Photonic Generation of Tunable Continuous-Wave Microwave Signals Using a Temporally-Stretched and Chirped Pulse-Train

We show analytically and experimentally that direct photodetection of a temporally-stretched and chirped optical pulse-train together with its time-delayed replica can be exploited to realize the generation of tunable continuous-wave microwave signals. The proposed scheme utilizes the chromatic dispersion of the standard single-mode-fiber (SMF) to temporally-stretch and chirp an optical pulse-train in such a way that the pulses overlap with each other. The temporally-stretched pulse-train is then sent to a Mach-Zehnder Interferometer (MZI) where it first splits and then recombines with a time-delayed replica of itself at the output. Proper management of both the dispersion in the system as well as the relative time-delay of the two arms of the MZI enables one to tune the frequency of the generated microwave signal to any integer multiple of the pulse source´s repetition frequency which is within the bandwidth of the photodetector. Based on the proposed scheme, using an initial 2 GHz pulse-train, we demonstrate generation of tunable continuous-wave microwave signals from 4 GHz to 14 GHz.