Fig. 4: Experimental results on time-mapped spectrogram analysis of two complex high-speed microwave signals using photonic sampling and dispersion.

a–c The results corresponding to the analysis of a 2-µs long microwave signal under test (SUT), which is composed by two superimposed frequency-chirped sinusoids, namely a sinusoid with an increasing quadratic frequency chirp, from 500 MHz to 2 GHz, and a sinusoid with the same but opposite frequency chirp. The signal exhibits two separate frequency bands at each instant of time. d–f The results corresponding to the analysis of a 2-MHz tone that is frequency modulated on a 1.215-GHz microwave carrier with a maximum frequency deviation of ±1.215 GHz. For each of the analyzed signals, the top plot, (a) and (d), respectively, shows the measured temporal waveform (voltage) of the input microwave SUT; the plot in the middle, (b) and (e), respectively, shows the numerically computed spectrogram (SP) distribution of the measured input signal, calculated using a 5.9-ns FWHM width Gaussian pulse as the analysis temporal window; and the bottom plot shows the 2D TM-SP distribution that is directly recovered from the measured temporal trace at the output of the experimental photonic sampling and dispersion scheme. To facilitate interpretation of the obtained results, in each spectrogram representation, only the positive axis of frequencies is represented.