High-finesse disk microcavity based on a circular Bragg reflector

We made disk-shaped microcavities of approximately $\text{10\hspace{0.17em}}{\mathrm{\mu m}}^2$ in area in a GaAs/AlGaAs waveguide structure by etching deep vertical concentric trenches. The trenches form a circular Bragg-like reflector that confines light in the remaining two lateral dimensions. We demonstrate from photoluminescence excited in the waveguide the confinement of discrete disk modes whose wave vector is mainly radial, in contrast with whispering gallery modes. Their quality factors up to $\text{Q=650}$ indicate in-plane reflectivities approaching 90%. In the near infrared, this represents a demonstration of wavelength-scale light confinement based on photonic crystal effects in two dimensions.