{"id":163373,"date":"2021-10-25T19:02:45","date_gmt":"2021-10-25T19:02:45","guid":{"rendered":"\/forum\/forums\/topic\/question-on-s-matrix-and-mode-overlap-in-fde\/"},"modified":"2022-01-05T19:26:53","modified_gmt":"2022-01-05T19:26:53","slug":"question-on-s-matrix-and-mode-overlap-in-fde","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/question-on-s-matrix-and-mode-overlap-in-fde\/","title":{"rendered":"Question on S matrix and mode overlap in FDE"},"content":{"rendered":"
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Hi All<\/p>\n

I'm designing a Fiber-chip coupler and find a wired thing. <\/p>\n

From this example, https:\/\/support.lumerical.com\/hc\/en-us\/articles\/360042305354-Edge-coupler<\/a><\/p>\n

The definition of total coupling efficiency is mode overlap between fiber mode and the coupler mode times the adiabatic mode transfer efficiency from coupler tip mode to the waveguide mode. <\/p>\n

In the example project, there is no problem, the mode over lap is about 90%(or higher) and the total coupling efficiency is about 85%. So we can know that the adiabatic transfer efficiency is also higher than 90%. <\/p>\n

When I make some change on the structure, something wired happened. For example, deleting the three silicon nitride layers. The mode overlap will drop greatly, to about 50% (without fiber position optimization). However, the transmission efficiency (S21^2) is 70%. This is wired because follow the principle of coupler, the 70% should come from 50% times the adiabatic transfer efficiency. Even if the second efficiency is 100%, the result should not be 70%. <\/p>\n

Do someone know where this problem comes from? I'm really confused…..?<\/span><\/p>\n","protected":false},"template":"","class_list":["post-163373","topic","type-topic","status-closed","hentry","topic-tag-adiabatic","topic-tag-coupler-1","topic-tag-fiber"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t