Study On Nonlinear Dynamics Of Vertical-Cavity Surface-Emitting Lasers With External Optical Feedback

Vertical-cavity surface-emitting lasers (VCSELs) are promising for applications in optical communication, optical interconnect, optical storage, optical sensing, and other fields because of their useful characteristics such as small volume, low threshold current, low power consumption, single-longitudinal-mode, effective coupling with fiber, and easy to form high density two-dimensional array. The researches about VCSELs have already become the hotspot of the optoelectronic field. However, in practical applications of VCSELs, external optical feedback (EOFB) phenomenon is often encountered and even tiny feedback can lead the laser to exhibit rich nonlinear dynamics, which greatly influence the system performance. The study on EOFB phenomenon of VCSELs is beneficial to deeply revealing the specially physical and optical characteristics shown by this kind of lasers with external perturbation and providing theoretical instructions for the optimization of VCSELs and optical communication systems. The purposes of this thesis are to deeply investigate EOFB-induced profound static and dynamic behaviors of VCSELs by taking account of the characteristics of VCSELs and the effects of EOFB, to explore the exterior exhibitions as well as the intrinsic physical origins of these behaviors, and to seek the corresponding controlling methods. My research includes following important issues: multi-transverse-mode behaviors of VCSELs, feedback-induced static and dynamic behaviors in single-mode and multi-transverse-mode VCSELs, dynamics of unidirectionally and mutually injected VCSELs, chaos synchronization of external-cavity VCSELs and their applications to chaotic optical communications.In the aspect of researching method, some visual and easy-extensible simulation models are established by using Simulink software and the research is then done by dint of these models together with other special controlling and handling programs; for weakly-index guided VCSELs, the spatial distribution functions of transverse modes held by this type of laser are obtained by employing optical waveguide theory, and the propagation constants as well as the specific spatial distributions are obtained in virtue of the curves plotted by computer according to the eigenvalue equations; for multi-transverse-mode VCSELs, two-dimensional finite-difference-division method and integration simplification method are used, respectively. These methods are efficient and easy-extensible and can be widely applied to optoelectronic researches.The study on multi-transverse-mode behaviors of VCSELs shows that a narrow (broad) disc contact or a center-vicinity (edge-vicinity) ring contact is favorable for excitation of low-order (high-order) transverse modes. The spatial ununiformity of modal intensity leads the carrier to exhibit similar nonuniform distribution and result in spatial hole burning (SHB) effects, which are seen to be suppressed by carrier diffusion. For disc contact, it also shows that VCSELs have better single-mode performances for a lower injection current or a current with weaker diffusion.The feedback characteristics of single- and multi-mode VCSELs are studied in detail. Besides the static behaviors under short external cavities and the typical nonlinear dynamics such as bifurcation and chaos wider long external cavities, it is also brought forward and verified that EOFB-induced nonlinear dynamics in VCSELs can be suppressed effectively by adjusting some device parameters (such as the spontaneous emission factor) or introducing controllable external optical injection or external optoelectronic feedback. For EOFB-driven multi-mode VCSELs, all modes show identical dynamics under conventional feedback; moreover, anti-phase variations induced by mode competition is observed. It is also found that, for polarization- or mode-selective EOFBs, other modes unaffected by feedback still exhibit the same behaviors as those with feedback, despite only one mode is affected directly. The mode (polarization) selection can be realized through mode-selective (polarization-selective) feedback.Rich dynamics including bifurcation and chaotic fluctuation are observed in both unidirectionally and mutually injected VCSELs systems. In both systems, frequency detuning can increase the system complexity. For mutual coupling case, frequency detuning can also drive the system to oscillate with the same frequency. Nonlinear and mode-locking behaviors are analyzed for the first time for both conventional and mode-selective injections. Results show that all mode exhibit similar nonlinear behaviors and are locked successfully by the corresponding injecting modes; with mode-selective injection, only those modes with the same or parallel polarization direction with the injecting modes show preceding behaviors, while the others polarized perpendicularly are suppressed due to mode competition.Complete and injection-locking synchronizations are observed in chaotic synchronization system consisted of two unidirectionally coupled external-cavity VCSELs. It is found that the complete synchronization will be affected greatly by the spontaneous emission noises of both lasers (the cross-correlation degree is decreased and the synchronization error is increased greatly), while the generalized one shows great tolerance. The synchronization characteristics of the system under conventional and mode-selective injections are investigated for the first time. Results show that all modes can achieve good synchronization for conventional configuration. However, with mode-selective injections, only those modes being pumped optically can synchronize well with the injecting modes; the other modes are greatly suppressed with a very low correlation degree.The chaotic optical communication system based on external-cavity VCSELs is investigated detailedly. It shows that, coinciding with the experimental reports, the original digital or analog messages sent in the transmitter part can be decoded correctly in the receiver part by using chaotic modulation (CM), chaotic masking (CMS), or chaos-shift keying (CSK) methods after the achievement of chaos synchronization. It is concluded firstly that: the transmission security of the system based on injection-locking chaos synchronization should be improved further due to the ultra-tolerance to parameter mismatches shown by this type of synchronization; additional optical feedback induced by external optical component might lead the sent information to be exposed completely out of the chaotic carrier; system decoding capability can be improved by decreasing the injection-locking-induced strength difference between the two chaotic signals from the transmitter and the receiver; based on the frequency-division multiplexing technique, multi-signal transmission can be realized in chaotic optical communication system. Besides, complete, generalized, and hybrid synchronizations are observed in cascade chaotic optical communication system composed of three unidirectionally-coupled VCSELs; moreover, the original message can be decoded correctly in both the intermediate and the slave parts, which shows that the system is with relay characteristics.