Niki Papachristou
Ansys Employee

Hi Deng,

Thank you for reaching out to us. I believe that your results can be explained if you do a mode overlap analysis. Please have a look on this article: Understanding the mode overlap calculation. It seems that in your case modes 4 and 5 have a stronger overlap with mode 1 while they are guided into your tapered waveguide comparing to modes 2 and 3.

Kind Regards,