Calculation of VCSEL lasing mode threshold gain with the weighted index method

We present an extension of the weighted index method (WIM) for calculation of VCSEL lasing mode threshold gain. The WIM is a modal technique which gives the best separable solution for the VCSEL modes in a variational sense. The approach for inclusion of threshold gain in the WIM is a generalization of the classic Fabry-Perot round-trip amplitude and phase conditions.