Low-noise synthesis of microwave signals from an optical source

The low-noise synthesis of a harmonic comb of microwave frequencies using a 1 GHz femtosecond-laser-based synthesiser that is referenced to a cavity-stabilised laser is demonstrated. The residual phase noise is ∼−110 dBc/Hz at 1 Hz offset from the 10 GHz harmonic. Phase noise is measured with an interferometric measurement system having low sensitivity to AM.