Figure 6-7. - Spring V-grooved mechanical splice.

uses a third positioning rod instead of a flat spring. The rods are held in place by a heat-shrinkable band or tube.

ROTARY SPLICES

In a rotary splice, the fibers are mounted into a glass ferrule and secured with adhesives. The splice begins as one long, glass ferrule that is broken in half during the assembly process. A fiber is inserted into each half of the tube and epoxied in place, using an ultraviolet cure epoxy. The end face of the tubes is then polished and placed together, using the alignment sleeve. Figure 6-8 is an illustration of a rotary mechanical splice. The fiber ends retain their original orientation and have added mechanical stability since each fiber is mounted into a glass ferrule and alignment sleeve. The rotary splice may use index matching gel within the alignment sleeve to produce low-loss splices.

FUSION SPLICES

The process of fusion splicing 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. Fusion splicing requires that all protective coatings be removed from the ends of each fiber. The fiber is then cleaved, using the score-and-break method. The quality of each fiber end is inspected with a microscope. In fusion splicing,

Figure 6-8. - Rotary mechanical splice.

splice loss is a direct function of the angles and quality of the two fiber end faces.

The basic fusion-splicing apparatus consists of two fixtures on which the fibers are mounted and two electrodes. Figure 6-9 shows a basic fusion-splicing apparatus. An 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.

MULTIFIBER SPLICES

Normally, multifiber splices are only installed on ribbon type of fiber-optic cables. Multifiber splicing techniques can use arc fusion to restore connection, but most splicing techniques use mechanical splicing methods. The most common mechanical splice is the ribbon splice.

A ribbon splice uses an etched silicon chip, or grooved substrate, to splice the multiple fibers within a flat ribbon. The spacing between the etched grooves of the silicon chip is equal to the spacing between the fibers in the flat ribbon. Before you place each ribbon on the etched silicon chip, each fiber within the ribbon cable is cleaved. All of the fibers are placed into the grooves and held in place with a flat cover. Typically, an index matching gel is used to reduce the splice loss. Figure 6-10 shows the placement of the fiber ribbon on the etched silicon chip.

Figure 6-9. - A basic fusion-splicing apparatus.