Photonic Generation of High-Repetition-Rate Arbitrary Microwave Waveforms Based on Fractional Temporal Talbot Effect

We propose and experimentally demonstrate a photonic approach to generating high-repetition-rate (HRR) arbitrary microwave waveforms based on fractional temporal Talbot effect. In the proposed generation system, a periodic optical pulse from an optical frequency comb source is spectrally manipulated by an incident microwave signal via a dual-drive Mach-Zehnder modulator (DD-MZM). After a length of dispersion medium propagation, if its dispersion meets a specific condition with the period of the input optical pulse, fractional-order temporal Talbot effect happens. As a result, the temporal profile of the spectrally-manipulated optical pulse is a scaled-version of its spectrum, and its repetition rate is multiplied. By controlling the incident microwave signals, arbitrary microwave waveforms with different duty cycles can be generated, and by carefully choosing the dispersion, its repetition rate can also be multiplied. A theoretical modelling is conducted, a numerical simulation is done and an experimental demonstration is also performed. By employing an optical comb source with a repetition rate of 5.1 GHz in the generation system, several microwave waveforms including rectangular, triangular and sawtooth profiles with different duty cycles are experimentally generated. Repetition rate multiplication is demonstrated by controlling the fiber dispersion. When the fiber dispersion is 3013 ps2, the repetition rate of the generated microwave signal is 10.3 GHz; when the fiber dispersion is 2009 ps2, the repetition rate is 15.4 GHz. The proposed approach holds great advantage where an HRR arbitrary microwave generator is enabled with the use of a low-frequency microwave source a small dispersion, paving the way for potential advancements in radar and communication technologies.