The Radio-over-Fiber (RoF) links play an important role in systems where mm-wave (60GHz) signals need to be distributed over many 100’s of meters. In 60GHz RoF systems, cost of modulating a laser is a problem. A potentially low cost solution is the use of mm-wave pulse repetition frequencies mode-locked lasers (MLLs). In this book, a novel concept of injection-locking these MLL to implement mm-wave phase shift is introduced. Both magnitude and phase of the modulation response are measured using VNA and a “plateau” is observed in magnitude response which corresponds to the locking range of the system. The MLL phase shifter operation makes them an ideal candidate for mm-wave RoF phased array antenna and advanced antenna beam steering systems. The wireless injection locking of MLLs is also presented which uses modular integration of a MLL and a planar antenna. Then, a novel Photonic Active Integrated Antenna approach is introduced to further improve the integration, where a MLL is hybridly integrated with a planar antenna to perform wireless injection-locking. Finally, a novel self oscillating mixer behavior of the MLL is studied under both homodyne and heterodyne configurations.