Fiber Optics Cables

8/3/2019 Fiber Optics Cables

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What is Fiber Optic Cable

Cabling is the process of packaging optical fibers in a cable structure for handling and protection.In some applications bare fibers work just fine, such as fiber optic sensors and laboratory use.

However for most communication applications fibers must be packaged in a cable for practical

use. The major benefits of fiber optic cabling are:

y Easy HandlingSome communication systems require tens or even hundreds of fibers (such as a metro

backbone system). Put fibers in a cable make it very easy to install and maintain.y Protection from damaging forces

Fiber optic cables have to be pulled into place through ducts (outdoor) or conduits(indoor). Pulling eyes are attached to the strength members or cable outer jackets. This is

critical for isolating the fibers from the applied pulling forces. Glass fibers cannot enduremore than 0.1% to 0.2% elongation during installation.

y Protection from harsh environment factorsCable structures protect fibers from moisture (outdoor cables), extreme temperature(aerial cables) and influx of hydrogen into the fiber (which causes light absorption peakat 1380nm which in turn impair fibers transmission properties).

Fiber Optic Cable Based on Fiber Types

Based upon fiber types in a cable, fiber optic cables can be categorized as three types.

Single Mode Fiber Optic CableAll fibers in the cable are single mode fibers.

Multimode Fiber Optic Cable - Multi Mode Fiber Optic CableAll fibers in the cable are multimode cables.

Hybrid/Composite Cable

Both single mode and multimode fibers are packaged in one cable, such as 4 multimode fibersand 4 single mode fibers in a single cable.

Fiber Optic Cable Color

For data center premise cables, the jacket color depends on the fiber type in the cable. For cables

containing single mode fibers, the jacket color is typically yellow, whereas for cables containingmultimode fibers, the jacket color is typically orange. For outside plant cables, the standard

jacket color is typically black.


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Gel CompoundGel compound fills buffer tubes and cable interiors, making the cable impervious to water. It

needs to be completely cleaned off when the cable end is stripped for termination.

Ripcord

Ripcord is a thin but very strong thread embedded just below the cable jacket. Its role is to splitthe cable easily without harming cable interiors.

Two Basic Fiber Structures

Fiber optic cable are available in a wide variety of physical constructions. Fiber cables can be

anything from simple simplex or duplex (zipcord) cables used for jumpers to 144-fiber cable forintercity transmission.

However most of the fibers used in these cables come down to two basic configurations 900umtight buffered fibers or 250um coated fibers (also called bare fibers). Actually tight buffered

fibers cover a coated fiber(the coating is soft plastic) with a thick layer of harder plastic, makingit easier to handle and providing physical protection.

The structure of a 250um coated fiber (bare fiber)

y Core (9um for standard single mode fibers, 50um or 62.5um for multimode fibers)y Cladding (125um)y Coating (soft plastic, 250um is the most popular, sometimes 400um is also used)

The structure of a 900um tight buffered fiber


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y Core (9um for standard single mode fibers, 50um or 62.5um for multimode fibers)y Cladding (125um)y Coating (soft plastic, 250um)y Tight buffer (hard plastic, 900um)

Fiber Optic Cable Construction - Two Basic Types

Based on 900um tight buffered fiber and 250um coated fiber there are two basic types of fiberoptic cable constructions Tight Buffered Cable and Loose Tube Cable.

Tight Buffered Cable

Multiple color coded 900um tight buffered fibers can be packed tightly together in a compact

cable structure, an approach widely used indoors, these cables are called tight buffered cables.Tight buffered cables are used to 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. Tight buffered cables are mostly built for indoor applications, althoughsome tight buffered cables have been built for outdoor applications too.


