Al bowtie chain


I decided to make a new post with regard to simulating the bowtie structure.
I’m trying to reproduce this paper results: Wang et al. - 2019 - Design of Aluminum Bowtie Nanoantenna Array with Geometrical Control to Tune LSPR from UV to Near-IR for Optical Se.pdf (2.8 MB)
However, I couldn’t get any of the presented results. I was trying different BCs and mesh size but nothing brought me closer to them.
Could you please help me find the mistake in my thinking? :slight_smile:
Thank you in advance.

This is my file with the model
Al_bowtie_paper_20200520.fsp (562.2 KB)

Hello @eks,

It should defintely be possible to replicate these results given that they used Lumerical FDTD in the paper with our standard material library. It seems they did a lot of analysis that may require some advanced scripting. I would check the material explorer to make sure you have a solid fit given the bandwidth of the simulation.Your sapphire for example:

The refer to the paper’s description.

Two detector boxes were used to measure the spectral response. The
periodic boundary condition was used in the x-direction, while
the perfect matching layers (PML) were used in the z- and ydirections (Figs. 3f and 8a). The time monitors were used to
detect the change in the electric field over time. An ultrafine 1-
nm mesh size was used in all simulations. A refractive index
of nsup = 1.0 was chosen for air to generate an asymmetric
environment while indices for Al and SiO2 were obtained by
dispersion relation provided by Palik. For the given geometric
parameters of BNA array, the angle of incidence and polarization orientation of the electromagnetic field were also swept
to understand their dependence on LSPR peak position and Efield EF. For a given BNA parameter, the effective index of
antenna environment was numerically changed in the range of
1.33 to 1.95 and spectral reflectance was simulated for normal
incidence to understand the applicability of these BNA structures as inexpensive refractive index sensors. The absorbed
power was calculated by P = −0.5ω|E|
2 Im(ε), where ω = 2πf,
f is the frequency of the light, |E|
2 is the electric field intensity,
and Im(ε) is imaginary part of the dielectric function

See setup Diagram

From what I can see they use air as the background, and they have employed a smaller mesh. The resonant wavelength is pretty sensitive to the mesh size. It seems that they are using a diffracting plane wave in y in order to use PML BC in this direction. Finally, you may want to clean up the time signal or increase your sim time. You are looking for a spectrum from the time monitor that looks like this.
Currently, it looks like this

I am not sure where the 2um artifact is coming from and there seems to be some noise around 1100nm. I think you could get better results apodizing the time-signal.

Thanks for the reply.

  1. For me, their setup diagram doesn’t converge with the description, based on that and their diagram it would mean that their FDTD field contains 2 bowties, but then the P0 point would be not in the gap between triangles but between two bowties. If the diagram is correct then as I understand they made a periodic condition parallel to the bowtie axes, which also is not in agreement with the description. I’m slightly confused here. :confused:

  2. Could you please explain to me more or give some tips on how to find a correct apodization type and time?

  3. and what does it mean clean up the time signal? I noticed that in my other model (similar but single bowtie) I have the same noise and spectrum shape like here. Which would mean that in both cases, I’m doing something wrong during the model set up.

Thank you in advance.