add tutorial about source normalization

[FilipeFcp]

Hi all,
This is the example of source normalization related to issue #900.
Let me know if you think we should add, remove, or modify anything.

It was run using version 2.9-rc.1, with the fixes to the diffraction monitor included.

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[alec-flexcompute]

Excellent work @Filipe, this will be a super useful resource - this answers a number of my questions as well!

A couple comments:

1. Above cell 5, it might help to plot a couple of these simulations, so the user can quickly visualize what you're measuring

2. For the plot in cell 21, maybe connect the data points with a line to better illustrate the behavior

3. Above cell 22, a bit more explanation of what the simulation will do will be helpful

Other than that, I think this is great - super clear, illustrative, and useful!

[tomflexcompute]

Thanks @FilipeFcp . Very helpful content, especially the error on the monitor position, which I didn't realize before.

1. Consider adding doc string to the get_sim function since it's relatively long with many arguments.

2. For plane wave, "|E_0| is proportional to the source plane area" is incorrect right? |E_0| should be proportional to the area**(-1/2) as the figure below shows?

3. Since we are on this topic, shall we spend some time on custom field source and current source normalization just to make the tutorial complete?

[momchil-flex]

Thanks @FilipeFcp, great stuff! A few comments from my side too:

• I am a bit surprised by the diffraction monitor result at 20 degrees. It seems to have jumped quite a lot compared to the trend from the previous degrees. Since you're focusing on that data point exactly, I want to be sure that it's actually correct (I mean, it seems that the error goes down with resolution, but still it looks a bit fishy if there's a sudden jump). Maybe, at least for internal consideration, could you run this with more angles and we can see if there's some discontinuity we need to look at? If there's a discontinuity, I wonder if it may be related to a second diffraction order appearing in the simulation? In which case it would be affected by the simulation domain size.

• For the point dipole, instead of saying for a classical radiating dipole, let's either explicitly say classical radiating current dipole (as opposed to electric dipole, which will be normalized differently), or infinitesimal antenna with a fixed current density as in our FAQ. Also, mention that the formula you give is specific to an electric current dipole in 3D (and maybe link to our FAQ again).

• Just wondering why you use nu for the frequency instead of f as in the rest of our documentation (I believe?), or even just omega directly.

[FilipeFcp]

Hi all.
Thanks for the comments. I've fixed the issue and am now adding the current and custom source components.

@momchil-flex, I did some tests with more angles, and it seems odd. Using 2.9rc, for a plane size of 1 µm:

Changing the plane size to 1.5 µm:

That doesn't happen in 2.8.3:

Is it some issue with the monitor, or should I adapt something in the simulation?

The $\nu$ name was just old habits. I will change to omega to be more consistent with our documentation.

[FilipeFcp]

It gets much better with increased resolution. The previous results used 10 steps per wavelength.

Using 20:

Using 30: