Mode Competition Dynamics in an Optoelectronic Oscillator: A Study Using an Extended Microwave-Photonic Iterative Nonlinear Gain (MING) Model

An extended microwave-photonic iterative nonlinear gain (MING) model is proposed to analyze the mode competition dynamics in an optoelectronic oscillator (OEO). The power trajectories of multiple longitudinal modes in the mode competition process are calculated using the proposed extended MING model, by which we observe that mode competition is affected by the loop nonlinearity. On one hand, when the nonlinearity is enhanced, gain saturation effect becomes more significant. The strongest mode will gain the most energy from the optical carrier and win the competition, leading to single-mode oscillation. On the other hand, with enhanced nonlinearity, the intermodulation distortions (IMDs) become more significant. The mixing between the longitudinal modes would lead to energy transfer, causing weaker longitudinal modes to receive more energy, thereby hindering mode competition. Therefore, through suppressing the IMDs by reducing the loop gain, multi-mode operation can be reduced, facilitating stable single-mode operation. The mode competition dynamics of an OEO at different loop gain levels is evaluated by simulations. The simulation results show that by decreasing the loop gain, multi-mode oscillation is quickly evolved to single-mode oscillation, which is validated by an experiment. The proposed extended model is the first comprehensive study of the nonlinear dynamics of an OEO, showing the evolution from an initial multimode oscillation to a stable single-mode oscillation.