We report single transverse mode operation of a blue GaN-based vertical-cavity surface-emitting laser (GaN-VCSEL) with a monolithically incorporated curved mirror. For a device with a 4 μm current aperture diameter and a curved mirror with a radius of curvature (ROC) of 51 μm, single transverse mode operation was confirmed up to an output power of 3.2 mW under continuous wave operation at 20 °C. For a device with a smaller ROC of 31 μm, multi transverse mode operation was confirmed, indicating that the transverse mode can be controlled by the cavity design of such GaN-VCSELs.

We report a narrow divergence angle in a blue gallium-nitride-based visible vertical-cavity surface-emitting laser (GaN-VCSEL) with a curved mirror. This device exhibited continuous-wave operation at a wavelength of 447.9 nm. The fullwidth at half-maximum divergence angle of the 8 µm-aperture VCSEL was 3.9°when the device was operated at a current of 1.2 × Ith, where Ith is the threshold current. In this type of cavity, the radius of curvature (ROC) of the curved mirror determines the near-field pattern (NPF) and far-field pattern (FFP). The authors fabricated devices having ROC up to 988 µm, which is more than 10 times greater than the ROC of the mirror used in the previously reported structures, allowing this narrow emission. The I-L characteristics showed that the Ith value increased with increasing ROC. The present study investigates the mechanism behind this tendency in detail.

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