Separable Optical Fiber Ribbons and Cables
for Advanced Mid-span Branchingby Tatsuya Oyama *, Ken Kanai *, Hitoshi Kaneda *, Masaru Nakajima *,Toshiaki Ozawa *, Yoshihisa Rintsu * and Yuichi Watanabe *2

With the growing popularity of fiber-to-the-home (FTTH), installation work of optical fiber cables to each household is increasing in number. But in the mid-spanbranching of conventional aerial cables, improvement of low efficiency in fiber
utilization has posed a problem to be solved. Accordingly, the authors have developed, with theaim of improving the fiber utilization efficiency in mid-span branching, both two-fiber and eightfiber ribbons that enable ease of separating into specified number of fibers at the point of midspan branching. This paper reports on the characteristics of the optical fiber ribbon of separable
type and the optical cable based on the ribbon, along with a special tool for mid-span branching
work that has been developed together.

ABSTRACT1.

INTRODUCTION

With the growing popularity of fiber-to-the-home (FTTH),
installation work of optical fiber cables to each household
is increasing in number. Implementation of FTTH requires
construction of a dense optical fiber network using opticalcables of small fiber counts, so that it inevitably needs
mid-span branching and jointing of cables at intermediate
points of distribution optical fiber cables. But in the midspan branching of conventional aerial cables, low efficiency in fiber utilization has posed a problem to be improved.
This is because, in the standard method for mid-spanbranching of conventional aerial cables, optical fibers
contained in a fiber ribbon are cut en bloc to take out therequired number of fibers, and the rest fibers are left
unused resulting in a decrease in fiber utilization efficiency.
Accordingly we have previously developed, and havealready reported 1), a separable four-fiber ribbon as wellas an optical cable using the fiber ribbon, which permits
easy separation of single fibers at intermediate positions.
In spite of the above mentioned, fiber branching
scheme has been diversified in recent years. For example,
whereas conventionally it was a mainstream practice tojoint the separated single fibers to a drop cable, recently
a number of cases are encountered where an aerial cableof multitudes of fibers is mid-span branched into an aerial
cable of small numbers of fibers 2). In order to deal with
* Technical & Products Development Dept.,
Telecommunications Co.
*2 Tokyo Electric Power Company

such cases, development of a new optical fiber ribbon
together with an aerial cable using the ribbon is required,
which is aimed at enabling mid-span branching of not
only from a high-count ribbon to single fibers but also
from a high-count ribbon to low-count ribbons.
To meet such a requirement, we have developed aneight-fiber ribbon of separable type, realizing mid-spanbranching from a high-count ribbon to a plurality of lowcount ribbons, together with, taking into consideration
branching from a low-count ribbon to single fibers, a separable type two-fiber ribbon. This paper reports on the
superior characteristics obtained by the evaluation of slotted-core cables using these optical fiber ribbons. Also
included are the development results of a special tool for
ribbon separation that enables easy and safe mid-spanbranching.

2.

DESIGN OF SEPARABLE RIBBON

The separable optical fiber ribbon and the special tool for
ribbon separation that have been developed here will be
described in this Section.
2.1 Concept of Separable Ribbon
The optical fiber ribbons used in the current aerial cables
are largely two-, four- and eight-fiber ribbons. Accordingly,
we have studied, in the development of new separable
ribbons, optical fiber ribbons of these fiber counts. Figure
1 shows cabling diagram for mid-span branching, andTable 1 shows the design concept for separable opticalfiber ribbons to be developed here.

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Separable Optical Fiber Ribbons and Cables for Advanced Mid-span Branching

Single-fiber cable

High-count cableLow-count cable

Figure 1
Table 1

ration in safety after the optical fiber ribbon is scrapedusing the sandpaper, a separation element made of plastic mesh was added to the special tool. It is thought that
scraping the ribbon using the mesh element will complete, after the separable ribbon is pre-treated using the
sandpaper to trigger fiber separation, the single fiber separation safely and easily. Thus, it is expected that adverse
effects such as fiber breakage and loss increase are eliminated while at the same time the work time is reduced.
Figure 2 shows the special tool developed here.

Cabling diagram for mid-span branching.

