Coupled waveguides in GaN-based lasers

GaN-based lasers include, apart from the separate confinement waveguide, a parasitic GaN buffer waveguide. The effect of coupling between the active laser waveguide and the buffer waveguide on the lasing modes is studied in terms of a coupled-mode formalism and a round-trip analysis. Assuming a low-reflectivity internal mirror, Fabry–Perot modes with an intensity envelope that resembles experimental measurements is obtained. The gradual change in the modes, taking part in the round-trip model, is presented as a function of wavelength and temperature. The influence of temperature changes on the peak wavelength of the output spectrum predicted by this analysis is in good agreement with experimental reports.