Xavier Porte

Real-time frequency dynamics and high-resolution spectra of a semiconductor laser with delayed feedback

The unstable emission of semiconductor lasers due to delayed optical feedback is characterized by combined intensity and frequency dynamics. Nevertheless, real-time experimental investigations have so far been restricted to measurements of intensity dynamics only. Detailed analysis and comparison with numerical models, therefore, have suffered from limited experimental information. Here, we report the simultaneous determination of the lasers optical emission intensity and emission frequency with high temporal resolution. The frequency dynamics is made accessible using a heterodyne detection scheme, in which a beat signal between the delayed feedback laser and a reference laser is generated. Our experiment provides insight into the overall spectral drift on nanosecond timescales, the spectral distribution of the unstable pulsations and the role of the individual external cavity modes. This opens new perspectives for the analysis, understanding and functional utilization of delayed feedback semiconductor lasers.

Bidirectional private key exchange using delay-coupled semiconductor lasers

We experimentally demonstrate a key exchange cryptosystem based on the phenomenon of identical chaos synchronization. In our protocol, the private key is symmetrically generated by the two communicating partners. It is built up from the synchronized bits occurring between two current-modulated bidirectionally coupled semiconductor lasers with additional self-feedback. We analyze the security of the exchanged key and discuss the amplification of its privacy. We demonstrate private key generation rates up to 11  Mbit/s over a public channel.

Dynamical properties induced by state-dependent delays in photonic systems

In many dynamical systems and complex networks time delays appear naturally in feedback loops or coupling connections of individual elements. Moreover, in a whole class of systems, these delay times can depend on the state of the system. Nevertheless, so far the understanding of the impact of such state-dependent delays remains poor with a particular lack of systematic experimental studies. Here we fill this gap by introducing a conceptually simple photonic system that exhibits dynamics of self-organised switching between two loops with two different delay times, depending on the state of the system. On the basis of experiments and modelling on semiconductor lasers with frequency-selective feedback mirrors, we characterize the switching between the states defined by the individual delays. Our approach opens new perspectives for the study of this class of dynamical systems and enables applications in which the self-organized switching can be exploited.

Experimental distinction of weak and strong chaos in delay-coupled semiconductor lasers

Semiconductor lasers subject to external perturbations often exhibit deterministic chaotic behaviour. Optical delayed self-feedback is a common way to induce chaotic laser emission. In recent years, chaotic semiconductor lasers have proven to be useful in a number of practical applications, ranging from chaos communications and secure key distribution to random bit generation or LIDAR systems [1]. In particular, chaos communications and secure key distribution rely on the synchronization or two or more lasers operating in the chaotic regime [2]. Thus, a high degree of synchronization is desired for practical applications.

Scaling Properties of the Dynamics of Semiconductor Lasers in External Cavities

We demonstrate scaling in amplitude and time of the dynamics of quantum well and quantum dot semiconductor lasers subject to optical feedback from long delays, providing insights into the underlying physics of both devices.

Bidirectional secure key-exchange using chaotic semiconductor lasers

Summary form only given. Semiconductor lasers coupled with delay can exhibit instabilities and chaos synchronization. Identical synchronization can be achieved when two semiconductor lasers are coupled via a relay [1]. The role of the relay is to symmetrically distribute the information between both lasers. It has been demonstrated that a passive relay in the form of a semitransparent mirror accomplishes this function [2].

Experimental characterization of bubbling in delay-coupled semiconductor lasers

Optically coupled semiconductor lasers are of particular interest in the study of synchronization of chaotic dynamics. A better understanding of the mechanisms that govern this synchronization and its robustness is for instance important in the field of secure communications. As observed in [1], the isochronous solution in the bidirectionally coupling setup is unstable. The coupling delay leads to spontaneous symmetry breaking and only leader-laggard synchronization occurs. We implement an experimental scheme of two bidirectionally coupled semiconductor lasers with an equidistant passive relay (semitransparent mirror) to achieve zero-lag synchronization. The stability properties of this zero-lag solution have been studied, in particular, the presence of noise induced desynchronizations, a behaviour called bubbling [2].

Zero-lag synchronization of two delay-coupled lasers: The role of detuning

Delay-coupled semiconductor lasers are of interest both from a fundamental and applied point of view. They serve as test-bed system to study coupling-induced dynamics and synchronization, and they have been proven valuable for novel applications based on chaotic dynamics.