Devika Padmakumar Nair
Ansys Employee

Hello,

Width of the waveguide coupler is fixed.

You can calculate the S-parameters of the coupling region in a physical solver like FDTD and import this data into an S-parameter element in INTERCONNECT for your design. 

You can refer the following Y branch example to learn S-parameter extraction Y branch – Ansys Optics.

Thank you.