Lateral mode selection in a surface DBR ridge-waveguide laser diode

The coupling coefficient for various geometric parameters of the surface DBR and ridge waveguide was calculated based on the coupled modes theory. The calculated reflection spectra of the DBR were obtained for various lateral modes depending on the width of the lateral waveguide. It is shown that the lateral modes selection is related to the optical confined factor of the two-dimensional TE mode distribution under the ridge. Selection is observed only for the last emerging mode, as long as it is weakly localized under the ridge. It allows to increase the width of the emitting area while maintaining the single-mode generation due to a significant difference in the DBR reflection for the fundamental and first lateral modes.