Observation of reflection with respect to pillar height

fdtd

#1

@bkhanaliloo
@ie5003_allison

I am trying to optimize the pillar height, radius and pitch of the attached structure where it will have to show the minimum reflection and maximum absorption at the wavelength (350 to 900).

Sweep_Design.fsp (425.3 KB)

Question:
(1) If I want to sweep the pitch and observe the reflection at the wavelength (350nm to 900nm), do I need to take 2 pillars inside a unit cell?

In the website, they optimized a parameter( thickness of a material) with respect to reflection. The thickness that has the minimum reflection. But it has considered only one particular wavelength (like 550nm). But I want to have my answers like the one below.


#2

Hi @sbs019

You can have only one unit cell, but you need to update the FDTD simulation span accordingly. This is because you are using periodic boundaries and periodicity will change for different pitch values.

You ca ndefine a new figure of merit (FOM) under model that calculates the average transmission and then feed it to optimization object. Please visit the link below for more details on this regard:
Broadband Reflection Optimization

Hope this was helpful.


#3

Using FOM it only shows the mean transmission for an optimized thickness. How do I obtain a graph out of that? I want to obtain a graph that shows how the reflection changes with respect to height of the pillar (including z span1, z span2, z span3…three needs to change simultaneously).

Would you please briefly explain with some screen shots?


#4

Please help me with how can I obtain a graph like the one I am attaching here. Optimization using FOM only shows a particular mean transmission for a particular thickness. How do I see a graph?


#5

If I am not mistaken the left figure is just a plot of absorption versus pillar height and wavelength, i.e. there’s no optimizing going on in this plot. If that is all you need, to get the colour plot like this, you just run the sweep and then plot the result (right click on the sweep and click “visualize” and “R”). It’s not clear how the right graph is generated. Probably it is a plot of the maximum absorption for each pillar height. If true, you can either do this at the end once you’ve got the sweep results, or you may be able to calculate it as you are performing the sweep (by adding another parameter to the sweep results, which is the maximum of the reflection in your case).

Before all of that the first step is to get your sweep set up correctly. A tip for this is to right click on the sweep and select “animate”. Currently it is clear that nothing in your simulation changes as you sweep. The pillars are moving apart, yes, but that is all outside of the FDTD region, so these changes are having no affect on the FDTD region and every single sweep gives the same result. Probably what you want to do is to add a new parameter to the sweep, which is the FDTD span in the x direction. (So that the boundary of the FDTD region is always midway between pillars.) This will then keep the symmetry correct and give you the result you want.