Photonic time‐stretch digitizer and its extension to real‐time spectroscopy and imaging

Abstract

Abstract Real‐time wideband digitizers are the key building block in many systems including oscilloscopes, signal intelligence, electronic warfare, and medical diagnostics systems. Continually extending the bandwidth of digitizers has hence become a central challenge in electronics. Fortunately, it has been shown that photonic pre‐processing of wideband signals can boost the performance of electronic digitizers. In this article, the underlying principle of the time‐stretch analog‐to‐digital converter (TSADC) that addresses the demands on resolution, bandwidth, and spectral efficiency is reviewed. In the TSADC, amplified dispersive Fourier transform is used to slow down the analog signal in time and hence to compress its bandwidth. Simultaneous signal amplification during the time‐stretch process compensates for parasitic losses leading to high signal‐to‐noise ratio. This powerful concept transforms the analog signal's time scale such that it matches the slower time scale of the digitizer. A summary of time‐stretch technology's extension to high‐throughput single‐shot spectroscopy, a technique that led to the discovery of optical rouge waves, is also presented. Moreover, its application in high‐throughput imaging, which has recently led to identification of rogue cancer cells in blood with record sensitivity, is discussed.