Lumerical Fdtd Tutorial !!better!! -

Let us apply the theory. You are designing a Silicon-on-Insulator (SOI) waveguide (220nm thick Si on 2um SiO2).

This object defines the "box" inside which the physics happens. lumerical fdtd tutorial

You should see a confined mode traveling down the silicon with minimal loss. You can then add a 90-degree bend and see how much power radiates out. Let us apply the theory