🎯 Learning objectives

Set up a 1D slab waveguide in OghmaNano and compute TE/TM modes.
Interpret fundamental and higher-order modal profiles across wavelength.
Configure 2D mode solving: axis selection, mesh density, wavelength sampling.
Use eigenmode search settings (X/Y indices) to target specific modes.
Recognize interface discontinuities in TM and leakage/anti-guiding at long λ.

📦 Prerequisites

OghmaNano installed and working.
Basic familiarity with refractive index and guided modes.

⏱ Estimated time

Part A (1D TE/TM): 10–15 min
Part B (2D modes): 10–15 min
Part C (2D complex modes): 10–15 min

Slab waveguide mode solver

In this tutorial we compute the optical modes supported by slab waveguide structures in OghmaNano. We begin with a classic 1D three-layer stack (low-n / high-n core / low-n) and find transverse electric (TE) and transverse magnetic (TM) modes. We then extend to 2D mode searches with configurable mesh density and wavelength sampling, and show how to control the number of eigenmodes solved in the X and Y directions.

OghmaNano new simulation window showing the Mode Solver folder highlighted among the available device types. — The **New simulation** window in *OghmaNano*, with the **Mode Solver** folder highlighted among the available device types.

OghmaNano mode solver submenu showing the 2D Fiber optic (TE) option highlighted. — The **Mode Solver submenu** showing the **2D Fiber optic (TE)** example. Double-clicking this option will create a new simulation using an arbitrary shape — in this case, a fiber optic mode.

1. Getting started: 1D slab (TE)

Open New simulation → Mode solvers and select the 1D slab waveguide example. Configure the layer stack (e.g., 500 nm / 500 nm / 500 nm) and refractive indices (n = 1 / 4 / 1 for cladding / core / cladding in this example). Set polarization to Transverse electric (TE).

OghmaNano 3D view showing the geometry of an optical fiber with an inner core object inside an outer cladding object. The right-click menu on the inner core is open. — Geometry view of an optical fiber defined by two nested objects — an inner core and an outer cladding. Although shown as spheres, the solver works in 2D so this represents a slice through a fiber cross-section. Right-clicking on the inner core object brings up the **Edit** menu.

OghmaNano object editor window showing options to configure the selected object including material, shape, position, and orientation. — The **Object Editor** window for the selected core. Here you can set the optical material (e.g. from the materials database), adjust the object shape, and configure its size, position, and orientation. Objects can also be dragged interactively within the 3D view.

OghmaNano Output tab showing the snapshots directory after running the fiber simulation. — The **Output tab** after clicking the **Run** button. The **snapshots** directory is generated, which contains the calculated field data.

The Snapshots window after selecting E.dat with the Add button, showing the 2D modal field profile of the fiber. The modes are not perfectly symmetric because the inner core is slightly offset from the center of the outer cladding. You can experiment by adjusting the core position, refractive index, or size to see how the modal profiles change.

OghmaNano main window showing the Optical ribbon with the Mode Calculator button highlighted. — The **Optical ribbon** in *OghmaNano*, with the **Mode Calculator** button highlighted. Clicking this button opens the mode solver configuration window.

OghmaNano Mode Calculator editor window with the TE/TM selection dropdown highlighted. — The **Mode Calculator editor** window, where you can configure solver parameters. The highlighted dropdown menu allows selection between *Transverse Electric (TE)* and *Transverse Magnetic (TM)* modes.

6. Next steps

Vary core thickness and index contrast to see cut-off behavior of higher-order modes.
Increase wavelength sampling for smoother dispersion plots.
Switch to TM in 2D and compare confinement vs. TE.
Try the “more complex 2D waveguides” templates (rib/strip) for realistic photonics layouts.