High-resolution microwave frequency measurement based on temporal channelization using a mode-locked laser

High resolution microwave frequency measurement based on temporal channelization using a mode-locked laser is proposed and demonstrated. In the proposed system, a highly chirped optical pulse is modulated by a microwave signal with its frequency to be measured. The temporal microwave waveform is then mapped to the spectral domain thanks to dispersive Fourier transformation in a dispersive fiber. An optical channelizer is then employed to filter the spectrum, which is equivalent to performing temporal sampling of the temporal waveform. The microwave signal can then be reconstructed and its spectral distribution can be analyzed. Our method features greatly improved measurement resolution, which is more than two orders of magnitude higher than that based on the direct use of an optical channelizer. To evaluate the proposed technique, frequency measurement of a single-tone and a two-tone microwave signals is demonstrated. A measurement resolution as high as 200 MHz is achieved using an optical channelizer with 25-GHz channel spacing.