Multiplexing, modulation WDM, DWDM

In any transmission, it is interesting to move at the same time in the same conductor (here a single fiber) up communications companies, neither of which comes another scramble. They are therefore each carries a different wavelength is multiplexing.
Multiplexing and its inverse are given by Mux / Demux. The different wavelengths are generally assembled and separated by means of optical filters such as thin films (the most commonly prevalent).
A bit like on a combined technology "common rail" a new generation of diesel engines more efficient, combining the different modulation types for different types of fiber optic transmission, and it is possible to choose a type of modulation for the same material, or need to know the physical principle to use in the SI.

For information, here are some words:

WDM (Wavelength Division Multiplexing) (G.692): several trains of digital signals at the same speed of modulation, but each to a separate wavelength.

DWDM (Dense Wavelength Division Multiplexing) technology is known as dense WDM spacing when used between two wavelengths is equal to or less than 100 GHz. It works now for long-distance transmissions. In practice, this means that we put in a lot of fiber signals carried by frequencies very close to each other.

U-DWDM (Ultra - Dense Wavelength Division Multiplexing) allows up to 400 channels.

CWDM (Coarse Wavelength Division Multiplexing) only 8 to 16 channels, but a less expensive technology used in particular for local loops (MAN).

Protocols
Protocols transmitted over fiber optics include:

SONET / SDH
ATM
Ethernet,
ESCON,
FICON,
Fiber Channel.


CWDM
DWDM technology has relatively high costs.
• high performance fiber
• cooled lasers
• fine wavelengths very close to each other.

Technology CWDM (Coarse Wavelength Division Multiplexing) is a WDM economy. The channels are removed (coarse). In fact, according to its quality, we only have 8 or 16 channels per fiber. The material used, a moderate cost and use without constraints, allows for installation in the equipment end (local loops, business).