Detection of low-power RF signals using active mode-locking based coupled optoelectronic oscillator

A novel method to detect and amplify broadband low power radio frequency (RF) signal with high gain based on coupled optoelectronic oscillator (COEO) is proposed and experimentally demonstrated. When the frequency of the weak signal matches the COEO oscillation mode, it can obtain the high gain of active mode-locking in the COEO optical loop. The system can selectively detect and amplify RF signals from 1 to 10 GHz by observing the optical pulse repetition rate state. The experimental results show that sensitivity of detection as low as −89 dBm with a maximum gain of 34.32 dB at 1.002 GHz, and an average gain of 30.52 dB for low power RF signals. The real application of the method for detecting low power Quadrature Phase Shift Keying (QPSK) modulation is investigated and the spectral waveforms is discussed.