Session 2:
Fiber Optic Cables Design
In
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this session we will discuss
Different types of cables
Cable specification
Guidelines for fiber optic design and installation
Optical cable pulling
Fiber Optic Components
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Hardware provides the mounting, protection,
etc. for connectors or splices
Cable protects fibers in the application
environment
Connectors join fibers or connect to active
devices so they can be disconnected for
rerouting, testing, etc.
Splices join two fibers permanently
Test equipment checks performance
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Main parts of a cable
(Polymer
coating
+ Buffer)
Kevlar
Main parts of a bare fiber
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Two Buffer Types
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Loose buffer and tight buffer
 Loose-tube cable, used in the majority of
outside-plant installations in North
America.
 tight-buffered cable, primarily used inside
buildings.
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Tight vs. loose buffer
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Property of loose buffer
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Loose buffered cables are constructed so the
fibers are decoupled from tensile forces that
the cable may experience during installation
and operation. Loose-buffered cables have the
following characteristics:
 More robust than tight buffered cables for
outdoor applications.
 Optimized and proven for long outdoor runs.
 Less expensive than indoor cable per fibermeter, specifically at fiber counts above 24.
 Have high fiber counts.
 Have better packing density.
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Advantages of Loose-Buffer Cable
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A hard color-coded plastic buffer tubes having
an inside diameter several times that of the
fiber.
Excess fiber length (relative to buffer tube
length) insulates fibers from stresses of
installation and environmental loading.
Less temperature sensitive
Loose-tube cables typically are used for outsideplant installation in aerial, duct and direct-buried
applications.
Yarn (Kevlar) strength members keep the tensile
load away from the fiber.
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Tight-Buffered Cable
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The buffer is in direct contact with the fiber.
The tight-buffered design provides a rugged cable
structure to protect individual fibers during
handling, routing and connectorization.
More temperature sensitive
This design is suited for "jumper cables" which
connect outside plant cables to terminal
equipment, and also for linking various devices in
a premises network.
Multi-fiber, tight-buffered cables often are used
for intra-building, risers, general building and
plenum applications.
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Advantage of tight buffer cable
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Tight-buffered fiber generally have a 900 um
plastic coating applied directly to the fiber.
 Increased physical flexibility.
 Smaller bend radius for low fiber-count
cables.
 Easier handling characteristics in low fiber
counts
The two typical constructions of tight-buffered
cables are:
 Distribution design, which has a single jacket
protecting all the tight buffered fibers.
 Breakout design, which has an individual
jacket for each tight-buffered fiber.
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Strength members-Handling the Load
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The strength member bears tensile load,
ensuring that it does not transfer to the fiber.
To be effective, strength members must have
lower net elongation than that of the optical
fibers they protect. For example, glass fibers
usually elongate 0.5 to 1.0% before breaking, so
strength members used for glass fibers must
elongate even less.
Most common materials are Kevlar aramid yarn,
steel and fiber glass epoxy rods. These materials
are distinguished by such unique properties as
wet strength, abrasion resistance and flexibility.
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Selecting the Proper Jacket
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The outer jacket is the remaining critical
component of a fiber optic cable.
Based on the environmental protection required
for the application.
 Chemical resistant
o
 Temperature requirement: from -60 C to
200oC
 Fire safety
Meets the requirement of National Electrical
Code (NEC) and Underwriters Laboratories (UL)
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Example of jacketing materials
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PVC - This family of plastics is commonly used
for jacketing because of its unique
combination of properties,
 low combustibility,
 toughness,
 weatherability, and
 dimensional stability.
It is versatile and can be formulated for
demanding applications.
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Industrial Cable Standards
• 5 cable types have emerged as de facto
standards
• Simplex and Duplex (Zipcord) cable
• Distribution cable
• Breakout cable
• Loose-tube cable
• Hybrid or composite cable
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Simplex Cables
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With an outer diameter of 1.7 mm to 3.0 mm
contain semi-tight tubes in a PVC jacket.
Product properties
 tight bending radius
 rugged design
 assembled with spring-loaded connectors
 buffering material is self-extinguishing, nontoxic and halogen-free
 Installation load – short term, 250 lb
 Operating load – long term, 10 lb (simplex)
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Duplex Cables
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Consist of two single-fiber cables (semi-tight
tube with strain relief and jacket). Duplex
cables are used for indoor applications.
