Theoretical investigation on semiconductor lasers with passive waveguides

Semiconductor lasers with vertically integrated passive waveguides are theoretically studied using the coupled mode theory and exact calculation. Formulas for the threshold current density and the far-field patterns are derived. The physical concepts of the modulation of the beam divergence by passive waveguides are given. The exact calculated results show that the beam divergence can be greatly improved by paying a price of only a slight increase of the threshold current density. The operation mode selection is discussed. Attention is also paid to the appearance of side lobes for very narrow far-field patterns. Discussions are given for device design.