Three-dimensional geometrically shaped constellation based on regular octahedron cells for IM/DD system

A three-dimensional (3D) constellation based on geometric shaping (GS) and probabilistic shaping (PS) is proposed for an intensity modulation/direct detection (IM/DD) system. The GS of 3D constellation is based on regular octahedron cells, and combined with PS using Huffman coding, the constellation figure of merit (CFM) and bit error rate (BER) performance of 3D constellation can be significantly improved. Results demonstrate that proposed 19-ary 3D constellation achieves a 2.2 dB receiver sensitivity gain compared with traditional 16-ary 3D constellation at the BER of 3.8 x 10-3. Moreover, the probabilistically shaped 19-ary 3D constellation exhibits a BER that is reduced by around one order of magnitude compared with the non-shaped 19-ary 3D constellation for the same transmission distance. In addition, the proposed 19-ary 3D constellation exhibits superior performance in terms of transmission distance and data rate compared with traditional 16-ary 3D constellation and GS 16-ary 3D constellation.