Product properties
 tight bending radius
 rugged design
 can be assembled with spring-loaded
connectors
 Buffering materials are self-extinguishing,
non-toxic and halogen-free
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Fiber Optic Ribbon Cable
Large fiber counts
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Tight Buffer/Distribution Cables
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Small-tight packed
 Several tight-buffer
fibers under the
same jacket
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Not individually
reinforced – with
only one Kevlar for
all fibers.
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Used for short and dry
conduit runs and riser
and plenum
applications.
1, 2 to .
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Breakout Cables
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Consist of 4 to 12 simplex single-fiber cables
around a central strength member and
unified in a single cable by a second outer
jacket.
More expansive
Product properties
 rugged design
 can be assembled with spring-loaded
connectors
 Buffering materials are self-extinguishing,
non-toxic and halogen-free
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Loose-Tube/Outdoor Cables
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This cable group includes jellyfree cables, nonarmored multi-fiber loose tube cables, glassarmored multi-fiber loose tube cables and steelarmored multi-fiber loose tube cables.
Applications
 Overhead – strung from telephone poles
 Direct burial – placed directly in a trench dug in
the ground and covered
 Indirect burial – inside a duct or conduit
 Submarine –underwater
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Composite/Hybrid cables
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integrate fiber optic and energy conductors in
one jacket. The installation of two cables is thus
avoided.
Properties
 Combination of fiber-optic cables with copper
power cables
 jacket material selection same as with fiberoptic cables (e.g. flame-retardant, halogen
free)
Field of application
 as data and power cable for industry, LAN,
video, telephone, customer-specific
applications, etc.
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Review: identify the type
a
b
c
d
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Specifying Fiber Optic Cable
Specifying the proper cable requires two major
considerations:
1. How the cable will be installed.
2. What environment it will be facing after
installation.
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Installation Specs
Max recommended installation load:
• 1 fiber: 67-125 lbs
• Multifiber (6-12) cables: 250-500 lbs
• Direct buried: 600 lbs
Min recommended installation bending radius:
• >20x the cable diameter
Cable diameter
Recommended temperature ranges for installation
Recommended temperature ranges for storage
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Environmental Specifications
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Temperature
 Long term bend radius (10x the cable dia.)
 Electrical codes (NEC)
 Long term tensile load
 Flame resistance
Rodent penetration (armored)
 Water resistance (filled and blocked)
 Crush loads
 Abrasion resistance
 Resistance to chemicals
 Impact resistance
 Vibration
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Six NEC770 Ratings
These 6 ratings are:
1. OFN
2. OFC
3. OFNG or OFCG
4. OFNR or OFCR
5. OFNP or OFCP
6. OFN-LS
optical fiber non-conductive
optical fiber conductive
general purpose
riser rated cable for vertical
runs
plenum rated cables for airhandling areas
low smoke density
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Cable Ratings and Markings
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All premises cables must carry identification
and ratings per the NEC (National Electrical
Code) paragraph 770.
Cables without markings should never be
installed indoors as they will not pass
inspections!
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Fiber Optic Cable Selection Criteria
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Cost
Proper for the application (building, riser,
plenum, aerial, direct burial, submarine, etc.)
Enough fiber for redundancy, upgrades
Meets environmental requirements
Choose hardware to fit cable needs
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Four Ways to Future-Proof
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Install the best multimode fiber
Include spare fibers
Include singlemode fibers in multimode cable
Include fibers in copper cables (rare)
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Cable Designs - Indoor
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Short distances - breakout cable
Longer lengths -distribution cable
All dielectric
Plenum PVC if available
Performance Specifications
 Tensile load: 200-500 lbs max.
 Temperature range: -10 to +60 C
 Strength members: Kevlar®
 Jacket: UL Rated
Do not install cable indoors without UL Fire Rating!
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Cable Designs - Outdoor
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Loose tube
Water-blocked gel-filled (dry water-blocked
cable is now also available)
Consider ribbon for high fiber count
All dielectric
Performance Specifications
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Tensile load when installed: 600 lbs max.
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Strength members: fiberglass & Kevlar®
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Temperature range -40 to +60 C
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Rodent resistance: armor or innerduct
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Jacket: black polyethylene (UV stability)
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Outside Plant Installation
Outside plant installations require more tools and test
equipment, such as pullers, splicers, OTDRs, etc.
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Outside Plant Installation
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all singlemode fiber with high fiber counts.
optimized for resisting moisture and rodent
damage.
