The Filter Wavelength Division Multiplexer is based on environmentally stable thin film filter technology. The devices combine or separate light at different wavelengths in a wide wavelength range. They offer very low insertion loss, low polarization dependence, high isolation and excellent environmental stability. High power handling capability can be achieved through unique pigtail processing and high quality AR coating. These components have been extensively used in EDFAs, Raman amplifiers, WDM networks and fiber optical instruments.