An apparatus and method for generating a millimeter-wave carrier signal for optical data transmission is disclosed. The apparatus includes stimulated Brillouin scattering source (101) that generates a variable stoke line multi-wavelength optical signal, optical amplifiers (102, 108), an optical splitter (103) that splits the amplified output of the SBS source (101) into two identical optical signals of the same magnitude, frequency, phase and electromagnetic mode, identical optical tuneable band-pass filters (104, 105) with the same band-pass, an optical coupler (107) that combines the optical signals emitted from the output of the optical filters (104, 105) such that the output of the coupler (107) is a dual wavelength optical signal with a wavelength separation equivalent to the desired millimeter wave frequency, a photo-detector (109) that converts the optical signal to an electrical signal by heterodyning process, and a controller circuit (106) that controls the gain of the optical amplifiers (102, 108), the tuning of the optical band-pass filters (104, 105) independently and the number of stoke lines produced by the stimulated Brillouin scattering source (101) depending on the electrical millimeter wave output.