198 CHAPTER 5. LIGHTWAVE SYSTEMS
Table 5.2 Terrestrial lightwave systemsSystem Year λ B L Voice
(μm) (Mb/s) (km) Channels
FT–3 1980 0.85 45 < 10 672
FT–3C 1983 0.85 90 < 15 1,344
FT–3X 1984 1.30 180 < 25 2,688
FT–G 1985 1.30 417 < 40 6,048
FT–G-1.7 1987 1.30 1,668 < 46 24,192
STM–16 1991 1.55 2,488 < 85 32,256
STM–64 1996 1.55 9,953 < 90 129,024
STM–256 2002 1.55 39,813 < 90 516,096fiber. However, an experiment, performed under such conditions, achieved a distance
of only 6000 km at 10 Gb/s even with 40-km amplifier spacing [41], and the situa-
tion became worse when the RZ modulation format was used. Starting in 1999, the
single-channel bit rate was pushed toward 40 Gb/s in several experiments [42]–[44].
The design of 40-Gb/s lightwave systems requires the use of several new ideas in-
cluding the CRZ format, dispersion management with GVD-slope compensation, and
distributed Raman amplification. Even then, the combined effects of the higher-order
dispersion, PMD, and SPM degrade the system performance considerably at a bit rate
of 40 Gb/s.
5.3.2 Terrestrial Lightwave Systems.................
An important application of fiber-optic communication links is for enhancing the ca-
pacity of telecommunication networks worldwide. Indeed, it is this application that
started the field of optical fiber communications in 1977 and has propelled it since then
by demanding systems with higher and higher capacities. Here we focus on the status
of commercial systems by considering the terrestrial and undersea systems separately.
After a successful Chicago field trial in 1977, terrestrial lightwave systems be-
came available commercially beginning in 1980 [45]–[47]. Table 5.2 lists the operating
characteristics of several terrestrial systems developed since then. The first-generation
systems operated near 0.85μm and used multimode graded-index fibers as the trans-
mission medium. As seen in Fig. 5.4, theBLproduct of such systems is limited to
2 (Gb/s)-km. A commercial lightwave system (FT–3C) operating at 90 Mb/s with a re-
peater spacing of about 12 km realized aBLproduct of nearly 1 (Gb/s)-km; it is shown
by a filled circle in Fig. 5.4. The operating wavelength moved to 1.3μm in second-
generation lightwave systems to take advantage of low fiber losses and low dispersion
near this wavelength. TheBLproduct of 1.3-μm lightwave systems is limited to about
100 (Gb/s)-km when a multimode semiconductor laser is used inside the transmitter. In
1987, a commercial 1.3-μm lightwave system provided data transmission at 1.7 Gb/s
with a repeater spacing of about 45 km. A filled circle in Fig. 5.4 shows that this system
operates quite close to the dispersion limit.