Nonlinear Equalizer Based on Absolute Operation for IM/DD System Using DML

The performance of high-speed intensity-modulation (IM)/direct-detection (DD) system implemented by using O-band directly modulated laser (DML) could be limited by the waveform distortions induced by nonlinear modulation dynamics of DML. The conventional polynomial nonlinear equalizer (PNLE) can be used at the receiver to compensate for such waveform distortions. However, this nonlinear equalizer suffers from high implementation complexity. In this letter, we propose nonlinear equalizers based on the absolute operation for IM/DD system using DML. We replace the square operation in PNLE with the absolute operation to lower the implementation complexity. The effectiveness of the proposed equalizers is evaluated over 100-Gb/s 4-ary pulse amplitude modulation transmission system implemented by using 1.31- $\mu \text{m}$ DMLs. The results show that the proposed equalizers perform similar to the PNLEs, but lower the implementation complexity.