RCWA/aRCWA - An efficient and diligent workhorse for nanophotonic/nanoplasmonic simulations - can it work even better?

In this contribution, fundamentals of both periodic rigorous coupled wave analysis (RCWA) technique as well as aperiodic (aRCWA) techniques will be reviewed, starting with standard algorithms and following with their important as well as alternative extensions and ingredients. Although today, these methods are also often called Fourier modal methods (FMM), we would prefer here their original name stemming from the diffraction grating analysis. The importance of these frequency-domain rigorous techniques has been even increased, as a plethora of novel designs of nanophotonic and nanoplasmonic structures is increasingly growing, not only bringing new physics into life, but also attracting photonics devices applications. As had been demonstrated, the original periodic RCWA method has become applicable also to modeling isolated structures, as photonic waveguides and cavities; these isolated objects being considered as a single period of “supergrating”, with a proper separation of neighboring “superperiods” in contrast to coupling in standard periodic structures. The extensions and ingredients primarily include, mostly, e.g. various correct (or fast) Fourier factorization schemes, adaptive spatial resolution techniques, symmetry considerations, incorporation of general fully anisotropic materials, as well as various variants of boundary conditions and correct field calculation procedures. Finally, several alternative approaches / modifications to several critical parts within the algorithm, which can improve the algorithm performance, in terms of time efficiency and / or computational requirements, will be presented. In previous couple of years, we have developed in-house 2D and 3D numerical tools based on RCWA / aRCWA methods for the analysis of nanophotonic and nanoplasmonic structures and systems. Also, such technical issues as computational capabilities, algorithm speed, memory and time requirements, and possibilities for their optimi- ation in terms of partial or even more pronounced improvements will be mentioned, too. These modeling techniques have significantly helped to the analysis of various subwavelength structures we have performed recently. Here, only two selected simulation problems will be discussed: (1) Bragg structures based on SWG structured waveguides, and (2) plasmonic arrayed structures with lattice resonances.