Long distances mean cables are fusion spliced
together, since cables are not made longer
than about 4 km (2.5 miles)
Connectors (SC, ST or FC styles) on factory
made pigtails are spliced onto the end of the
cable.
After installation, every fiber and every splice
is tested with an OTDR.
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Fiber Optic Installations - Premises
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Premise Cable Installation
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multimode in short lengths (a few hundred feet),
with 2 to 48 fibers per cable typically.
Some users install hybrid cable with both
multimode and singlemode fibers.
Splicing is not needed.
Most connectors are SC or ST style. Termination
is by installing connectors directly on the ends of
the fibers, primarily using adhesive technology.
Testing is done my a source and meter, but
every installer has a flashlight type tracer to
check fiber continuity and connection.
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Prism Dispersion
For visible light, most
transparent materials (e.g.
glasses) have:
1 < n (red) < n (yellow) < n
(blue)
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that is, refractive index n decreases with increasing
wavelength λ.
At the interface of such a material with air,
predicted by Snell's law, the blue light, with a
higher refractive index, will be bent more strongly
than red light, resulting in the well-known rainbow
pattern.
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Dispersion in Fiber
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No power is lost due to dispersion, but the peak
power has been reduced.
Dispersion distorts both analog and digital signals.
Dispersion is normally specified in nanoseconds
per kilometer.
input
output
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Pulse spreading
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The data which is carried in an optical fibre
consists of pulses of light energy following
each other rapidly.
There is a limit to the highest frequency, i.e.
how many pulses per second which can be
sent into a fibre and be expected to emerge
intact at the other end. This is because of a
phenomenon known as pulse spreading which
limits the "Bandwidth" of the fibre.
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Different Types of Dispersion
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Dispersion is the spreading of a light pulse as
it travels down the length of an optical fiber.
Dispersion limits the bandwidth or information
carrying capacity.
There are 4 main types of dispersion:
1. Modal dispersion
2. Material dispersion
3. Waveguide dispersion
4. Polarization mode dispersion
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Dispersion and Chirp
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Dispersion produces a frequency chirp
in the bit pulse
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Dispersion Compensation
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1. Modal dispersion
input
Output ?
A well defined pulse of single wavelength is
coupled into a multimode step-index fiber.
Compare two modes in travel time –
 One along optical axis
 One close to the critical angle
 Which one moving faster?
 What will happen to the pulse shape?
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Modal Dispersion
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Occurs only in multimode fibers
Due to the different path for each mode in a fiber
and consequently each mode arrives at the other
end of the fiber at different time
Typical modal dispersion is about 15-20
nanoseconds/km
Modal dispersion can be reduced by using
 a single mode fiber – a single path
 a smaller core diameter – less modes
 a graded-index fiber - ?
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Graded-index vs. step-index fiber
n
n
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In a graded-index fiber, the light rays that
follow longer paths travel at a faster speed
and arrive at the other end of the fiber at
nearly the same time as the rays follow shorter
paths.
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2. Material (chromatic) dispersion
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n = c/v, v changes for
each wavelength
Different wavelengths
(colors) travel at different
speeds through even a
single mode fiber
The amount of dispersion of a fiber depends
The spectrum range of the light injected
The nominal operating wavelength
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Dispersion vs. Wavelength
zero-dispersion wavelength. For
standard single-mode fibers, this is
in the region of 1310 nm.
zero-dispersion wavelength means maximum
information-carrying capacity.
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Anomalous and normal dispersion
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In a standard SMF:
the dispersion D > 0 for l >1.31 mm
 this is called anomalous dispersion
 Shorter l components travel faster than for
longer l components
the dispersion D < 0 for l <1.31 mm
 this is called normal dispersion
 Longer l components travel faster than for
shorter l components
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Consequences of pulse spreading
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The Bandwidth is the highest number of pulses
per second, that can be carried by the fiber
without loss of information due to pulse
spreading.
Frequency Limit (Bandwidth)
 If signal pulses follow each other too fast (max
frequency), then by the time they reach the end
fibre they will have merged together and
become indistinguishable. This is unacceptable
for digital systems which depend on the precise
sequence of pulses as a code for information.
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Consequences of pulse spreading
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Distance Limit
A given length of fibre, as explained above,
has a maximum frequency (bandwidth) which
can be sent along it.
If we want to increase the bandwidth for the
same type of fibre we can achieve this by
decreasing the length of the fibre.
Another way of saying this is that for a given
data rate there is a maximum distance which
the data can be sent.
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