Coupled lateral modes in narrow stripe injection lasers

A modal description of lasers having a facet intensity distribution with deep central minimum and beam profile in the junction plane with strong forward maximum, such as have been observed in various types of narrow stripe lasers is presented. The difference in symmetry between near and far field prevents analysis in terms of either simple Hermite-Gaussian or simple box modes. Simultaneous resolution in wavelength and beam angle shows that the longtudinal mode groups are doublets of which one member radiates a beam of even and the other odd symmetry. The observations are interpreted in terms of the theory of a pair of strongly coupled dielectric waveguides, one located under each edge of the metal stripe contact. A model calculation of a thin double-heterojunction wafer enclosing a pair of dielectric waveguides formed by small abrupt discontinuities, with parameters adjusted to reproduce the observed intensity distribution along the junction plane, gave a frequency splitting of about 0.1 A compared to the observed splitting of 0.6 A. (U.S.)