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Tight Buffered Fiber Optic Cable Sample

Structure of a Tight Buffered Cable

Elements in a tight buffered fiber optic cable

1. Multiple 900um tight buffered fibers (stranded around the central strengthmember)

2. Central strength member (in the center of the cable)3. Aramid Yarn (trade name Kevlar, Kevlar was developed by Dupont) (wrapped

around the fibers, for physical protection and cable pulling)

4. Ripcord (for easy removal of outer jacket)5. Outer jacket (also called sheath, PVC is most common for indoor cables because

of its flexible, fire-retardant and easy extrusion characteristics. )

Cross Section of a Tight Buffered Fiber Optic Cable

Loose Tube Cable

On the other hand multiple (up to 12) 250um coated fibers (bare fibers) can be put inside a colorcoded, flexible plastic tube, which usually is filled with a gel compound that prevents moisture

from seeping through the hollow tube. Buffer tubes are stranded around a dielectric or steelcentral member. Aramid yarn are used as primary strength member. Then an outer polyethylene

jacket is extruded over the core. These cables are called loose tube cables.

Loose tube structure isolates the fibers from the cable structure. This is a big advantage in

handling thermal and other stresses encountered outdoors, which is why most loose tube fiberoptic cables are built for outdoor applications.


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Loose-tube cables typically are used for outside-plant installation in aerial, duct and direct-buriedapplications.

Fiber Optic Loose Tube Cable Samples

Structure of a Loose Tube Cable

Elements in a loose tube fiber optic cable:

1. Multiple 250um coated bare fibers (in loose tube)2. One or more loose tubes holding 250um bare fibers. Loose tubes strand around

the central strength member.3. Moisture blocking gel in each loose tube for water blocking and protection of

250um fibers4. Central strength member (in the center of the cable and is stranded around by

loose tubes)5. Aramid Yarn as strength member6. Ripcord (for easy removal of outer jacket)7. Outer jacket (Polyethylene is most common for outdoor cables because of its

moisture resistant, abrasion resistant and stable over wide temperature rangecharacteristics. )


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Cross Section of a Loose Tube Fiber Optic Cable

Indoor Fiber Optic Cable Fire Rating and U.S. National

Electric Code (NEC code)

Per National Electrical Code (NEC) requirements all indoor fiber optic cables must be markedand installed properly for its intended use. There are three types of indoor spaces identified by

NEC: plenums, risers and general purpose areas.

What is a plenum area and plenum rated fiber optic cable?

Plenum is an air-handling, air flowing and air distribution system space such as that found above

drop ceiling tiles or heating and ventilation ducts. Plenum rated cables must meet UL-910specification and their outer jacket are made of materials that retard the spread of flame, produce

little smoke and protect electronic equipment from damage in fires. Plenum cables can be runthrough plenum spaces without special conduits. Plenum rated cables are more expensive,

because of the jacket material, but the added safety and extra conduit cost savings (if using riserrated cables) pays that back.

What is a riser are and riser rated fiber optic cable?

Riser is a pathway such as floor opening, shaft or duct that runs vertically through floors. Riser

rated cables can be run through building vertical shafts (risers) or from one floor to another floor.Riser rated cables must meet UL-1666 fire-resistance specification and cannot be installed in

plenum area. However plenum rated cables can be used as a substitute for it and installed in riserspaces.


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What is a general purpose area?

Any space on the same floor which is not plenum or rise is identified as general purpose area.

Special note regarding outdoor cables and unmarked cables

Per NEC code outdoor cables and unmarked cables can be installed indoors but they have to be

completely installed in metal conduit or electrical metallic tubing.

Indoor Fiber Optic Cable Categorization

Based on NEC code, indoor fiber optic cables can be categorized as six types. You can see theirdesignation and respective UL test below.

NEC CodeDescription Cable Application UL Test

Possible

Substitute

OFNPOptical Fiber

NonconductivePlenum Cable

Plenum, overhead, fiber

onlyUL - 910

OFCP

Optical Fiber

Conductive PlenumCable

Plenum, overhead, hybrid(fiber/wire)

UL - 910

OFNROptical Fiber

Nonconductive Rise

Cable

Riser, backbone, fiber only UL - 1666 OFNP

OFCROptical Fiber

Conductive Rise CableRiser, backbone, hybrid UL - 1666 OFCP

OFNOptical Fiber

NonconductiveGeneral purpose,

horizontal, fiber onlyUL - 1581 OFNP, OFNR

OFCOptical Fiber

Conductive

General purpose,

horizontal, hybridUL - 1581 OFCP, OFCR

Types of Fiber Optic Cable (Most Popular Fiber Optic

Cable Types)

1. Indoor Cables

Simplex Fiber Cables


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A single cable structure with a single fiber. Simplex cable varieties include 1.6mm & 3mmjacket sizes.

