The Optical Communications Reference

an EDFA site. An alternative scheme involves the use

of the compensating fiber within the cable itself after

having been jointed with the transmission fiber as part

of the overall fiber link. Such DCFs are referred as

reverse/inverse dispersion fibers (RDF/IDF) [60–62].

Reverse dispersion fibers are used with the transmission

fiber almost in the ratio of 1:1, meaning their character-

istic dispersion parameters D and S are almost the same

as that of the trans mission fiber except for the signs.

Thus, for the reverse dispersion fiber used in [60], D

and S were 16 ps/nm$km and 0.050 ps/nm

2

$km,

respectively. Dispersion ramped fiber links, which in-

volve use of RDFs, alternate fiber segments with the

link and consist of positive and negative dispersion

fibers, so that the overall dispersion is low, and D versus

length curve mimicks a sawtooth curve. One major at-

tribute of these fibers was that loss in such fibers was

low (in contrast to high negative D DCFs), ~ 0.25

dB/km. Terabit transmission experimen ts through a re-

peater span of over 125 km were reported in such

dispersion managed fiber links in volving RDFs in con-

junction with G.652 fibers over a bandwidth of 50 nm

[63]. Alternate fiber segments in these links consist of

positive and negative D (in 1:1 ratio) fibers such that

overall dispersion is low and D versus length curve

mimicks a sawtooth curve. RDFs were also used with

NZ-DSFs (in a ratio of 1:2) [64].

3.1.4 Fibers for metro networks

In recent years, metro optical networks have attracted

a great deal of attention from lightwave communication

engineers due to potentials for high growth. A metro

network provides generalized telecommunication ser-

vices trans porting any kind of signal from point to point in

a metro. First-generation metropolitan optical networks

based on SDH/SONETrelied on rings laced with nodes at

which information is electronically exchanged. Access

that aggregates a wide variety of traffic from business and

residential end users is required to port this traffic directly

to the transport product for distribution throughout an

optical network. In transport, DWDM is the key enabli ng

technology to expand the capacity of existing and

new fiber cables without optical-to-electric al-to-optical

Table 3.1.5 Important performance parameters of the designed DSCFs for 6.655 fibers (After [58]; copyright Optical Society of America).

Designed dual-core

DSCF for

D

(ps/nm km)

RDS

(nm

L1

)

A

eff

(mm

2

)

Mode field

diameter (mm)

FOM

(ps/nm dB)

Bend loss *

(dB)

LEAF

Ô

(C-band) 264 0.033 41.8 3.34 1248 2.54  1.0e–02

LEAF

Ô

(L-band) 172 0.017 43.63 3.47 885 4.28  1.0e–03

True Wave RS

Ô

(C-band) 173 0.0099 49.92 3.68 760 2.35  1.0e–06

True Wave RS

Ô

(L-band) 173 0.0075 61.4 4.02 851 1.89  1.0e–06

TeraLight

Ô

(S-band) 201 0.01 45.97 3.42 844 5.2  1.0e–02

TeraLight

Ô

(C-band) 187 0.0084 49.99 3.55 873 6.51  1.0e–03

TeraLight

Ô

(L-band) 150 0.006 57.77 3.92 771 1.4  1.0e–02

Values correspond to central l in each band as in Table 1.4.

*

For a single-turn bend of diameter 32 mm.

0.2

0.1

0

0.1

0.2

0.3

1.53

(a)

Wavelength (μm)

1.54 1.55 1.56

D

ave

(ps/nm.km)

DCF for

LEAF

TM

DCF for

Teralight

TM

DCF for

TrueWave-RS

TM

DCF for

LEAF

TM

DCF for

Teralight

TM

DCF for

TrueWave-RS

TM

Wavelength (μm)

(b)

0.2

0

0.2

0.4

1.57 1.58 1.59 1.6 1.61

D

ave

(ps/nm.km)

Fig. 3.1.26 (a) Net residual dispersion spectra at the C-band of

standard NZ-DSF fiber links jointed with designed dual-core

DSCFs. (b) Net residual dispersion spectra at the L-band of

standard NZ-DSF fiber links jointed with designed dual-core

DSCFs.

104

SECTION THREE Optical Fibers