Experimental observation and simulation of mode-locking phenomena in coupled-oscillator arrays

Systems of coupled oscillators possess a wealth of interesting and useful nonlinear dynamical phenomena. Arrays of coupled oscillators have been used to model complicated biological and neural activity, and have proved useful in power-combining applications. The analysis of such arrays is difficult, and has generally been restricted to the case where all oscillators are synchronized to a common frequency through the phenomenon of injection locking. When the natural (or free-running) frequencies are very widely distributed, this mutual synchronization is impossible, and the system can exhibit chaotic behavior. However, by carefully choosing the frequency distribution, a stable mode-locked state can be established in which the collective output of the oscillator array consists of a train of pulses, similar to a mode-locked laser. Due to the different physical mechanisms involved, and due to a spatial as well as spectral separation of the oscillators, the mode-locked array exhibits new phenomena not present in mode-locked lasers. A theory describing the coupled-oscillator dynamics is developed to explore these new effects, and the theory is amply supported with empirical evidence obtained with a linear array of Gunn diode oscillators operating at 11 GHz.