Photonic generation of a linearly chirped microwave waveform with long temporal duration using a dispersive loop

We propose and experimentally demonstrate a photonic approach to generating a linearly chirped microwave waveform with a large time bandwidth product (TBWP) based on spectral shaping and wavelength-to-time (SS-WTT) mapping. The spectral shaping is performed using a Fabry-Perot interferometer (FPI) consisting of two linearly chirped fiber Bragg gratings (LCFBG) with complementary dispersion to produce a spectral response with a linearly increasing or decreasing free spectral range. The wavelength-to-time mapping is performed using a dispersive loop incorporating a third LCFBG. Thanks to the multiple-time use of the third LCFBG, an extremely large equivalent dispersion can be achieved, which leads to the generation of a linearly chirped microwave waveform with a long temporal duration. The proposed technique is validated by an experiment. Two linearly chirped microwave waveforms with a TBWP of 225 and a temporal duration of 25 and 45 ns are generated.