This study obtained highly uniform and efficient GaN-based vertical-cavity surface-emitting lasers (VCSELs) with curved mirror from a single wafer. The average threshold current (Ith) and the optical output power (Pmax) of 14 nominally identical chips measured up to 7 mA were 0.64 mA and 4.5 mW, respectively. The standard deviations of Ith and Pmax were 0.043 mA and 0.23 mW, respectively. Additionally, the best chip shows maximum values of wall plug efficiency and output power of 13.4% and 7.6 mW, respectively, at 5.2 mA and 12.8 mA operating currents.
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.
A single cavity filtering mirror with a highly varying reflectivity spectrum was used to demonstrate single longitudinal mode operation for a VCSEL with a ~25 μm cavity length. The 443.5 nm lasing peak had an SMSR of 42 dB at 9 mA, 70kA/cm2. Increasing the number of DBR pairs between the VCSEL and filtering mirror cavity reduced the simulated optical standing wave in the mirror cavity by 57% and experimentally gave a 42% increase in the slope efficiency to achieve 2.56 mW at 7 mA from a device with a 4 μm aperture with a single longitudinal mode.
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