Theoretical and experimental study on stable oscillation of dual-frequency signals in an optoelectronic oscillator

Due to the gain competition effect, it is hard to simultaneously maintain oscillation at two frequencies in an optoelectronic oscillator (OEO) loop. In this paper, a study of the gain competition effect in a dual-frequency OEO is theoretically and experimentally demonstrated. The steady-state conditions in the dual-frequency OEO are theoretically analyzed by deriving dynamic equations. A nonlinear time-varying model, as well as its calculation methods, is carried out to design and study the dynamic process of the dual-frequency OEO. Thanks to this model, the waveform, spectrum, and amplitude evaluation of generated signals, as well as the gain variation in the OEO loop, are numerically simulated. Based on the theoretical analysis and numerical simulation results, three schemes that can suppress the gain competition effect are proposed, and the one based on wavelength division multiplexing (WDM) technology is experimentally realized. The experimental results show that the novel independently tunable dual-frequency OEO, to the best of our knowledge, can generate two-tone RF signals in a range from 1.8 to 18.6 and 1.5 to 18.3 GHz, respectively.