Optical fiber approximation of GaN-based vertical-cavity surface-emitting laser diodes with a curved mirror

This study introduces an improved optical fiber approximation method for analyzing GaN-based vertical-cavity surface-emitting lasers (VCSELs) with a curved mirror. Unlike previous approaches, the proposed model incorporates, for the first time to the best of our knowledge, horizontal geometric consistency in addition to conventional vertical considerations, enabling more accurate prediction of beam characteristics, particularly under strong diffraction conditions. The calculated beam radius shows good agreement with experimental results. Furthermore, the model is applied to evaluate the effect of mirror tilting on optical loss by simulating it as fiber bending. The results reveal that VCSELs with a curved mirror exhibit almost zero additional loss under tilt, owing to the shift-rather than deformation-of the equivalent refractive index profile. In contrast, VCSELs with two planar mirrors suffer increased optical loss with tilt. These findings demonstrate the robustness of curved-mirror VCSELs against fabrication-induced tilts and suggest a pathway to improve device uniformity and yield.