Abstracts

An important aspect of vertical-cavitysurface-emitting lasers (VCSELs) that needs to be improved is itsstable operation in a single transverse mode. Due to relativelylarge dimensions of VCSELs (~ 10 m radius), spatial hole-burningand carrier diffusion affect device performance significantly,especially because VCSELs often operate in several transverse modesat high injection currents. In this thesis, a comprehensivenumerical study of such spatial effects on the static, dynamic, andnoise characteristics of VCSELs is presented. The computer modelincludes the spatial dependences of both the optical field and thecarrier density. Device characteristics are analyzed underdifferent operating conditions, including continuous-wave (CW)operation, gain-switched operation, optical feedback, and opticalinjection. Both single-mode and two-mode operations are analyzed.
Under CW operation, transverse-modecompetition induced by spatial hole-burning is found to affect thestatic and noise characteristics significantly. In particular,transverse-mode competition affects the mode-partition noise. Undersingle-mode gain-switched operation, it is shown that by using anappropriate electrical contact, spatial hole-burning can be avoidedand shorter pulses can be obtained. Under two-mode gain-switchedoperation, transverse-mode competition gives rise to rich nonlineardynamics. The effect of external influence has also been studied.It is found that optical feedback or optical injection can force atwo-mode VCSEL to operate in a single transverse mode underappropriate conditions. However, distant feedback or injectionoutside the locking region can destabilize the CW operation andlead to interesting nonlinear dynamics. The feedback strength andthe injection power at which oscillations occur depend criticallyon the strength of intermodal coupling. In general, resultsindicate that strong intermodal coupling reduces the sensitivity ofthe VCSEL towards external influence.
Experiments have been conducted on a VCSEL toinvestigate the multiple-transverse-mode emission characteristics.Results show that multimode operation leads to considerabledegradation of device performance, such as the distortion oflight-current curves of the orthogonally polarized components,degradation of spatial beam quality, broadening of the opticalspectrum, and modification of the mode-partition noise. Opticalfeedback effects on VCSEL characteristics have also been explored,and it is found that feedback leads to quasi-periodicoscillations.