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Fiber Optics

FUSION SPLICING

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Fiber Optics

Fusion splicing is the process of fusing or welding two fibers together usually by an electric arc.

Fusion splicing is the most widely used form of splicing since it provides for the lowest loss and least reflectance, as well as providing the strongest and most reliable joint.

Virtually all singlemode splices are fusion.

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Fiber Optics

Single mode fiber is good up to 15 miles so at some point it will need to be spliced.

This means working out of a manhole, because fusion splices are made by an electric arc it isn’t safe to splice directly in the manhole.

Manholes are known to have flammable gases like methane and the gas would ignite during the arcing procedure.

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Fiber Optics

Fusion splicing is usually done above ground in a truck or trailer set up for the purpose.

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Fiber Optics

In some cases a fiber optic cable entering a building from outside will also need to spliced and networked onto the existing fiber cable plant.

This done using pre-terminated factory pigtails that are spliced onto the cable.

Pigtails come in any connector array needed; SC, ST, LC in MM or SM.

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Fiber Optics

In the past pigtails were used in preference to field terminations because of the complexities at the time of manually terminating optical fibers.

These days pigtails are mainly used where the environment isn't suitable for manual terminations or where speed is a factor.

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Fiber Optics

Fiber patch panels are always placed at the top of the relay rack in a telecom room to prevent people from inadvertently looking into live fiber ports.

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Fiber Optics

Indoor fusion splices are normally done on large count (144 strands) loose tube OSP fiber.

There is a great deal of upfront prep time to dress the fiber into the relay racks and set up for the fusion splice.

The fibers to spliced will come into the rack from the left and right side of the rack, after the splice it will be looped and placed in a tray.

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Fiber Optics

The tray will then slide back into the LIU (light integration unit).

The splice tray is normally below the fiber patch panel it serves.

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Fiber Optics

Fusion splicing machines are mostly automated tools that require you to use preset splicing parameters or choose factory recommended settings that will control the splicing process itself.

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Fiber Optics

Fusion splicing may be done one fiber at a time or a complete fiber ribbon from ribbon cable at one time.

A splicing machine is used because an extremely high degree of accuracy is needed, the machine first has to align the cores and then apply the exact amount of heat to melt the ends before pressing them together.

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Fiber Optics

Automatic fiber alignment of the fibers are on moveable stages which are used to align the fibers and set the end gap automatically. During the automated process, the splicer will align the fibers using one of two methods:

Optical Core or Profile Alignment Systems (PAS)

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Fiber Optics

The two fibers are illuminated from two directions, 90 degrees apart. From the images in a video camera, software recognizes the core of the fibers and aligns them automatically using movable stages.

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Local Injection and Detection (LID System)

Light is coupled into the fiber by bending the fiber and shining a light source (LED or laser) on the outside of one fiber, so some light is coupled into the core.

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Fiber Optics

An LCD screen provides a visual of the alignment process and will provide a notification when the fibers are properly aligned.

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Fiber Optics

The fusion splicers will then initiate a pre-arc which is designed to ionize and clean any residue on the cleaved fiber before actually fusing them together.

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Fiber Optics

Once the fusion is complete the machine will test the splice for loss, if it is a successful splice you can expect to see a dBm loss of about 0.05 down to 0.01dBm.

Compare that loss to a hand terminated connector that is 2dBm or less.

The loss test is strictly for the splice and not the whole fiber link, that would require a separate test.

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Fiber Optics

All fusion splices require the use of a precision fiber cleaver that scribes and breaks (cleaves) the fibers to be spliced precisely, as the quality of the splice will depend on the quality of the cleave.

HIGH END CLEAVE TOOL USED FOR FUSION SPLICING.

THESE CAN COST ANYWHERE FORM $1500 TO $3500.

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Fiber Optics

Using a fusion splicer is all about following the menu navigation on the LCD screen which will prompt you to choose the fiber type and manufacture.

The actual process of splicing two fibers together is fairly simple there are only four steps;

1. Strip back all coatings down to the bare fibers and clean them using isopropyl alcohol.

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Fiber Optics

2. Cleave the fibers using a precision cleaving tool and put the heat shrink tube on to one of the ends.

The cleaver first scores the fiber and then pulls the fiber apart to make a clean break. It is important that the ends are smooth and perpendicular to get a good joint, this is why a hand held cleaver will not do.

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Fiber Optics

3. Place the fiber ends into the splicer from both directions and fuse the fibers together in the fusion splicer.

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HINGED FIBER HOLDERS

FIBER STRANDS TO BE FUSED

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Fiber Optics

4. Put the heat shrink protector on the fiber joint.

Splicing machines also generally have a heating device for heat shrinking a protective sleeve over the finished splice to protect it from moisture or other environmental hazards.

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Fiber Optics

Protective sleeves used for splicing also have a small metal rod to further protect the splice from breaking.

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Fiber Optics

Good Splices;

Visually inspect splice after the program has run, using both X and Y views.

Some flaws that do not affect optical transmission are acceptable, as shown. Some fibers (e.g. fluorine-doped or titanium coated) may cause white or black lines in splice region that are not faults. (Graphic from Sumitomo manual)

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Fiber Optics

These are acceptable. Not acceptable