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Dense wavelength division multiplexing (DWDM) is wavelength division multiplexing (WDM) with typical channel spacing of 100 GHz for 40 channels and 50 GHz for 80 channels. Each channel contains a TDM (time division multiplex) signal. And each of up to 80 channels can carry 2.5 Gbps for a total of 200 billion bits per second by the optical fiber. These signals use the 3rd transmission window, called the C-Band, meaning the light beam wavelengths are between 1530nm to 1565nm. (nm = a nanometers or a billionth of a meter)
Techopedia Explains Dense Wavelength Division Multiplexing
A basic Dense Wavelength Division Multiplexing contains five main components:
- DWDM Terminal Multiplexer: This device contains a one wavelength converting transponder for each wavelength carried. It receives an input optical signal, converts it to an electrical signal and then retransmits it as an optical signal (a process abbreviated as O/E/O) using a 1550 nm laser beam. The MUX (multiplexer) takes a number of 1550 nm optical signals and places them on a single optical fiber. This terminal multiplexer may also contain an EDFA (Erbium Doped Fiber Amplifier) to amplify the optical signal.
- Intermediate Line Repeater: These are amplifiers placed every 80 to 100 kilometers to compensate for loss of optical power; amplification is done by an EDFA, usually consisting of several amplifier stages.
- Intermediate Optical Terminal, or Optical Add/Drop Multiplexer: This is a remote site amplifier placed where the signal may have traveled up to 140 kilometers; diagnostics and telemetry signals are extracted or inserted.
- DWDM Terminal Demultiplexer: This device breaks the multi-wave signal back into individual signals; these may be sent to O/E/O output transponders before being relayed to their intended destinations, i.e. client-layer systems.
- Optical Supervisory Channel (OSC): This channel carries information about the multi-wave optical signal and may provide data about conditions at the site of the intermediate line repeater (component 2 above).
DWDM is sometimes called wave division multiplexing (WDM) and WDM is growing denser as the technology evolves. Thus, the two terms are often used synonymously.
Even newer technology, called Raman Amplification, is using light in the L-Band (1565 nm to 1625 nm), approximately doubling the maximum capacities above; thus, with 25 GHz spacing, sometimes called ultra dense wavelength division multiplexing, the system allows up to 160 channel operation.
