Coupled-mode structure in oxide aperture vertical-cavity surface-emitting lasers and its effects on lasing threshold

Abstract

Mode coupling caused by the presence of an oxide dielectric aperture is addressed. For rays passing through the dielectric, we apply the complex reflection coefficient that corresponds to a Fabry–Perot subcavity formed by a slab dielectric and the nearest distributed Bragg reflector (DBR) mirror. The DBR reflectivity applies to rays passing through the aperture opening. The diffraction effects for curved wave-front incidence are also included. The expansion coefficients of the cavity eigenmodes into pure Gauss–Laguerre (GL) modes are obtained for the lowest eigenmodes in the optimum waist representation. The effects of the aperture location in the cavity standing wave are addressed. Over the entire range of aperture diameters, higher cavity losses and higher threshold currents result for antinode placement, owing to wide-angle scattering. This agrees with experimental results and earlier scattering analysis by use of pure GL (uncoupled) eigenmodes. Mixing with higher modes increases round-trip losses at small apertures, compared with uncoupled-mode results. In the limit of a large aperture diameter, the cavity eigenmodes decouple to pure GL modes.