Learning Forum

[Soufiane El kabil]

Can You someone explain for me, why I see this lign in my Simulation

[Guilin Sun]

WIthout device configuration and simulation settings it is hard to know the cause. Please refer to 

Ansys Insight: Ansys Innovation Space–Forum and Feed and provide more details.

[Soufiane El kabil]

the wave is Plane in the Z-direction 

the BC is PML on all sides (2D)

a sample with 100 nm 

[Guilin Sun]

I do not know why you cannot post some screenshots. From your description it seems you used a plane wave source but used PML BCs. This is wrong since PML will truncate the plane wave causing diffraction.https://optics.ansys.com/hc/en-us/articles/360034382914-Understanding-the-diffracting-option-of-the-plane-wave-source

The correct way is to use periodic BC if it is normal incidence, or Bloch BC it is angled in xy plane since the propagation is along z axis.

[Soufiane El kabil]

Thank you for your answer, the screenshots of my simulation are

[Soufiane El kabil]

[Soufiane El kabil]

thank you for your answer, I hope that these screenshot will be helpful 

[Guilin Sun]

Thank you. As I repiled previously, plane wave cannot be combined with PML. Please refer the link I gave.

If this is a periodic structure, please use periodic BCs in the periodic axes, or Bloch BC in the plane of angled source.

If this is a non periodic structure, and you want to use plane wave, please use TFSF: 

Total-Field Scattered-Field (TFSF) source - Simulation object

Understanding source normalization in the TFSF source

Tips and best practices when using the FDTD TFSF source

Usually TFSF is not used to calculate transmission and reflection. If you have questions please write a new post.

 

[Soufiane El kabil]

Thank you for proviode for me some solution, but you should to know that The sample is infinite along x but it is not along y, where is semi infinite (no periodic), some other question, my Field must be along z, can you help me more to understand more why I can't use PML even the space between the edge of the sample and the monitor is so long .

[Guilin Sun]

Yes, when x dimension is infinite and if it has no isolated nano objects you should use periodic BCs;

Finite sized y diraction should use PML.

For 2D simulation, you can set the source polarization angle 90 to excite Ez.

I would strongly suggest you to watch some videos:https://optics.ansys.com/hc/en-us/sections/360007813194-FDTD100-List-of-videos

to get more information.

[Soufiane El kabil]

I use FDTD in Lumerical for 2D simulations, and I wonder why the simulations are limited to the x-y plane and not the x-z or y-z planes. If I want to conduct a 2D simulation in the x-z or z-y plane when the field is in the z-direction, how can I achieve this?

 

[Guilin Sun]

Yes you are right, currently it is only in xy plane for 2D simulation. Temporarily a possible solution for other plane 2D simulation is to set the 3rd dimension only one cell in size and use periodic BCs in this dimension.