Hello,

I have some questions about the source defined in Lumerical FDTD, especially on how source term in Lumerical relates to the FDTD governing equations in the code. I will use an example to explain my questions.

First question I have is: what the signal I see in “Source” object really is. Say I choose a dipole source in FDTD, and set the parameters as Fig 1. Since this is a dipole source, it should be a vector. However, in the “signal vs time” panel, it seems that the raw source signal is a scalar, changing in time. So is the signal actually the normalized amplitude of dipole source? The vector dipole moment in time is just the directional unit vector of the dipole multiply this signal?

Now, there are two ways to connect this source to electric field, charge source (Eqn 1 in Fig 2) or current source (Eqn 2). These two quantities are connected by the continuity equation, Eqn 3. Normally, I would think that the dipole moment is defined as usual by the charge source as in Eqn 4. But the governing equation of electric field in FDTD normally uses J (from Eqn 2) as source (governing equation Eqn 5). So my second question is: the source signal we defined in Fig 1 and the line we see in the “signal vs time” panel in Fig 1, are they rho as in Eqn 1 or J as in Eqn 2?

Third question is related to the second. I need to get the data for the source signal I use in my FDTD calculations, so I use a script provided by the Lumerical website (https://kb.lumerical.com/en/ref_sim_obj_sources_dipoles.html), shown in Fig 3. The parameters (namely frequency, pulselength, and offset) are obtained from the settings in Fig 1. The The third question is very similar to the second question: the “pulse” term calculated in this script, is it the same as what we see in the “signal vs time” panel in Fig 1? Is it rho as in Eqn 1 or J as in Eqn 2?

Thank you very much.

Fig 1:

Fig 2:

Fig 3: