Fiber Optic Networks

Passive CWDM VS DWDM – Which to choose?

With current industry advancements trend that has equalized costs of transceivers, in technical battle of CWDM vs DWDM more advancements are in DWDM.

 

Lets compare passive CWDM vs DWDM from pure technical application viewpoint:

 

CWDM vs DWDM – Channel Uniformity:

As CWDM spectrum for 18 channels spans from 1260nm up to 1620nm compared to DWDM C-band 1530 – 1565 nm, CWDM has weakness from channel uniformity aspect. Attenuation in wide spectrum is different based on wavelength – for example, typical attenuation of G.652.C optical fiber is 0.38 dB/km at 1310nm wavelength and 0.22 dB/km at 1550nm. So in CWDM system You can get quite great disparity of channel optical performance using different CWDM wavelength. Uniformity of optical channels across whole 1260-1620nm spectrum depends on fiber cable specification. – we suggest checking carefully if You plan using passive CWDM. Especially it is very important for old G.652 specification fiber – it has so called “water-peak” phenomena in range of 1390 and 1490 nm that are not usable for CWDM connections at all. DWDM is clear winner here – due it’s narrow spectrum channel properties on same fiber will be almost identical.

 

CWDM vs DWDM – Capacity:

It’s clear winner here – while maximum capacity of CWDM system is 18 wavelengths all spectrum, DWDM using traditional C-Band 1530 – 1565 nm allow to have 45 100GHz spaced DWDM channels, but with introduction of 50 GHz spaced transceivers we can double number of channels up to 90. In future, we can expect to have 25 GHz and even 12.5 GHz frequency offset even multiplying number of possible channels to 180 or 360. If that is not enough – there is S-band (1460-1530 nm) and L-band (1565-1625 nm) which can be used with DWDM as well, just is not mainstream yet.

 

CWDM vs DWDM – Distance:

Maximum distance of xWDM connection depends on two main factors – maximum budget of optical transceivers and attenuation of all passive elements – fiber itself, number of joints and splices, attenuation of passive filters (Chromatic dispersion as well, but we don’t consider it much a factor up to 80km). If looking on 10G connection data rate, with both, CWDM and DWDM, passive technologies You can have up to 23 dB guaranteed budget using popular SFP+ transceivers (With XFP You can have 26dB budget), what is enough to have 80km WDM link with both technologies. But big advantage of DWDM is, that due it’s narrow spectral width it’s possible to use cost efficient and widely available EDFA (Erbium Doped Fiber Amplifier) boosters, which is one very cost efficient way allowing extension of DWDM reach.

 

CWDM vs DWDM – Spare Parts:

Even optical transceivers are mature elements and failure-rates are very uncommon, introducing WDM technology You would like to have backup stock of all active elements. If You are planning to have just small scale deployment and connect just two or few network nodes, it could mean that You basically need to back up everything – resulting on doubling up of your investment. DWDM is a winner here as well, due availability of Tunable DWDM transceivers, with can replace all Your different wavelength DWDM transceivers with one or two units.

 

Conclusion

CWDM still has price advantages for connection rates below 10G and for short distances with low data rates it’s currently most feasible technology. For more information,welcome to visit www.fiber-mart.com, pls feel free to contact me at service@fiber-mart.com

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