Wavelength domain multiplexers and demultiplexers are
manufactured by using on-fiber diffraction gratings for the
DWDM systems. The coupling and waveguide losses are at
minimum since the incoming light is coupled to the regular
silica glass core. Crosstalk is minimized as well by
carefully designing the on-fiber grating parameters. These
devices can be used for wavelength filtering and
multiplexing applications, and in every DWDM systems for
the 64 local Add-Drop operations.