Subwavelength grating

I need to extract the effective index of a subwavelength grated structure and import it for FDTD. I have my file attached but I don’t know how to
get the effective index for the whole structure. Can you please guide me? Thanks.
swg_s1.lms (9.2 MB)


Sorry I noticed I have uploaded a wrong file. Here is the corrected file.

swg_s1_corrected.lms (409.1 KB)

Hi @sanammoslemitabrizi

The FDE solver calculates the mode in the cross section of the waveguide and returns the filed profile and effective index for the supported mode.

Can you please elaborate what you mean by the effective index of the entire structure? Are you trying to calculate the bandstrcuture?


Thanks for your reply.
I’m building a new structure using swg in which I can control the effective index of the new structure by controlling the pitch and duty-cycle of the swg. Then I will use this new structure as building blocks for another circuit in FDTD.
For this purpose I need to find the characteristics of this newly built swg based structure to import to FDTD as a new material/structure.

Hi @sanammoslemitabrizi

I am not sure about your workflow. The bandstructure can be calculated in FDTD, and to calculate the effective index, you need to use FDE solver. You can learn more about FDE by looking at our online course or getting started examples:

Hope this answers your question.

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Sorry for the late reply. Thanks so much, I used FDE for normal grating (not sub wavelength) and it was useful. For now I don’t need swg but at some point I will and I’ll try FDE at that time. Thanks for you help.


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I saw that you were asking how to calculate the effective index of a SWG. I am really interested in this subject. If you managed to find a way, would it be possible to share it ?
Thank you


Hi @charbel.tannoury,

You can take a look at the following topic for a discussion on calculating the effective index of grating structures:

Let me know if you have any questions.