All-Optical Multilevel Amplitude Regeneration Based on Polarization-Orthogonal Continuous-Wave-Light-Assisted Nonlinear-Optical Loop Mirror (PC-NOLM) Subsystem

We demonstrate a multilevel amplitude regeneration experiment for non-return-to-zero 4-level pulse amplitude modulated (NRZ-PAM4) signals in the proposed polarization-orthogonal continuous-wave-light-assisted nonlinear-optical loop mirror (PC-NOLM) subsystem. A uniform regenerative behavior including the same noise-suppression efficiency and the noise-handling capability is observed across multiple amplitude levels. The pre-phase modulation is carried out for the input signal enabling the multilevel amplitude regeneration directly on highly-spectral-efficient modulated formats. An overall improvement of 2.33 dB is achieved by optimizing the launched optical power and the distortion strength in the all-optical NRZ-PAM4 regeneration experiment. The uniform regenerative performance for the proposed PC-NOLM regenerator is also analyzed numerically to reveal the regenerative mechanism and the influence from the operational parameters.