Band structure calculation of layered dielectric media
I would like to calculate and plot the band structure of the following structure in Lumerical FDTD:
- 1D photonic crystal which consists of periodic layered dielectric slabs (alternating GaAs and Air)
- the structure is periodic in x-direction and homogeneous in y- and z- direction
- unit cell size is 1um in x and in y and z i also set it to 1um (however y&z should not be relevant since it is a 1D photonic crystal and i am only interested in knowing the band structure along the x-direction)
This is what I did:
- the FDTD is set to Bloch B.C. in x-direction and periodic in y&z (see screenshot)
- I added the band structure analysis object and the dipole cloud as the source
- under the 'model' in the object tree I defined also the parameters (see screenshot) with a script I adapted from the examples on the lumerical webpage (https://support.lumerical.com/hc/en-us/articles/360042038213-Bandstructure-of-planar-photonic-crystal-with-a-square-lattice and https://support.lumerical.com/hc/en-us/articles/360041566614-Rectangular-Photonic-Crystal-Bandstructure), see screenshot of my 'model' setup
- I run a kx sweep (see screenshot) where I pick the kx parameter from the model and sweep from 0 to 0.5 with number of sweep points = 4 (to minimize computational time for debugging)
- with a script (also from the examples mentioned above) I plot the band structure (max_bands = 50 and number of points in kx sweep = 4)
These are the problems and questions:
- the band structure object seems to return acceptable results in the 'fs' and 'spectrum', however the kx sweep gives wrong results (see screenshot) after plotting it with the script
- It seems to be that the kx sweep is not executed properly, how can I fix this? I do not fully understand how the kx sweep is performed and thus do not know how to fix my problem
- what/how is the importance of defining parameters under the 'model' in the object tree? To my understanding the kx needs to be changed in the FDTD and dipole cloud for the sweep, and this is why i need to 'overwrite' the parameters through the model setup; is this correct?
- in the settings of the FDTD, when do i enter kx = pi/a as a value in SI units and when do i pick 'band structure' as unit?
If someone can explain me the proper setup and important points/steps to consider when calculating the band structure, I would be very thankful. I do not have a full overview of it yet and would like to learn how to adapt it to other cases as well.