Unidirectional incident wave for an electromagnetic wave simulation using the finite element method

In many simulations, the interference between the reflection from the structure and incident wave makes obtaining the reflectance difficult. This problem can be solved using unidirectional incident waves. This study developed a novel method to generate a unidirectional source using a simulation. For the periodic boundary condition, Gaussian source and nanobeam, we obtained an intensity ratio along the backward and the forward directions of the unidirectional incident wave of up to 0.45%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.45\mathrm{\%}$$\end{document} after optimization. The optimized source width for the given wavelength λ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda$$\end{document} was νλ/(2neff)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu \lambda /(2{n}_{\mathrm{eff}})$$\end{document}, where ν\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu$$\end{document} was a positive integer and neff\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${n}_{\mathrm{eff}}$$\end{document} the effective refractive index. This study was able to demonstrate that achieving a unidirectional incident wave for the periodic boundary condition, Gaussian source and nanobeam is possible using a simulation. This method can reduce the simulation time and computation memory needed for conventional calculations.