Accurate Nonlinearity Characterization of Dual-Polarization 16QAM Transmitter Using Four-Level Probability-Maintained Notch Signal

Probability-maintained notch method based on four-level signal instead of two-bit signal is proposed to evaluate the nonlinearity of PAM4/16QAM formats. By introducing appropriate diffusion in the four-level signal, the large two-bit quantization error is avoided, and a 28 dB notch depth is achieved.