# Phase discontinuity

I always have a discontinuity in the phase of the Electric field either along x (angle(Ex)), or along y (angle(Ey)) or along z (angle(Ez)). I attached an example file.
I’m not understanding the origin of the problem!

discontinuity_question.fsp (279.5 KB)

Dear @abeer.al-mohtar

This is because angle command returns the phases between -pi to +pi. If you want to avoid discontinuity, you can use unwrap command. This link might be also useful for you to read:

Thanks

Thank you for your answer, however of course by discontinuity I didn’t mean a jump from pi to -pi. I understand that the phase comes wrapped with values between pi and -pi. The discontinuity that is bothering me is a step of like 2 radians at the center of the image that stays there after the unwrap command.

Dear @abeer.al-mohtar

To answer your question, I need some clarification from you. Can you please explain how you are getting this data? There were few monitors and I was not sure what you were referring to as the center of the image. A screenshot of the results will be very useful too.

Also, can you explain why you are not expecting to see such a jump in phase? DFT monitors record time domain field data, and then by Fourier transforming them, they extract the field data in frequency domain. While interpreting phase data might be easy in some cases (like a plane wave propagation), it will not be trivial in complicated cases. This is because the way that the DFT monitor works in which what is shown as the phase is the phase of all electric field recorded in these monitors. Thus, in complicated geometries, phase can be affected by reflected light, or the light that is trapped inside a cavity.

Thanks

Hello again!
I detailed in the attached document what do I mean by phase discontinuity and how I’m getting it. I’m not expect to see such a jump in the phase because physically all the phase of Ex, Ey, Ez should be the same. The phase are actually the same except for this phase jump. though I’m not understanding the origin of it.
Thanks for your help.inquiry_lumerical.docx (267.2 KB)

Dear @abeer.al-mohtar

Thank you for additional information. I think I understand your question now.

As I explained in my earlier post, DFT monitors record the time domain electromagnetic field data. Since this data is accumulated over the entire simulation time, it includes all the field data that passes through any specific point. This basically means that for complicated structures that includes reflection from edges or can trap electromagnetic filed inside a geometry, light can pass a point multiple times. Thus, interpreting the phase data for these cases will be quite challenging.

For example, you can try to set a simulation with a plane wave source shined on a substrate at angle. If you fulfil total internal reflection, recorded data at a point will include both incoming and reflected data. Even for such a simple geometry, you will get a very complicated phase data.

Please let me know if you have any supporting reference that verifies your claim i.e. you should not see a phase jump on your profile and I will be glad to discuss it further.

Thanks