Modeling photonic-crystal surface-emitting lasers by guided mode expansion: Finite-size effects and higher-order modes

We investigate a three-dimensional simulation method for finite-sized photonic-crystal surface-emitting lasers (PCSELs) based on guided mode expansion (GME), which is capable of estimating lateral and vertical modal loss rates. The approach generalizes established three-dimensional coupled-wave theory (3D-CWT) by considering an arbitrarily large set of basis functions including higher-order lateral and vertical (waveguide) modes. Detailed comparisons between the two methods for an UV-C AlGaN PCSEL with hexagonal lattice reveal corrections with respect to modal wavelengths and threshold gains. Furthermore, we demonstrate that interactions with higher-order waveguide modes, which can only be taken into account by GME, could enable the experimentally observed wide-angle lasing modes that distort the far-field.