Development of Optical Fiber-Composite PVC Insulated Drop Wireby Fuminori Nakajima *, Soichiro Otosu *, Yoshiyuki Kamata *,Takashi Kijima *2 and Jun'ichi Kawashima *3

In order to promote broad use of optical communications in common homes,
installation of optical fiber cables to subscribers' premises should be much lower
in cost, necessitating further studies on the wiring materials including optical fiber as well as on
the installation method. Thus, it was considered that combining optical fiber with DV wire (PVC
insulated drop wire) widely used for electric power distribution to private premises would be
advantageous since the DV wire could serve as a tension member for optical fibers, thereby cutting the number of cable pieces to be installed. In an effort to develop an optical fiber drop cable,
the authors investigated the structure of optical fiber unit suitable for combining with the DV wire,and subsequently evaluated their characteristics when they were integrated with the DV wire. As
a result, optical fiber-composite PVC insulated drop wires with satisfactory performance havebeen developed. It is hoped that these cables promote the installation of optical fiber cables tosubscribers' premises.

ABSTRACT1.

INTRODUCTION

Recently, with the increasing popularity of Internet in common homes as well as the demand for optical communications to enable distribution of moving pictures, implementation of FTTH (Fiber To The Home) is being studied by avariety of telecommunications service providers. In orderto implement FTTH on a large scale, however, it is essential that the access network be constructed at an economical cost. As shown in Figure 1, conventional optical drop
wire for subscribers' premises has been designed, assuming an independent installation of the optical fiber cable
only, to have a steel suspension member to protect the
optical fiber against the wire tension during and after
installation. In electric power distribution, meanwhile, DV
wire (PVC insulated low voltage drop wire) shown in
Figure 2 is widely used for supplying electric power to private premises, so that integration of the DV wire with theoptical fiber is considered to be advantageous in the following terms:• The DV wire can be utilized as a tension-resistantmember for the optical fiber, thereby simplifying thestructure of optical drop cables.
• Installation of optical fiber on subscribers' premises isenabled without increasing the number of installedlines.
• The DV wire and the optical fiber can be installed
simultaneously, so that installation costs can be minimized.

The authors investigated, therefore, the structure of
optical fiber cable that is suited for combination with the
DV wire, and developed two types of optical fiber-composite PVC insulated drop wires (hereafter called OPDV):
bundle type OPDV in which an optical fiber unit is stranded around the DV wire as well as tube type OPDV in
which a tube is integrated with the DV wire allowing forpost-insertion of optical fiber unit when need arises. A 2fiber ribbon was used in these OPDVs assuming separation of up- and down-links. Figure 3 schematically illustrates the cable route configuration.

Suspension member(steel wire)
PVC sheath
Optical fiber
Steel wire

Figure 1

Conventional optical drop cable.

PVC sheath
Conductor

3.2 mm
5.6 mm*Engineering Dept., Optcom Div.
Engineering Dept., Electric Wire and Equipment Div.
*3 Distribution Dept., Chubu Electric Power Co. Inc.
*2

Figure 2

Stranding pitch: 400 mm

PVC insulated drop wire.

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Low-voltage power
distribution line

OPDV
Optical fiber
unit

Conventional optical
drop wire(Optical drop cable)

Figure 3

Residence

Opticaljunction box

4 mmCable route configuration of OPDV.

(a)

0.7 mm φ G-FRP

2.5 mmClosurefor
optical drop

tance using a square member. It was assumed that the
optical fiber unit had different mechanical characteristics
in the directions of parallel to and perpendicular to the twotension members as shown in Figure 7, so that the unit
was tested by changing the direction of the load. Table 1
shows the test results. Furthermore, Figure 8 and Table 2
show the evaluation method and the results of thesqueezing test, respectively.

SM 2-fiber ribbon
4 mm

2.

BUNDLE TYPE OPDV

2.1 Cable Structure
The basic structure of optical fiber unit for bundle type
OPDV has been designed to be such that two tension
members are disposed on both sides of a 2-fiber ribbon
followed by PVC sheathing. The sheath is provided with
two notches on the top and the bottom allowing for easy
access to the fiber. To prevent the fiber from possible
breakage due to electromagnetic repelling forces at thetime of DV wire short-circuiting, the tension member
employed non-metallic, glass FRP rod; and its diameter
was decided to be 0.7 mm, taking into consideration its
tensile properties and ease of stranding onto the DV wire.
PVC was adopted as the sheathing material for its flame
retardance equivalent to that of DV wire as well as
because of its low cost. We carried out the following
investigation in order to decide on the optimum cable
geometry.
2.1.1 Investigation on the cable geometry
The OPDV is often squeezed, during its stringing work,through the supporting arm of electric poles as shown in
Figure 4. We therefore fabricated prototypes of opticalfiber unit having structures shown in Figure 5 (a) to (c),and evaluated each of them for their crush and squeeze
resistance assuming stringing on the supporting arms.
Figure 6 shows the evaluation method of crush resis-

(b)

6 mm

(c)

Figure 5

Prototypes of optical fiber unit.

