# Find the Modes of a Waveguide

Editor: Mode project › Model, Setup and Results tabs · Python: td.ModeSimulation

You get the two lowest-order modes of a silicon strip waveguide surrounded by vacuum, with their effective index and field profile, from 1.5 to 1.6 µm.

# Before You Start

Cloud only

This run costs about 0.005 FlexCredits.

# Steps

  1. In Model › Structures, click +, then Strip under Waveguide Templates. The editor adds the structure waveguide, the medium core_medium, and three parameters.

    Add Structure panel in a Mode project, with Waveguide Templates (Strip, Rib, Slot, Slanted, Fiber) above the primitive geometries

    Add Structure panel

  2. Open Parameters in the bottom bar. Set core_width to 0.5, core_thickness to 0.22 and core_n to 3.48 (silicon at 1.55 µm).

  3. In Setup › Mode Specifications, set Number of modes to 2. Keep the wavelength range 1.5–1.6 µm with 5 points.

  4. Click Check Simulation. Wait for Validation Passed.

  5. Click Run Simulation.

# Check the Result

The Results tab opens with n_eff of mode 0 plotted against wavelength. The effective index falls from about 2.40 at 1.5 µm to about 2.28 at 1.6 µm.

Results tab with n_eff of mode 0 against wavelength, and the Mode Summary Table

Results tab

Click Mode Summary Table in the toolbar to compare the modes at one wavelength. At 1.5 µm, mode 0 has an effective index of about 2.40 and mode 1 about 1.33. Both are above 1, the index of the vacuum around the core, so both modes are guided.

To see a field profile, open E › Magnitude (abs). Pick the wavelength and the Mode Index in Mode Selection.

Field magnitude of mode 0 at 1.5 µm, confined in the waveguide core

Results tab: field profile

If the check shows an error or the modes look wrong, see Mode Troubleshooting.

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