Optical Splices

In contrast to optical connectors, optical splices are used for fixed (more-or-less permanent) joints.
Generally speaking, splices offer a lower return loss (light reflected back from a connector), lower attenuation (light loss), and greater physical strength than connectors. Also, because only one splice is required where there might be two connectors, splices are usually less expensive and less labor-intensive than connectors. In addition, they offer a better hermetic seal than connectors, constitute a smaller joint for inclusion into splice closures, and allow either individual or mass splicing.
The two basic types of splices are fusion and mechanical.
Fusion splices are made by using an electric are to ionize the space between prepared fibers to eliminate air and to heat the fibers to 2,000º F. The heated fibers take a semi-liquid form and meld together, producing a single fiber (rather than two joined fibers) when done properly. The splice is then covered with a plastic sleeve or other protective device.
The completed splice is placed in an appropriate splicing tray, which is then fit into a splice organizer and, in turn, into a splice closure.
One downside to fusion splicing is that it generally must be performed in a dust- and contaminant-free environment, such as a splicing van or trailer. In addition, fusion splicing is prohibited in manholes because the gases frequently found in such locations could create a deadly explosion when exposed to the electric arc generated during the splicing process.
Mechanical splicing is considered a quick and easy method for repairing joints, though it's also used in new construction, especially on small projects.
In this method, cleaned and prepared fibers are glued, crimped, or faced together. The splice is then covered with some type of index matching gel or liquid and placed in a V-groove or tube-type device to align the fibers. Finally, the groove or tube is either crimped or snapped to hold the fibers in place. As with fusion splicing the completed splice is placed in an appropriate splicing tray, then splice organizer, then splice closure.
Unlike fusion splicing, mechanical splicing does not require a controlled environment other than a reasonable level of dust control. Mechanical splices are not without drawbacks, however. For instance, the index matching gel or liquid is subject to contamination and aging, as is any adhesive glue used.
These factors, along with the following others, usually determine which splicing method to use.

Type of fiber: Most single-mode fiber is fusion-spliced. Multi-mode fiber, with its complicated core structure, does not always fusion-splice easily, so mechanical splices are generally used.

Attenuation, including return loss: New fusion splicers provide incredibly low loss when used properly, while a mechanical splice may allow as much light loss as a properly terminated connector.

Physical durability: The "welding" process used in the fusion splice results in higher strength and greater durability than a mechanical splice. In addition, with fusion splices, the mechanical tensile strength of the fiber remains near that of the original fiber.

Ease of installation: Today's fusion splicers are at least partially automated if not fully automated in a one-button process. Mechanical splicing devices vary, but are usually easier to use than connector kits.

Cost per splice: While mechanical splices typically cost only $7 to $12 a piece, a fusion splicer can run anywhere from $3,000 to $30,000. Once this machine is purchased, however, the per splice cost is negligible.




Source:www.elec-toolbox.com/communications/classifications/fiber/fiber.htm