Reply To: How to calculate the transmission characteristics of a coupler with symmetry

[Guilin Sun]

OK, I got it. I took an online example https://support.lumerical.com/hc/en-us/articles/360042322794-Ring-Modulator

and got
As you can see, they are similar. The difference if from their different calculation method.
As there is no documentation on T_in and T_out, I tend to believe they are the T_forward and T_backward.

I will file a feature request to correct this.