Wavelength selective devices for WDM communication systems

Depending on the application in optical communication systems different wavelength division multiplexing devices are used to increase network capacity by allowing several wavelength channels to be transmitted by one fiber, to add or drop different wavelength channels or to separate or put together channels carrying different services. Depending on the application such devices can have wide, coarse or dense channel spacing. Furthermore they can handle different number of channels. In this paper we present some of such devices, their functionality, structures and fabrication technologies.