Design concept of separable optical fiber ribbon.

Development
objective

Mid-span branching

Remarks

Two-fiber ribbon

Separable to single fiber—

Separable to single fiber

Already developed

Four-fiber ribbon
Eight-fiber ribbon

After separation,
separable in turn toSeparable to four-fiber ribbon
single fiber
Separable to two-fiber ribbon

The two- and four-fiber ribbons are mainly packaged inaerial cables of low-fiber counts, and their destinations of
mid-span branching are mostly single-fiber drop cables toindividual household. For this reason, the two- and fourfiber ribbons for mid-span branching have to be separable into single fibers.
On the other hand, the eight-fiber ribbon is packaged inaerial cables of high-fiber counts, and thus, besides being
dropped as single fibers, it is sometimes mid-spanbranched into aerial cables of low-fiber counts as shownin Figure 1. Therefore, the eight-fiber ribbon of separable
type has to be adapted to both of these branching
schemes in order to improve the efficiency of fiber utilization as well as the work efficiency. To put it simply, theeight-fiber ribbon for mid-span branching has to be separable, at arbitrary intermediate points, to two- or four-fiber
ribbons that are widely used in low-count fiber cables aswell as to single fibers.
2.2 Special Tool for Mid-span Branching
A special tool was needed to carry out the mid-spanbranching work easily and safely.
Basically the branching work is performed as aerial
work, so that the design is required to be such that thetool is compact and lightweight permitting operations
using one hand. In addition, fiber separation work must
be done quickly and yet safely, which suggests that materials raising the possibilities of damaging the fiber should
be discarded in designing the tool. We accordingly selected sandpaper as the separating element for mid-spanbranching of optical fiber ribbons, and mounted it on thespecial tool developed here.
In order not to apply excessive forces on the opticalfiber ribbon at the time of scraping, the tool was also provided with a gap adjustment mechanism to enable scraping with a suitable working gap.
Moreover, with the aim of carrying out single-fiber sepa-

Gap adjustment pin

Sandpaper element
Mesh element

Figure 2

Fiber ribbon separation tool for mid-span branching.

2.3 Separable Four-fiber Ribbon
The four-fiber ribbon was investigated for its material andstructure in order to make single-fiber separation using
the special tool possible. The structure of the ribbon isshown in Figure 3. Generally speaking, the lower theadhesion between the colored layer and the ribbon
matrix, the easier becomes peeling, thereby improving
the ease of single-fiber separation. And, thinner the thickness of the ribbon matrix, the higher becomes the ease of
taking out fibers. We accordingly studied the four-fiber ribbon of single-layered structure with different thickness
levels of the colored layer and the ribbon matrix, andobtained an optimized solution that permits single-fiber
separation using the special tool. The details have beenreported elsewhere 1).

Optical fiber

Thickness ofribbon matrix

Coloredlayer
Ribbon matrix

Figure 3

Structure of four-fiber ribbon.

2.4 Design of Separable Two-fiber Ribbon
Based on the design concept of the separable four-fiber
ribbon described in Section 2.3, a separable two-fiber ribbon was studied. Ease of single-fiber separation was
evaluated for the ribbon matrices of different thicknesses
using the same material as for the four-fiber ribbon. In theevaluation, the ribbon was scraped once using the sandpaper element then several times using the mesh element

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Separable Optical Fiber Ribbons and Cables for Advanced Mid-span Branching

to carry out fiber separation. The results are shown in
Table 2, from which it is clearly shown that the ease of
separation is dependent on the matrix thickness, and thatthe matrix thickness has to be 0.6 or lower in relativevalue to achieve good single-fiber separation.
Table 2

Success rate of ribbon separation.

Young’s modulus and two different thicknesses, and evaluated their ease of separation using the special tool. Table
3 shows the three materials with different Young’s modulus. Two methods of separation were evaluated, i.e. scraping by sandpaper followed by mesh, and scraping bymesh only. The separation performance was evaluatedbased on the number of times of tool usage required until
separation to ribbons but not until separation to fiber, andthe results are shown in Table 4.

