A frequency synthesizer for generating a multiple tone lightwave signal that can be converted into an RF carrier or local oscillator signal. The frequency synthesizer comprises a multiple mode master laser, two slave lasers injection-locked to the master laser, an optical coupler coupling the optical outputs of the two slave lasers, which produces an optical heterodyne output. The frequency synthesizer further comprises a homodyne phase-lock loop providing feedback control over one of the slave lasers and a heterodyne phase-lock loop providing feedback control over the other slave laser. A local oscillator selector is used to select the optical mode to which one of the slave lasers is locked, thus providing selection of the frequencies of the heterodyne output.