Spatio-temporal emission dynamics of VCSELs: modal competition in the turn-on behavior

Abstract

We present 2D-spatially and temporally resolved measurements of the emission of selectively oxidized stateof-the-art VCSELs of intermediate aperture sizes, showing their rich modal, polarization, spectral, and spatial dynamics. For the characterization of the repetitive dynamics we performed experiments with a technique we developed called TRIDA (Temporally Resolved Imaging by Differential Analysis) providing a temporal resolution down to 10 ps. From the temporal evolution of the near-field emission we provide a comprehensive overview of the phenomena in the turn-on dynamics. The evolution of the spatial intensity distribution of the transverse modes over a range of some nanoseconds is presented and discussed. Complementary, we have taken single-shot images of the near-field emission of 3 ns short pulses in order to characterize the nonrepetitive part of the dynamics and to get a deeper understanding of the dynamical processes arising from the interaction of transverse modes in the turn-on process. We find strong variations in the intensity distribution among the transverse modes and the polarization directions, indicating the onset of spatio-temporal chaos. A correlation analysis for the modal intensities is performed showing the influence of the competition for the available spatial and spectral gain.

Evolution from modal to spatially incoherent emission of a broad-area VCSEL

“…The FF exhibits structured and divergent emission and reflects the highly multimode emission of the corresponding NF profile. The FF and NF at τ ∼ 10 ns are in agreement with the results obtained so far for multimode VCSELs [6,7,8].…”

“…The multi-transverse mode emission is accompanied by complex emission dynamics, which can be observed as a combination of spatiotemporal and polarization dynamics. The build-up of transverse modes, the spatiotemporal emission dynamics, and the interplay of the responsible mechanisms have been studied previously [4,5,6,7,8,9].…”

Nonlinear polarization and transverse mode dynamics of a broad-area VCSEL in continuous wave operation

“…Figure 6 also confirms the anticorrelation of the spatial orientation of the two polarization states: the maxima for u polarization are almost always found right between the maxima for v polarization. The same effect has been previously observed in experiments with BA-VCSELs [37,38,51,52] and was attributed to spatial hole burning and a finite spin-flip relaxation rate in Refs. [12,53].…”

“…Furthermore, fluctuations on the scale of 10-30 GHz caused by mode competition were observed in BA-VCSELs [32,33], however, these do not match the FCs observed here either. Moreover, almost all investigations of the dynamics of BA-VCSELs only considered short pulses, observing relaxations oscillations and the onset of mode competition [32][33][34][35][36][37][38], however, it is not clear how and with which frequency scales mode competition persists in cw operation. We thus cannot clearly identify the origin of all the FCs observed here, but it strongly appears that they are due to processes different from those previously observed for BA-VCSELs.…”

“…This study thus extends investigations into the dynamics of narrow VCSELs and broad-area edge-emitting SCLs alike. Previous experimental works on the dynamics of BA-VCSELs have studied the transient dynamics during short pulses [32][33][34][35][36][37][38], observing relaxation oscillations and the onset of mode competition and beating between transverse modes, whereas experiments in cw operation were restricted to the dynamics on long time scales [39]. Numerical studies of BA-VCSELs [12,[40][41][42][43][44][45] mostly concentrated on short pulses and transient dynamics as well, and a systematic investigation of the ultrafast dynamics and bifurcations of a BA-VCSEL under cw pump is still missing.…”