External cavity mode structure of a two-mode VCSEL subject to optical feedback

We consider a multi-transverse-mode vertical-cavity surface-emitting laser (VCSEL) subject to optical feedback. The system is modeled by a partial differential equation for the spatial carrier population, which is coupled to delay differential equations for the electric fields of the participating transverse modes that are subject to external optical feedback. We consider here the case that the VCSEL supports the two basic, rotationally symmetric, linearly polarized optical modes L