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Wavelength-division multiplexing: Difference between revisions

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Optical receivers, in contrast to laser sources, tend to be wideband devices. Therefore the demultiplexer must provide the wavelength selectivity of the receiver in the WDM system.
 
WDM systems are divided in different wavelength patterns, ''conventional'' or ''coarse'' and ''dense'' WDM. Conventional WDM systems provide up to 8 channels in the 3rd [[Fiber-optic communication#Transmission windows|transmission window]] ([[Optical_band#Optical_bands|C-Band]]) of silica fibers around 1550 nm. Dense wavelength division multiplexing (DWDM) uses the same transmission window but with denser channel spacing. Channel plans vary, but a typical system would use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing. Some technologies are capable of 12,5 GHz spacing (sometimes called [http://kylia.com/ultradw.html ultra dense WDM]). Such spacings are today only achieved by Free space technology. New amplification options ([[Raman amplification]]) enable the extension of the usable wavelengths to the [[L-band]], more or less doubling these numbers.
 
Coarse wavelength division multiplexing (CWDM) in contrast to conventional WDM and DWDM uses increased channel spacing to allow less sophisticated and thus cheaper transceiver designs. To again provide 8 channels on a single fiber CWDM uses the entire frequency band between second and third [[Fiber-optic communication#Transmission windows|transmission window]] (1310/1550 nm respectively) including both windows (minimum dispersion window and minimum attenuation window) but also the critical area where OH scattering may occur, recommending the use of OH-free silica fibers in case the wavelengths between second and third transmission window shall also be used. Avoiding this region, the channels 31, 49, 51, 53, 55, 57, 59, 61 remain and these are the most commonly used.
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