Matrix thickness (relative value)

Use of special tool
Sandpaper plus mesh

0.1

Separation possible

0.3

Separation possible

0.6

Separation possible

Material

Young’s modulus (relative value)

Manufacturability

1.0

Separation impossible

A

1.0



B

0.4



C

0.3



2.5 Design of Separable Eight-fiber Ribbon
Conventionally, the destination of mid-span branching of
aerial cables was mainly drop cables containing a single
fiber, so that single-fiber mid-span branching was generally required. Recently, however, cases of mid-spanbranching to drop cables containing multiple numbers offibers and to aerial cables containing small numbers offibers occur, raising requirements such that an eight-fiber
ribbon is branched into two- or four-fiber ribbons, which
are in turn jointed to other optical fiber ribbons in anothercable. Thus, development of optical fiber ribbons for midspan branching is required that are separable to lowcount ribbons.
Separable multi-fiber ribbons can be realized by combining the single-layered ribbons described in Sections
2.3 and 2.4, whereby a plurality of single-layered ribbons
are arrayed followed by covering them en bloc to make adouble-layered multi-fiber ribbon. An eight-fiber ribbon of
double-layered structure that is separable to two- or fourfiber ribbon was investigated here. Figure 4 shows anexample of separable eight-fiber ribbon of double-layered
structure that is separable via two-fiber ribbons to single
fibers.

Table 3

Table 4Layermaterial

Structure of separable eight-fiber ribbon.

It was thought that an important point in designing theseparation from a double-layered ribbon to single-layered
ribbon is the material property of the second layer and its
thickness. We accordingly prototyped samples for thesecond layer in six levels in total, i.e. three different

Separation performance of separable eight-fiber
ribbon.
Sandpaper plus mesh

Mesh only

Relative layer Relative layer Relative layer Relative layer
thickness 0.2 thickness 1.0 thickness 0.2 thickness 1.0

A

×*1

×*2

B

×*1





C

×*





1

×*2

×*2

Note *1: Separated into single fibers before separating into ribbons.
*2: Impossible to be separated into either ribbon or fiber.

The results show that, in spite of the fact that a thinner
layer generally leads to superior ribbon separation, thethinner layers tested here results in separation into fibers
when processed by the sandpaper. While materials B andC showed good separation performance by the meshonly method, it can be said that material B with a moderate Young’s modulus is the best suited taking manufacturability into consideration.
The single-layered ribbon separated from the separable
double-layered ribbon is based on the same design as forthe ribbons separable into single fibers described in
Section 2.3 or 2.4. Thus, the ribbon is separable, after ribbon separation, into single fibers using the sandpaper
and mesh elements on the special tool. Hence, the separable double-layered ribbon permits both separation
schemes for either ribbon jointing or fiber jointing, byselecting a suitable separation method in the aerial midspan branching.

3.

Figure 4

Material property for the second layer.

CHARACTERISTICS OF SEPARABLE
RIBBONSThe separable two- and eight-fiber ribbon developed here
are required to exhibit a level of characteristics equivalent
to that of conventional optical fiber ribbons. Accordingly,
we have evaluated the main characteristics of the developed optical fiber ribbons. In addition, in order to evaluate
their workability for mid-span branching, changes intransmission loss and optical fiber reliability due tobranching work were also measured.

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3.1

Main Characteristics of Separable Fiber Ribbons

3.1.1. Characteristics of Separable Two-fiber Ribbon
Based on the design described in Section 2.3, a separable two-fiber ribbon was developed which permits separation into single fibers for single-fiber jointing at an intermediate point in an aerial span. The developed ribbon was
evaluated for its initial characteristics, crush resistance,
temperature stability and long-term reliability. The results
are shown in Table 5. It was confirmed that the separable
two-fiber ribbon developed here exhibited a level of characteristics equivalent to that of conventional fiber ribbons.
Table 5

Test condition

Transmission loss

λ=1550 nm≤0.21

Figure 5

dB/km

500 N/100 mm

≤0.02

dB

85°C x 85%, 30 days

≤0.05

dB/km

Temperature cycling-40~+70°C, 10 cycle ≤0.05

dB/km

Fusion splice loss

MFD: 8.6±0.4 µm

≤0.10

Mesh

dB

3.1.2. Characteristics of Separable Eight-fiber Ribbon
Based on the design described in Section 2.5, a separable eight-fiber ribbon was prototyped which permits separation into two- or four-fiber ribbon as well as into single
fibers at an intermediate point in an aerial span. Its characteristics were also evaluated in the same way as
described in Section 3.1.1 and the results are shown in
Table 6. The fusion splicing loss with conventional ribbons
and two- and four-fiber ribbons after mid-span branchingis satisfactory. It was confirmed that other the characteristics are equivalent to that of conventional ribbons.

