REMSOL

REMSOL (Rust-based Electromagnetic Multi-layer Solver) is a high-performance solver for guided electromagnetic modes in 1D planar multilayer (slab waveguide) structures. The core engine is written in Rust for speed and exposed to Python via PyO3 bindings, built with Maturin.

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Capabilities

• Mode solving — computes the effective refractive indices (neff) of all guided modes supported by a given layer stack at a given free-space wavenumber k₀ = 2π/λ.
• Both polarizations — full support for TE (transverse electric) and TM (transverse magnetic) polarizations.
• Field profiles — reconstructs the complete vectorial field distribution (Ex, Ey, Ez, Hx, Hy, Hz) across the cross-section for any guided mode, normalized so that the integrated Poynting vector equals 1.
• Index profile — samples the refractive index profile of the stack for plotting and inspection.
• Two numerical backends:
  • Transfer Matrix Method (TMM) — full-featured; supports both neff and field.
  • Scattering Matrix Method (SMM) — supports neff only; useful as a cross-check.
• Boundary conditions — each side of the stack can be set to:
  • Semi-infinite cladding (default) — field decays evanescently outward.
  • Perfect Electric Conductor (PEC) — tangential electric field forced to zero at the wall; useful for modelling symmetric structures with half-domain tricks.
• Arbitrary stacks — any number of layers, each with an independent real refractive index and thickness (in µm).

Known limitations

• Refractive indices are real-valued only (lossless, non-gain media).
• Only guided modes (real neff) are computed; leaky modes are not supported.
• Geometry is strictly 1D planar; no 2D or 3D structures.
• The SMM backend does not support field calculation.

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Python package

Installation

The package is available on PyPI:

pip install remsol

To build from source, see the documentation.

Quick example

import math
import remsol as rs

# 1D slab waveguide: air | Si (600 nm) | air
k0 = 2 * math.pi / 1.55   # free-space wavenumber at 1550 nm (rad/µm)
layers = [
    rs.Layer(1.0, 0.0),    # left cladding  (semi-infinite, thickness ignored)
    rs.Layer(3.48, 0.6),   # waveguide core (600 nm Si)
    rs.Layer(1.0, 0.0),    # right cladding (semi-infinite, thickness ignored)
]
ml = rs.MultiLayer(layers)

# Effective index of the fundamental TE mode
neff = ml.neff(k0, rs.Polarization.TE, mode=0)
print(f"neff = {neff:.6f}")

# Full vectorial field profile
field = ml.field(k0, rs.Polarization.TE, mode=0)

# Refractive index profile
index = ml.index()

For more examples, see the documentation.

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Rust crate

The Rust crate is available on crates.io. API documentation is on docs.rs.

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Contributing

Contributions are welcome. Feel free to open an issue or a pull request on GitHub.