Waveguide modes¶

kind: "mode", model lightsmith.problems.ModeProblem. The eigenmodes of a waveguide cross-section in the xy plane, propagating along +z. The waveguide can be straight or bent.

Fields¶

Field	Meaning
`structures`	2D structures (profile and material) of the cross-section
`background`	Cladding material
`window_center_nm`, `window_size_nm`	The computational window. Set the y size to 0 for a slab (1D) problem.
`wavelengths`	Vacuum wavelengths in nm
`num_modes`	Number of modes (default 2)
`target_neff`	Search near this effective index. Default: the highest index in the window.
`bend_radius_nm`	Bend about the y axis; `None` means straight
`include_fields`	Return the mode fields
`options`	Per-method solver options

Result¶

ModeResult.modes[wavelength][mode], sorted by decreasing neff_real. Each mode is a ModeData with:

neff_real and neff_imag;
ng, the group index;
te_fraction, the share of transverse |E|² in Ex;
loss_db_per_cm;
effective_area_um2;
field, when requested.

Solvers¶

FDE: full-vector finite differences, with bends and PML.
lightsmith.circuits.waveguide_from_modes turns a mode result into a waveguide compact model for circuits.

Example¶

import lightsmith as ls
from lightsmith.problems import ModeProblem, Rectangle, Structure2D

strip = ModeProblem(
    structures=[Structure2D(profile=Rectangle(size_nm=(500, 220)), material=ls.ConstantIndex(n_real=3.476))],
    background=ls.ConstantIndex(n_real=1.444),
    window_size_nm=(3000, 2000),
    wavelengths=[1500, 1550, 1600],
    num_modes=2,
    options={"fde": {"grid_spacing_nm": 20}},   # coarse grid for a quick look; refine to converge
)
res = ls.solve(strip)
print(res.modes[1][0].neff_real, res.modes[1][0].ng)