Load
Flat plate

Optical fiber unit

Square member

Figure 6

Crush test using a square supporting arm.

[Perpendicular to the tension members] [Parallel to the tension members]
Load
Supporting arm
Electric poleLoad
Lie down

OPDV
Resistance: 980 N

Figure 428

Stringing of OPDV.

Figure 7

Unable to measure
due to lying down

Crush test configuration.

Furukawa Review, No. 21

2002From the results shown in Tables 1 and 2, it was concluded that the optimum geometry of the optical fiber unit
is that shown in Figure 5 (a). Figure 9 shows the crosssection of an OPDV which integrates this optical fiber unit
with the DV wire.

3.

TUBE TYPE OPDV

Tube type OPDV has been studied, in which a tube for
optical fiber unit is integrated with the DV wire allowing forpost-insertion of optical fiber unit when need arises. For its
small friction, polyethylene was used as the material for

Table 1Results of the crush test using square supportingarm.

Optical fiber unit Perpendicular to tension member Parallel to tension member
Unable to measure due

Figure 5 (a)980 N or lessFigure 5 (b)780 N or less390 N or lessFigure 5 (c)1180 N or less390 N or lessto unit lying down

* Crush load with which no residual optical loss is detected at 1.55 φm
is shown.

135°

the tube and the sheath of optical fiber unit, and the tube
was sheathed with PVC to a thickness of 0.5 mm to provide flame retardance.
One of the key points in the development of tube type
OPDV was how to assure an insertion length of opticalfiber unit as far as 60 m, i.e., the maximum span of DV
wires. Whereas air-blowing using compressed air has
already been implemented for insertion of optical fiber
units conventionally, this method needs dedicated equipment of large size and high cost such as compressors,
making it difficult to be applied in space-limited working
areas --e.g., on bucket vehicles and on electric poles.
Consequently, we investigated various structures of tube
type OPDV, bearing in mind the manual insertion of low
cost and easy implementation.
3.1 Optical Fiber Unit for Manual Insertion
It was learned, according to the studies on insertion characteristics of optical fiber units into the tube, that theallowable insertion length of an optical fiber unit is correlated with its flexural rigidity. Figures 10 and 11 show themeasurement method of the flexural rigidity and the relationship between the flexural rigidity and the insertion
length of optical fiber units in straightened condition,
respectively. A polyethylene tube with an inner diameter of
4.5 mm was used in the measurement. Based on theseresults, an optical fiber unit shown in Figure 12 was developed and achieved manual insertion of up to 60 m.

Optical fiber unit
or OPDVSquaremember
Squeeze direction

Figure 8

Squeeze direction

Squeezing test using a square supporting arm.

Equation for flexural rigidity calculation
Flexural rigidity B = FR2
where, R: Bending radius (= 30 mm)
F: Repelling force

Repelling force

Bending radius: R

Results of the squeezing test using square supporting arm.

Optical fiber unit

Figure 5 (a)Figure 5 (b)Figure 5 (c)Squeezing test on

Appearance

optical fiber unitof OPDVNo residual optical loss
No external damage seen
No residual optical loss
No external damage seen
No residual optical loss
No external damage seen

Optical fiber unit for insertion

No disorderFigure 10 Measurement method of flexural rigidity.

Disorder seen
100

Disorder seen

*Measured at 1.55 µm

Optical fiber unit
bundled by stranding
DV wireDeveloped optical fiber unit

90

Insertion length (m)Table 280

Targeted insertion length

70
60
50
40
30
20
10
0
0

1

2

3

4

5

6

Flexural rigidity (×10-4 N.m2)

Figure 9

Cross section of bundle type OPDV.

Figure 11 Relationship between the flexural rigidity and insertion length of optical fiber unit.

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3.2.2 Tube lashing type
In view of the conclusion that the tube stranding type was
not suited for practical application, we employed a cablestructure in which the tube was placed lengthwise the DV
wire without stranding, and a lashing wire was used tobundle them. To prevent the fiber from possible breakage
due to electromagnetic repelling forces caused by DV wire
short-circuiting, aramid fiber was employed as the lashingwire material for its excellent tensile properties. Moreover,a PVC sheath 0.5 mm thick was applied on the aramidlashing wire, taking into account the weathering resistance, ease of handling and flame retardance upgradingof aramid fiber. Figure 13 shows the cross section of a
tube lashing type OPDV.

PE sheathNotch

SM 2-fiber ribbon

2.5 mmFigure 12 Optical fiber unit for insertion.

