Optical orthogonal frequency division multiplexing(O-OFDM) technology is a novel optical communication technology which combines electrical OFDM technology and optical fiber communication technology. O-OFDM will be widely employed in the large-capacity and long-haul fiber-optic communication systems and optical access networks because of its high frequency efficiency, effective resistance to the chromatic dispersion, polarization-mode-dispersion and non-linear effects. The principles, structures and key technologies for O-OFDM at home and abroad are introduced. The technologies and theoretical problems to be studied for O-OFDM applications are discussed and moreover, the future development trends and application prospects of O-OFDM technologies are penetrated.