Investigation of anomalous lasing in vertical-cavity surface-emitting lasers of the 850-nm spectral range with a double oxide current aperture at large gain-to-cavity detuning

Results of investigation of static characteristics of the vertical-cavity surface-emitting lasers (VCSEL) of the 850-nm spectral range based on strained InGaAs/AlGaAs quantum wells in a wide range of current-aperture sizes are presented. The reasons for their anomalous behavior at large design gain-to-cavity wavelength detuning are analyzed. Lateral spreading of carriers in the plane of quantum wells and specific profile of oxide aperture (leading to formation of an effective two-step waveguide) in the studied VCSELs makes possible the existence of higher-order modes localized at the current-aperture periphery. Inhomogeneity of carrier injection across the current aperture in wide-aperture lasers leads to initial onset lasing via the higher-order modes. Subsequent transition to classical lasing via the lower-order modes with increase in current is caused by changes in the gain-to-cavity detuning with increase in internal laser temperature. Anomalous lasing via higher-order modes in the case of narrow-aperture VCSELs becomes possible due to increase in the diffraction losses at the edge of the oxide current aperture for the fundamental mode. In the process, not only a decrease in the gain-to-cavity detuning but also the effect of thermal lens are responsible for subsequent laser hopping to the regime of co-lasing via two modes.