Wavelength Division Multiplexers or Demultiplexers (WDM) combine or separate two optical signals with different wavelengths. They are passive optical components for uni- or bidirectional operation. WDMs are manufactured on the basis of the FBT (Fused Biconical Taper) principle in singlemode technology. They are pure optical-fibre components. W-WDM are multiplexer or demultiplexer which are used to combine or seperate signals with wavelength from different optical windows.