Lights travel in optical fibers need a continuous, non-disruptive path in order to travel a long distance without too big signal loss. But in a hundreds of kilometers fiber link, the light signals need to be amplified, cross-connected, added or dropped and many other processing. In these connections, two fibers are connected together as a standard practice. This connection can be done with connectors and splicing.

Splicing is the practice of joining two fibers together without using connectors. Two types of fiber splices exist: fusion splicing and mechanical splicing. Splicing may be made during installation or repair.

Splices generally have lower loss and better mechanical integrity than connectors, while connectors make system configuration much more flexible. So typically, splices are used to connect fiber cables in outdoor applications and connectors terminate fiber cables inside buildings.

:: Fusion Splicing

Fusion splicing is to use high temperature heat generated by electric arc and fuse two glass fibers together (end to end with fiber core aligned precisely). The tips of two fibers are butted together and heated so they melt together. This is normally done with a fusion splicer, which mechanically aligns the two fiber ends, then applies a spark across the fiber tips to fuse them together.

:: Mechanical Splicing

Mechanical splicing uses mechanical fixtures to join two fibers together end to end(again, fiber cores are aligned precisely). Mechanical splicing join two fiber ends either by clamping them within a structure or by gluing them together.

Single mode fiber requires much tighter tolerances than multimode fibers for splicing. So special equipment are often required for single mode mechanical splices. This makes single mode fiber mechanical splicing much more expensive than multimode fiber mechanical splicing.

:: The advantages of mechanical splicing

Mechanical splicing doesn't need costly capital equipment to work, but it does require higher consumable costs. So for organizations that don't make a lot of splicing, mechanical splicing is the best choice. It is also best suited for emergency repairs.

:: Types of mechanical splicing

1. Capillary type

In capillary type mechanical splicing, two fibers are inserted into a thin capillary tube. The tube has a inner diameter that matches the fiber's cladding diameter. (The fibers must first have coatings removed and cladding exposed and cleaned). These two fiber ends are pushed inwards until they meet. Index matching gels are often inserted in the center to reduce back reflections. The fibers are then held in place with compression or friction.

2. Ribbon V-Groove type

For multiple fiber cables such as ribbon fibers, capillary type doesn't work anymore. Instead, fiber ribbon is put in a V-shaped groove array, with each fiber place in its own v-groove. Two ribbon fibers are butted together in this V-groove array and then a cover plate is applied on top. This V-groove splice is extremely useful in multifiber splicing.

3. Elastomeric type

Elastomeric splice is for lab testing or emergency fiber repairs. Very like aforementioned V-groove type, it has a single fiber v-groove but the v-groove is made of flexible plastic. First an index matching gel is injected into the hole, then one fiber is inserted until it reaches about halfway. The other fiber is then inserted from the other end until it meet the first one.