FTTH DROP AND INDOOR CABLES - Draka Communications

FTTH DROP AND INDOOR CABLES
Alexander Weiss 1 , Arnie Berkers², Eva Boncidai³, Knud Bundgaard Jen sen 4 ,
Marta Garcia S.Emeterio 5 , Klaus Nothofer 5 , Olivier Tatat 6
Draka Comteq Cable Solutions
1 Moenchengladbach, Germany, ²Delfzijl, The Netherlands, ³Nuremberg, Germany,
Abstract
Since some years FTTH networks are installed in many areas. For
FTTH outdoor installation different cable designs are applied, such
as common outdoor duct or direct buried cables, but also
indoor/outdoor designs with halogenfree flame retardent sheath.
Most of them are too large to fit as small subscriber drop or indoor
FTTH cables. Requirements for small drop cables with HFFR jacket
are seen in the market.
Being aware of challenging requirements on the field of fire
performances of fiber optical cables, the selection of suitable HFFR
materials has been made with special accuracy in order to fulfil
relevant technical regulations.
The cables shall be suitable as drop cables, subscriber cables as well
as for indoor installation and offer high mechanical strength.
Preferably they shall be applicable as FTTH as well as FTTD
cables. The required fiber count is limited; in the first attempt max 4
fibers were requested; except for the riser cable, which has a higher
fiber count. Preferably no or just limited amount of gel shall be used
in the designs.
In this paper we describe different developed new designs. The
results of mechanical, environmental and installation tests are
presented and discussed.
Keywords: FTTH, optical cable, drop cable, subscriber cable,
riser cable, optical fiber, bend optimized fiber, flame retardent, fire
test
1. Introduction
FTTH networks require many different kinds of cables, because
such networks cover indoor and outdoor sections, but also the
transition in between. To fulfil these requirements outdoor, indooroutdoor
as well as indoor cable designs are necessary.
Another fact to be taken into consideration is that a huge variety of
installation methods are in practical use, too. Commonly applied
technologies are (micro-) duct and direct buried installation, aerial
installation, but also on-wall, inside and outside the buildings.
In dependence of the local environment of the network the best
suited installation methods are selected. Regarding this need cable
designs should be suitable for as many as possible installation
technologies.
To address general requirements of fire protection set by law or
customers a HFFR jacket is mandatory. The best suited the HFFR
grade is chosen according to the local requirements and fire test
specifications to ensure the requested fire protection level.
4 Brøndby, Denmark, 5 Santander, Spain, 6 Calais, France
+49-2166-134-1419 · alexander.weiss@draka.com
Out of the large range of different cable designs this paper focuses
on small subscriber drop and indoor cables with high mechanical
strength and outstanding low bending radii. All cable constructions
described have a HFFR sheath. To address requirements for dry
cables a completely dry cable and designs with tight respectively
semi-tight buffer tubes are presented.
To offer the best achievable cable bend performance bend
optimized BendBright XS® fibers were used for some cables, too.
These fibers fulfil both, the ITU-T specifications G.652 class D and
G.657 class A. Their bend performance is even better, it is
according to ITU-T G.657 class B.
They are especially suited for indoor cables, where their capability
to withstand bends with exceptional low radius without increase in
attenuation is highly appreciated and offers superior advantages
compared to standard SM fibers, since installation routes of indoor
cables frequently pass areas where small bends occur, like around
edges and corners. As an additional advantage the possible small
bend radius allows reduced size connection equipment, like quite
small splice closures and termination boxes.
2. Cable Design
For FTTH networks as described above no cable design is dedicated
or preferred, neither for subscriber drop nor for indoor cables.
Different approaches are suitable like central, loose or (semi-) tight
buffer tube constructions. Optional cable elements are tapes or yarns
which may carry waterswellable materials in case a dry design is
desired. Possible other cable elements are strength members or
copper conductors. The design is finally completed with a HFFR
sheath.
