Questions about source

[yu-ting-py]

I have some questions:

1. Your script "perform_fdtd.py" uses a magnetic current as a point source. Why not use electric current?
2. How do choose "cfreq" and "fwidth" parameters in "perform_fdtd.py"? What do they change?

Thanks!

[Trel725]

Hello,

1. Magnetic field in Z direction will cause electric fields lying in the XY plane. Quotation from the MEEP documentation:

The consequence of this is that the fields can be chosen purely polarized: either Hz polarized (electric field in the plane and magnetic field in the z direction) or Ez polarized (magnetic field in the plane and electric field in the z direction).

2. These parameters define a frequency range for the simulation. E.g. if you want to cover the range 1-1.5 um, then you first need to calculate the corresponding meep frequencies (since meep uses its own frequency definition, see docs)

   f1 = 1/1 um = 1  
   f2 = 1/1.5 um = 0.667 

   With that freqs in mind:

   cfreq  = (f1+f2)/2 (central frequency of Gaussian pulse)
   fwidth = (f1-f2) (width of Gaussian pulse)

That's it.

[yu-ting-py]

Hi

Thanks for your response.

If I want to change source into a plane wave propagating along x- or y-axis, what do I need to change?

[Trel725]

Please see the Meep documentation here or here. However it makes little sense since you will be limited to a single frequency.