Characterization of Nonlinear Distortion in 8QAM Optical Coherent Transmitter Using Probability-Maintained Notch

The novel probability-maintained (PM) notch generation method is proposed for non-grid complex modulation format, e.g., 8QAM. The nonlinearity of optical coherent transmitter is precisely characterized by using PM notch and optical spectrum analyzer, and its penalty is evaluated by the equivalent additive noise model with the accuracy of ~0.3 dB.