A novel method of optical generation millimeter-wave (mm-wave) signals employing two cascaded optical modulators and four-wave-mixing effect in semiconductor optical amplifiers is proposed. This approach is capable of generating signals of four times, eight times, and 12 times microwave source frequency with high spectral purity and stability. A mm-wave of 42 GHz (12 x fundamental) with a 3-dB linewidth less than 30 Hz and a phase noise less than - 83 dBc/Hz at 10-kHz offset is obtained.