Chaos on a chip

Semiconductor lasers are normally sensitive to perturbations that can induce unstable or noisy behavior. As the lasers become integrated into tiny photonic circuits, such chaotic nonlinearities might become magnified and thwart any desired uses of the circuitry. Mirvais Yousefi and his colleagues at the Eindhoven University of Technology in the Netherlands have developed a method to investigate nonlinearities in coupled lasers and have found surprising regularities. The researchers use a pair of lasers so close to each other on a chip that each affects the operation of the other. By monitoring the system’s output dynamics as a function of the pump current, the researchers could directly visualize the period-doubling route to chaos. They discovered that integrated optics show intrinsically nonlinear dynamics but that the nonlinear behavior is remarkably stable over the life of the chip and reproducible from one batch of chips to another. Thus, according to Yousefi, far from being a problem, the dynamics can be exploited to optimize the integrated photonic circuits. (M. Yousefi et al. , Phys. Rev. Lett. 98 , 044101, 2007 .)