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8 Digital Optical Fiber Links
(a) Solving for the bit-rate distance product yields, where B is the data rate in Gb/s,
B L C D ≤
0.491
D C D σ λ
=
0.491
[(18 ps/nm km) × 1 nm
= 27Gb/s km
This spectral width imposes a severe limitation on the transmission distance.
The chromatic dispersion-limited repeaterless transmission distances L CD are
plotted as a function of the bit rate in Fig. 8.9.
(b) Solving for the bit-rate distance product yields, where B is the data rate in Gb/s,
B L C D ≤
0.491
D C D σ λ
=
0.491
[(18 ps/nm km) × 0.2 nm
= 135 Gb/s km
Narrowing the spectral width to 0.2 nm shows some improvement in the transmission distance, but it is still not adequate for high-speed long-distance optical
communication systems. The chromatic dispersion-limited repeaterless transmission distances L CD for this case also are plotted as a function of the bit rate
in Fig. 8.9.
1
1
10
100
10
100
1000
10000
Data rate (Gb/s)
Distance (km)
σ λ = 0.2 nm
σ λ = 1.0 nm
L = 3406/B 2
Fig. 8.9 Chromatic dispersion limits for two different chromatic dispersion values and two different
source spectral widths