Exemplary the following designs are described, a completely dry
central tube drop cable, semi-tight buffered fiber cables, a riser
cable, a zipcord cable and a composite subscriber cable with tight
buffer tubes and copper conductors.
2.1 Central Tube Drop Cable
The presented central tube drop cable consists of a HFFR tube and
sheath. The tube is completely dry, without gels or yarns, just
housing the optical fibers. In the sheath aramid yarns were
embedded as strength elements. It has an outer diameter of 4 mm.
The design fulfills extremely high mechanical requirements
regarding crush and impact properties. Therefore it is perfectly
suited for on-wall installation with staples. In parallel it is absolutely

free of gels. If needed, swellable materials can be added to get a
watertight design.
Both, standard ESMF fibers and bend optimized BendBright XS®
fibers were tested in the design. Main difference between the two
fiber types is, as expected, the behavior in bend test. Bend
optimized fibers allow 10 mm minimum cable bend radius, whereas
standard ESMF fibers allow only minimum 20 mm, which is
approximately twice as low than of bend optimized fibers (figure 2).
The absolute difference looks small, but the gain in practical safety
margin is much bigger, especially since the cables are dedicated to
installation environments, where such small bends frequently occur.
To achieve a high level of flame retardency a highly flame retardent
HFFR grade is necessary. Grades with LOI values up to
approximately 40 are not sufficient to pass severe fire tests, because
the empty inner tube acts like a chimney.
Figure 1. Central Tube Drop Cable
Table 1. Type Test Results
test result
crush test
2000 N, plate-plate,
100 mm, 15 min
impact test
10 Nm, 3 impacts,
r = 300 mm
pass
pass
comment
BBXS ® fibers ESMF fibers
0.04 dB,
no damage
0.00 dB,
no damage
0.02 dB,
no damage
0.00 dB,
no damage
temperature cycle test
-5°C to +70°C pass 0.05 dB/km av 0.08 dB/km av
bend test (RT)
6 turns, 10 cycles pass
Attenuation measured at 1550 nm.
Change in
Attenuation [dB]
1,2
1,0
0,8
0,6
0,4
0,2
0,0
Bend Test Result
r = 10mm
0.09 dB max
r = 20mm
0.08 dB max
5 mm 10 mm 18 mm 20 mm 25 mm
Bend Radius
BBXS ESMF
Attenuation measured at 1550 nm.
Figure 2. Bend Test, ESMF versus BendBright XS® Fibers
2.2 Dry Semi-Tight Design
Dry semi-tight designs with one or two fibers are dedicated to
subscriber indoor branching. Therefore, such cables are mainly
installed on-wall by stapling or gluing.
The single fiber cable is a 2.8 mm diameter construction, the cable
with two fibers a 4.2 mm diameter construction. Both are based on
900 µm semi-tight buffered fibers. In such a design the fiber is
decoupled from the 900 μm buffer tube. This semi-tight
construction guarantees easy end-access of the optical fibers over
one meter in less than a minute.
Both cables were made with bend optimized BendBright XS® fibers.
In both cases a highly flame retardant HFFR was used, allowing to
pass the vertical burner test according to EN50265-1.
Cross sections of the cables and test results are shown below.
Figure 3. Semi-Tight Buffered Designs
Table 2. Type Test Results
test result
crush test
1000 N, plate-plate,
100 mm, 15 min
impact test
(RT and –5°C)
3 Nm, 3 impacts,
r = 300 mm
pass
pass
single fiber
design
0.03 dB,
no damage
< 0.01 dB,
no damage
comment
dual fiber
design
0.00 dB,
no damage
0.03 dB,
no damage
temperature cycle test
-5°C to +60°C pass < 0.01 dB/km < 0.01 dB/km
bend test (RT)
6 turns, 10 cycles pass
Attenuation measured at 1550 nm.
r = 10mm
0.13 dB
r = 10mm
0.04 dB
2.3 Riser Cable
When there is a need to get many fibers to several distribution
points or separate flats in different floors of a building, a riser
design is chosen for the vertical installation. This cable has really
low weight and size, something very important for a riser
application. However, its main advantage in this case is the ability
to segregate one or more bundles of fibers per flat, just by opening
small windows of approximately 5 cm in length in the outer jacket.
