Real-time experimental demonstration of optical OFDM symbol synchronization in directly modulated DFB laser-based 25km SMF IMDD systems

A simple optical OFDM (OOFDM) synchronization technique utilizing subtraction and Gaussian windowing at the symbol rate is proposed and implemented in FPGA-based OOFDM receivers. End-to-end real-time symbol synchronization of 128-QAM-encoded OOFDM signals at raw bit rates of 6.56Gb/s is experimentally demonstrated, for the first time, over directly modulated DFB laser-based 25km SMF intensity modulation and direct detection (IMDD) systems. Experimental investigations show that the proposed synchronisation technique offers a number of salient advantages including low complexity, fast tracking speed, high accuracy and suitability for high-capacity optical transmission systems.