Spectral identification of transverse lasing modes of multimode index-guided vertical-cavity surface-emitting lasers

The identification of lasing modes in vertical-cavity surface-emitting lasers (VCSELs) is usually based on the polarization-resolved near-field pattern identification, a method difficult to apply in the presence of multiple transverse modes. We study lasing modes of a multitransverse mode index-guided VCSEL under dc pumping conditions by considering in detail the modes' spectral positions. The experimentally observed spectra are compared with theoretical calculations, based on a recently developed method for vectorial VCSEL eigenmodes [D. Burak and R. Binder, Appl. Phys. Lett. 72, 891 (1998)]. This allows for the identification of transverse lasing modes as a function of the pumping current. Two main effects that influence the spectral characteristics of the VCSEL are considered in our approach: temperature-induced linear shift of lasing wavelengths with increasing pumping current and switching of the lasing mode between different eigenmodes of the VCSEL cavity. The obtained temperature-dependent shift of the lasing frequencies agrees reasonably well with the value known from previous experimental estimations.