{"id":397296,"date":"2024-12-12T15:48:15","date_gmt":"2024-12-12T15:48:15","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/diverging-simulation-gain-layer-under-periodic-metallic-grating\/"},"modified":"2024-12-12T15:48:15","modified_gmt":"2024-12-12T15:48:15","slug":"diverging-simulation-gain-layer-under-periodic-metallic-grating","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/diverging-simulation-gain-layer-under-periodic-metallic-grating\/","title":{"rendered":"Diverging simulation: gain layer under periodic metallic grating"},"content":{"rendered":"<p>&lt;p&gt;Hello,&lt;br&gt;&lt;br&gt;I&#8217;d like to share with you an issue regarding the convergence of my simulations. I&#8217;m trying to reproduce some partial results from a previous work in which the authors propose the following syste: a gain layer under a metallic grating. The permittivity of the gain medium is modelled follwing the KB recomendations as a linear gain medium with the permittivity&#8217;s imaginary part negative. When I simulate the response of the layer in absence of the metallic grating, that is, the layer inmersed in an homogeneous medium with constant refractive index, it converges really fast. However, it diverges when the grating is activated. I think that the problem may be related to the angle of incidence of the modes generated by the grating. However, I have tried to work on the PML conditions to short it out (I tried steep agle PML with an increased kappa) but unfortunatelly It didn&#8217;t work. The simulation is 2D, with periodicity (double antisymmetric boundaries along the x-axis) and illuminated by a plane wave at normal incidence. I attach a screenshot with the system (gain medium=purple region) and the permittivity used (the fitting in the picture is wrong because I actually perform the simulation by sweeping over wavelength).&nbsp;&lt;br&gt;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734018260-mceclip0.png\" width=\"306\" height=\"442\" \/>&lt;br&gt;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/12-12-2024-1734018349-mceclip1.png\" width=\"563\" height=\"136\" \/>&lt;\/p&gt;&lt;p&gt;Does anyone have any idea what the problem might actually be and how to solve it?&lt;br&gt;&lt;br&gt;Thank you in advance for the help!&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-397296","topic","type-topic","status-publish","hentry","topic-tag-2d-simulation-1","topic-tag-gain","topic-tag-metasurface-1"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Hello,I&#039;d like to share with you an issue regarding the convergence of my simulations. 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