Broadband Instantaneous Multi-Frequency Measurement Based on a Fourier Domain Mode-Locked Laser

Broadband instantaneous multi-frequency measurement based on frequency-to-time mapping using a Fourier domain mode-locked (FDML) laser source is proposed and experimentally demonstrated. An electrically controlled silicon microdisk resonator (MDR) with an ultra-narrow linewidth of 60 pm (~7.5 GHz) functioning as a fast tunable optical filter is used to implement the FDML to generate a linearly chirped optical waveform (LCOW) with a wide frequency-sweeping range of 0.5 nm. The LCOW is then mixed at a modulator with a microwave signal with its frequency to be measured, detected at a low-speed photodetector (PD) and sent to a narrow bandpass filter (BPF). When the difference between the instantaneous frequency of the LCOW and that of the signal to be measured is equal to the center frequency of the BPF, a short-duration temporal signal is produced, and the time location of the temporal signal represents the frequency of the signal to be measured. A proof-of-concept experiment is carried out. Both single and multi-tone microwave frequency measurements are experimentally demonstrated. The measurement range is as large as 20 GHz with a measurement resolution of 200 MHz and an accuracy better than ±100 MHz. The proposed method showcases a new method for instantaneous frequency measurement (IFM) with high performance in terms of multi-frequency identification, real-time measurement, and high measurement speed compared with traditional approaches, which is attractive for applications in modern radar, electronic warfare, communication, and cognitive radio systems.