I received your attachments through the support email. The plot for the observation line is reporting the amplitude of the selected field component (either Ey or Hx) along the observation line. The second plot is the power spectrum on the observation line. Assuming this observation line is one of your output ports and you have it normalized with your source this plot should be your transmission efficiency (Pout / Pin) versus wavelength.
I am a bit concerned with the magnitude of the plot as it appears to be values in the 10’s of thousands and you should not be seeing this level of magnification. I am assuming your source is a pulse, can you please provide the specifications for the source? Also Can you provide me with the file that you obtain by using the “Save as…” button on the Power Spectrum form?