Page 69 - Optical Communications Essentials

Optical Fibers

Optical Fibers 59

TABLE 4.4. ITU-T Recommendations for Single-Mode Fibers
ITU-T recommendation no. Description
G.651 Multimode fiber for use at 850nm in a LAN
G.652 Standard single-mode fiber (1310-nm optimized)
G.652.C Low-water-peak fiber for CWDM applications
G.653 Dispersion-shifted fiber (made obsolete by NZDSF)
G.654 Submarine applications (1500-nm cutoff wavelength)
G.655 Nonzero dispersion-shifted fiber (NZDSF)
G.655b Advanced nonzero dispersion-shifted fiber (A-NZDSF)

ITU-T G.652. This recommendation deals with the single-mode fiber that
was installed widely in telecommunication networks in the 1990s. It has a Ge-
doped silica core which has a diameter between 5 and 8µm. Since early
applications used 1310-nm laser sources, this fiber was optimized to have a
zero-dispersion value at 1310nm. Thus it is referred to as a 1310-nm
optimized fiber. With the trend toward operation in the lower-loss 1550-nm
spectral region, the installation of this fiber has decreased dramatically.
However, the huge base of G.652 fiber that is installed worldwide will still be
in service for many years. If network operators want to use installed G.652
fiber at 1550nm, complex dispersion compensation techniques are needed, as
described in Chap. 15.
ITU-T G.652.C. Low-water-peak fiber for CWDM applications is created by
reducing the water ion concentration in order to eliminate the attenuation
spike in the 1360- to 1460-nm E-band. The fibers have core diameters
ranging from 8.6 to 9.5µm and an attenuation of less than 0.4dB/km. The
main use of this fiber is for low-cost short-reach CWDM (coarse WDM)
applications in the E-band. In CWDM the wavelength channels are
sufficiently spaced that minimum wavelength stability control is needed for
the optical sources, as described in Chap. 13.
ITU-T G.653. Dispersion-shifted fiber (DSF) was developed for use with
1550-nm lasers. In this fiber type the zero-dispersion point is shifted to
1550nm where the fiber attenuation is about one-half that at 1310nm.
Although this fiber allows a high-speed data stream of a single-wavelength
channel to maintain its fidelity over long distances, it presents dispersion-
related problems in DWDM applications where many wavelengths are packed
into one or more of the operational bands. As a result, this fiber type became
obsolete with the introduction of G.655 NZDSF.
ITU-T G.654. This specification deals with cutoff-wavelength-shifted fiber
that is designed for long-distance high-power signal transmission. Since it has
a high cutoff wavelength of 1500nm, this fiber is restricted to operation at
1550nm. It typically is used only in submarine applications.
ITU-T G.655. Nonzero dispersion-shifted fiber (NZDSF) was introduced in
the mid-1990s for WDM applications. Its principal characteristic is that it has

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