CWDM optical multiplexing

In CWDM equipment, we can use lasers in unregulated temperature, lower cost and which emit at wavelengths spaced 20 nm in the transmission window 1270-1610 nm. CWDM is the subject of the ITU-T recommendation G.695, which provides for flexible and scalable solutions, including the solution of 8 to 16 channels with two optical fibers (one for each direction of transmision), offering data rates of 1.25 Gb / s to 2.5 Gb / s per channel.

However, systems CDWM not compatible with optical amplifiers, are limited in scope. Two lengths are indicative of connection specified in Recommendation G.695: up to 40 km and up to about 80 km, which is usually enough for the needs of metropolitan networks.

In contrast, in the record books in 2004, Alcatel was just topped mythical 10 Terabit / s, in a multiplex fiber Alcatel TeraLight 256 channels each operating at 40 Gb / s over a distance of 100 Km This error-free transmission was achieved by combining amplifiers hybrid Erbium / Raman.

In addition, Alcatel has managed to pass 3 terabit / s over a distance of 300 Km 7, in 300 multiplex channels each operating at 10 Gb / s, with optical amplifiers doped with erbium (EDFA) broadband

WDM technology

The majority of optical networks are currently based on spectral multiplexing WDM
(Wavelength Division Multiplexing), is injected in a same fiber signals dedicated to several applicationsor different users and it performs a correspondence between the colors of beams light and interfaces Client ends
optical links.
Each node in the network, it has the possibility to extract or insert at channel of choice.
Recommendations of the ITU (International Telecommunications) define very precisely the characteristics of channels to use, including their central wavelength and width of each beam.

Two main types of WDM exist:
- The CWDM (Coarse WDM) is used to multiplex simple and inexpensive way to eighteen
lambdas on access networks, or metropolitan on a spectrum ranging from 1270 to 1610 nm.
The spacing between each lambda is important (20 nm), the temperature of each laser is not controlled and the wavelengths plants can therefore suffer no significant deviations from about 6 or 7 nm.
The scope of such a system has limited the lack of function of re-amplification, 80 km at most.
- The DWDM (Dense WDM) is a solution to transport of several dozen high lambdas
flow over long distances, the spacing between lambdas can vary from 1.6 nm (200 GHz) to 0.1 nm (12.5 GHz).
An enslavement of laser temperature necessary to avoid any deviation of the lengths
wave.
The use of electronics and photonics accuracy that results justify the cost differences between CWDM and DWDM.

The DWDM channels are located on the C and L bands, it is known technically amplifier, distances transmission can reach several thousand km.