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# Concentric grating setup of blazed DOE imaging lens using RCWA

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Is it possible to set user-defined concentric planes of the grating in the features of a blazed DOE imaging lens?

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Best answer by Michael Cheng 9 September 2022, 11:01

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Userlevel 5
+2

Hi Kazuki,

As Sandrine mentioned, we cannot truly include multi periods in the grating with this RCWA model. However, if you are looking at a compond grating, such like the paper below, I think it’s possibl.

https://www.researchgate.net/publication/313799572_Simulation_methods_for_multiperiodic_and_aperiodic_nanostructured_dielectric_waveguides

The grating in this paper has several sub periods, but they are all inside a larger single period. We can simply build the model with User-Defined text. As you mentioned, this means you will need to manually add several sections as needed.

The above example only includes one section, but you can define more than one. The format will be something like below.

Layer
*****
Section
*****
Section
*****
Layer
*****
Section
*****
Section
*****

I hope this is clear. Please let me know if you have any more questions.

Thank you.

Userlevel 6
+2

Hi Kazuki

For the DOE like a Fresnel lens, you might have a solution in this article: https://support.zemax.com/hc/en-us/articles/7772225130259-Realistic-modeling-of-relief-type-diffractive-intraocular-lenses-using-User-Defined-Surface-DLLs. The lens sag is described in a dll. Basically it uses rays in the near field and then a Fourier transform (PSF) for the far field. Not sure it can help but I would recommend having a look at the article.

For the periods in one layer, I think you can only have one period. I’ll check with my colleagues.

Hello Sandrine Thank you for your mention.

(1) DOE shape What I was considering was a DOE shaped like a Fresnel lens. However, after reading the FAQ in the article below, I understand that this shape cannot be RCWA simulated at this stage. Thank you.

(2) Section There were people who often touched on other questions, I'm looking for details on how to have multiple Periods in one layer. Can it be achieved by adding sections with the attached layer editor?

Userlevel 6
+2

Hi Kazuki

Would you have a sketch or image to share of what you’d like to model?