When measured with a standard OSA, the optical spectrum of SLEDs in the region of 1400nm is characterized by many deep and narrow dips.  However, these dips are not due to residual reflections, they are caused by absorption lines from OH molecules that are located in the optical path. The main contribution to these dips originates from absorptions suffered by the optical beam when propagating from the exit fiber to the detector array within an optical spectrum analyzer.