INFOCOMMUNICATIONS
Ultra-High-Fiber-Count and High-Density Slotted
Core Cable with Pliable 12-Fiber Ribbons
Fumiaki SATO*, Keisuke OKADA, Takao HIRAMA, Kentaro TAKEDA,
Ryoei OKA and Ken TAKAHASHI
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------This paper describes the configuration of a new ultra-high-count and high-density slotted optical fiber cable with 12-fiber pliable
ribbons. We combined the pliable ribbon technology with a slotted core cable design to create the cable that doubles the fiber
count while the diameter remains the same as conventional cables. The pliable ribbon consists of fiber adhesive parts and nonadhesive parts coming in turns in a longitudinal and transverse direction, enabling high fiber density within a limited duct space
and mass fusion splicing. A slotted core cable is designed with a non-preferential bending axis, allowing for easy installation in
space-constrained areas. Its best characteristics, such as easy handling, good identification, and mass fusion splicing, are
retained in our new cable. This paper describes the design of the 12-fiber ribbon and the test results of mass fusion splicing. It
also refers to the designs and characteristics of 3456-fiber-count slotted core cables, which are the highest fiber-count optical
cables in commercial use, and 1728-fiber-count slotted core cables.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Keywords: ultra-high-fiber-count, high-density, mass-fusion splicing, pliable 12-fiber ribbon, slotted core cable
1. Introduction
Reflecting the recent advancement of cloud computing
and other big-data processing technologies, a growing
number of large-scale data centers are currently being
constructed. As future increase in data transmission
capacity between these facilities is expected, the demand
for high-count, high-density optical cables is growing.
Optical cables that connect these data centers are usually
installed in cable ducts located outdoors, which requires
technology that allows high-density installation of these
cables in a limited conduit space. To meet this demand, we
have developed a series of high-fiber-count, high-density
optical cables that are flexible in all directions. In particular, the new optical cables use pliable 12-fiber ribbons to
ensure high flexibility and facilitate mass-fusion splicing.
Table 1. Structures of newly developed ultra-high-count
optical cables
Conventional optical
cable
Structures of newly
developed optical cable
1.5-inch
cable duct
864-fiber-count
1728-fiber-count
1728-fiber-count
3456-fiber-count
2.0-inch
cable duct
In addition, the core of these cables is slotted and a strength
member*1 is passed through the center of the core. This
paper describes the designs and characteristics of 1728and 3456-fiber-count slotted core cables shown in Table 1.
These two cables are representative models of the new
cable series that has been developed to increase the fiber
density in 1.5-inch and 2.0-inch cable ducts, which are in
wide use today.
2. Design and Evaluation of Pliable 12-Fiber
Ribbon
The pliable ribbon that we used for the new cables is
schematically illustrated in Fig. 1. The flexibility of the
ribbon and the alignment of its fibers for mass-fusion
splicing can be controlled by adjusting the lengths and the
ratio of the adhesive part to the non-adhesive part. This study
compared the mass-fusion splicing workability of a singlefiber type pliable ribbon shown in Fig. 1 (a) and with that of
a two-fiber type pliable ribbon shown in Fig. 1 (b).
For the comparison, we measured the total time required
to complete the following work procedures:
(1) Setting test ribbon on fiber holder of fusion splicer
(2) Removing coating resin with heating type remover
(3) Cutting off fiber end with fiber cutter
(4) Setting test ribbon on fusion splicer to splice fibers
together
In particular, we compared the fusion splicing time
between the pliable ribbons (a) and (b) shown in Fig. 1
by varying the adhesive pitch “P” with the ratio between
the adhesive part “a” and non-adhesive part “c” kept
constant.
The results of fusion splicing time measurement are
shown in Fig. 2. The single-fiber type pliable ribbon required
relatively long time even for a shorter adhesive pitch range.
The main reason for this is that the single-fiber type pliable
10 · Ultra-High-Fiber-Count and High-Density Slotted Core Cable with Pliable 12-Fiber Ribbons
Adhesive pitch P
Adhesive
part length
a
Non-adhesive
part length
c
(a) Single-fiber type pliable ribbon
Adhesive pitch P
Adhesive
part length
a
Non-adhesive
part length
c
Fig. 3. Fusion splice loss of 12-fiber ribbons
(b) Two-fiber type pliable ribbon
Fig. 1. Schematic illustration of pliable 12-fiber ribbons
In addition to the above test, we carried out a heat
cycle test of the new 12-fiber ribbon with its fusion-spliced
joint covered with a protective sleeve. The objective of this
test was to check the functional reliability of the fusionspliced joint. In the test, we connected 10 fusion-spliced
joints in series as shown in Fig. 4, and exposed them to 20
heating cycles at a temperature range from -40°C to 70°C.
The test specimen did not exhibit any increase in fusion
splice loss even after exposure to the heating cycle, thereby
verifying the functional reliability of the fusion-spliced
joints on the new pliable 12-fiber ribbons.
