Optical OFDM Synchronization With Symbol Timing Offset and Sampling Clock Offset Compensation in Real-Time IMDD Systems

End-to-end real-time Optical Orthogonal Frequency Division Multiplexing (OOFDM) signal synchronization that is capable of simultaneously compensating for both Symbol Timing Offset (STO) and Sampling Clock Offset (SCO) is experimentally demonstrated, for the first time, over 64-quadrature amplitude modulated (QAM)-encoded, 11.25-Gb/s, 25-km, Intensity-Modulation and Direct-Detection (IMDD) single mode fiber (SMF) systems employing directly modulated distributed feedback lasers. In comparison with manual synchronization, almost-perfect compensations of arbitrary STOs are achieved. The OOFDM synchronization technique can also compensate for the SCO effect with an accuracy of < 1 ppm for initial SCOs as large as 4000 ppm. The technique has a number of salient advantages including low complexity, fast tracking speed, high accuracy, and suitability for high-speed optical transmission systems.