Poonam,
There should be no confusion for the output efficiency. I have already explained that when you normalize the power spectrum you are looking at the power output efficiency. If you see 0.8 on your graph you have 80% efficiency.
Looking at the results from your observation line I believe there is something wrong with your design as it appears not a significant amount of power at the 1.55 mu range is reaching it. Are you able to just send the design file?
The “x axis” of the power spectrum is in fact the wavelength. The wavelength range that is calculated is based on the central wavelength of your source so yes this axis will change depending on what your source wavelength is set to.
Scott