Time-stretched short-time Fourier transform
ABSTRACT The authors propose and demonstrate the time-stretched short-time Fourier transform (TS-STFT) technique to overcome the limitation of an analog-digital converter (ADC) in the time-frequency analysis of ultrafast signals. Experimentally, the time-frequency analysis of highly chirped RF signals, with a chirp rate as high as 350 GHz/ns, is demonstrated. An effective real-time sampling rate of 320 GSa/s is achieved. Time stretching enhances the analog bandwidth and the effective sampling rate of the ADC and enables measurement of the instantaneous behavior of highly nonstationary ultrawideband signals.
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ABSTRACT: An all-optical approach to implementing short-time Fourier transform (STFT) of a high-speed and broadband elec- trical signal is proposed and demonstrated for the first time to our knowledge. The STFT is implemented based on a temporal pulse shaping system incorporating an array of cascaded linearly chirped fiber Bragg gratings (LCFBGs). An electrical signal to be analyzed isappliedtoaMach-Zehndermodulator(MZM)tomod- ulate the optical spectrum of a time-stretched optical pulse from a mode-locked laser (MLL). Each individual LCFBG in the LCFBG array functions as a bandpass filter to filter a specific range of the spectrum, which is equivalent to applying a window function to the corresponding section of the temporal signal, and at the same time, as a dispersive element to implement real-time Fourier transform. Atheoreticalanalysisisperformedwhichisverifiedbyanumerical simulation and a proof-of-concept experiment. The key feature of this technique is that STFT can be implemented in real time which can find applications in analyzing an electrical signal with a band- width up to several hundreds of gigahertz.IEEE Photonics Technology Letters 01/2011; 23(20):1439-1441. · 2.04 Impact Factor