Empirical loss model for tidy3d mode solver

[simbilod]

Users can now empirically model the impact of surface scattering on waveguide propagation loss

This is done by adding a small parametrizable layer of imaginary index at the waveguide boundary as per this reference that can be calibrated to data. Top and side interfaces are treated independently.

While it is less robust than a full scattering treatment as per other references, the latter still requires external knowledge of RMS roughness and correlation length, in practice also calibrated from data. Both approaches also agree somewhat in the sense that ultimately, both only consider the overlap of the mode with the waveguide interface.

Example use:

wg = Waveguide(nmodes=2, 
                    wg_width=500*nm, 
                    wavelength=1.55, 
                    wg_thickness=220 * nm, 
                    slab_thickness=90 * nm, 
                    ncore=si, 
                    nclad=sio2,
                    loss_model=True, # boolean flag to trigger loss evaluation, default to False
                    sidewall_k = 1E-4, # imaginary index of scattering layer (sides)
                    top_k = 1E-4, # imaginary index of scattering layer (top)
                    sidewall_sigma = 20*nm, # thickness of scattering layer (sides)
                    top_sigma = 20*nm, # thickness of scattering layer (top)
                    resolution = 400,
                    cache=None,
                    precision='double'
                    )
wg.plot_index(func=np.imag) # new argument to pass callable to plotting function

This results in

print(wg.neffs)
print(wg.get_loss()) # new function to get loss in dB/cm

[2.58589854+6.95743124e-06j 2.16344   +9.52938134e-06j]
[2.44969153 3.35526776]

Note that fine resolution is required, which makes this method better suited to FEM, see the new package femwell if interested

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 0.80%.

Quality metrics	Before	After	Change
Complexity	6.31 ⭐	6.57 ⭐	0.26 👎
Method Length	116.55 🙂	122.47 😞	5.92 👎
Working memory	14.71 😞	14.70 😞	-0.01 👍
Quality	52.09% 🙂	51.29% 🙂	-0.80% 👎

Other metrics	Before	After	Change
Lines	907	954	47

Changed files	Quality Before	Quality After	Quality Change
gdsfactory/simulation/gtidy3d/modes.py	52.09% 🙂	51.29% 🙂	-0.80% 👎

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
gdsfactory/simulation/gtidy3d/modes.py	Waveguide.compute_modes	19 😞	822 ⛔	28 ⛔	17.37% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
gdsfactory/simulation/gtidy3d/modes.py	Waveguide.get_n	11 🙂	497 ⛔	19 ⛔	28.01% 😞	Try splitting into smaller methods. Extract out complex expressions
gdsfactory/simulation/gtidy3d/modes.py	plot	6 ⭐	183 😞	15 😞	45.96% 😞	Try splitting into smaller methods. Extract out complex expressions
gdsfactory/simulation/gtidy3d/modes.py	plot_sweep_width	5 ⭐	206 ⛔	13 😞	47.80% 😞	Try splitting into smaller methods. Extract out complex expressions
gdsfactory/simulation/gtidy3d/modes.py	Waveguide.compute_mode_properties	2 ⭐	207 ⛔	11 😞	54.00% 🙂	Try splitting into smaller methods. Extract out complex expressions

Legend and Explanation

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The 👍 and 👎 indicate whether the quality has improved or gotten worse with this pull request.

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[codecov]

Codecov Report

Merging #831 (69705fc) into master (d759947) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #831   +/-   ##
=======================================
  Coverage   74.66%   74.66%           
=======================================
  Files         425      425           
  Lines       20979    20979           
  Branches     2840     2840           
=======================================
  Hits        15664    15664           
  Misses       4444     4444           
  Partials      871      871           

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[simbilod]

fixing pre-commit now

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
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[joamatab]

Thank you Simon!