Sandpaper plus mesh

Test item

Test condition

Transmission loss

λ=1550 nm

≤0.21

dB/km

Crush resistance

500 N/100 mm

≤0.02

dB

Temperature/humidity aging

85°C x 85%, 30 days

≤0.05

dB/km

Temperature cycling-40~+70°C, 10 cycle ≤0.05

dB/km

MFD: 8.6±0.4 µm

dB

Transmission Loss Changes at Mid-span
Branching
The separable optical fiber ribbons developed here were
evaluated for transmission loss changes during mid-spanbranching work. The evaluation method is as follows. As
illustrated in Figure 5, the two-fiber ribbon was scraped at
its intermediate point once using the sandpaper elementon the special tool, followed by scraping the same portion
with the mesh element on the tool, thereby being separated into single fibers. The optical fiber ribbon of doublelayered structure was, as illustrated in Figure 6, scrapedusing the mesh on the special tool to be separated into
ribbons of single-layered structure, which in turn were
scraped at its intermediate point using the sandpaper andthen mesh, thereby being separated into single fibers.
Table 7 shows the attenuation loss changes occurred at

Separation of separable eight-fiber ribbon.

Table 7

Loss increase during ribbon separation.

RibbonSingle fiber

Test results≤0.10

Figure 6

Type of separation

Characteristics of separable eight-fiber ribbon.

Fusion splice loss

Separation of separable two-fiber ribbon.

Test results

Temperature/humidity aging

Crush resistance

3.2

Sandpaper plus meshCharacteristics of separable two-fiber ribbon.
Test item

Table 6each work step. The measurement was carried out at awavelength of 1550 nm and a measurement interval of 10
msec. From the results, it was confirmed that the losschanges were small, thus posing no problems.

MethodTwo-fiber ribbon Eight-fiber ribbon

Mesh

—

≤0.3 dB

Sandpaper≤0.1 dB≤0.1 dB

Mesh≤1.0 dB≤0.1 dB

3.3

Evaluation of Reliability after Mid-span
Branching
In order to verify whether fibers were damaged during the
mid-span branching work, the tensile fracture strength of
two groups of fibers were measured to evaluate the possible degradation in strength. The first group comprised
fibers before ribbon forming, and the second group comprised those after separation using the sandpaper andmesh elements on the special tool. Figures 7 and 8 show
the test results, i.e. the Weibull distribution of fracture
strength of two groups of fibers, respectively. Since thefibers before ribbon forming and those after separation
using the special tool both exhibited comparable Weibull
distributions, it was confirmed that no strength degradation occurred due to the mid-span branching using thespecial tool.

4.

CHARACTERISTICS OF CABLES FOR
MID-SPAN BRANCHING

Aerial cables for mid-span branching were developed
using the separable optical fiber ribbons described above,

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10

Main characteristics of the developed cable describedabove were evaluated, and the results are shown in Table
8. Both 24-fiber type and 48-fiber type showed good performance in terms of transmission loss, mechanical characteristics and temperature stability, and it was confirmedthat the obtained characteristics are comparable to thoseof SZ cables using conventional optical fiber ribbons.

-ln (1-Fk)

1

0.1

Table 8Characteristics of SZ cable using two-fiber ribbon.

0.01

0.001

1

Figure 7

10

Fracture strength σ f (GPa)Weibull distribution of fiber fracture strength before
separation.

