Fiber Count Fiber Optic Cables
fiber optic communications systems are expanded to
accommodate rapidly growing communications needs, thre has
been a demand for higher density cables with higher fiber
count. This has led to two new cable designs, microcables
with up to 288 or even 432 fibers and high fiber count
cables. High fiber counts began with loose tube cable at 432
fibers, doubled to 864 fibers. The demand for even higher
fiber counts and higher cable density came from two fronts,
data centers and metro backbones, particular in plans to
support cellular networks, mainly small cells and 5G.
Prysmian cable with 1728 fibers was one of the first high
fiber count cables
first cables introduced were 1728 fibers, then 3456 fibers
and finally 6912 fibers. To make these cables, manufacturers
introduced several innovations in fiber and ribbon
technology. First, to pack such a high density of fibers
required using bend-insensitive
fiber to prevent losses due to stress on the fibers.
Then the buffer coating was reduced from 250 microns to 200
microns or even less. Since ribbons were desirable from the
standpoint of splicing cables with so many fibers, but
normal "hard" ribbons limited the design of cables,
manufacturers went to a ribbon design that was flexible,
allowing ribbons to be rolled up to fit more ribbons into
the cable design. Some use construction similar to loose
tube cables, others use ribbon designs including some
slotted core, and some are new and unique.
OFS Rollable Ribbon
Fiber Count Cables may not be for everyone. Maybe only
for a very few. A single cable that has as many fibers
as 12-144 fiber cables (1728 fibers) in a cable with a
diameter of only twice that of a conventional 144 fiber
cable can present challenges.
of all, the cost - it's high. You do not want to waste
cable at this price. Engineering the cable length
precisely will save lots of money.And it's worse for
higher fiber counts.
making mistakes when preparing the cable for termination
can be expensive.
cable may require special preparation procedures to
separate fibers for termination. Most use new methods of
identifying cables and bundles.
skill, the tech working with high fiber count cables
needs lots of patience.
multiple cables at a joint can get complicated keeping
all fibers straight.
cables will generally use 200 micron buffered fiber and
often a flexible ribbon instead of a typical rigid
ribbon structure to reduce fiber sizes. This may
complicate splicing as the methodology to splice the
flexible fibers and splice 200 micron fibers to regular
250 micron fibers is a work in progress with splicer
200 to 250 micron fibers may be easier with the flexible
ribbon designs which make it easier to spread fibers to
the same spacing.
heard the splicing time for flexible ribbons is about 50-100%
longer than that of conventional rigid ribbons.
So if you use that table below, you may need to increase
your ribbon splicing estimates when working with
We've been looking for directions on how to deal with high
fiber count cables. Several contractors tell us ribbon
splicing is the way to go, and most of these cables now use
a version of the new ribbon types that are flexible.
We've put together the table below from some articles
on splicing ribbons.
Fiber Count Cable Designs
generously sent FOA some samples of 1728 and 3456
"RocketRibbonTM" cable. We took some photos and
must admit that these cables are fascinating updates on the
traditional fiber optic cables.
are Corning RocketRibbon 1728 fiber (bottom) and 3456 fiber
(top) cables. To get an idea of these cables size, look at
this photo of a cross section of the fiber:
3456 fiber cable (R) is 32mm diameter, ~1.3 inches. The 1728
fiber cable (L) is 25mm, ~1 inch diameter.
These are cables made from conventional "hard" ribbons, not
the "flexible" ribbons used on some cable designs. As a
result of using hard ribbons, the fibers are arranged in
regular patterns to get high density.
are the tubes of ribbons from these cables. Each of those
tubes of ribbons has the equivalent of 24 ribbons of 12
fibers each (actually 8 X 12 fibers and 8 by 24 fibers
stacked up) for 288 fibers total. The 1728 fiber cable has 6
tubes and a center foam spacer, with 144 ribbons total. The
3456 fiber version has 12 tubes and no spacers, 288 fiber
What amazes us is the density of fibers.
We calculated the "fiber density" of this 3456 fiber cable
based on 200 micron buffered fibers and determined that 54%
of the cable is fiber. Compare that to a typical 144 fiber
loose tube cable, which is about 14% fiber or a 144 fiber
microcable which is about 36% fiber.
Looking at the end of this cable reminded us of nothing so
much as this PR photo from AT&T from their intro of
fiber in 1976:
Not the fiber, the dense cable of copper pairs!
Of course the cable is much lighter than copper but much
heaver than you are used to with fiber - it weighs 752 kg/km
or about 1/2 pound per foot. And it's stiff. Very stiff. The
minimum bend radius is 15 times the cable diameter or 480mm
(~19 inches), about a meter or yard in diameter.
As we noted in the photo above, Ian Gordon Fudge of FIBERDK
taught some data center techs how to handle a 1728 fiber
Sumitomo cable with a slotted core. Ian sent FOA this photo
to illustrate the number of fibers in the cable he was using
for training. Impressive!
Here is the slotted core that separates the flexible fiber
in the Sumitomo cable:
Ribbon Splicing For High Fiber Count Cables
fiber count cables are all ribbon cables, some with hard
ribbons and some with flexible ribbons, All require ribbon
splicing because of the construction and the time it would
take to terminate them. This is a table of estimated
termination times. Is that realistic? We've heard the
flexible ribbons may take 50-100%
longer than conventional ribbons due to the need to
carefully arrange and handle fibers.
