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Hi
indeed you have mised to define any material on the "small" domain 3 which is your Au I assume, there is a red "X" on the material showing something not OK ;)

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Good luck
Ivar

Hi Ivar:
thanks so much for the quick reply. It works now. However, the solution does not seem right. There is another thing that has to be fixed.
I did use the same parameters and material constants in version 3.5a and I was able to get the right mode.
My question is why I am not able to get the right mode with this version of comsol (4.3)?

I am attaching the 3.5a comsol file in which I got the right mode.

Hi

when I solve your 3.5a model as is in my 4.3a I get the same value for the effective mode index, but another field value. Now in eigenmode analysis, normally the field absolute value is arbitrary, its the mode shape that is important and the shapes looks similar.

So it could be that there is a slightly different normalisation factor between the two COMSOL versions, check the release notes,

But I cannot really say more, I haven't been working in optics/RF for some time so I do not have many references in changes over versions lately, but you could also ask "support" they must know ;)

But there are also users working in the optics field out here that might have some good remarks

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Good luck
Ivar

Hi Ivar:
thanks for the reply. I actually did not get the same refractive index for both comsol files(3.5a and 3.4) as you did.
I suppose to have the same index in both of them because I am solving the same problem and the solution is only one. I know you got the same index for both(3.5a and 3.4) comsol files but I do not know how.

to better explain what I need:
I attaced a comsol file called 50t_100w_2( done with version 3.5a) in which I got the right solution. Please open it again because I have modified it.

I also attached another comsol file called spp2( done with version 4.3) in which I have tried to get the same solution as in ( 50t_100w_2) . However, I did not get succees in doing this.

As you will see in the file (50t_100w_2) , I am trying to plot the y-component of the electric field.


I will look forward for your reply,
Naema

Hi:
the attachments are here
sorry for forgetting them,

Naema

Hi

the main error you are doing is that your total domain is less than a wavelength across, you need much more "free space to avoid that the exteral boundaries makes a "box" and change completely the behaviour of your model. Even using "infinite elements" to exend the model would be of interest.

Then you need a much finer mesh, it should be at least 5-10 elements across a wavelength in the material, hence 1300 nm/3.5/10 or some max 40 nm

This wil lend upt with quite some RAM requirements, you might need to consider to model only the half of your model and use a symmetry condition.

Check the model library,and the doc there should be some RF examples on how to adapt the max mesh size with the wavelength

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Good luck
Ivar