Distribution of millimeter-wave signals over optical fiber has been considered a promising technology for future broadband wireless access networks, thanks to the low loss and broad bandwidth of optical fibers operating at the 1550 nm window. Different schemes have been proposed to distribute millimeter-wave signals using optical fiber, which include intensity modulation and direct detection (IM/DD) scheme and remote heterodyne (RHD) scheme. In a millimeter-wave-over-fiber system using IM/DD scheme, two sidebands located at the two sides of the optical carrier are generated. For frequencies higher than 20 GHz, the chromatic dispersion becomes a serious problem which leads to high power penalty. The dispersion problem can be solved if RHD scheme is used. In an RHD scheme, two wavelengths that are phase correlated are generated using single-side band with carrier modulation, optical carrier-suppressed modulation, optical offset injection locking or optical offset phase locking of two laser sources. Ideally, the laser sources are considered to have very narrow linewidth, which will not introduce phase noise at the remote side when beating the two wavelengths. However, in real applications laser diodes usually have a finite linewidth, which leads to the phase de-correlation in the fiber links; phase noise is then generated at the remote end. In this paper, we will analyze the effects of the finite linewidth of optical sources on the performance of millimeter-wave over fiber systems. Simulation and experimental results will be provided.