Meng Yao Wang

Chaos synchronization communication using extremely unsymmetrical bidirectional injections

Chaos synchronization and message transmission between two semiconductor lasers with extremely unsymmetrical bidirectional injections (EUBIs) are discussed. By using EUBIs, synchronization is realized through injection locking. Numerical results show that if the laser subjected to strong injection serves as the receiver, chaos pass filtering (CPF) of the system is similar to that of unidirectional coupled systems. Moreover, if the other laser serves as the receiver, a stronger CPF can be obtained. Finally, we demonstrate that messages can be extracted successfully from either of the two transmission directions of the system.

Polarization Switching and Hysteresis of VCSELs With Time-Varying Optical Injection

We study the influence of time-varying orthogonal optical injection on polarization switching (PS) of vertical-cavity surface-emitting lasers (VCSELs). Three cases are considered: scanning injection strength, and scanning frequency detuning in two different reference ranges. In all the three cases, fast sweep rates make PSs happen at higher (lower) values for upward (downward) scans, and thus enlarge the hysteresis region. Furthermore, types of PS and the emission states of the laser can be controlled, if the scanning parameter and scanning range are chosen properly. Statistical analysis indicates PS for the third case is not so stable as that for the first two cases.

One-to-Many and Many-to-One Optical Chaos Communications Using Semiconductor Lasers

A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications.

Theoretical study on polarization dynamics of VCSELs with negative optoelectronic feedback

We investigate theoretically the polarization dynamics of vertical-cavity surface-emitting lasers (VCSELs) subjected to negative optoelectronic feedback. As we vary the feedback delay and strength, the VCSEL exhibits interesting nonlinear dynamics in the two-linear polarized directions. The output instability and negative current modulation induced by delayed feedback can also cause polarization switching (PS) to happen. In addition, we investigate the case when the free-running VCSEL emits in the modulated-elliptical state and find that the laser experiences in succession the elliptical polarization, the x-mode polarization, and the mixed-mode polarization states with an increasing feedback strength.

Synchronization performance comparison of vertical-cavity surface-emitting lasers with two different feedback chaos schemes

Most of the previous treatments of chaos synchronization use common optical feedback. In this paper, we introduce a new feedback type called phase conjugate feedback in vertical-cavity surface-emitting lasers (VCSEL) to achieve synchronization. For comparison, models of synchronization using both phase conjugated feedback (PCF) and common optical feedback (COF) are given, where the nonlinear and dispersion effects on transmitted signals in a fibre link are also considered. Numerical simulation shows two peaks when calculating the shifted correlation coefficient. In the phase conjugate feedback scheme, the larger peak always corresponds to anticipating synchronization while this does not hold true in the common optical feedback scheme. When anticipating synchronization takes place, the value of the correlation coefficient for phase conjugate feedback is larger than that for common optical feedback, and their discrimination is more than 0.1. Decoded messages in chaotic shift keying undergo less distortions when the phase conjugate feedback scheme is considered, because of the distortion correction characteristics of phase conjugate light. All this indicates that the synchronization performance of the former scheme is better than that of the latter.

Polarization dynamics of vertical-cavity surface- emitting lasers with optical feedback

The standard two-mode rate equations are extended to discuss polarization behavior of vertical-cavity surface-emitting lasers (VCSELs) with optical feedback. In the rate equations, a logarithmic gain formula and unit step function are used to simulate the experimental conditions more truly. Our simulation results show that weak polarization-preserving feedback will cause multiple polarization switches (PSs) with increasing bias current; strong feedback can suppress PSs and make the VCSEL work in a single polarized mode. The case is similar when y-polarized feedback is considered. The PS point does not disappear even under strong x-polarized feedback. Bifurcation diagrams show that the interplay of PSs and delayed feedback makes the nonlinear dynamics of the two polarized modes more complex. If the feedback is large enough, both chaotic pulses due to feedback and low-frequency fluctuations due to gain competition emerge in the time traces of the two modes. Polarization modulation is also demonstrated when a quarterwave plate is added to the external cavity, which agrees with the experimental observations.