Random number generator based on an integrated laser with on-chip optical feedback

Mid-infrared hyperchaos of interband cascade lasers

Chaos in nonlinear dynamical systems is featured with irregular appearance and with high sensitivity to initial conditions. Near-infrared light chaos based on semiconductor lasers has been extensively studied and has enabled various applications. Here, we report a fully-developed hyperchaos in the mid-infrared regime, which is produced from interband cascade lasers subject to the external optical feedback. Lyapunov spectrum analysis demonstrates that the chaos exhibits three positive Lyapunov exponents. Particularly, the chaotic signal covers a broad frequency range up to the GHz level, which is two to three orders of magnitude broader than existed mid-infrared chaos solutions. The interband cascade lasers produce either periodic oscillations or low-frequency fluctuations before bifurcating to hyperchaos. This hyperchaos source is valuable for developing long-reach secure optical communication links and remote chaotic Lidar systems, taking advantage of the high-transmission windows of the atmosphere in the mid-infrared regime.

Prediction of robust chaos in micro and nanoresonators under two-frequency excitation

Robust chaos in a dynamical system is characterized by the persistence of the chaotic attractor with changes in the system parameters and is generally required in practical applications based upon physical sources of chaos. However, for applications that rely upon continuous time chaotic signals, there are now very few alternatives of dynamical systems with robust chaos that could be used. In this context, it is important to find a new dynamical system and, particularly, new physical systems that present robust chaos. In this work, we show through simulations that a relevant physical system, suspended beam micro and nanoelectromechanical resonators, can present robust chaos when excited by two distinct frequencies. To demonstrate the existence of robust chaos in the system, we perform an extensive numerical analysis, showing that the attractor is unique and changes smoothly in a large region of the relevant physical parameter space. We find that the robustness of the chaotic dynamics depends crucially on the dissipation, which must be sufficiently small. When the dissipation is small, we find a large range of frequencies, frequency ratios, and applied voltages where robust chaos is observed. These findings turn these systems into viable and strong candidates for practical applications since the chaotic dynamics becomes quite insensitive to fabrication tolerances, changes in the physical parameters induced by the environment, and aging.

Introduction to Focus Issue: Time-delay dynamics

The field of dynamical systems with time delay is an active research area that connects practically all scientific disciplines including mathematics, physics, engineering, biology, neuroscience, physiology, economics, and many others. This Focus Issue brings together contributions from both experimental and theoretical groups and emphasizes a large variety of applications. In particular, lasers and optoelectronic oscillators subject to time-delayed feedbacks have been explored by several authors for their specific dynamical output, but also because they are ideal test-beds for experimental studies of delay induced phenomena. Topics include the control of cavity solitons, as light spots in spatially extended systems, new devices for chaos communication or random number generation, higher order locking phenomena between delay and laser oscillation period, and systematic bifurcation studies of mode-locked laser systems. Moreover, two original theoretical approaches are explored for the so-called Low Frequency Fluctuations, a particular chaotical regime in laser output which has attracted a lot of interest for more than 30 years. Current hot problems such as the synchronization properties of networks of delay-coupled units, novel stabilization techniques, and the large delay limit of a delay differential equation are also addressed in this special issue. In addition, analytical and numerical tools for bifurcation problems with or without noise and two reviews on concrete questions are proposed. The first review deals with the rich dynamics of simple delay climate models for El Nino Southern Oscillations, and the second review concentrates on neuromorphic photonic circuits where optical elements are used to emulate spiking neurons. Finally, two interesting biological problems are considered in this Focus Issue, namely, multi-strain epidemic models and the interaction of glucose and insulin for more effective treatment.