Low-Complexity Time-Domain Averaging-Based DAC Clock Tone Leakage Compensation for Short-Reach PAM4 Transmission

High sampling-rate digital-to-analog converters (DAC) are usually applied in optical fiber communication systems for the signal generation with advanced modulation formats such as four-level pulse amplitude modulation (PAM4). There exist various imperfections for high sampling-rate DACs. Clock tone leakage (CTL) is one of the imperfections and may seriously degrade the bit error rate (BER) performance, especially for single-carrier transmission systems. In this paper, we study a low-complexity time-domain averaging (TDA) based CTL compensation (TDA-CTLC) method for short-reach PAM4 transmission. By numerical simulation, we investigate the impacts of chromatic dispersion, CTL interference-to-signal power ratio (ISPR), and vertical resolution of the analog-to-digital converter on the BER performance. The results exhibit that the TDA-CTLC enabled PAM4 transmission system in the presence of a wide range of ISPR has a similar BER performance with the one without CTL interference. Moreover, we experimentally evaluate the compensation performance of the TDA-CTLC in a directly-modulated laser-based short-reach PAM4 transmission system. Up to −4 dB ISPR can be compensated with a slight BER performance degradation due to nonlinear distortions.