Photonic generation of tunable multi-frequency microwave source

A flexibly tunable multi-frequency microwave source is presented based on optical heterodyning between the intensity-modulated optical carrier (incorporated four-wave mixing equalisation and stabilisation) and the frequency-shifted Stokes light generated by fibre stimulated Brillouin scattering. About 20 microwave frequencies centred at 10.77 or 21.62 GHz are experimentally observed. The central frequency and the frequency spacing of the multi-frequency microwave source can be freely tuned by changing the frequency shift of the beating optical waves and the driving frequency on the modulator.