Design of AlGaInP visible lasers with a low vertical divergence angle

AlGaInP visible lasers with depressed index cladding layers are studied theoretically and experimentally. Using the above low-refractive-index layer, we can significantly improve the characteristics of the transverse beam divergence. According to our experimental results, the transverse beam divergence can be reduced from 41.4° to 26.2°. These values also agree well with our theoretical calculations. In addition, we have optimized this structure theoretically. With a proper choice of structure parameters, we can design an AlGaInP laser diode with a transverse divergence angle as narrow as 8° while maintaining a low threshold current density.