10-ln (1-Fk)

1

0.1

Test results
Measurement
wavelength
2448Unit(nm)
fiber fiber

Test item

Test condition

Transmission
loss—

Temperature
cycling-30~+70°C
x 3 cycles

Tensileperformance

0.2% elongation≤0.01 ≤0.01

dB

Squeezing

1.47 kN, 90°
R=300nm≤0.01 ≤0.01

dB

Bending

R=10D·10
cycles≤0.01 ≤0.01

dB

Crush
resistance1960 N/100 mm≤0.01 ≤0.01

dB

Impact500g·1m falling≤0.01 ≤0.01

dB

Twist

245 N, ±180°≤0.01 ≤0.01

dB

1310

≤0.34 ≤0.34 dB/km

1550≤0.21 ≤0.20 dB/km≤0.01 ≤0.01 dB/km

1550

0.01

4.2
0.001

1

Figure 8

10

Fracture strength σ f (GPa)Weibull distribution of fiber fracture strength after
separation.

and cables using the two-fiber and eight-fiber ribbons
were evaluated for main cable characteristics.

Mid-span Branching Cable Using Eight-fiber
RibbonFigure 10 shows the structure of 640-fiber cable for midspan branching using the separable eight-fiber ribbon
developed here. Ten separable eight-fiber ribbons arestacked in each groove of the SZ slot. The slot pitch andthe slot turning angle were optimized in design so as tosatisfy both fiber strain and ease of taking out of fiber.

4.1

Mid-span Branching Cable Using Two-fiber
RibbonFigure 9 shows the mid-span branching cable using thetwo-fiber ribbon developed here. A tension member islocated at the center, and separable two-fiber ribbons areaccommodated in each groove of the SZ slot. The 24fiber and 48-fiber type of the cable were developed.

Tension member
SZ slot

Separable
eight-fiber ribbon
Wrapping

Tension member
SZ slot
Separable two-fiber
ribbonWrapping
SheathFigure 9

Rip cord

Structure of SZ cable using two-fiber ribbon.
(24-fiber cable)

Sheath

Rip cord

Figure 10 Structure of 640-fiber SZ cable using eight-fiber
ribbon.

Main characteristics of the developed cable describedabove were evaluated, and the results are shown in Table
9. The cable exhibited good performance in terms oftransmission loss, mechanical characteristics and temperature stability, and it was confirmed that the obtained
characteristics are comparable to those of SZ cables
using conventional optical fiber ribbons.

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Table 9Characteristics of SZ cable using eight-fiber ribbon.

Test item

Transmission loss—

Temperature cycling-30~+70°C
x 3 cycles

Tensile performance

0.2% elongation

Squeezing
Bending

5.

Test condition

Measurement
wavelength(nm)

Test results

1310≤0.36 dB/km

1550≤0.25 dB/km≤0.06 dB/km

1.47 kN, 90°
R=300nm
R=10D·10
cycles

1550

≤0.01

dB

≤0.01

dB

≤0.01

dB

Crush resistance1960 N/100 mm

≤0.01

dB

Impact500g·1m falling

≤0.01

dB

Twist

245 N, ±180°

≤0.01

dB

CONCLUSION

Optical fiber ribbons for mid-span branching have beendeveloped including two-fiber ribbon and eight-fiber ribbon that are separable to either ribbons or single fibers,
together with a special tool that can separate these optical fiber ribbons easily and safely. It was confirmed thatthe optical fiber ribbons prototyped showed the characteristics comparable to those of conventional ribbons,thus posing no problems in terms of attenuation loss
increase and fiber strength degradation during thebranching work. Moreover, optical cables using these
optical fiber ribbons showed the characteristics comparable to those of conventional aerial optical cables.
Thus it is expected that the cables for mid-span branching developed here can improve the efficiency of fiber utilization at mid-span branching, making themselves a useful optical fiber in the implementation of the FTTH infrastructure.

REFERENCES
1) H. Kaneda, M. Nakajima, T. Ozawa, F. Nakajima and Y. Rintsu,“Development of Optical Separable Ribbon Cable,” IWCS 53rd
(Nov, 2004).
2) H. Hayashi, “Outline of the FTTH Service Programs of TEPCO,”
6th Workshop for Well-balanced Development of National
Broadband Infrastructure, Information and Communications
Research Workshop, Ministry of Internal Affairs and Communications (2005). (in Japanese)

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