Real-time Fourier transformation based on the bandwidth magnification of RF signals

We demonstrate a novel real-time Fourier transformation scheme with megahertz-level resolution realized by bandwidth magnification of radio frequency (RF) signals. Before the frequency-to-time mapping, the RF signal is modulated on an optical frequency comb, and then extracted by a Vernier comb filter. As a result, RF components can be separated in the spectrum with a greatly magnified optical bandwidth. Thus, even with limited dispersion provided by an ordinary optical fiber, the frequency-dependent pulses can be distinguished in the time domain. Experimentally, the RF signal with the frequency difference of 60 MHz is separated by around 123 ps in the time domain, equivalent to the dispersion of 1975.5 ps/GHz (2.47×10⁵  ps/nm), while the physical dispersion is 1500 ps/nm. Thus, based on the bandwidth magnification of signals, the dispersion is equivalently amplified by 165 times.