Coarse Wavelength Division Multiplexing s one of the optical transport technologies that make use of the light wavelengths and fiber high band capacities along with SDH and DWDM technologies. CWDM is not the latest technology developed for optical transmission but it has its own advantages for choice in particular circumstances.
1.Simpler implementation and operation versus the DWDM implementation.
Simpler refers in this case to simpler optical hardware components necessary to implement the transmission system. Wavelengths spacing is much wider than in classical DWDM systems. Spacing is usually 20nm between lamdas instead of 50GHZ and 100GHZfrom DWDM. CWDM systems are using 8 or 16 or 32 lamdas versus 96 channels in DWDM systems. In 2002 the ITU standardized a channel spacing grid for use with CWDM (ITU-T G.694.2), using the wavelengths from 1270 nm through 1610 nm with a channel spacing of 20 nm. (G.694.2 was revised in 2003 to shift the actual channel centers by 1 nm, so that strictly speaking the center wavelengths are 1271 to 1611 nm..
Lower cost:
Fewer channels to transmit are reflecting in ⅓ fewer costs to implement. Transponders use a wider band to transmit channels being less sophisticated design. There is no need for optical amplifiers since the spacing between the channels are not making them suitable for EDFA amplification. The resulting distances are smaller, like 60Km for 2.5Gbit/s signal. Passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components such as bandpass filters and prisms. Many manufacturers are promoting passive CWDM to deploy fiber to the home. CWDM is based on uncooled distributed-feedback (DFB) lasers and wide-band optical filters. These technologies provide several advantages to CWDM systems such as lower power dissipation, smaller size, and less cost. The commercial availability of CWDM systems offering these benefits makes the technology a viable alternative to DWDM systems for many metro and access applications.
Easy to expand
Upgrading a 8 channel CWDM system to 16 channel system is easy and is a matter of combining the mux/demux filters without the pain of adjusting the optical power or dispersion compensation DCM – modules like in case of DWDM. Low incremental cost: “Pay as you grow” Architecture. In DWDM systems, one connector can carry a whole cable’s-worth of traffic. If more than one connector is pulled and several incorrectly reconnected, the crap can truly hit the fan. Replacing, for instance, an amp (with DCM, OSC, and local connections) means everything disconnected has to be put back exactly as it was – or it might simply not work at all. Provisioning can be equally similarly disastrous. And these days, training exposure to these systems is minimal.Another benefit to the passive CWDM technology is that no configuration is necessary.The most complex step in CWDM integration is aligning and connecting the patch cables from the correct wavelength optic to the correct port on the multiplexers on each end of the link.
Specialized application evolve
CWDM – continues to evolve into specialized applications. Combination transport and optical routing or switches are being developed now. Add- on CWDM cards are being included in more transport devices as low cost options. Suppliers are continuing to drive down costs and increase capacity. CWDM and DWDM provides a unique “fit” and will complement not replace the other.
To sumarize the advantages of CWDM technology, it is worth to mention the following :
Lower power consumption – 20%
Smaller space requirements – 30%
Can use SMF or MMF cable
Can use LED or Laser’s for power
Smaller and cheaper wave filters
Cost saving on start up and expansion
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