Strange PC behaviour changing some parameters

[davcm]

Hello,
I made the Sample 2—Plane wave simulation based on the periodic cell of PhC of the third tutorial you propose in your Background tutorial. I changed a little bit the initial parameters (basically the initial radius) and I simulated. The graphics that I obtain can be seen in the attached word. In there we can realize that the sum of the reflected and transmited wave is constant: where there is a reflection, there is no transmision, and vice versa. But if I change the wafer material (from air to PBG_atom) and the structure profile (from PBG_atom to air) we can notice that the addition of the reflected and the transmited signals do not sum a constant value. Which is strange and I don’t know why it happens.

Do you know where am I doing something bad?

Thanks a lot,

DCM

PD: I attach the file that contains the second case (wafer: PBG_atom and structure: air). Simulations are done in 2D.

[davcm]

The graphics.

[Damian Marek]

This is a good question and the answer is not so simple. Basically though if the observation points are too close to the reflecting/transmitting medium you can get interference effects from the input pulse interfering with itself (near field). Even though this is a photonic application it is similar to this wikipedia page:

http://en.wikipedia.org/wiki/Near_and_far_field

which describes the complicated relation between power and electromagnetic fields close to an antenna. With this in mind I have redesigned your project file to be larger and with detectors father away from the crystal. I believe now the results make more sense!

As an aside, you should make sure that your input pulse is short enough to cover a wide enough spectrum for you results.

[davcm]

Hello Damian,
First of all, thanks a lot for your fast and helpful response. I see a little bit better why my simulation is not working as I would expect. But the fact is that it would be great for me to check the project you attached me and I can not open it because I am working with a 32.bit version. Could you attach it it ne in this version please?

Thanks a lot, again.

DCM

[Damian Marek]

Hi dacvm,

Unfortunately, I don’t have that version of the software installed, but the changes are very simple. I extended the wafer length to 25 um and placed the input field at 9 um.

The transmission observation point was moved to 24.6 um, the input detector was moved to 9.1 um and finally the reflection observation point was moved to 1 um. The photonic crystal structure was offset to 10 um.

I have attached a screen shot of the layout, hopefully that is clear enough.

Regards

[davcm]

Uau!
Thanks a lot!

Let’s see if the results are the expected ones! You’ve been very helpful Damian!

[davcm]

Hi again Damian,
I am sorry to ask so much but I still have the same result. I have realized that the project I attached in the first conversation was wrong: I told you that the material ofthe wafer was silicon and it was air. Also I made a mistake telling you that the cylinders were made with air: actually their material was PBG_atom. So I attach again the project (sorry about that). I made the same distribution you told me in your last message but the reflected and the transmitted signals don’t sum a constant factor (‘analyzer_picture.png’). If I change the materials, I check that it also works uncorrectly (reflection is not the initial signal – transmission (‘analyzer_picture_opposite.png’)) but not in the opposite case and that’s weard I think …

Regards,

David.

[Damian Marek]

You might have to modify the project a little more then. Try expanding the domain and see if that helps. Also instead of an observation point try observation lines, perhaps some of the power is being reflected at an angle and is missing the observation point.

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