3.2 Investigation on Tube Integration
3.2.1 Tube stranding typeAs a method to integrate the tube with the DV wire,
stranding was studied first, and insertion lengths of the
optical fiber unit were evaluated as described in Clause
3.1 by changing the stranding pitch. It was found, as
shown in Table 3, that the stranding pitch of the tube
should be 1 m or longer in this case where the DV wire
itself was stranded with a pitch of 0.4 m. However, when atube type OPDV with a stranding pitch of 1.4 m underwent
an actual stringing work, disorder in the stranding pitch
was generated and an insertion length of 60 m proved to
be impossible, making clear that the cable was practicallyunusable. Moreover, such problems as collapsing of
stranded tube surfaced when OPDVs with long stranding
pitches were coiled, so that it was concluded that the tube
stranding type was not suited for practical application.

4.

CHARACTERISTICS OF OPDV

Characteristics of the two types of OPDV and the respective optical fiber units were evaluated. Table 4 shows thecharacteristics of the bundle type OPDV including its optical fiber unit for stranding, and Table 5 those of the tube
type OPDV including its optical fiber unit for insertion. It
has thus been confirmed that they have achieved excellent characteristics.

Lashing wire
(PVC sheathed aramid fiber)
2.6 mmφ

DV wireLashing pitch: 200 mm

Table 3

Relationship between stranding pitch and insertion
length.
Stranding pitch of tube

Insertion length

0.6 m

35 m

1.0 m

60 m or more

1.2 m

60 m or more

PVC sheathed PE tube
4.5 mm in inner diameter
7.0 mm*Stringing conditions: Span: 60 m; Sag: 1.2 m

Table 4

Figure 13 Cross section of tube type OPDV.

Characteristics of bundle type OPDV and optical fiber unit for stranding.
Optical fiber unit for stranding

Bundle type OPDV
Item
Test conditions

Test results (@1.31 µm)

Test conditions

Test results (@1.31 µm)

—

—

—

0.34 dB/km-20~60°C

0.01 dB/60 m or less-20~60°C

0.01 dB/km or less

100 N

No residual loss

Transmission characteristics
Attenuation
Temp. dependence
Mechanical characteristics
2820 N

Bending

R70 mm, 180°, 5 times

No residual loss

R30 mm, 180°, 5 times

No residual loss

980 N/50 mm

No residual loss

1960 N/50 mm

No residual loss

Impact0.5 kg/1 m, 10 spots

No residual loss

1 kg/1 m, 10 spots

No residual loss

Vibration±5 mm, 10 Hz, 1 million times

No residual loss

±5 mm, 10 Hz, 1 million times

No residual loss

Compression

Twist
Flame retardance30

No residual loss,

TensionElongation: 0.14 %245 N, ±90°, 3 times

No residual loss

10 N, ±270°, 3 times

No residual loss

JIS C 3005, inclined burning

Extinguished within 10 sec.

JIS C 3005, inclined burning

Extinguished within 10 sec.

Furukawa Review, No. 21

2002

Table 5

Characteristics of tube type OPDV and optical fiber unit for insertion.
Optical fiber unit for insertion

Tube type OPDV
Item
Test conditions

Test results (@1.31 µm)

Test conditions

Test results (@1.31 µm)

Transmission characteristics
Attenuation
Temp. dependence

—

—

—

0.34 dB/km-20~60°C

0.01 dB/60 m or less-20~60°C

0.01 dB/km or less

5.7 N

No residual loss

R30 mm, 180°, 5 times

No residual loss

Mechanical characteristics
2820 N

Bending

R70 mm, 180°, 5 times

No residual loss

Compression

Elongation: 0.17 %980 N/50 mm

No residual loss

1760 N/50 mm

No residual loss

Impact0.5 kg/1 m, 10 spots

No residual loss

0.5 kg/1 m, 10 spots

No residual loss

Vibration±5 mm, 10 Hz, 1 million times

No residual loss

±5 mm, 10 Hz, 1 million times

No residual loss

245 N, ±90°, 3 times

No residual loss——

JIS C 3005, inclined burning

Extinguished within 10 sec.

—

—

Twist
Flame retardance5.

No residual loss,

TensionSUMMARY

For accelerated implementation of FTTH, it is essentialthat optical fiber cable and its installation be low in cost. In
this work, the authors have studied optical drop cables inorder to reduce the cost of the cable as well as its installation, whereby prototype cables integrating optical fiber unit
and DV wire were fabricated and were subsequently evaluated. As the result, two types of optical fiber-composite
PVC insulated drop wire (OPDV) with excellent characteristics have been developed. It is hoped that the use of
these OPDVs will promote broad installation of opticalfibers to common homes.
Manuscript received on November 1, 2001.

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