Inter-Symbol Differential Detection-Enabled Sampling Frequency Offset Compensation for DDO-OFDM

Sampling frequency offset (SFO) between digital-to-analog converters and analog-to-digital converters will seriously degrade the receiver performance of the asynchronous direct-detection optical OFDM (DDO-OFDM), due to the SFO-induced inter-symbol interference, inter-channel interference, and phase rotation. In this letter, a simple and overhead-free SFO compensation scheme enabled by inter-symbol differential detection (ISDD) is proposed and experimentally demonstrated in a short-reach and low-cost directly modulated laser-based DDO-OFDM system with an optimal fast Fourier transform size. The experimental results exhibit that the SFO up to ±200 ppm can be compensated with acceptable error vector magnitude (EVM) penalties after 20-km standard single-mode fiber transmission. Moreover, the EVM performance can be further enhanced by using a decision-aided residual phase compensation method after ISDD when SFO is large.