Learning Forum

[Then Elango]

When simulating a waveguide, in FDE or FDTD, for 1550 nm wavelength source,

• for 250nm x 150nm , the 1st mode with TE polarization fraction is 73 
• 
• for 400nm x220nm, the  1st mode with TE polarization fraction is 96
• for 800nm x 400nm  , the 1st mode with  TE polarization fraction is 100
• 

So am I correct in concluding that the optimal geometry of the waveguide is 800nmx400nm, as I want fundamental TE mode(TE00) since TE polarisation fraction is 100?

[Guilin Sun]

not necessarily. I am not sure if you are aware that, in photonic waveguides, unlike the weak waveguide, the polarization is not purely TE or TM, as it has at least the non-zero axial field component.  The concept of TE/TM has been eveloved.

Please visit this link for TE Fraction  https://optics.ansys.com/hc/en-us/articles/360034396734-FDE-solver-analysis-Mode-List-and-Deck

In general, people do not use TE fraction to design a waveguide, in most cases. 

Of course, if your goal is to design a waveguide that requires 100% TE fraction, you can do so.  But it might not be exactly 100% as you can check the other transversal component, which in many cases is non-zero.

[Then Elango]

Thank you very much Sir. 

My goal is to design a waveguide which supports only TE mode. So is my observation is right?

[Guilin Sun]

Might not be right, as you can check that such waveguide will support other mdoes if you have a TE mode with larger modal area. Please check the number of modes with more number of trial modes. Before the cut off condition such waveguide may support more modes. I believe that you can find an analytical expression for the single mode condition. Please serach "ridge waveguide, single mode", or refer this article  https://optics.ansys.com/hc/en-us/articles/1500008021262-Optimizing-waveguide-geometry-for-single-mode

[Then Elango]

Thank you very much sir