This paper presents an overview on millimeter wave radio over fiber systems based on millimeter wave generation by
optical frequency multiplication (OFM). The disadvantage of original OFM technique is checked and a novel
bi-directional mm-RoF system based on new OFM technique using dual-drive MZM as high-order optical side-modes
generator is proposed in principle and experimentally verified by a bi-directional mm-RoF system which not only
produces 38 GHz information bearing signal in downstream, but also provides 40GHz local reference for
down-conversion of upstream signal. Finally the advantage of OFM technique in reducing fading effect of fiber
dispersion is theoretically proved.