3D Hybrid Constellation With a Regular Octahedral Structure for Few-Mode Transmission

This letter proposes a three-dimensional (3D) geometric shaping (GS) and probabilistic shaping (PS) constellation based on a regular octahedral structure in mode-division multiplexing transmission. The regular octahedron structure is adopted to improve the utilization rate of 3D space effectively and reduce the average power of the constellation. Spatial mode multiplexer/demultiplexer is used to achieve high-capacity transmission. As a result, the proposed scheme can be used to improve the constellation figure of merit and bit error rate (BER) performance. Experimental results show that the 3D hybrid constellation has a 0.6dB receiver sensitivity gain compared with that of the traditional regular 3D constellation at the BER
$\sim 3.8\times 10 ^{-3}$
with the information entropy of 3.52 bits/symbol. Meanwhile, as the received optical power increases, the gain grows larger, indicating that the proposed scheme will provide more opportunities for short-distance optical transmission and 3D constellation modulation with more points in the future.