, trying to reduce the gap to the Shannon limit, we show that a potential gain of more than 2 dB is still available if different constellations are adopted.