Guilin Sun
Ansys Employee

 coupling coefficients  have different definitions. Lumerical has an example for power coupling coefficient, since this is what is used in INTERCONNECT:

Waveguide Coupler (C) - INTERCONNECT Element

"The coupling coefficient is the fraction of power that couples from the fundamental TE-mode in the straight waveguide to the fundamental TE-mode of the curved waveguide. "

But what you require is the amplitude coupling coefficient. The diagram shown above is for complex amplitude with a mode incidence, dominate field component Ei1; and then you can use a frequency monitor in the bus to get Et1 if it records the single mode. Similarly for others.

It might be better to have the mode S parameters, where S31 reprents t1, S41 represents k1:

You will need to think which method you want to use, and what the text in the reference tells you. Once you know exactly what quantities you want to simulate, I can help you for the simulation.