Uploading diffraction beam splitter example

[FilipeFcp]

No description provided.

[FilipeFcp]

Hi Guys,

I created an ID notebook based on some interesting results I found while working on a customer model. I thought this might be a good candidate for the Autograd example library.

Could you please take a look when you have the time? Your comments on whether this is a good fit for the library are greatly appreciated.

If you decide it's not quite right for the public examples, no problem, we can just keep it as an internal reference.

[github-actions]

Spell Check Report

Autograd26DiffractiveBeamSplitter.ipynb:

Cell 19, Line 1: 'analyse'
  > Next, we will define a function to analyse the [DiffractionMonitor]() data and evaluate the total power inside the desired diffraction orders, and also a penalty to ensure equal distribution of the intensities.

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[tomflexcompute]

Thanks @FilipeFcp this is a very informative and practical example that we should definitely include in the documentation. A few comments:

1. For the figure of merit, can you explain the exact function you defined and why you chose this form in the markdown comment above it?

2. For the diffraction power plot, I would suggest a higher contrast colormap like hot for example. viridis is little weak in my opinion.

3. The final design performs very well, but it seems to contain small features. Maybe add a comment about it, or even better, use something to characterize (qualitatively maybe) the minimal feature size. Then put a note that to ensure minimal feature size is compliant with fab, users can play with the fab panelty, filter, etc.