Mode characteristics and vertical radiation loss for AlGaInAs/InP microcylinder lasers

Mode characteristics are experimentally and numerically investigated for the AlGaInAs/InP microcylinder lasers with radii R ranging from 3.25 to 5.5 μm. The measured lasing spectra suggest wavelength crossing between different radial-order modes at R=3.5  μm, and the threshold current dramatically increases as R<3.5  μm, which can be well explained by three-dimensional finite-difference time-domain simulation. The simulated mode Q factors greatly degrade in the microcylinder resonators as R<3.5  μm and strongly depend on the mode wavelength because of vertical radiation loss, which results in a limitation for low threshold lasing. In addition, the near coincidence of mode wavelengths for different radial modes indicates the possible mode coupling at R=3.5  μm.