How to get confinement factor in 2D photonic crystal



I’m making a 2D photonic crystal (by etching) in a homogenous substrate.
because the PC layer and substrate below PC are the same material, the confinement from refraction index difference is very weak, the PC effect is hard to estimate.

How can I know the confinement factor in this structure? what wavelength&power leaks to the substrate and disappear?

Can I use the FDTD solution to get this answer? Thanks.


Hi KuanYu,

Do you have a specific definition of the confinement factor which you would like to use? If so, I may be able to help you with that.

We do have a modal volume analysis group in FDTD Solutions which can be used to characterize the size of the resonant mode, and there’s more information about it here:

You can also analyze the Q factor of the cavity to characterize the resonant frequency and decay rate of the resonant mode supported by your structure:

Regarding determining the wavelengths at which power flows into the substrate, I would suggest adding a 2D frequency domain power monitor at the interface of the cavity and substrate and looking at the transmission result through the monitor which will give the net power flowing through the monitor into the substrate as a function of wavelength or frequency. By default, the transmission result is normalized to the analytic power injected by the source, so if you are using dipole sources, you may need to re-normalize the results by the power which is actually injected by the dipoles which is discussed here:

I hope this helps!


Hi KuanYu,

I used a similar method as described in nlui’s post for the extraction of photonic crystal cavity leakage in the following paper: JOSA B, Vol. 31, pp. 3008-3017 (2014)

By enclosing the cavity with a box of 2D frequency domain transmission monitors, you can see the fractional leakage in each direction. If your cavity is symmetric, you might only need one monitor per direction.

Hope this helps!