Learning Forum

[Eugene Su]

In the Lumerical 2023 R1.3 Version 8.29.3401 RCWA simulation, two simulations were performed with the same structure and settings, except for the materials and maximum wavelength.

In the first simulation, the materials and minimum wavelength were 0.24 μm, and the maximum wavelength was 0.44 μm.

In the second simulation, the materials and minimum wavelength were 0.24 μm, and the maximum wavelength was 0.64 μm.

When comparing the Es.Ex data from the RCWAFieldMonitor at a wavelength of 2.4e-07, they are completely different.

Is this correct?

Thanks.

[Guilin Sun]

It is most likely due to material fitting. Although RCWA is frequency-domain solver, currently it still uses multi-coefficient model:

so when the wavelength range changes, the fitted result may be different. For the same geometry, different material will lead to different result. So please make sure the fitting wavelength range is the same for the two cases:

Please try and check if the result is about the same, if not exactly the same.

 

[Eugene Su]

Thank you for your response.
Both simulation settings have the option "override materials frequency range" checked.

[Guilin Sun]

 

Then please check if the diffraction angles (theta and phi) are the same. The monitor should give E field for each diffraction order (defined by theta and phi).

 

[Eugene Su]

Both are the same.

The first simulation:

 The second simulation:

We upgraded Lumerical to R2.0 yesterday. We will test if the same phenomena occur.

[Eugene Su]

We re-simulated two experiments using the latest version of Lumerical, and the results still do not match.

The first simulation:

The second simulation:

[Guilin Sun]

I tested a dispersive material but could not duplicate this issue when I used:

setnamed("RCWA","use wavelength spacing",1);

and override the material fitting wavelength range to be the same, for exmple 0.4~0.7um, whereas I tested 0.4~0.5um for 6 points,and 0.4~0.6um for 11 points for a silicon slab with air holes (adpoted from online example https://optics.ansys.com/hc/en-us/articles/4414567929235-rcwa-Script-command the script "rcwa" is depreciated now).

Maybe you can choose visualze the max frequency point and see if they agree.