Reduced-size lookup tables enabling higher-order QAM with all-silicon IQ modulators

We experimentally demonstrate 20 Gbaud 256QAM and 40 Gbaud 128QAM in an all-silicon IQ modulator. We combine a linear equalizer and a nonlinear predistortion implemented in a lookup table (LUT). We achieve bit error rate (BER) below the 20% forward error correction threshold; linear equalization alone cannot achieve this performance. To keep LUT size manageable, we use one dimensional LUTs and prune entries. We achieve good BER even when LUT size is halved. Finally, we verify the generality of the proposed methods on different data sets.