ADVANCED WAVELENGTH DIVISION MULTIPLEXING NETWORK
WAVELENGTH DIVISION MULTIPLEXING
The fiber optic industry first deployed single wavelength transmission links. As requirements changed, the industry responded with wavelength-division multiplexing (WDM), which sends two distinct signals per fiber, doubling transmission capacity. Similar to a simple splitter, WDMs typically have a common leg and a number of input or output legs. Unlike the splitter, however, they have very little insertion loss. They do have the same range of excess loss. Two important considerations in a WDM device are crosstalk and channel separation. Crosstalk, also called directivity, refers to separation of demultiplexed channels. Each channel should appear only at its intended port. The crosstalk specification expresses how well a coupler maintains this port-to-port separation. Channel separation describes a couplerâs ability to distinguish wavelengths. In most couplers, the wavelengths must be widely separated allowing light to travel in either direction without the penalty found in splitters. WDMs allow multiple independent data streams to be sent over one fiber. The most common WDM system uses two wavelengths, although four or more-wavelength systems are available.