134
3 Optical Signal Attenuation and Dispersion
Although many long-distance cable plant installations now are using nonzerodispersion-shifted fiber, the huge base of G.652 fiber that is installed worldwide will
be in service for many years. If the G.652 fiber is used at 1550 nm, the chromatic
dispersion value of about 17 ps/(nm km) must be taken into account. This requires
implementation of chromatic dispersion-compensation techniques or special data
formats at high data rates. As an example, a number of field experiments have demonstrated the ability to transmit 160 Gb/s data rates over long distances of installed
G.652a/b fiber.
In G.652c/d fibers the water ion concentration is reduced in order to eliminate
the attenuation spike in the 1360–1460 nm E-band. They are called low-water-peak
fiber and allow operation over the entire wavelength range from 1260 to 1625 nm.
One use of this fiber is for low-cost short-reach CWDM (coarse wavelength division
multiplexing) applications in the E-band. In CWDM the wavelength channels are
spaced by 20 nm, so that minimum wavelength stability control is needed for the
optical sources, as described in Chap. 10. Another important application is in a
passive optical network (PON) for FTTP access networks.
3.4.3 Recommendation G.653
Dispersion-shifted fiber (DSF) was developed for use with 1550 nm lasers. As
Fig. 3.18 illustrates, in this fiber type the zero-dispersion point is shifted to 1550 nm
where the fiber attenuation is about half that at 1310 nm. Therefore, this fiber allows
a high-speed data stream of a single-wavelength channel at or near 1550 nm to maintain its fidelity over long distances. However, it presents problems associated with
nonlinear effects in dense wavelength division multiplexing (DWDM) applications
in the center of the C-band where many wavelengths are packed tightly into one or
more of the operational bands. As noted in Chap. 10, to prevent undesirable nonlinear
effects in DWDM systems, the chromatic dispersion values should be positive (or
negative) over the entire operational band. Figure 3.18 shows that for G.653 fibers the
chromatic dispersion has a different sign above and below 1550 nm. Therefore, the
use of G.653 fibers for DWDM should be restricted to either the S-band (wavelengths
lower than 1550 nm) or the L-band (wavelengths higher than 1550 nm). These fibers
are seldom deployed anymore because G.655 fibers offer a better solution.
3.4.4 Recommendation G.654
This recommendation deals with cutoff -wavelength-shifted fiber that is designed for
long-distance high-power signal transmission. It describes the geometrical, mechanical, and transmission characteristics of a single-mode optical fiber, which has the
zero-dispersion wavelength around 1300 nm. The fiber has a very low loss in the
1550 nm band, which is achieved by using a pure silica core. Because it has a high
3 Optical Signal Attenuation and Dispersion
Although many long-distance cable plant installations now are using nonzerodispersion-shifted fiber, the huge base of G.652 fiber that is installed worldwide will
be in service for many years. If the G.652 fiber is used at 1550 nm, the chromatic
dispersion value of about 17 ps/(nm km) must be taken into account. This requires
implementation of chromatic dispersion-compensation techniques or special data
formats at high data rates. As an example, a number of field experiments have demonstrated the ability to transmit 160 Gb/s data rates over long distances of installed
G.652a/b fiber.
In G.652c/d fibers the water ion concentration is reduced in order to eliminate
the attenuation spike in the 1360–1460 nm E-band. They are called low-water-peak
fiber and allow operation over the entire wavelength range from 1260 to 1625 nm.
One use of this fiber is for low-cost short-reach CWDM (coarse wavelength division
multiplexing) applications in the E-band. In CWDM the wavelength channels are
spaced by 20 nm, so that minimum wavelength stability control is needed for the
optical sources, as described in Chap. 10. Another important application is in a
passive optical network (PON) for FTTP access networks.
3.4.3 Recommendation G.653
Dispersion-shifted fiber (DSF) was developed for use with 1550 nm lasers. As
Fig. 3.18 illustrates, in this fiber type the zero-dispersion point is shifted to 1550 nm
where the fiber attenuation is about half that at 1310 nm. Therefore, this fiber allows
a high-speed data stream of a single-wavelength channel at or near 1550 nm to maintain its fidelity over long distances. However, it presents problems associated with
nonlinear effects in dense wavelength division multiplexing (DWDM) applications
in the center of the C-band where many wavelengths are packed tightly into one or
more of the operational bands. As noted in Chap. 10, to prevent undesirable nonlinear
effects in DWDM systems, the chromatic dispersion values should be positive (or
negative) over the entire operational band. Figure 3.18 shows that for G.653 fibers the
chromatic dispersion has a different sign above and below 1550 nm. Therefore, the
use of G.653 fibers for DWDM should be restricted to either the S-band (wavelengths
lower than 1550 nm) or the L-band (wavelengths higher than 1550 nm). These fibers
are seldom deployed anymore because G.655 fibers offer a better solution.
3.4.4 Recommendation G.654
This recommendation deals with cutoff -wavelength-shifted fiber that is designed for
long-distance high-power signal transmission. It describes the geometrical, mechanical, and transmission characteristics of a single-mode optical fiber, which has the
zero-dispersion wavelength around 1300 nm. The fiber has a very low loss in the
1550 nm band, which is achieved by using a pure silica core. Because it has a high