Characterization of Lateral and Longitudinal Mode Competition in Blue InGaN Broad-Ridge Laser Diodes

In blue GaN-based laser diodes with a 40 mu m broad-ridge waveguide, lateral modes of different order are selectively observed by high-resolution spectroscopy combined with lateral near-field scanning. Longitudinal mode clusters contribute to different lateral modes, close above the threshold current. Longitudinal mode competition is observed in each longitudinal mode cluster as intensity modulation and wavelength shift, repeating itself with a frequency of around 60-80 MHz. Despite the spectral separation of the different clusters and different lateral mode order, the mode competition processes share the same frequency and show a stable phase relation, especially at low currents. This indicates coupling of separate mode clusters via the charge carrier density. Due to the lateral modes occurring at separate wavelengths, lateral-longitudinal mode competition is found, which not only causes spectral effects but also time-dependent periodic variations in the lateral near field.