Hi, I am doing an experiment to investigate the propagation loss in some nanophotonics structures. The laser light is coupled to the input of the DUT chip via a tapered lensed fiber and the output of the chip is go through a objective then a photodetector. The chip is design for telecommunication propose, so wavelenght of interest is around 1550nm. I did a spectrum scan for 1500 - 1600 nm and obtained the spectrum as below.. http://img134.imageshack.us/img134/7893/clipboard01ww2.th.jpg [Broken] Unfortunately , the spectrum is with the fabry perot effect.. (the oscillation), i try to calculated the path from the spectrum , but the calculated dimension doesnot match the fiber-chip facet or both end facet of chip . So if you gurus outthere can help _?