Abstract. For achieve fast and reliable power data transmission, we propose a novel Intensity Modulation and Direct Detection (IM/DD) optical Orthogonal Frequency Division Multiplexing (OFDM) system. In this system, we utilize Discrete Hartley Transform (DHT) instead of Discrete Fourier Transform (DFT) which is used in traditional optical OFDM systems, in order to complete the signal demodulation and modulation procedures, thus leading to the orthogonality of data-carrying subcarriers. Simulation results show that the similar bit error rate performance can be achieved between the DHT-based optical OFDM system (BPSK, 4-Pulse Amplitude Modulation (PAM) and 8-PAM) and the DFT-based optical OFDM system (4-QAM, 16-QAM, 64-QAM).