Time resolved measurement of longitudinal mode competition in 405 nm (Al,In)GaN laser diodes

Abstract

We investigate the spectral and temporal behavior of conventional narrow ridge (Al,In)GaN laser diodes (LDs) emitting at a wavelength of about 405 nm, grown on low dislocation density GaN substrate. In time resolved measurements of the lasing spectra we find a quasi‐periodic hopping among several longitudinal modes, which leads to time‐averaged multimode‐like output spectra. The experimental data are compared to a multimode rate equation model that was adapted to the (Al,In)GaN material system. While mode hopping is well studied for other material systems, we investigate whether this mechanism is identical in blue (Al,In)GaN LDs (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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

“…The same sublinear trend has also been reported in previous papers. [28,29] In the investigated current range, in each mode cluster, there is only one predominant lateral mode to which multiple longitudinal modes belong. Mode competition between these longitudinal modes follows exactly the same mechanism as mode competition in narrow-ridge laser diodes, where only the fundamental lateral mode is active.…”

“…The sublinear dependency of mode competition frequency on the current is not straightforward to see from the equations, but numerical simulations of the spectral-temporal mode rolling behavior using the full set of rate equations [27,29,30] have been showing quantitative agreement with the measured behavior in narrow-ridge laser diodes. [28,29]…”

“…[19][20][21][22][23] In singlelateral-mode laser diodes, the interaction between neighboring longitudinal modes is known to result in symmetric and asymmetric cross-saturation, where the latter gives rise to self-repeating mode rolling through the spectrum. [24][25][26][27][28][29][30][31] Additionally, the laser spectrum is influenced by the formation of longitudinal mode clusters, [29,[32][33][34][35] which is attributed to fluctuations in quantum well thickness, indium content, optical gain, as well as spectral hole burning or plasma oscillations. We experimentally investigate devices with a 40 μm wide ridge at currents close above the threshold, because in this case the presence of fewer, lower order modes allows better to trace their dynamics.…”

Implementation and investigation of mode locking in GaN‐based laser diodes in external cavity configuration

“…Hereby, the center wavelength of a pulse chain moves toward longer wavelengths with a period in tens of ns. This behavior was found to play an important role in GaN‐based single‐section LDs and is explained by photon‐induced gain saturation of every longitudinal mode with itself and neighboring modes. In case of mode competition, the asymmetric gain saturation of the lasing mode is the driving force to decrease the gain of neighboring shorter wavelength modes and to amplify the gain of the longer wavelength modes.…”

Fast self-heating in GaN-based laser diodes

“…8 Mode competition, as described in Ref. 9 can also be ruled out as a possible explanation, as this would cause intensity oscillations of the individual modes. From the observations of a constant initial center wavelength of 443.1 nm and the increase in the total redshift with increasing input power, we conclude that this shift is a thermal effect.…”