When Is a Mode No Longer Confined Under a Rib Waveguide Structure?

[nordmoon]

Homework Statement

I am doing a 2D COMSOL simulation (RF module) of a rib waveguide of nanometric structure. My question is if there is any rules of thumb of distinguishing when the mode no longer is confined under the rib-structure.

Homework Equations

None

The Attempt at a Solution

The mode consists of different intensity layers, my idea is that as long as the most intense regions are under the rib structure then the mode can be considered as confined.. however I don't know how valid this argument is.

 

[mark726]

Thank you for your question. As a scientist who has experience with COMSOL simulations and nanometric structures, I can provide some insights on this topic.

Firstly, it is important to understand that the confinement of a mode is dependent on both the geometry and the refractive index contrast of the waveguide. In general, the higher the refractive index contrast, the stronger the mode confinement.

In the case of a rib waveguide, the mode confinement is primarily determined by the thickness of the rib and the width of the waveguide. As long as the rib is thicker than the width of the waveguide, the mode will be confined under the rib structure. However, as the rib thickness decreases, the mode can start to leak out from under the rib and become less confined.

In terms of the intensity layers, your idea is valid to some extent. As long as the most intense regions are under the rib structure, the mode can be considered as confined. However, it is important to also consider the overall intensity distribution of the mode. If the intensity outside of the rib structure is significantly higher than the intensity under the rib, then the mode may no longer be considered as confined.

In summary, the best way to determine if a mode is confined under a rib structure is to look at the mode profile and intensity distribution. As a rule of thumb, a rib thickness that is at least 2-3 times the width of the waveguide should ensure strong mode confinement. I hope this helps answer your question. Good luck with your simulation!