I have a problem when I use FDTD Solutions to get the simulation of the SPPs structure presented in this paper: Plasmonic analog of electromagnetically induced transparency in multi-nanoresonator-coupled waveguide systems
the structure as shown in th picture:
The insulator is chosen to be Air. The metal is chosen to be silver whose frequency-dependent complex relative permittivity can be described by the well-known Drude model:
In the section II part D, the author realize the slow-light effect using the structure they designed. They described it by the group index ng. And in order to get the group index ,they use the equation:
Here vg stands for the group velocity in the plasmonic waveguide systems. τg and ψ(ω) are the optical delay time and transmission phase shift, respectively.
And they are shown in the follow picture:
Since I am a beginner of the FDTD Solutions，I don’t know how to get these results especially the transmission phase shift(because we can get another results from the equation if we know the transmission phase shift).
How can I get the transmission phase shift at plasmonic waveguide-resonator systems like this?
Thanks for your help!