Fig. 2. Comparison of mass-fusion splicing time between
single-fiber type and two-fiber type pliable ribbons
ribbon was easily dislocated when set on the holder of the
fusion splicer, and required the time for realignment. In
contrast, the fibers of the two-fiber type pliable ribbon
remained in position after being placed on the holder. We
confirmed that, as long as an appropriate adhesive pitch is
selected, the two-fiber type pliable ribbon is spliced no
later than splicing time for conventional 12-fiber ribbons,
which is shown by the dotted box in Fig. 2. In this comparative study, we used 1.5 times the adhesive pitch to
conventional pliable ribbon. At this adhesive pitch, the
12-fiber ribbon exhibited high flexibility while maintaining
its original alignment.
Figure 3 compares the distribution of mass fusion
splice loss between the pliable 12-fiber ribbon used in the
newly developed optical cables and a conventional 12-fiber
ribbon. The results confirm that the fusion splice loss of the
new 12-fiber ribbon is comparable to that of the conventional 12-fiber ribbon.
Fig. 4. Heat cycle test results for fusion spliced joints (10 joints)
of pliable 12-fiber ribbon
3. Ultra-High-Fiber-Count and High-Density
Slotted Core Optical Cable
3-1 Design of the optical cable
The newly developed optical cable comprises a
stranded steel wire passing through the axial center and a
slotted core that makes the cable significantly flexible. As
typical examples of the optical cable, the design of a
1728-fiber-count slotted core optical cable and the cross
SEI TECHNICAL REVIEW · NUMBER 83 · OCTOBER 2016 · 11
section of a 3456-fiber-count slotted core optical cable are
schematically illustrated in Figs. 5 and 6, respectively. The
optical fibers used in these cables are single-mode fibers
(ITU-T G.657A1) with enhanced bending property.
Combined use of these bendable optical fibers and pliable
ribbons has significantly contributed to the increased fiber
density in the cable core, thereby reducing the cable size
and weight compared with conventional optical cables.
Identification of pliable fiber ribbons according to
the number of bars printed on them
Fig. 7. Schematic illustration of bars printed on pliable 12-fiber
ribbon
Sheath
Ripcord
Water-blocking tape
Pliable 12-fiber ribbon
Slotted core
Stranded steel strength member
Outer diameter: 26 mm
Fig. 5. Schematic illustration of 1728-fiber-count optical cable
with pliable 12-fiber ribbon
Stranded steel strength member
Slotted core
Identification mark
Pliable 12-fiber ribbon
3-2 Study of water-sealing mechanism
Unlike slotted core optical cables with conventional
fiber ribbons, the newly developed ultra-high-fiber-count,
high-density optical cable consists of grooves packed with
fiber ribbons at a high density. At the development stage of
the new optical cable, the conventional water-sealing
system was unlikely to be able to deliver the effect of the
water absorbing powder to the bottom of the grooves. To
clear the above problem, we investigated the effects of the
fiber density in the slotted optical fiber grooves on the
water absorption performance of the optical cable. The
relation (relative value) between fiber density in the groove
and water penetration after 240 hours is shown in Fig. 8.
Water penetration increases as fiber density increases. For
the new optical cable, we determined the optical fiber
packaging density so that it would not significantly degrade
the water penetration length.
Water-blocking tape
Ripcord
Sheath
Outer diameter: 34mm
Fig. 6. Cross sectional view of 3456-fiber-count optical cable
with pliable 12-fiber ribbon
In a high-fiber-count optical cable, each fiber ribbon
needs to be identified. For the new optical cable, we printed
a series of bars on each fiber ribbon as shown in Fig. 7 so
that they can be identified according to the number of the
bars. The use of bars in place of conventional numerical
figures offers better legibility and easy recognition.
Each groove of a 3456-fiber-count slotted core optical
cable housed 36 pliable 12-fiber ribbons. Thirty six pattern
markings allow the identification of each ribbon in the
groove. The grooves in the optical cable are distinguished
from each other by identification marks printed on the
surface of the slot ribs.
Fig. 8. Relationship between optical fiber density in groove and
water penetration length
3-3 Study of cable installation workability
In contrast to conventional optical cables containing
strength members on both sides of the outer jackets, the new
slotted optical cable is characterized by its omnidirectional
flexural property owing to a strength member passed through
the longitudinal center of the core. In addition, the flexural
12 · Ultra-High-Fiber-Count and High-Density Slotted Core Cable with Pliable 12-Fiber Ribbons
property of the new cable can be enhanced by optimally
selecting the type of the strength member and the structure
of the outer jacket. To check the difference of flexural property between the newly developed 1728-fiber-count slotted
core optical cable and a conventional central-tube type
optical cable, we carried out a flexural rigidity test.
The flexural rigidity test system is shown in Fig. 9,
and the test results are shown in Table 2. As the table
shows, the flexural rigidity of the new cable was nearly
one-half that of the conventional cable. This result suggests
that the new cable is advantageous in that it is easier to be
installed in a hand-drilled duct or other restricted spaces.
