Learning Forum

[pdaghlian]

hello, I'm trying to set up a simulation to optimize material thickness to maximize reflectivity. I'm doing a 2D simulation with PML for all axes (since I plan to add particle substructures in the material eventually). This is currently just a slab of titanium dioxide with n=1 background. I've been experimenting between using plane / tfsf wave sources, but either way, I keep getting weird oscillatory behavior in my reflectivity/transmission plots. I'm unsure why this is happening, especially since I'm using PML boundaries and the movie monitor is suggesting that there isn't very good absorbance at the boundaries. 

any feedback is greatly appreciated.

[Kirill]

Hello,

 

- The oscillatory behavior you’re observing might be due to thin-film interference, which is typical when working with a thin dielectric slab like titanium dioxide. Interference patterns naturally arise based on the slab thickness and the wavelength of light.

 

- Depending on the specifics of your simulation, you might want to consider using periodic boundary conditions in the transverse direction (Y, in your case). This should help reduce unwanted reflections at the edges by allowing the waves to wrap around seamlessly, instead of reflecting off the simulation boundaries. Check also: Periodic boundary conditions in FDTD and MODE

 

- Otherwise, consider experimenting with the PML settings. See more on this topic in the article: PML boundary conditions in FDTD and MODE

 

- Finally, you may want to consider using other solvers to verify your simulations, like STACK or RCWA, see reference: STACK Optical Solver Overview