Jia-Gui Wu

Suppression of time delay signatures of chaotic output in a semiconductor laser with double optical feedback.

We experimentally and numerically demonstrate the time delay (TD) signature suppression of chaotic output in a double optical feedback semiconductor laser (DOF-SL) system. Two types of TD signature suppression are demonstrated by adjusting the lengths and the feedback power ratios of the two external cavities. One can significantly eliminate all TD signatures of the DOF-SL system and the corresponding power spectrum distribution becomes quite smooth and flat, the other suppresses one of two TD signatures and remains another one.

Evolution of time delay signature of chaos generated in a mutually delay-coupled semiconductor lasers system.

In this paper, evolution of time delay (TD) signature of chaos generated in a mutual delay-coupled semiconductor lasers (MDC-SLs) system is investigated experimentally and theoretically. Two statistical methods, including self-correlation function (SF) and permutation entropy (PE), are used to estimate the TD signature of chaotic time series. Through extracting the characteristic peak from the SF curve, a series of TD signature evolution maps are firstly obtained in the parameter space of coupled strength and frequency detuning. Meantime, the influences of injection current on the evolution maps of TD signature have been discussed, and the optimum scope of TD signature suppression is also specified. An overall qualitative agreement between our theoretical and experimental results is obtained.

Time delay signature concealment of optical feedback induced chaos in an external cavity semiconductor laser

The time delay (TD) signature concealment of optical feedback induced chaos in an external cavity semiconductor laser is experimentally demonstrated. Both the evolution curve and the distribution map of TD signature are obtained in the parameter space of external feedback strength and injection current. The optimum parameter scope of the TD signature concealment is also specified. Furthermore, the approximately periodic evolution relation between TD signature and external cavity length is observed and indicates that the intrinsic relaxation oscillation of semiconductor laser may play an important role during the process of TD signature suppression.

Isochronous Synchronization Between Chaotic Semiconductor Lasers Over 40-km Fiber Links

A long-distance isochronous chaos synchronization system, composed of a driving chaotic semiconductor laser and twin semiconductor lasers, is demonstrated experimentally. Via a driven chaotic signal which is generated by the driving chaotic semiconductor laser subject to external feedback and then injects into the twin semiconductor lasers by a pair of 20-km single-mode fibers, respectively, isochronous synchronization between the twin semiconductor lasers is experimentally observed. Further results show that high-quality isochronous synchronization can still be maintained even though the correlation coefficient between the driving laser and twin lasers is low. In addition, the bandwidth of synchronized chaotic signals is enhanced to more than 10 GHz although the bandwidth of driving signal is about 5.7 GHz.

Time-Delay Signature Suppression of Polarization-Resolved Chaos Outputs from Two Mutually Coupled VCSELs

Time-delay (TD) signature performances of polarization-resolved chaos outputs from two mutually coupled vertical-cavity surface-emitting lasers (MC VCSELs) are investigated through detailed simulations by means of self-correlation function (SF) and permutation entropy (PE). The results show that, under suitable coupling strength (η) and frequency detuning (Δf) between the two MC VCSELs, the TD signatures of two polarization modes from each VCSEL can be suppressed simultaneously. Furthermore, based on the map of TD signature evolution in the parameter space of Δf and η, the optimal parameter region of TD signature suppression has been determined.

Simultaneous Generation of Two Sets of Time Delay Signature Eliminated Chaotic Signals by Using Mutually Coupled Semiconductor Lasers

Simultaneous generation of two sets of time delay (TD) signature suppressed chaotic signals is experimentally demonstrated by using a mutually delay-coupled semiconductor laser (MDC-SL) system. The experimental results show that under proper conditions, TD signatures of chaotic output signals in such a system can be eliminated, and two sets of low TD signature chaotic signals can be simultaneously obtained. Furthermore, both the TD signature evolution pattern and the optimum scope for TD signature elimination are experimentally specified by modulating the coupling strength and adjusting frequency detuning between the two mutually coupled lasers.

Simulation of Bidirectional Long-Distance Chaos Communication Performance in a Novel Fiber-Optic Chaos Synchronization System

A novel fiber-optic chaos synchronization system allowing bidirectional long-distance chaos communication is proposed. For this system, chaos synchronization between two response lasers (RLs) is achieved via an identical driven chaotic signal injection from a remote driving laser (DL) over a long-distance fiber. The simulated results show that under suitable operation conditions, high-quality chaos synchronization between the two RLs can be obtained while the synchronization quality between any one of RLs and the DL is bad, which is useful for improving the system security. Using the two synchronized chaos output signals from RLs as two chaotic carriers and adopting a novel message encryption and decryption method, the communication performances, the impact of long-distance fiber channel and the security of this system, have been analyzed. After adopting an optimized system configuration, two 10 Gb/s messages propagating along opposite direction can be effectively decrypted over 100 km fiber channel.

Chaos synchronization in mutually coupled semiconductor lasers with asymmetrical bias currents

We experimentally and numerically investigated the chaos synchronization characteristics of mutually coupled semiconductor lasers (MCSLs) with asymmetrical bias currents. Experimental results show that, asymmetrical bias current level of two MCSLs has obvious influence on chaos synchronization between them, and stable leader-laggard chaos synchronization can be realized under relatively large asymmetrical bias current levels. Moreover, the influences of frequency detuning and mutually coupling strength between the two lasers on chaos synchronization performance have also been discussed. Theoretical simulations basically conform to our experimental observations.

Theory and simulation of dual-channel optical chaotic communication system

A theoretical model based on a novel experiment scheme of dual-channel optical chaotic communication has been presented, and is proved to be reasonable by comparing the numerical simulations with the experimental results. After deducing the transmission function of semiconductor laser by small-signal analysis, how to reasonably select the system parameters has been given in order to realize the effective transmission of signal. Moreover, the cross talk between two channels has been analyzed quantitatively. For a 250MHz modulation message, the numerical simulation shows that it can be hidden efficiently during the transmission and decoded easily in the receiver.

Direct generation of broadband chaos by a monolithic integrated semiconductor laser chip

A solitary monolithic integrated semiconductor laser (MISL) chip with a size of 780 micrometer is designed and fabricated for broadband chaos generation. Such a MISL chip consists of a DFB section, a phase section and an amplification section. Test results indicate that under suitable operation conditions, this laser chip can be driven into broadband chaos. The generated chaos covers an RF frequency range, limited by our measurement device, of 26.5GHz, and possesses significant dimension and complexity. Moreover, the routes into and out of chaos are also characterized through extracting variety dynamical states of temporal waveforms, phase portraits, RF spectra and statistical indicators.