This article describes in detail the design and implementation of a 240 Gbit/s Orthogonal Frequency Division Multiplexing（OFDM） real-time optical communication system.It first generates 3×15 orthogonal optical subcarriers by using a multi-carrier generating device

and modulates each subcarrier with OFDM signals at 4 Gbaud/s using a 4QAM signal format.Then it demodulates the optical OFDM signals in every channel at the receiver end using the corresponding intrinsic subcarrier and implements real-time processing of the sampled signals using FPGA.The total effective data rate reaches 240 Gbit/s

the highest among the reported real-time OFDM transmissions.