Learning Forum

[ANKITA CHOUDHARY]

I am not able to explain why by adding a symmetric and antisymmetric BC the purcell enhancement shows an enhanced Fabry perot like behaviour?

I tried it for 3 different unit cell length. I have attached a Picture to show the result . Which results are more trustworthy?

Is the BC set wrong for a fundamental TE mode diapole?

When I use the inbuilt mesh it gives no purcell enhancement why?

Should the mesh be set depending on the lattice parameter?

[Guilin Sun]

It is due to mesh change and possibly the dipole location on the mesh changes.

When symmstry BCs are used, it forces the meshing to be symmetric. The other aspect is, the location of the dipole on the Yee mesh can affect the result. It is better to locate the dipole on the polarization component place:

Please check the meshs. 

If you force the mesh to be symmetric:

Then using symmetry BCs will lead to the same result. Please try, and check the location of the dipole relative to the Yee mesh.

[ANKITA CHOUDHARY]

Thank you for the suggestion. I tried all of them and Unfortunately I dont get the same results as the one with just PML. Do you consider each mesh cell as a Yee cell. I here attach a screenshot maybe you can tell me here how and where the dipole should be placed employing the boundary condition? Or is there anyway how I could send you the simulation file to have a look. 

thank you 

[Guilin Sun]

Have you tried to force the mesh symmetric and then compare with symmetry BCs?

make sure the dipole is located at the Ey position in the Yee cell. You can zoom in the mesh and make sure it is there.

You can also use a monitor, and compare the monitor xy data with symmetry BCs and without, as well as force the mesh symmetric.

The change of the result is mainly due to the mesh change.

If you want to know more about Yee mesh and FDTD, please find a FDTD book, or some online resources.