Compensation of DAC clock leakage in short-reach DMT system in the presence of sampling frequency offset

Abstract

Digital-to-analog converter (DAC) with a high sampling-rate has been extensively applied in optical discrete multi-tone (DMT) system for high data-rate signal generation. However, there exist various imperfections during the manufacturing of DAC when its sampling rate is tens of giga-samples per second and beyond. Clock tone leakage (CTL) is a kind of interference in high-speed DACs. One or more data subcarriers of the generated DMT signal may suffer from additional clock tones, which may degrade the overall bit error rate (BER) performance of the optical DMT system. In the literature, several schemes have been proposed to compensate CTL for short-reach applications. Nevertheless, these compensation schemes may not work effectively in the asynchronous DMT system in the presence of sampling clock frequency offset (SFO) between DAC and analog-to-digital converter. In this paper, an effective CTL compensation (CLC) with the digital interpolation scheme is proposed and experimentally investigated in a short-reach 100G DMT transmission system with direct detection. The results indicate that the proposed CLC with a fourth-order interpolation (FOI) scheme can effectively compensate the CTL in the presence of an SFO up to ±1000 parts per million (ppm). What is more, we discuss the impact of SFO estimation error on the BER performance of the 64-ary quadrature amplitude modulation-encoded DMT system. It shows that the BER performance penalty can be ignored by shortening the DMT frame even though the estimation error is up to 2 ppm.