This could also allow termination of several fibers in a distribution
box of a floor.
The riser cable carries a maximum of 48 optical fibers in a 8x6
configuration with several small semi-tight buffer tubes made of a
soft material. These modules are loosely placed into the cable
center, surrounded by some aramid yarns as strength elements and a

HFFR flame retardant jacket. The overall outer cable diameter is
approximately 7.6 mm, the weight 50 kg/km.
Figure 4. Riser Cable
The riser cable has been mechanically and thermally tested in two
versions, with standard ESMF fibers and with bend resistant fibers
BendBright XS® . The results of the tests show, as expected, a better
behavior of the bend-optimized fibers, even so both versions passed
the targeted requirements. The most amazing difference has been
found, as always, in the bend test, where the bend optimized fibers
reach max change in attenuation of 0.02 dB for a mandrel of 10 mm
radius. This test has been carried out on each module, since the
complete cable cannot easily be bend in such small radius. The test
is therefore even more severe. Table 3 shows a short summary of
the main results.
Table 3. Type Test Results
test result
crush test
2000 N, plate-plate,
100 mm, 15 min
impact test
5 Nm, 3 impacts,
r = 300 mm
pass
pass
comment
BBXS ® fibers ESMF fibers
0.04 dB
no damage
(reversible)
0.00 dB,
no damage
1.5 dB (*)
no damage
(reversible)
0.01 dB,
no damage
temperature cycle test
-5°C to +60°C pass 0.05 dB/km Δα 0.10 dB/km av
bend test (RT)
6 turns, 10 cycles (on
modules)
pass
r = 10 mm
0.02 dB, max
r = 20 mm
1.0 dB max
Attenuation measured at 1550 nm.
(*) For information purposes only. The specification requested 1400 N
load.
The attenuation increase through processes during cable
manufacturing showed a small difference depending on the fiber
type, since the maximum change in attenuation was 0.01 dB/km (at
both, 1550 nm and 1625 nm), for the BendBright XS® fibers and up
to 0.02 dB/km for the ESMF fibers. This confirms that bendoptimized
fibers can withstand higher stress on fibers during cabling
process than standard ESMF fibers.
2.4 Zipcord Cable
Basically, the zipcord cable consists of 2 patchcords of 2.8mm
outer diameter each. Each one is made of 900µm tight buffered
tube surrounded by aramid yarns and a HFFR jacket. The zipcord
is splittable into the two single fiber patchcords
For a simple demonstration of the behavior of a BendBright XS®
fiber in comparison with a standard ESMF fiber a zipcord cable
having in each branch one fiber of the different fiber types
became bend around a single sharp bend like shown in the picture
below.
Figure 5. Zipcord Cable
Figure 6. Bend Test
The measured loss during this test was 5.45 dB for the ESMF fiber
and only 0.01 dB for the BendBright XS® fiber at 1550 nm.
2.5 Composite Cable
The presented composite cable consists of four transmission
elements, two tight buffered BendBright XS® fibers and two
insulated copper conductors, wrapped with a polyester non-woven
tape, aramid yarns and a HFFR sheath. The cable has an outer
diameter of 5.5 mm.
This cable is designed for indoor use to connect an optical-electrical
converter and supplying that equipment with power using just one
cable.
Figure 7. Composite Cable

Table 4. Type Test Results
test result comment
crush test
3000 N, plate-plate,
100 mm, 5 min
pass
0.00 dB
temperature cycle test
-30°C to +70°C pass 0.00 dB, 1550nm & 1625 nm
bend test (RT)
2 turns, 5 cycles,
r = 10 mm
pass
0.01 dB, max
bend test (RT)
90° turn, r = 5 mm pass 0.01 dB, max
Attenuation measured at 1550 nm, if not stated otherwise.
