Dynamics of Optoelectronic Oscillators with Electronic and Laser Nonlinearities

We present a theoretical and experimental study of a low-frequency optoelectronic oscillator featuring both laser-diode and Van der Pol-like nonlinearities. In this architecture, the device performing the electrical-to-optical conversion is the laser-diode itself instead of an external electro-optical modulator, while the electric branch of the oscillator is characterized by a Van der Pol nonlinear transfer function. We show that the system displays a complex autonomous dynamics, induced by the competition between these two nonlinearities. In the case of small delay, the system displays harmonic and relaxation oscillations. When the delay is large, the interplay between the two nonlinearities leads to a period-doubling route of bifurcations as the feedback gain is increased, and ultimately to fully developed chaos. Our experimental measurements are in good agreement with the theoretical analysis.