Theoretical investigation on semiconductor lasers with passive waveguides

Abstract

Semiconductor lasers with vertically integrated passive waveguides are theoretically studied using the coupled mode theory and exact calculation. Formulas for the threshold c w e n t 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 caluclated results show that the beam divergence can be greatly improved by paying a price of only a slight increase of the theshold current density. The operation mode selection is discussed. Attention i s also paid to the appearance of side lobes for very narrow far-field patterns. Discussions are given for device design. Recently, lasers with very small beam divergence have been achieved by engineering the cladding layers [9]-[ 131. Wu et al. utilized periodic-index confining layers to replace the conventional cladding layers and achieved high power coupling into a fiber[9]. Cockerill et al. used a depressed index cladding graded barrier structure to obtain a large size Manuscript