Fiber Count Cables - Installation
our ongoing research on high fiber count cables,FOA was
invited to visit Corning's OSP test and training facility to
experience the processes of installing these cables for
ourselves. We had the opportunity to handle some of these
cables ourselves and see how experienced techs worked with
Once you get a chance to handle this cable and see how big,
stiff and heavy it really is, you understand that it's quite
different from any fiber optic cable you have worked with,
with the possible exception of some hefty 144/288 fiber
loose tube cable that's armored and double jacketed. With a
bend radius of 15X the diameter of the cable, the minimum
bend radius of a 1728 fiber cable is 15" (375mm) and that's
a 30" (750mm - 3/4 of a meter) diameter. Just the reel it's
shipped on is outsized - it should have a ~750mm (30 inch)
core and will be probably ~1.8m (6 feet ) in overall
diameter. 3300 feet (1km) of this cable will weigh 550-750kg
(1200-1700 pounds.) and the reel will weigh another
~300-400kg (700-900 pounds). Will that fit on your loading
dock? Can you handle a ton of cable? (Metric or English)
I tried bending one of the 1728 fiber cables and (with the
manufacturer’s OK) tried to break it. The 1728 fiber cable I
was bending took an enormous amount of muscle to bend, and
when I got down to about an 8 inch radius, it broke, with a
sound like a tree limb of similar diameter cracking. In the
field, that would have been an expensive incident.
The stiffness of these cables affects the choice of other
components and hardware. You will not fit service loops into
a typical handhole, you need a large vault like the one
shown in the photos taken at Corning. You will also need
close to 100 feet (30m) of cable for a service loop. You may
need to figure 8 the cable on an intermediate pull and that
will require lots of space and a crew to lift the cable to
flip it over.
This 1728 fiber cable is stiff, does not easily twist and
only bends in one direction because there are stiff strength
members on opposite sides of the cable. Placing it into a
manhole or vault and fitting service loops into it is not
easy. In this case, it helped to have two people and one was
the trainer. You need to have a "feel" for the cable - how
it bends and twists - to make it fit. The limits of bend
radius, stiffness and unidirectional bending makes it
necessary to work carefully with the cable to fit loops into
the vault. Sometimes it's necessary to pull a loop out and
try in a different way to get it to fit. But it can be done
as you see at the right.
the cable out of conduit in the vault without damaging it
also requires care. You can see in the back the orange
duct coming into this vault. When pulling the cable, it's
important to not kink the cable while pulling it out of a
duct. A length of stiff duct can be attached to the
incoming duct to limit bend radius. Capstans, sheeves and
radius cable sheaves need to be chosen to fit the required
cable bend radius. A a radius cable sheave with small
rollers can damage the cable under tension and are bot a
good choice unless the rollers are used with a piece of
conduit to just set the bend radius.
Corning also showed us a new feature of their RocketRibbon
Cables. A high fiber count cable has a lot of fibers, even
a lot of ribbons, so identifying ribbons can be a problem.
In addition to printing data on each ribbon, Corning now
tints the ribbons with color codes to simplify
identification. Great idea.
Fit: 6912 Fiber Cable Pulled in 1.25 inch Conduit
Electric Co., Ltd. (FEC) conducted an experiment in its Mie,
Japan facility to demonstrate the installation of a
6912-fiber optic cable with an outer diameter of 1.14 inches
(29 mm) in a 696 foot (200m) long conduit with three 90
degree curves and an inner diameter of 32mm. The conduit
used was a standard product installed in conventional data
center campuses. Engineers confirmed a maximum pulling
tension of 84 pounds (372N), well below the maximum pulling
tension of 600 pounds (2700N) specified for the cable.
The cable was installed in a 1.25 inch (32mm) conduit with a
maximum length of 1,411 feet (430m) in a North American data
center campus in 2020 to support live traffic. The high fill
ratio in this application is not typically recommended for
Outside Plant (OSP) cable installation. However, in this
application, the end-user was willing to accept the
installation risk in return for maximum fiber density. The
installation demonstrated that FEC’s 6912 fiber optic cable
can be successfully installed into 1.25 inch (32mm) conduit
using appropriate tools, work procedures, and optimum
“The FEC 6912 fiber optic cable at least doubled the fiber
count possible in a 1.25 inch conduit, compared to competing
available designs,” said Ichiro Kobayashi, General Manager
of optical fiber & cable engineering department, FEC.
PR also on OFS
Website. OFS is a FEC company.
Here's links to some of the information we've been
reading and watching online:
sticks with solid ribbons in high density cables.
ribbon splice closure for 1728 fibers.
Directions from Corning
on ultra high-density cabinets
a high fiber count cable with flexible ribbons - SEI.
(Japan) Highest density Optical Fiber Cable.
Presentation on 200micron buffer, bend insensitive, high
fiber count cables.
250 micron loose tube fibers for splicing, AFL Fujikura.
AFL "SpiderWeb ribbon cable.
250 micron loose tube fibers for splicing, Sumitomo.
for ribbonizing and de-ribbonizing fibers. (Telonix).
things you need to know about splicing 200micron buffered
things you need to know about the new ribbon cables
These current links to news may disappear over time.
fiber count cables allow extremely high fiber counts
in small cable sizes, perfect for dense applications
in data centers and metro areas
so many fibers, ribbon splicing is the only sensible
way to splice them
you splicing machines can handle 200micron buffer
bend radius limits are so high, they require special
consideration for installation and storage - BIG
manholes for example