Duplex Fiber Optic Cable

Duplex-zip. This cable contains two optical fibers in a single cable structure. Light is not coupled

between the two fibers; typically one fiber is used to transmit signals in one direction and theother receives.

Distribution Fiber Cables

This compact building cable consists of individual 900m buffered fiber, is smaller in size andcosts less than breakout cable. Connectors may be installed directly on 900m buffered fiber at

breakout box location.


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Breakout Fiber Cables

Breakout cables are also called fanout cables. In tight buffered cables each fiber is only a 900um

tight buffered fiber, but in breakout cables every fiber is a subcable by itself. Each fiber has a2~3mm jacket, then outer jacket covers these subcables, aramid yarn and ripcord inside. This

design allows users to divide the cable to serve users with individual fibers, without the need forpatch panel. Breakout cable enables the quick installation of connectors onto 2+mm robust

jacketed fiber.

Ribbon Fiber Cables

Consists of up to 12 fibers contained side by side within a single jacket. Often used for network

applications and data centers.

LSZH Fiber Cables

Low Smoke Zero Halogen cables are offered as an alternative for halogen-free applications. Lesstoxic and slower to ignite, they are a good choice for many internal installations. They are


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available as simplex, duplex and 1.6mm designs. This cable may be run through risers directly toa convenient network or splicing closet for interconnection.

2. Outdoor Fiber Cable

Indoor/outdoor Tight Buffered Fiber Cables

Indoor/outdoor rated tight buffered cables have riser and plenum rated versions. These cables areflexible, easy to handle and simple to install. Since they do not use gel, the connectors can be

terminated directly onto the 900um fiber without difficult-to-use kits. This provides an easy andoverall less expensive installation.

Outdoor Loose Tube Fiber Optic Cables

Tube encloses multiple coated fibers that are surrounded by a gel compound that protects thecable from moisture in outside environments. Cable is restricted from indoor use, typically

allowing entry not to exceed 50 feet.


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Indoor/Outdoor Dry Loose Tube Fiber Optic Cable

This cable is suitable for both indoor and outdoor applications. One advantage of this cable is

that it eliminates the need for a splice or connector at the point where the cable transitionsbetween an outdoor and indoor environment.

3. Aerial/Self-Supporting

Figure 8 Fiber Optic Cables (Aerial/Self-Supporting Fiber Cables)

Figure 8 (aerial/self-supporting) fiber cables are designed to be strung from poles outdoors andmost can also be installed in underground ducts. They have internal stress members of steel of

steel or aramid yarn that protect fibers from stress.

Aerial cable provides ease of installation and reduces time and cost. Figure 8 cable can easily beseparated between the fiber and the messenger. Temperature range -55 to +85C.

4.Direct-buried


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Armored Fiber Optic Cable

Armored cables are similar to outdoor cables but include an outer armor layer for mechanicalprotection and to prevent damage. They can be installed in ducts or aerially, or directly buried

underground. Armor is surrounded by a polyethylene jacket.

Armored cable can be used for rodent protection in direct burial if required. This cable is non-gelfilled and can also be used in aerial applications. The armor can be removed leaving the inner

cable suitable for any indoor/outdoor use. Temperature rating -40 to +85C.

5. Submarine Fiber Optic Cable(Undersea Fiber Optic Cable)

Submarine cables are used in fresh or salt water. To protect them from damage by fishingtrawlers and boat anchors they have elaborately designed structures and armors. Long distancesubmarine cables are especially complex designed.

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Fiber Optics Cables