Optimum Three-Dimensional Constellations for Stokes Vector Direct Detect Receivers

We propose optimum 3D signal constellations for short reach intra-datacenter interconnects using stokes vector receivers. These optimum 3D alphabets maximize the so-called constellation figure of merit, which is the ratio between the squared minimum Euclidean distance and the average energy of the constellation points. Compared to dual-polarization 4-ary and 8-ary pulse amplitude modulation formats, the optimized 16-point and 64-point 3D signal constellations theoretically achieve 4 and 6 dB improved receiver sensitivity at low symbol error rates of ~10 ⁻⁵ , while delivering similar spectral efficiencies of 4 and 6 bits per 3D symbol, respectively. Next, we experimentally verified the significant improvement in receiver sensitivity at symbol rates of 44 and 64 Gbaud that result from using the proposed optimized 3D signal alphabets.