Session 2: Fiber Optic Cables Design In this session we will discuss Different types of cables Cable specification Guidelines for fiber optic design and.

Session 2:

Fiber Optic Cables Design

In this session we will discuss • Different types of cables• Cable specification• Guidelines for fiber optic design and

installation• Optical cable pulling

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Fiber Optic Components

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

Main parts of a bare fiber

(Polymer coating

+ Buffer)Kevlar

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Two Buffer Types

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

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

fiber-meter, specifically at fiber counts above 24.

Have high fiber counts. Have better packing density.

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Advantages of Loose-Buffer Cable

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

outside-plant 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 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

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

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

The outer jacket is the remaining critical component of a fiber optic cable.

Based on the environmental protection required for the application. Chemical resistant Temperature requirement: from -60oC to

200oC Fire safety

Meets the requirement of National Electrical Code (NEC) and Underwriters Laboratories (UL)

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Example of jacketing materials

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

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,

non-toxic and halogen-free Installation load – short term, 250 lb Operating load – long term, 10 lb

(simplex)

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Duplex Cables

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

Tight Buffer/Distribution Cables

Small-tight packed Several tight-

buffer fibers under the same jacket Used for short and

dry conduit runs and riser and plenum applications.

Not individually reinforced – with only one Kevlar for all fibers.

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1, 2 to .

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Breakout Cables

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

This cable group includes jellyfree cables, non-armored multi-fiber loose tube cables, glass-armored multi-fiber loose tube cables and steel-armored 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

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

fiber-optic 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

Specifying Fiber Optic Cable

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Specifying the proper cable requires two major considerations:1. How the cable will be installed.2. What environment it will be facing after installation.

Installation Specs

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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 diameterRecommended temperature ranges for

installationRecommended temperature ranges for

storage

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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

Environmental Specifications

Six NEC770 Ratings

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These 6 ratings are:1. OFN optical fiber non-

conductive2. OFC optical fiber conductive3. OFNG or OFCG general purpose4. OFNR or OFCR riser rated cable for

vertical runs5. OFNP or OFCP plenum rated cables for air- handling areas6. OFN-LS low smoke density

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Cable Ratings and Markings

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

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

Four Ways to Future-Proof

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1. Install the best multimode fiber2. Include spare fibers3. Include singlemode fibers in multimode

cable4. Include fibers in copper cables (rare)

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Cable Designs - Indoor

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

Loose tube Water-blocked gel-filled (dry water-blocked cable is now also available) Consider ribbon for high fiber count All dielectricPerformance Specifications

Tensile load when installed: 600 lbs max.

Strength members: fiberglass & Kevlar®

Temperature range -40 to +60 C Rodent resistance: armor or innerduct 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.

Outside Plant Installation

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

Premise Cable Installation

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

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.

For visible light, most transparent materials (e.g. glasses) have:

1 < n (red) < n (yellow) < n (blue)

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Dispersion in Fiber 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

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

• 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 dispersion2. Material dispersion3. Waveguide dispersion4. Polarization mode dispersion

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Dispersion and Chirp

Dispersion produces a frequency chirp in the bit pulse

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Dispersion Compensation

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1. Modal dispersion

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?

input Output ?

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Modal Dispersion

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

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.

n n

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2. Material (chromatic) dispersion

n = c/v, v changes for each wavelength

Different wavelengths (colors) travel at different speeds through even a single mode fiberThe amount of dispersion of a fiber

dependsThe spectrum range of the light injected

The nominal operating wavelength

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Dispersion vs. Wavelength

zero-dispersion wavelength means maximum information-carrying capacity.

zero-dispersion wavelength. For standard single-mode fibers,

this is in the region of 1310 nm.

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Anomalous and normal dispersion

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

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

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.