With the exponential growth in communications, caused largely by the wide acceptance of the Internet, many carriers have found their estimates of fiber needs have been highly underestimated. Although most cables included many spare fibers when installed, this growth has used many of them and new capacity is required. Make use of a number of ways to improve this problem, eventually the WDM has shown more cost effective in most cases.
Wave Division Multiplexing (WDM) enables multiple data streams of varying wavelengths (“colors”) to become combined right into a single fiber, significantly enhancing the overall capacity from the fiber. WDM can be used in applications where considerable amounts of traffic are needed over long distance in carrier networks. There’s two types of WDM architectures: Course Wave Division Multiplexing (CWDM) and Dense Wave Division Multiplexing (DWDM).
WDM System Development History:
A WDM system uses a multiplexer in the transmitter to become listed on the signals together, and a demultiplexer at the receiver to separate them apart. With the right type of fiber it is possible to have a device that does both simultaneously, and can work as an optical add-drop multiplexer. The optical filtering devices used have conventionally been etalons (stable solid-state single-frequency Fairy¡§CP¡§|rot interferometers by means of thin-film-coated optical glass).
The idea was first published in 1980, and by 1978 WDM systems appeared to be realized in the laboratory. The first WDM systems combined 3 signals. Modern systems are designed for as much as 160 signals and can thus expand a fundamental 10 Gbit/s system over a single fiber pair to in excess of 1.6 Tbit/s.
WDM systems are well-liked by telecommunications companies because they allow them to expand the capacity of the network without laying more fiber. By utilizing WDM and optical amplifiers, they can accommodate several generations of technology rise in their optical infrastructure without needing to overhaul the backbone network. Capacity of a given link can be expanded by simply upgrades towards the multiplexers and demultiplexers at each end.
This is often made by use of optical-to-electrical-to-optical (O/E/O) translation in the very edge of the transport network, thus permitting interoperation with existing equipment with optical interfaces.
WDM System Technology:
Most WDM systems operate on single-mode fiber optical cables, which have a core diameter of 9 µm. Certain forms of WDM may also be used in multi-mode fiber cables (also referred to as premises cables) which have core diameters of fifty or 62.5 µm.
Early WDM systems were expensive and complicated to operate. However, recent standardization and better understanding of the dynamics of WDM systems make WDM less expensive to deploy.
Optical receivers, as opposed 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 split into different wavelength patterns, conventional/coarse (CWDM) and dense (DWDM). Conventional WDM systems provide up to 8 channels within the 3rd transmission window (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 ultra-dense WDM). Such spacing’s are today only achieved by free-space optics technology. New amplification options (Raman amplification) enable the extension of the usable wavelengths towards the L-band, pretty much 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 supply 8 channels on one fiber CWDM uses the whole frequency band between second and third transmission window (1310/1550 nm respectively) including both windows (minimum dispersion window and minimum attenuation window) but the critical area where OH scattering may occur, recommending using OH-free silica fibers in case the wavelengths between second and third transmission window ought to be used. Avoiding this region, the channels 47, 49, 51, 53, 55, 57, 59, 61 remain and these are the most commonly used. Each WDM Optical MUX includes its optical insertion loss and isolation measures of every branch. WDMs are available in several fiber sizes and kinds (250µm fiber, loose tube, 900µm buffer, Ø 3mm cable, simplex fiber optic cable or duplex fiber cable).
WDM, DWDM and CWDM are based on the same idea of using multiple wavelengths of sunshine on one fiber, but differ within the spacing of the wavelengths, quantity of channels, and also the capability to amplify the multiplexed signals within the optical space. EDFA provide an efficient wideband amplification for that C-band, Raman amplification adds a mechanism for amplification in the L-band. For CWDM wideband optical amplification is not available, limiting the optical spans to many tens of kilometers.
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