Specifically, CWDM
uses much wider channel spacing, typically 20 nm, and precludes the need for costly
EDFA amplifiers. In fact, the CWDM grid (ITU-T G.694.2) spans the entire SMF spectrum,
as shown previously in Figure 8.2, and supports much smaller channel counts,
typically about 16??“32 per fiber. The main cost savings of this technology comes from its
use of low-power/wider-line-width (uncooled) laser sources and lower-cost coarse filtering
devices. These laser types mitigate center-wavelength temperature drift and allow
unamplified transmissions up to 40 km.
In general, CWDM is very cost effective for client interface speeds under OC-48/
STM-16 (2.5 Gbps), and hence this technology makes sense for Gigabit Ethernet services.
Alternatively, faster 10 Gigabit CWDM transceivers are also available but offer less cost
reduction than their DWDM counterparts. Moreover, the larger economies of scale in
the DWDM market will, over time, erode the first-cost advantage of CWDM [3]. Finally,
Fiber and WDM 209
CWDM systems require opto-electronic conversion in order to interface with larger
metro/regional DWDM networks, i.e., signal relaunch on DWDM.
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