1 DWDM Enabling Component Technologies
?– Optical fiber The main physical difference between SMF and MMF types is
in their core thicknesses. Namely, MMF features much wider cores than SMF,
e.g., 50??“62.5 ?µm versus 8??“10 ?µm, and this in turn induces multiple transmission
modes (see Figures 8.1 and 8.2). Therefore, achieving high bit-rate transmission
over MMF is very distance-limited owing to severe differential mode delay (DMD)
effects. Hence, most MAN deployment networks use SMF (ITU-T G.652), which
gives multiterahertz transmission windows. In particular, SMF is ideal for single
channel transmission in the 1310 nm range since it has relatively low loss (0.5 dB/
km) and zero chromatic dispersion [1]. As a result, many standalone SONET/SDH
and Ethernet systems operate at this wavelength. Furthermore, SMF has even
lower attenuation in the 1550 nm window (0.2??“0.3 db/km), albeit with variable
(wavelength-dependent) dispersion. The latter characteristic poses notable chromatic
dispersion challenges for bit-rates over 10 Gbps and requires compensation
for spans over 60 km. Hence, newer non-zero dispersion shifted fiber (NZDSF) and
negative dispersion fiber (NDF) types have been developed, delivering extended
uncompensated long-haul reaches over 200 km.
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