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We have proposed a scheme of radio-over-fiber (RoF) system employing a dual-parallel Mach-Zehnder modulator (DP-MZM) based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). In this scheme, the pump and the signal are generated by properly adjusting the direct current bias, modulation index of the DP-MZM, and the phase difference between the sub-MZMs. Because of the pump and the signal deriving from the same optical wave, the polarization states of the two lightwaves are copolarized. The single-pump FWM is polarization insensitive. After FWM and optical filtering, the optical millimeter-wave with octuple frequency is generated. About 40-GHz RoF system with a 2.5-Gbit/s signal is implemented by numerical simulation; the result shows that it has a good performance after the signal is transmitted over 40-km singlemode fiber. Then, the effects of the SOA's injection current and the carrier-to-sideband ratio on the system performance are discussed by simulation, and the optimum value for the system is obtained. [ABSTRACT FROM AUTHOR]