In addition, various ???metrooptimized???
fibers have also been developed to increase fiber capacity by removing the
1350??“1450 nm ???water-peak??? (see Figure 8.2), i.e., low water-peak fiber (LWPF) [3].
?– Laser transmitters SMF transmission is done using laser transmitters, and
advanced integration techniques have yielded narrow line-width sources with very
good thermal stability. To standardize channel values, the ITU-T has defined a
wavelength grid for the SMF C (1525??“1565 nm) and L (1570??“1610 nm) bands
using 100 or 50 GHz channel spacing. This grid yields over 100 wavelengths per
fiber at 10 Gbps each (ITU-T G.694.1), and new ???hyper-WDM??? 25 GHz spacing is
Fiber and WDM 201
also available. Now a variety of laser types have been developed. Namely, directly
modulated distributed feedback lasers (DFB) can deliver 2.5 Gbps speeds across
metro domains up to 100 km. Meanwhile more powerful (costly) externally modulated
variants can overcome dispersion issues at 10 Gbps speeds. After many years
of development, tunable lasers have also come to market. These devices enable
significant services automation by allowing carriers to select transmission wavelengths
automatically.
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