We report on transverse mode discrimination in long-wavelength wafer-fused vertical-cavity surface-emitting lasers (VCSELs) incorporating ring-shaped air gap patterns at the fused interface between the active region and the top distributed Bragg reflector (DBR). These 60-nm deep patterns were implemented with the aim of favoring the fundamental mode while preserving high output power. The VCSELs under consideration emit in the 1310-nm band and incorporate an AlGaInAs-based quantum well active region, a regrown circular tunnel junction and undoped GaAs/AlGaAs DBRs. A large batch of devices with varying pattern dimensions was investigated by on-wafer mapping, allowing significant statistical analysis leading to conclusions on their typical behavior. We observe experimentally a dependence of the side-mode suppression ratio on the geometrical parameters of the patterns. In particular, we identified a design that statistically increases the maximal single-mode emitted power by more than 20%. Numerical simulations of the patterned-cavity VCSELs based on our fully three dimensional electrical, thermal and optical VCSEL computational model support these observations. They show that patterns with a large inner diameter actually confine the first-order transverse mode and enhance its modal gain. In smaller devices, this mode is pushed out of the optical aperture and suffers larger losses. Optimized parameters were found numerically for enhancing the single-mode properties of the devices with negligible penalty on emitted power and threshold current.
We investigate the use of MOVPE-grown ordered nanostructures on non-planar substrates for quantum nano-photonics
and quantum electrodynamics-based applications. The mastering of surface adatom fluxes on patterned GaAs substrates
allows for forming nanostrucutres confining well-defined charge carrier states. An example given is the formation of
quantum dot (QD) molecules tunneled-coupled by quantum wires (QWRs), in which both electron and hole states are
hybridized. In addition, it is shown that the high degree of symmetry of QDs grown on patterned (111)B substrates
makes them efficient entangled-photons emitters. Thanks to the optimal control over their position and emission
wavelength, the fabricated nanostructures can be efficiently coupled to photonic nano-cavities. Low-threshold, optically
pumped QWR laser incorporating photonic crystal (PhC) membrane cavities are demonstrated. Moreover, phononmediated
coupling of QD exciton states to PhC cavities is observed. This approach should be useful for integrating more complex systems of QWRs and QDs for forming a variety of active nano-photonic structures.