Konstantinos E. Chlouverakis

Stability maps of injection-locked laser diodes using the largest Lyapunov exponent

In this paper, we discuss the dynamics of a semiconductor laser subject to optical injection using the method of the Largest Lyapunov Exponent (LLE). The system’s stability is investigated as a function of the frequency detuning ω, the injection strength K and the linewidth enhancement factor α. Chaotic regimes and locking stability areas are found by integrating the rate equations and calculating the LLE for each solution in the (K–ω) plane. Periodic solutions are tracked inside the chaotic islands and very good agreement is demonstrated with experimental data in the literature. The LLE’s strength lies in the ability to map the amount of chaos and the amount of stability inside the stable locking regions. We also demonstrate that as we increase the linewidth enhancement factor, the system becomes more chaotic on average and the LLE is greater for each map.

Feedback Phase in Optically Generated Chaos: A Secret Key for Cryptographic Applications

The feedback phase in a chaotic system consisting of a semiconductor laser subject to delayed optical feedback is considered for the first time as a secret key for secure chaotic communications not exclusively based on hardware uniqueness. Extensive numerical simulations illustrate that the feedback phase is of extreme importance as far as synchronization is concerned. The ability of an eavesdropper to attack the intensity-modulated message when a pseudorandom variation of the feedback phase is imposed at the transmitters side is numerically quantified by bit-error-rate calculations. The analysis demonstrates that the eavesdropper is not able to synchronize and hence to extract the message when he is not aware of the phase variations even if he is equipped with an identical chaotic device.

Subcarrier modulation in all-optical chaotic communication systems.

The enhancement of the encryption properties of chaotic signals generated by a semiconductor laser subject to optical feedback is numerically demonstrated by applying subcarrier modulation. The numerical analysis shows that the message can be very efficiently encrypted when the radio frequency carrier is within the frequency range where the chaos power density is maximized. Decoding performance is also numerically assessed considering both open- and closed-loop schemes at the receiver side. The impact of subcarrier modulation on systems performance under the influence of parameter mismatch is highlighted.

Chaotic dynamics of semiconductor microring lasers

The complexity and dynamics of chaotic attractors generated in an InGaAsP-InP microring laser are calculated and evaluated by using a multimode rate equation model. Chaos originates from the continuous mutual injections from each mode to the other because of the bus waveguides residual reflectivity at high values of the injection current. The data analysis of the filtered output power reveals high-dimensional chaos, and phase-dependent behavior is demonstrated.

Temperature sensitivity of injection-locked vertical-cavity surface-emitting lasers

The dynamics of injection-locked vertical-cavity surface-emitting lasers (VCSELs) are studied as a function of temperature. The temperature dependence of the slave VCSELs parameters is used in a rate-equation analysis and parametric maps in the injection strength K- and frequency detuning /spl omega/-planes are calculated in order to investigate the temperature dependence of the systems stability. We demonstrate that, as we increase temperature for the range where the linewidth enhancement factor /spl alpha/ starts to stabilize, approximately 10 K above the temperature of where the minimum of the threshold carrier density occurs, the locking region tends to be suppressed and the nonlinearities to grow due to the increase of the relaxation resonance frequency /spl omega//sub R/ and the total loss rate /spl Gamma//sub 0/. Below that range, the opposite route is followed due to the enhanced value of the linewidth enhancement factor /spl alpha/, and the results are sensitive to the intraband relaxation time /spl tau/. It is finally concluded that, to take advantage of the stable locking region and to avoid the nonlinearities, it is better for the VCSEL device to have a minimum carrier density of 40 K-50 K below room temperature, thus allowing a good operating tolerance in the range /spl plusmn/20 K around room temperature.

Two-section semiconductor lasers subject to optical injection

We investigate the dynamic properties of two-section semiconductor lasers subject to optical injection. A self-pulsating laser with a saturable absorber is used as the slave laser in the usual master-slave configuration of optically-injected lasers and a new model of the rate equations is applied. The dynamic properties are pictured in stability maps in the parameter space of the frequency detuning /spl omega/ and the injection strength K. New chaotic regions in the parameter space are found and investigated that are not observed in a simple injected semiconductor laser and also regions are reported where the field intensity pulsates periodically.

Temperature sensitivity of injection-locked VCSELs and a new result for the Hopf bifurcation minimum

We focus on the change of the dynamical behaviour of an optically injected VCSEL by varying its material parameters with temperature. Dynamical characteristics of the system are studied via stability maps in the plane of frequency detuning versus injection strength calculated for different temperatures. One of the most clearly defined features of stability maps is the minimum of the Hopf bifurcation with respect to injected optical power. The calculated variation of the Hopf minimum with temperature is shown. It is concluded that the temperature dependence of injection-locked VCSELs has been simulated using a comprehensive model of the relevant material parameters.

Antimonotonicity and maximal complexity in optically injected two-section lasers

In this paper, we investigate some special dynamic characteristics of two-section semiconductor lasers subject to optical injection. Forward and reverse period-doubling cascades are presented in the parameter space of frequency detuning /spl omega/ and injection strength K, a phenomenon known as antimonotonicity. Furthermore, we investigate the Kaplan-Yorke dimension (D/sub KY/) and the largest Lyapunov exponent (LLE) of chaotic attractors in this laser setup. It is found that the latter is a dynamical system that can possess a dimension D/sub KY/ anywhere between 2 and close to 4 as the control and material parameters are varied, making it the most complex laser setup using optical injection. Finally, the criteria for achieving a high LLE and a high D/sub KY/ are examined (by varying all possible material and control parameters) and presented with potential applications to chaotic communications.

WDM transmission of chaotic signals

The transmission performance of wavelength division multiplexed chaotic signals is numerically investigated. The impact of transmitted power, bit-rate and channel arrangement on the overall performance is highlighted.

Optical sources for chaos based communications

Two new types of integrated broadband optical sources generating a wide range of nonlinear dynamics are presented. The new sources are compact potential emitters for high-speed optical communication systems employing chaos data encryption.