Showing papers by "Luis Pesquera published in 2002"

Criteria for synchronization of coupled chaotic external-cavity semiconductor lasers

Abstract: We study the synchronization of two unidirectionally coupled single-mode external-cavity semiconductor lasers, that operate in a chaotic regime. A simple theory is developed to obtain synchronization conditions and to analyze the effects of the detuning between the two lasers. We find that numerical simulations are in good agreement with the theory.

Analytical calculation of transverse-mode characteristics in vertical-cavity surface-emitting lasers

Abstract: An analytical method to calculate the multi-transverse-mode static characteristics of index-guided vertical-cavity surface-emitting lasers is presented. The steady-state solution of a model that takes into account the spatial dependence of both the electrical field and the carrier-density profiles is calculated. Power of the transverse modes is then obtained by solving a linear set of equations of which the coefficients are simple integrals involving modal and injected-current-density profiles. Analytical expressions are then derived for threshold currents of the transverse modes. Finally, simple analytical expressions are derived for single- and two-mode operation.

Diffusive turn-off transients in current modulated multitransverse mode VCSELs

Abstract: Secondary pulsations are an example of diffusive turn-off transients that can limit the performance of VCSELs in optical communication systems. Secondary pulsations are firstly analysed by using a model where a modal expansion of the electric field is performed. The maximum power of the secondary pulsations and the time at which they appear fluctuate when the spontaneous emission noise is present. A linear relation between the two previous quantities for each individual turn-off event is found. In the single-mode regime, the averaged maximum power during turn-off transients increases when increasing the injection current. However, in the multi-mode regime, the strength of secondary pulsations decreases when increasing the current. Secondary pulsations are also analysed by using a spatio-temporal description of the VCSEL dynamics, where the modal profiles are determined from the distribution of injected carriers and the thermal lens. This model also incorporates polarization effects and a frequency-dependent susceptibility. In this model, the carrier-induced refractive index changes increase the strength of secondary pulsations as compared to that obtained with the modal expansion. It is also shown that the use of ring-shaped electrical contact enhances the strength of secondary pulsations, while it decreases when multi-transverse mode operation is present.

Nonlinear dynamics of current-modulated multitransverse-mode vertical-cavity surface-emitting lasers

Abstract: An analysis of the nonlinear dynamics of current modulated weakly index-guided VCSELs in a multi--transverse mode regime is performed by using a model that takes into account all the transverse modes supported by the waveguide. Nonlinear dynamical behavior is studied when applying current modulation of high frequency and large modulation depth. Chaotic behavior is obtained in the multitransverse mode regime due to transverse mode competition. Chaotic operation is such that multistability of the chaos-chaos type is observed. Injection of appropriate optical pulses can switch between different stable chaotic solutions. The case of a VCSEL in which the fundamental mode is selected is also analyzed. Nonlinear dynamics of the single mode VCSEL is such that the chaotic behavior is not present for the considered range of current modulation amplitudes and frequencies. Only periodic behaviors are observed, in such a way that multistability of different periodic solutions also appears. Switching between different stable periodic solutions also appears when appropriate external optical pulses are injected. Finally, we show that spontaneous emission noise increases the number of available channels in chaotic optical communication systems in which frequency division multiplexing with multi-transverse mode VCSELs is used.

Theoretical analysis of synchronization of chaotic self-pulsating semiconductor lasers

Abstract: Chaotic dynamics in a self-pulsating laser diode has been shown theoretically to occur by modulation of the laser current. It has been also shown that synchronization of two chaotic self-pulsating lasers can be achieved by small amounts of optical coupling. This result has been obtained with a deterministic model for the laser intensity. We study coherent synchronization of single mode self-pulsating laser diodes by means of a field-equation model that takes into account phase-effects and spontaneous emission noise. It is shown that the size of the coupling required to achieved synchronization is influenced by spontaneous emission noise and by the linewidth enhancement factor. Numerical simulations are then used to identify the optimum regime for efficient synchronization. It is found that good synchronization can be obtained for large values of the bias current, such that the spontaneous emission plays a minor role. The degree of synchronization is studied as a function of the differences between the master and slave laser parameters. Finally, a sinusoidal signal is used to analyze a chaotic communication system based on self-pulsating laser diodes.