Transverse Mode Mixing in a Coupled-Cavity VCSEL

Coupled-cavity VCSELs typically support two fundamental longitudinal modes. Their wavelengths as a function of the difference of the optical lengths of the two cavities display avoided wavelength crossing (or anticrosing). In this article, we numerically solve the set of Maxwell equations for a coupled-cavity VCSEL. We show that when brought closer spectrally higher transverse-order modes of different orders display not only wavelength crossing (as anticipated by the Helmholtz equation) but also avoided crossing.