Incoherent simulation



Is it impossible to get incoherent results of far field? I would like to reproduce sunlight in FDTD.



Please check the link below for source dipole with spatial incoherence.

In the example, it has 2 dipole for spatial incoherent. However if you want more than 2 dipole for “spatial incoherent” then you can use the sum operator in the sweep tab that will apply a simple sum over the farfield results (which is a matrix).

The intensity E2 of 2 dipole with spatially incoherence will calculate by simulating each dipole and measure intensity each dipole, then 2 intensity of 2 dipole will be sum. And we will have the intensity of 2 dipole with spatially incoherent E1^2+E2^2.

The reason is that you are simulating one dipole at a time (using sweep) and then adding the farfield results, you are incoherently summing the farfield intensity results. However, to calculate the coherent farfield results, you need to simulate all dipoles in one simulation.

Here are two more links for your further help:

Hope this helps.


Thank you for your kind answer.

So, to reproduce sunlight in FDTD, do I have to use multiple dipoles, right?

I’ll try it, thank you.


Please let us know if it solves your query.
Thank you.


Hi @yamashita

I am not quite sure what is your specific goal, but if you are interested in sun light spectrum, we simply run the linear simulations in FDTD and then multiply the results by sun light spectrum in the post processing step. Please visit the link below for more details in this regard:



I am simulating optical properties of what we(our research group) fabricated before. However, they are obviously different from real properties.

I think this is due to neglecting of time coherence. In reality, sunlight is incoherent, but in FDTD, the source is usually coherent. So, I’d like to make time incoherence in FDTD. Transverse coherence length has already been taken into account.



Hi @yamashita

The dipole emission will depend on its polarization. You can obtain unpolarized light results by running three simulations for each dipole polarization and adding them incoherently, but the spatial distribution will not be same as sun light. For sun light, you can use plane wave source or TFSF source.

I hope this was helpful.


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