Metal-free Optical Drop Cable

1.

INTRODUCTION

Recent years have seen rapid development of optical fiber
networks and implementation of fiber-to-the-home (FTTH)
in common homes, along with the increased demand for
optical communications to support the proliferation ofInternet as well as delivery of moving pictures.
Conventional method of optical fiber installation useddrop cables for connection between distribution cables
and subscribers' premises, and indoor cables for connection within subscribers' residences. See Figure 1 (a). In
such a method it was necessary to joint the drop andindoor cables, giving rise to such additional costs as thoseof cable jointing and materials for joint box installed on thewall of subscriber's residence. In order to reduce suchcosts related with cable jointing, therefore, a new methodof cable installation is becoming widespread where a drop
cable is led directly into the residence without using anindoor cable. See Figure 1 (b).

Drop cable

Dropping point

Residence

Anchoring fitting

2.

FEATURES

2.1 Structure
Figure 2 shows a cross section of the metal-free optical
drop cable that has been developed. The structure has
not completely eliminated metals from the entire cable; ituses a steel wire as conventionally for the suspension
member while eliminating metals from the cable portion.
The cable main body is made metal-free, using a 0.4 φ
G-FRP for its tension members, with provision made sothat influences due to lightning does not reach inside theresidence.
A steel wire is used for the suspension portion. Although
this portion comprises metal members, the portion is severed by cable anchoring before entering the residence, sothat lightning influences are also isolated posing no problems. The use of steel wire suppresses cost increase andmaintains the favorable cable performance equivalent tothat of conventional drop cables in terms of tensioning
characteristics and ease of installation.

Anchoring fitting

Drop cable

Joint box

Drop cable

Flame-retardant
polyethylene

5.0

φ 1.2 Zn-galvanizedsteel wire

Residencewall
2.0

Residencewall

However, in such an installation method where a drop
cable is led into the residence without segmentation, there
is a danger that a surge current due to lightning would
reach indoors, adversely influencing the communicationequipment installed in the residence. To cope with thisproblem caused by lightning, we have developed an optical drop cable using a non-metal tension member of glass
fiber reinforced plastic (G-FRP), which will be described inthis report.

Indoorcable(a) Conventional method

Figure 1(b) New method where drop cable isdirectly led into residence

Dropping installation method of optical drop cables.

φ 0.4 G-FRP rod

Figure 22-core single-mode fiber tape or colored
single-mode fiber

Structure of metal-free optical drop cable.

1Table 1
Test itemCharacteristics of metal-free optical drop cable.
Contents of test

Transmission loss

OTDR measurement

Temperature cycling-30~70°C, 3 cycles

TensileBending
Lateral force

Test results
1.55 µ m: 0.20 dB/km
1.31 µ m: 0.33 dB/km≤0.05 dB/km

Load: 700 N≤0.05 dB

Cable length: 10 m
Bending radius: 30 mm≤0.05 dB

Load: 1200 N≤0.05 dB

25-mm plate, 1 min
Height of fall: 1 m

Impact≤0.05 dB

Weight: 0.3 kg
Radius of impact area: 10 mmTwist

Angle of twist: ±180°C/ 1 m

Flame retardance

Inclined burning test in JIS C 3005

≤0.05 dB
Extinguished spontaneously

Note: Wavelength of measurement is 1.55 µ m.

Halogen-free, flame-retardant polyethylene is used forthe cable sheath, making the cable environmentally friendly compared to conventional drop cables which used PVC.
With such a structure described above, the developed
drop cable permits direct installation indoors the residence
from an electric pole, thus reducing costs of cable jointing
as well as those of materials for joint boxes, etc.
2.2 Characteristics
Table 1 shows the characteristics of the metal-free optical
drop cable. The cable is seen to be provided with satisfactory performance in terms of transmission loss besides
thermal and mechanical characteristics. Although G-FRP
has been introduced in the structure, the performance ofthe cable is equivalent to that of conventional drop cableusing steel wires.

23.

IN CONCLUSION

A metal-free optical drop cable has been introduced whichis capable of not only reducing installation costs but also
solving problems related with surge currents due to lightning. The cable also features full adaptability to a varietyof network, installation and residential environments simply by changing the type and the number of containedfiber. Thus the cable can cope with diversified optical fiber
configurations that are expected to develop in the future.
For more information, please contact:
Engineering Department, OptCom Division.
TEL: +81-3-3286-3435
FAX: +81-3-3286-3190

Furukawa Review, No. 222002