Time-stretched short time Fourier transform

We propose and demonstrate time-stretched short-time Fourier transform (TS-STFT) to overcome the limitation of analog to digital converter (ADC) in time-frequency analysis of nonstationary signals. Experimentally, time-frequency analysis of highly chirped RF signals with chirp rate as high as 350 GHz/ns is demonstrated. An effective real-time sampling rate of 320 GSa/s is achieved. In our TS-STFT system, first ultra short window is applied on highly chirped signals. Then the window is stretched in time by photonic time stretch technique to allow its capture by the ADC to perform STFT in digital domain. This method enhances the analog bandwidth and effective sampling rate of the sampling ADC and enable us realize the instantaneous behavior of highly chirped ultra fast signal.