3. Results of Installation and Fire tests
3.1 Installation Tests
3.1.1 Semi-Tight Design
The dual fiber dry semi-tight subscriber cable was submitted to a
stapling installation tests.
The cable has been stapled against a wall, around a doorframe and
around two support beams above the door as shown on the
following scheme and pictures.
A stapling gun was used, with round shaped staples.
Figure 8. Test Setup with Door and Support Beams
cable
Figure 9. Installation around a Doorframe
cable
Figure 10. Installation around a Corner
The installation path included 15 angles with 90° with relatively
sharp bend radius as shown on the pictures; 89 staples were used.
During the installation the attenuation was measured at 1550 nm.
The attenuation change at the end of the test was 0.05 dB.
Figure 11. Tacker, Staples and Cables
3.1.2 Riser Cable
For vertical installations in buildings the fiber units of the riser cable
will be individually segregated on request to every subscriber. The
use of BendBright XS® fibers allows to pass significantly smaller
bends in the installation route as shown in the following picture.

Figure 12. Installation around a Corner
3.1.3 Composite Cable
The composite cable was installed on skirting passing four 90°
corners using cable clips as shown in the picture. The resulting
attenuation increase was only 0.01 dB at 1550 nm, so within the
measurement accuracy of 0.05 dB.
Figure 13. Installation around Corners
3.2 Fire Tests
Flame test requirement for the semi-tight drop cables described in
section 2.2 was EN 50265-1. It turned out, that a standard HFFR
compound with an LOI in the range of 37 to 40 was not suitable to
always safely pass the test on the small cable designs with outer
diameters below 5 mm.
Usually indoor optical fiber cables with diameter ranging from
8 mm and above only need a standard HFFR compound (LOI of
about 35) for passing a single burner test.
Compared to larger cables the low wall thickness of HFFR is key
for this behavior.
Therefore several HFFR materials were tested for making the one
and two fiber dry semi-tight subscriber cables, having limit oxygen
index (LOI) between 36 to 45.
The target was to consistently pass five times in a row, an
EN 50265-1 burner test both on the non-aged but also on an aged
cable (accelerated aging 7 days 100°C).
For small subscriber optical fiber cable, it appeared from our tests
results that only a highly flame retardant material with a LOI of
about 45 allowed to pass this test, especially for the two fiber cable.
The test was not consistently passed with a material having a LOI of
38. When the burner is stopped after one minute the flame
sometimes continued to very slowly progress along the cable,
reaching the top of the sample after 8 to 10 minutes. The sustained
burning was due to the autocatalytic effect occurring in the flame
retardant material, supported also by the tendency of hot gases to
rise in vertical positioned cable, a chimney effect. As secondary
impact, the structure of material got porous and friable allowing
diffusion of hot vapours from the core through the outer sheath,
maintaining a high temperature in the environment. All these
undesired factors could be solved by using of high performance
flame retardant material.
Figure 14. Sample with Low LOI HFFR Compound
Figure 15. Sample with High Performance HFFR
Compound

4. Conclusions
Different types of FTTH subscriber drop, indoor and riser cables
were successfully developed. They are approved by many
customers for different applications. In parallel to the cables some
customers approved bend optimized fibers to benefit from their
superior low bending radii.
The presented cables are suitable for all applications of FTTH
subscriber drop, indoor and riser cables. The range of designs
includes completely dry cables as well as designs with tight and
semi tight buffer tubes and copper conductors.
Their extended robustness allows on-wall installation with staples
without damage to fibers and cables. The fire retardence behavior is
also quite well, giving the possibility to install cables in fire
restricted areas. However, it must be considered, that for small
cables HFFR compounds with high LOI must be selected to pass
fire tests.
All cables can be equipped with standard ESMF fibers as well as
with bend optimized fibers like BendBright XS® . Bend optimized
fibers offer additional advantages, but no constraints in comparison
with standard ESMF fibers. The presented BendBright XS® fulfil
both, the ITU-T specifications G.652 class D and G.657 class A.
