Photonic generation of microwave signal using a rational harmonic mode-locked fiber ring laser

A novel method for microwave signal generation using a rational harmonic actively mode-locked fiber ring laser is proposed and demonstrated. The microwave signal is generated by beating the actively mode-locked longitudinal modes from the rational mode-locked fiber ring laser at a photodetector. The phases of the longitudinal modes are phased locked, which ensures a generated microwave signal with very low phase noise. In the proposed approach, the generated microwave signal has a frequency a few times higher than the microwave drive signal. Therefore, only a low-frequency reference source and a low-speed modulator are required. A rational harmonic actively mode-locked fiber ring laser is experimentally demonstrated. With a microwave drive signal at 5.52 GHz, a microwave signal with a frequency that is four times the frequency of the microwave drive signal at 22.08 GHz is generated. The generated microwave signal is very stable with a spectral width of less than 1 Hz.