Broadened graded asymmetric waveguide structure for low divergence 915nm diode laser

Multi-chip beam combining is applied for high-power laser diodes. In this method, fast collimation of the laser diode is an important process. Diode laser beam divergence is the primary parameter to couple the fiber optic and beam shaping. Expanding the waveguide layer thickness in epitaxial design is the usual approach to reduce the beam divergence. The 915nm broadened graded asymmetric structure is presented in this study, to reduce the divergence without raising the threshold current ($\mathrm{I}_{\mathrm{t}\mathrm{h}}$). The asymmetric waveguide shifted the vertical optical field to the n-section, which has smaller free carrier loss than the p-section. Furthermore, the linearly graded refractive index was used to control the modes. The main goal of this research is to decrease the divergence. In the proposed structure, fast divergence (FWHM) of24 degrees and $\mathrm{I}_{\mathrm{t}\mathrm{h}}$ density of less than 650A/c$\mathrm{m}^{2}$ was achieved. Decreasing the beam divergence can increase the coupling efficiency to the optical fiber without increasing the $\mathrm{I}_{\mathrm{t}\mathrm{h}}$.