Their bend performance is even better, it is according to ITU-T
G.657 class B. Such bend optimized fibers allow bend radii of about
10 mm for the cables and lead to cables, which are very insensitive
regarding kinking and therefore perfectly suited for indoor
installation where small bends frequently occur.
The presented cables offer a complete range of FTTH cables,
covering subscriber drop cables, indoor, indoor/outdoor applications
as well as riser cables.
5. References
[1] K.Nothofer, “Indoor Cabling with Bend-Optimized Fibers”
Proc. FTTH Council Europe 2007 Conference (2007).
[2] Gerard Kuyt, Piet Matthijsse, Laurent Gasca, Louis-Anne de
Montmorillon, Arnie Berkers, Mijndert Doorn, Klaus
Nothofer, Alexander Weiss, “Bend-insensitive single mode
fibers used in new cable designs ,” OC&I conference (2007).
[3] M.Garcia, C.Cortines, "Easy-to-Split and Bend Resistant Fig-8
Drop Cable for FTTH Applications", Proc 55 th IWCS (2006),
5-10.
6. Biographies
Alexander Weiss obtained his
D.Sc. in chemistry of the
University of Tübingen in 1990.
In the same year he joined AEG
(now Draka Comteq). He held
various management positions in
manufacturing and development
of optical fiber cables and is
currently Manager Materials of
Draka Comteq Cable Solutions
EMEA in Moenchengladbach,
Germany.
E-mail: alexander.weiss@draka.com
Arnie Berkers received his
M.Sc. degree in Electrical
Engineering in 1987. In the
same year he joined Draka
Comteq Telecom, IJzerweg 2,
9936 BM Delfzijl, The
Netherlands. Today he is
responsible for the development
of fiber optic cables.
E-mail: arnie.berkers@draka.com
Eva Boncidai received her Dipl.
Ing. Chem. degree in
Technology of Organic
Chemistry in 1982. Early career
in the pharmaceutical industry,
study of the stereoisomery of
drugs. In 1986 she joined Philips
(PKI), now Draka Comteq Cable
Solutions EMEA, in Nuremberg
Germany. Since then she is
responsible for material
development with focus on fire
performances of materials and
cables.
E-mail: eva.boncidai@draka.com
Knud Bundgaard Jensen
received his M.Sc degree in
Electrical Engineering and
joined NKT in 1968. From 1975
he worked with development of
optical fibers and from 1986
with optical fiber cables. Since
1994 responsible for
development of fiber optic
cables in Draka Comteq
Denmark in Brøndby.
E-mail: knud.bundgaard@draka.com
Marta Garcia S. Emeterio
received her Masters degree in
Physics (with a specialty in
Microelectronics) in 1992, from
the University of Cantabria
(Spain). In 1994, she joined
Alcatel Cable Iberica, now
Draka Comteq, working as a
Product Engineer. During 1997
and 1998 she was as Project
leader for the Design
Technology Group of Alcatel’s
Development Center (OFCCC)in Claremont, NC. Nowadays, she
manages the Development Group of Draka Comteq Iberica, in
Spain.
E-mail: marta.garcia@draka.com

Klaus Nothofer (1956) received
his Dipl.-Ing. degree in
Telecommunications and joined
AEG-Kabel (now Draka
Comteq) in 1981. From 1984 he
held various management
positions in O.F. cable
manufacturing, development,
and marketing in Alcatel Europe.
He is now Manager
Development and Engineering
for Optical Fiber Cables in Draka Comteq Cable Solutions EMEA.
E-mail: klaus.nothofer@draka.com
Olivier Tatat received his
Engineering degree with a
specialty in Materials in 1982.
In 1985, he joined Alcatel
Cable France (now Draka
Comteq). He held several
positions in France, USA and
Germany in Materials and
Optical Fiber Cable
Development. Since 2001, he is
leading the Development and
Engineering Group of Draka Comteq France in Calais.
E-mail: olivier.tatat@draka.com