Hi Hyeong-Min,
I assume the step 6 you are talking about is the following:
– “… Repeat step 3 to 4 for Observationline2, reflection spectrum can be calculated, (refer to Figure 9).”.
Being this the case, I think the reflection spectrum is referring to the Observation Line window when on the Analyzer. If you look at https://optiwave.com/optifdtd-manuals/fdtd-enhancement/ on “Performing data analysis” there is a description on how to do it.
Best regards.
PL