{"id":396856,"date":"2024-12-10T00:27:41","date_gmt":"2024-12-10T00:27:41","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/incorrect-refractive-indices-from-sellmeier-model-in-fde\/"},"modified":"2024-12-10T20:19:41","modified_gmt":"2024-12-10T20:19:41","slug":"incorrect-refractive-indices-from-sellmeier-model-in-fde","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/incorrect-refractive-indices-from-sellmeier-model-in-fde\/","title":{"rendered":"Incorrect Refractive Indices from Sellmeier Model in FDE"},"content":{"rendered":"<p>&lt;p&gt;&lt;span style=&#8221;font-size: 12pt;&#8221;&gt;Hello,&lt;\/span&gt;&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;font-size: 12pt;&#8221;&gt;I have created a Sellmeier model for a material I am simulating. My model parameters follow this <a href=\"https:\/\/optics.ansys.com\/hc\/en-us\/articles\/360034394634-Standard-optical-permittivity-material-models-in-FDTD-and-MODE#toc_8\">equation on Lumerical&#8217;s documentation<\/a>. This equation also closely matches&nbsp;<a href=\"https:\/\/en.wikipedia.org\/wiki\/Sellmeier_equation#:~:text=the%20equation%20consisting%20of%20three%20terms\">Wikipedia&#8217;s equation<\/a> under the assumption of long wavelength. Using these equations, I&#8217;ve verified by hand that the model parameters (picture below) I&#8217;ve entered into my Sellmeier material give me the refractive index I desire (n~2.13).&lt;\/span&gt;&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;font-size: 12pt;&#8221;&gt;However, when I run my FDE simulation, the index profile shows me a waveguide with an index of n~1.6. I&#8217;m not sure where this is coming from. When I go to the materials database and materials explorer, this value is also n~1.6. I&#8217;ve already made sure to switch from epsilon to n in the materials explorer when plotting the data. What&#8217;s further confusing is that 1.6^2 = 2.56 =\/= 2.13, so it is not simply a confusion between the materials database model accepting parameters for epsilon (~n^2) as opposed to parameters for n.&lt;\/span&gt;&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;font-size: 12pt;&#8221;&gt;Are there any recommendations on what else I should check to ensure that my waveguide refractive index is correctly modeled via my Sellmeier parameters? Using the Sellmeier model is important since the dispersion model is crucial for the simulations I am running. Please let me know if any additional information is required from my end. Thank you for your time and help!&lt;\/span&gt;&lt;br&gt;&lt;br&gt;&lt;span style=&#8221;font-size: 12pt;&#8221;&gt;Best regards,&lt;\/span&gt;&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;font-size: 12pt;&#8221;&gt;AD&lt;\/span&gt;&lt;\/p&gt;&lt;p&gt;&lt;span style=&#8221;font-size: 12pt;&#8221;&gt;Relevant Photos:&lt;\/span&gt;&lt;\/p&gt;&lt;p&gt;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/10-12-2024-1733788827-WG_Model.png\" alt=\"\" width=\"424\" height=\"309\" \/>&lt;\/p&gt;<\/p>\n<ul>\n<li>The red material here is my Sellmeier material.<\/li>\n<li>The teal material is an object defined dielectric with n=2.1344.<\/li>\n<li>The sea blue material below the teal one is also an object defined dielectric with n=1.486.<\/li>\n<li>When I replaced the red material with my teal one (n=2.1344), I have observed my desired TE mode. Therefore, I know my FDE simulation works as expected.<\/li>\n<\/ul>\n<p>&lt;p&gt;&nbsp;&lt;\/p&gt;&lt;p&gt;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/10-12-2024-1733790015-MaterialsDatabase.png\" alt=\"\" width=\"433\" height=\"400\" \/>&lt;\/p&gt;<\/p>\n<ul>\n<li>These are the parameters that I have set up into the materials database. The relevant one for this FDE simulation is the zz direction, I believe.<\/li>\n<li>The anisotropy is important for my material, especially when I transfer these simulations to FDTD.<\/li>\n<\/ul>\n<p>&lt;p&gt;&nbsp;&lt;\/p&gt;&lt;p&gt;<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/12\/10-12-2024-1733790267-Eigensolver_Results.png\" alt=\"\" width=\"435\" height=\"211\" \/>&lt;\/p&gt;<\/p>\n<ul>\n<li>These are the results from my FDE simulation. With 20 trial modes, a signle mode was found with an effective index of 1.66.<\/li>\n<\/ul>\n","protected":false},"template":"","class_list":["post-396856","topic","type-topic","status-closed","hentry","topic-tag-3DFDTD-1","topic-tag-database","topic-tag-eigenmode","topic-tag-FDE-1","topic-tag-material-database","topic-tag-refractive-index"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Hello,I have created a Sellmeier model for a material I am simulating. My model parameters follow this equation on Lumerical&#039;s documentation. This equation also closely matches Wikipedia&#039;s equation under the assumption of long wavelength. 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