High-Resolution Spectroscopy of Blue High-Power Laser Diodes with a Fabry-Pérot Interferometer

In this work, it is aimed to study the interplay of different longitudinal mode combs corresponding to higher-order lateral modes of broad-area Fabry-Perot-type laser diodes. Coherent coupling of longitudinal modes of different mode combs influences the near- and far-field pattern of the diode. Herein, commercial state-of-the-art high-power laser diodes based on the (Al,In)GaN material system in the blue spectral range with a 40 mu m broad ridge are investigated. To spectrally resolve the different lateral modes, a sequential combination of a high-resolution double grating spectrometer and a Fabry-Perot interferometer (FPI) is used. The grating spectrometer acts as bandpass with a spectral width smaller than the free spectral range (FSR) of the FPI. The FPI with a finesse of approximately F=60$& amp;amp;Fscr; = 60$ boosts the resolution to 0.08 pm. A spectral clustering of lateral modes with increasing current and also a variation of the number of distinguishable lateral modes between 7 and 11 are observed. Within the current range from 1.25Ith to 2.25Ith, there is no clear evidence for coherent coupling. It is concluded that mode-pulling is not strong enough to coherently couple modes on the investigated time and wavelength range. Blue broad-ridge high-power laser diodes are investigated with ultrahigh-resolution spectroscopy. Utilizing a grating spectrometer and a Fabry-Perot interferometer allows to differentiate several longitudinal mode combs with sub-picometer resolution. No mode-pulling effects are observable. Mode spacing of 1 pm supports a coupling of the modes through carrier density in contrast to a process involving coherent coupling of the light fields.image (c) 2024 WILEY-VCH GmbH