Confinement Factor

[smgitrep]

Does Tidy3D have a method to compute the confinement factor of waveguide modes in user specified regions? Tidy3D does have a FluxMonitor, but it only applies to FDTD simulations. Is there a similar monitor that can be used to compute the confinement factor from ModeSolverData?

[momchil-flex]

Could you specify what you mean by confinement factor? If you run the mode solver and then use to_dataframe, you can get various information about the modes, including mode area. Is this what you are referring to?

[smgitrep]

What is the unit for mode area? By confinement factor, I mean the ratio of the power flow through a 2D-region to the total power flow of a mode (which is normalized to unit power or 1).

[momchil-flex]

The unit of mode area is micron ** 2. The definition is as given e.g. here

If you want to get the confinement factor the way you define it, I'm afraid we don't have a super explicit way to do it. However, I think you can do something like this to get the partial flux. Say you have mode_data computed already. mode_data.dot(mode_data) should be 1 as you say since we normalize to unit flux. Then you can do

# partial_size is the size of the plane over which you want to integrate
# make sure that one of the partial_size values is 0 as in the original mode solver (the normal direction)
monitor_partial = mode_data.monitor.updated_copy(size=partial_size) 
mode_data_partial = mode_data.updated_copy(monitor=monitor_partial)
partial_flux = mode_data_partial.dot(mode_data_partial)

Let me know if this works for you!

[smgitrep]

Thanks! While it only returns the real part, this also works:

mode_data_partial.flux.isel(mode_index=0, f=0)

It returns a FluxDataArray, while the .dot() method returns a ModeAmpsDataArray.