Splicing is needed when you need to mix a number of different types of cables (like bringing a 48 fiber cable in and splicing it to six 8 fiber cables). Fusion splicing refers to the process of joining, or splicing, two optical fibers end-to-end. The fibers are heated to the point that the ends soften and pushed together. Optical fiber fusion splices play a crucial role in the optical network.

The goal of fusion splicing 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.

The Process Of Fusion Splicing

Stripping the fiber
Stripping is the act of removing the protective polymer coating around optical fiber in preparation for fusion splicing, 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 stripper.

Cleaning the fiber
The bare fibers are cleaned using alcohol and wipes.

Cleaving the fiber
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 fiber 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.

To avoid damage to the sensitive optical fibers during the fusion splicing process, special tools, heat sources and methods are used in the termination and splicing of optical fibers. The options for the protection of a fusion splice include recoating with a chemical protectant or the use of a fiber optic splice protector. Recoating is accomplished using a resin that is cured by ultraviolet (UV) light, and this is usually the preferred method of protecting fusion splices as it returns the fiber to its pre-spliced condition.

The Advantages of Optical Fiber Fusion Splicing

1. Fusion splicing is very compact
2. Fusion splicing has the lowest insertion loss
3. Fusion splicing has the lowest back reflection (optical return loss ORL)
4. Fusion splicing has the highest mechanical strength
5. Fusion splicing is permanent
6. Fusion splicing can withstand extreme high temperature changes
7. Fusion splicing prevents dust and other contaminants from entering the optical path

Fusion splices give very low back reflections and are preferred for singlemode high speed digital or CATV networks. 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 in the x,y,z plane, then are fused together. Prior to removing the spliced fiber from the fusion splicer, a proof-test preformed to ensure that the splice is strong enough to survive handling, packaging and extended use.