Among the key features gained from FSG® inscription are the ability to reduce the Full Width Half Maximum (FWHM) of the reflection peak to about 200pm, independent of the length of the grating. However, for a fixed grating length, the reflectivity has a slight influence on the FWHM. The following graph shows the dependency between the FWHM of the FSG®s with increasing reflectivity for a fixed grating length of 4mm.