Mode control in ring lithographic aperture VCSELs

Multimode vertical-cavity surface-emitting lasers (VCSELs) often display broad spectra, increased beam divergence, and limited control over the spatial profile of the emitted light. To address this, we introduce VCSELs with lithographically defined ring-shaped tunnel-junction apertures, which spatially tailor gain and optical confinement. Spectrally resolved measurements and simulations show that the ring geometry fundamentally reshapes the supported modal set. This reduces spectral width and far-field divergence compared to conventional circular apertures. At the same time, Gaussian-like far-field intensity profiles are achieved even in nominally multimode devices. Comparable output power is obtained from ring and circular apertures with identical external diameters, despite the significantly reduced active area of the ring geometry. This confirms enhanced mode–carrier overlap and improved thermal behavior. Beyond reshaping multimode emission, the same ring-aperture platform is combined with engineered surface-relief losses and gain design to favor selected transverse modes. Through the interplay of spatially selective gain injection and tailored modal loss, we demonstrate stable single-mode emission with output powers exceeding 8 mW. Rather than relying only on suppression of unwanted higher-order modes, this approach enables transverse modes to be reshaped, stabilized, and selectively exploited. These results establish VCSELs with ring lithographic apertures as a scalable route toward high-power beam shaping and structured-light generation in semiconductor cavities.