Alxenses's Athermal Packaged FBG is a low-loss narrowband reflective optical filter with wavelength drift of less than 0.1nm over the temperature range of 0°C-75°C. Negative thermal expansion material was to assemble the FBG package for temperature-compensation. The athermal packaged FBG is much less temperature-sensitive than normal FBG and is suitable for applications where optical filter with high thermal stability is required. They can be used as channel filters/blockers for DWDM systems as well as wavelength references for fiber sensor systems.