setting up simulation parameters in FDTD

[perveen akhter]

Hi there,
I am working on this simple layout. it does work but simple Si 3.45 index is giving some oscillations at lower wavelengths and I have tried almost everything to fix this. but didn’t get it. can anyone please help me.

Attachments:

1. si-waveguide-reflection-test.fdt

[Aurelien Duval]

Hi Perveen,

I’ve tried to run your example. However I don’t really anything wrong with it. Could you be more specific, for example a plot of the oscillations?

Thanks

Aurelien

[perveen akhter]

Thanks Aurelien for your reply.
the problem is that it doesn’t give a constant reflection,but with variations between 0.3 and 0.34 probably due to interference. so I was trying to get a more smoother reflection ,coz I plan to add metal nanoparticles on this subs and the plasmoinc effect is not as clear as it should be coz of this reflection interference. I am trying hard to find best APML no. of layers to minimize this.
I hope you got my question.
waiting for reply.
Perveen.

[Aurelien Duval]

Hi, with the project file you attached, I get 10^-18 W on the reflection observation area! It’s the computer’s way of saying 0.
Could you be more specific, for example giving a plot of the oscillations?

Which version of OptiFDTD are you using?

Thank you

Aurelien

[perveen akhter]

please find the attached reflection plot. I want to get a smooth/constant reflecion.
we have version 9.
thanks,
Perveen.

Attachments:

1. si-ref.ppt

[Aurelien Duval]

Ok, I understand better, thank you.

You should increase the number of PML layers to absorb more incoming light. For example with 64 layers, almost all oscillations are gone.

[perveen akhter]

did you change anything else too. coz I am still getting the same results. also I am using APML boundary conditions, not PML?
and no. of APML layer coefficients is 30.
any suggestions?
thanks.

[Aurelien Duval]

I cannot easily tell you if the inner workings or the simulation engine changed for that particular point between version 9 and 12.
Like I said, the more layers, the less reflections you will get, but the slowest the simulation will run.

[perveen akhter]

Hi there,
it seems that for a layout which is working fine, changing xy wafer dimestions changes the results a lot, keeping same mesh size and even increasing the timesteps doesn’t produce the same restuls as original layout. how to compensate the wafer size effects?
thanks.

[perveen akhter]

Hi there,
it seems that for a layout which is working fine, changing xy wafer dimestions changes the results a lot, keeping same mesh size and even increasing the timesteps doesn’t produce the same restuls as original layout. how to compensate the wafer size effects?
thanks.

[Damian Marek]

Do you have a more recent project file? I could take a look.

[perveen akhter]

please find the attached layout and the results. I started with gold np sample# 52 and change the size n getting a lot of noisy peaks.
thanks,
Perveen.

Attachments:

1. Ag_np_in_Si.fdt
2. transmission-of-50nm-Ag-np-in-Si.pptx

[Damian Marek]

Ah, the first thing I notice is that you are using periodic boundary conditions for the x and y dimensions. When you modify the x and y; lengths you are effectively changing your periodic lattice, or the distance between nano-particles.

[perveen akhter]

so bigger wafer size, means larger distance betweeen particles, so no interaction, so I should get better results. but doesn’t work that way.

[Damian Marek]

Are you trying to simulate a periodic structure? If not I would suggest simply using absorbing boundary conditions on all boundaries and use a Gaussian spatial input instead of the rectangular.

[perveen akhter]

thanks, if you can send me a layout. or modify my layou n send to me. I am using version 9. thanks a lot.

[perveen akhter]

Hi Damien,
I need your help with this layout simple thin film on si substrate with input at 45 deg. for some reasons I am getting negative absorption.
attached is the layout and plot.
thanks,
Perveen.

Attachments:

1. 45-degree-input-results.ppt
2. SiC-film-on-Si.fdt

[Damian Marek]

Hi Perveen,

The silicon carbide material is defined with a positive imaginary part of the index of refraction. In engineering convention (and OptiFDTD convention) this means an amplifying medium, not a lossy one. You may want to change that to a negative imaginary part. This amplifying effect is what I assume is giving you a negative absorption.

Regards

[perveen akhter]

still getting negative absorption. could this be coming from any interference coz of input angle being 45 deg????
thanks,
Perveen.

[perveen akhter]

first slide is for radius50 nm, second for 10 nm

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