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Fibre Optic Guide - Fusion Splicing

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See Fusion Splicing

Fusion splicing is the act of joining two optical fibres end-to-end using heat. The goal is to fuse the two fibres together in such a way that light passing through the fibre is not scattered or reflected back by the splice and so that the splice and the region surrounding it are almost as strong as the fibre itself.

Process

The process of fusion splicing normally involves using localized heat to melt or fuse the ends of two optical fibres together. The source of heat is usually an electric arc, but can also be a laser, or a gas flame, or a tungsten filament through which current is passed. The splicing process begins by preparing each fibre end for fusion.

Stripping the fibre

Stripping is the act of removing the protective polymer coating around optical fibre in preparation for fusion splicing. The splicing process begins by preparing both fibre ends for fusion, which requires that all protective coating is removed or stripped from the ends of each fibre. Fibre optical stripping is usually carried out by a special stripping and preparation unit that uses hot sulphuric acid or a controlled flow of hot air to remove the coating. There are also mechanical tools used for stripping fibre which are similar to copper wire strippers.


Cleaning the fibre

The bare fibres are cleaned using alcohol and wipes.

Cleaving the fibre

The fibre is then cleaved using the score-and-break method so that its end face is perfectly flat and perpendicular to the axis of the fibre. The quality of each fibre end is inspected using a microscope. In fusion splicing, splice loss is a direct function of the angles and quality of the two fibre-end faces. The closer to 90 degrees the cleave angle is the lower optical loss the splice will yield.

Splicing the fibres

Current fusion splicers are either core or cladding alignment. Using one of these methods the two cleaved fibres are automatically aligned by the fusion splicer before being fused together. Prior to removing the spliced fibre from the fusion splicer, a proof-test preformed to ensure that the splice is strong enough to survive handling, packaging and extended use. The bare fibre area is protected either by recoating or with a splice protector. A splice protector is a heat shrinkable tube with a strength membrane.

Optical splicing procedure:

  1. Checking fibre optic splice closure content and supplementary kits.
  2. Cable installation in oval outlet.
  3. Cable preparation.
  4. Organization of the fibres inside the tray.
  5. Installing the heat shrinkable sleeve and testing it. 

Hardware

The basic fusion splicing apparatus consists of two fixtures on which the fibres are mounted and two electrodes. These fixtures are often called sheath clamps. Inspection microscope assists in the placement of the prepared fibre ends into a fusion-splicing apparatus. The fibres are placed into the apparatus, aligned, and then fused together. New fusion-splicing techniques have replaced a nichrome wire with carbon dioxide (CO2) lasers, electric arcs, or gas flames to heat the fibre ends, causing them to fuse together. The small size of the fusion splice and the development of automated fusion-splicing machines have made electric arc fusion (arc fusion) one of the most popular splicing techniques in commercial applications.

Alternatives to fusion splicing include using optical fibre connectors or mechanical splices both of which have higher insertion losses, lower reliability and higher return losses than fusion splicing.