Fusion splicing

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Fusion splicing is the act of joining two optical fibers end-to-end using heat. The goal is to fuse the two fibers together in such a way that light passing through the fibers 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 virgin fiber itself. 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.

Process[edit]

The process of fusion splicing normally involves using localized heat to melt or fuse the ends of two optical fibers together. The splicing process begins by preparing each fiber end for fusion.

Stripping the fiber[edit]

Stripping is the act of removing the protective polymer coating around optical fiber in preparation for fusion splicing. The splicing process begins by preparing both fiber ends for fusion, which requires that all protective coating is removed or stripped from the ends of each fiber. Fiber 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 fiber which are similar to copper wire strippers. Fiber optical stripping and preparation equipment used in fusion splicing is commercially available through a small number of specialized companies, which usually also designs machines used for fiber optical recoating.

Cleaning the fiber[edit]

The bare fibers are cleaned using alcohol and wipes.

Cleaving the fiber[edit]

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

Splicing the fibers[edit]

Fiber spliced, still unprotected

Current fusion splicers are either core or cladding alignment. Using one of these methods the two cleaved fibers are automatically aligned by the fusion splicer[1] in the x,y,z plane, then are fused together. Prior to removing the spliced fiber from the fusion splicer, a proof-test performed to ensure that the splice is strong enough to survive handling, packaging and extended use. The bare fiber area is protected either by recoating or with a splice protector. A splice protector is a heat shrinkable tube with a strength membrane.

A simplified optical splicing procedure includes:

  1. Characteristics of placement of the splicing process.
  2. Checking fiber optic splice closure content and supplementary kits.
  3. Cable installation in oval outlet.
  4. Cable preparation.
  5. Organization of the fibers inside the tray.
  6. Installing the heat shrinkable sleeve and testing it.[2]

Hardware[edit]

The basic fusion splicing apparatus consists of two fixtures on which the fibers are mounted and two electrodes. These fixtures are often called sheath clamps. Inspection microscope assists in the placement of the prepared fiber ends into a fusion-splicing apparatus. The fibers are placed into the apparatus, aligned, and then fused together. Initially, fusion splicing used nichrome wire as the heating element to melt or fuse fibers together. New fusion-splicing techniques have replaced the nichrome wire with carbon dioxide (CO2) lasers, electric arcs, or gas flames to heat the fiber 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 fiber connectors or mechanical splices both of which have higher insertion losses, lower reliability and higher return losses than fusion splicing.

Governing standards[edit]

ANSI/EIA/TIA-455

See also[edit]

References[edit]

Further reading[edit]