Figure 6

Real (full line) and naively (dashed line) estimated secret key rates for an imbalanced AM&PM modulation stage. Shapes and colours indicate the different constellation formats, blue circles indicate the 256-QAM constellation, orange diamonds indicate the 256-APSK with 32 states per ring and yellow squares indicate the 256-APSK with 64 states per ring. The parameters assumed were \(T=01585\), \(\nu =0.9\), \(\epsilon _{\text{thermal}}=0.3\) SNU and \(\epsilon =0.01\) SNU. In the naive scenario the excess noise ϵ is added to the contribution of the deformation of the constellations