Fig. 10. Attenuation change of 3456-fiber-count slotted core
optical cable
Table 3. Transmission and mechanical properties of 1728-fibercount and 3456-fiber-count slotted core optical cables
Load cell
Test cable
Item
Test load F
Displacement y
Distance x
IEC60793-1-40
Temperature
Cycling
FOTP-3
-40°C/+70°C × 2 cyc.
< 0.10 dB/km
Compressive
Loading
FOTP-41
220 N/cm, 1 minute followed by
110 N/cm, 10 minutes
Impact Test
FOTP-25
Impact Energy: 4.4 N-m
2 impacts, 3 locations
λ = 1550 nm
Cyclic Flexing
Table 2. Flexural rigidity comparison test results for two types
of optical cables
Conventional optical cable
Newly developed optical cable
864-fiber count
(outer diameter: 25 mm)
1728-fiber count
(outer diameter: 26 mm)
Flexural rigidity: 11.4 N･m 2
Flexural rigidity: 5.5 N･m 2
* The flexural rigidity of the conventional optical cable was measured in the
diagonal direction to strength member (the direction in which the cable could
be bent).
Evaluation result
< 0.25 dB/km
(1550 nm)
IEC60794 Stiffness (Method E17A): flexural rigidity B = x3/48•(F/y)
Fig. 9. Flexural rigidity test system for optical cable
Test method
Attenuation
Coefficient
FOTP-104 I and IV
Sheave diam. ≤ 20 × cable diameter
25 cycles at 30 cyc./min
λ = 1550 nm
Cable Twist Test
FOTP-85
Sample Length ≤ 2 m
10 cycles ± 180°
λ = 1550 nm
Long Tensile
Loading and
Fiber Strain Test
FOTP-33
a) 600 Ib (rated)
b) 180 Ib (residual)
< 0.1 dB
No defect in cable's
external appearance
Fiber strain (Rated)
≤ 60% fiber proof strain
Fiber strain (Residual)
≤ 20% fiber proof strain
< 0.1 dB
3-5 Comparison of fiber count
Figure 11 compares the outer diameter and fiber count
of the new optical cables with those of conventional ribbon
3-4 Evaluation of transmission and mechanical properties
We evaluated the transmission and mechanical properties of the newly developed 1728-fiber-count and
3456-fiber-count slotted core cables. The heat cycle test
was conducted at a temperature range from -40°C to +70°C
for a prototyped 3456-fiber-count cable wound around a
drum. As shown in Fig. 10, the 3456-fiber-count optical
cable is stable in attenuation even after it is exposed to the
heat cycle. Table 3 summarizes the results of the transmission and mechanical property evaluation for the 1728-fibercount and 3456-fiber-count slotted core cables, confirming
that both of them have sufficient properties.
Fig. 1 1. Comparison of fiber count between conventional and
newly developed optical cable
SEI TECHNICAL REVIEW · NUMBER 83 · OCTOBER 2016 · 13
loose tube optical cables.*2 The fiber density of 1728-fibercount and 3456-fiber-count slotted core optical cables is
twice that of a conventional optical cable of the same outer
diameter.
4. Conclusion
We have developed a series of ultra-high-fiber-count,
high-density slotted core optical cables with pliable
12-fiber ribbons. The ribbon is so constructed as to enhance
its fiber density without deteriorating mass fusion splicing
workability. The newly developed cable comprises a slotted
core and a strength member passed through the center of
the core. Out of the new series of optical cables, the
1728-fiber-count cable has an outer diameter of 26 mm or
less while the 3456-fiber-count cable has an outer diameter
of 34 mm or less. These optical cables are expected to
enhance optical transmission density and contribute to the
effective use of restricted spaces.
Technical Terms
＊1Strength member: a tensile strength member that is
used to relieve the tension that is loaded to the optical
fibers of an optical cable when it is installed.
＊2Loose tube optical cable: an optical cable that is made
by twisting optical fibers after installing them in a
thin plastic tube.
Contributors
The lead author is indicated by an asterisk (*).
F. SATO*
• ‌Assistant General Manager, Optical Fiber & Cable
Division
K. OKADA
• ‌Assistant General Manager, Optical Fiber & Cable
Division
T. HIRAMA
• ‌Assistant Manager, Optical Fiber & Cable Division
K. TAKEDA
• ‌Assistant General Manager, Optical Fiber & Cable
Division
R. OKA
• ‌Assistant General Manager, Optical Fiber & Cable
Division
K. TAKAHASHI
References
• ‌Group Manager, Optical Fiber & Cable Division
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(6)
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with Pliable 8-fiber Ribbons for Underground Deployment,” IWCS
(2015), p.659
14 · Ultra-High-Fiber-Count and High-Density Slotted Core Cable with Pliable 12-Fiber Ribbons