Spectrum at any time


In the process of the evolution of the spectrum, the spectrum is constantly changing with time. In the Rsoft,it can give the spectrum at any time about the Photonic crystals cavity by DFT,
So I want to konw whether the FDTD can give the same function.


Hi @phd.wangbo
In FDTD Solutions there are monitors like “frequency domain profile” monitors and “frequency domain power” monitors. These monitors perform Discrete Fourier Transforms (DFT) to calculate the electromagnetic fields as a function of angular frequency.
Please read this : https://kb.lumerical.com/en/index.html?ref_sim_obj_cw_norm_ring.html


Thank you for your help!@konslekk
In fact,I want to plot or image these figure as below.
These spectrum is about time variation with frequency or wavelength .Do you know how to plot or image it?


Hi @phd.wangbo,

To generate these kind of plots I think we need to know a bit more about what is being calculated in the simulation. Can you provide a link to the reference where these results are shown?


First,I think the FDTD method is an linear methord, so the there should not be energy transfer between different wavelength.But modes are not indecating the wavelength but a kind of fieled distribution so the energy transfer between modes still obey the linear law.

Then my suggestion is listed below:

First using mode expansion monitor to get the modes discussed ,

Second, using time monitor at the plane you are interested inand get the field
distribution. Using the modes from mode expansion monitor to decompose the field at a specific time and plane.Then you will get the amplitude of each mode at a specific time.