Efficient wavelength-scale VCSELs via lithographically defined cavities

The miniaturization of lasers is essential for advancing on-chip optical communication, energy-efficient data processing, and quantum photonics. Vertical-cavity surface-emitting lasers (VCSELs) are a leading platform for these applications, but scaling toward near- and sub-wavelength dimensions exposes fundamental limitations of conventional oxide-confined designs. Here, we investigate a lithographically defined cavity (Li-cavity) architecture incorporating an intracavity phaseshifting mesa to achieve transverse photonic confinement through effective-index engineering. Three-dimensional optical simulations show that the Li-cavity suppresses optical scattering and supports high Q and Purcell factors at wavelengthscale dimensions, enabling stable single-mode operation over a broad range of aperture sizes. Based on these insights, we experimentally demonstrate Li-VCSELs with cavity diameters from 0.75 to 2.0 µm, exhibiting room-temperature continuous-wave lasing with power conversion efficiencies up to 31%. A wavelength-tuning layer further enables over 10 nm of emission tunability. These results establish lithographically defined VCSELs as a scalable and versatile platform for high-Q, wavelength-scale light sources with enhanced light–matter interaction, suitable for dense photonic integration and next-generation optoelectronic systems.