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Fiber Splices

Author: the photonics expert Dr. Rüdiger Paschotta

Fiber splicing means joining two optical fibers such that light guided in one fiber and reaching the joint (splice) can be transferred into the second fiber. More precisely, in the ideal case any light in guided modes of the first fiber will after the splice propagate in guided modes of the second fiber, although not necessarily in the same modes. One generally tries to minimize the insertion loss which can result mainly from light getting into cladding modes of the second fiber or light being reflected at the splice.

There are two primary types of fiber splicing:

• Fusion splicing involves strongly heating the two fiber ends until the material becomes soft and then joining them so that they fuse together. This process results in a permanent splice, often with very low insertion loss.
• Mechanical splicing means firmly holding the accurately aligned fiber ends with suitable consumables, without fusing them. Between the fiber ends, one may apply some index-matching gel or adhesive.

Each method has its own techniques, advantages, and applications:

• Fusion splicing requires expensive equipment, but does not need consumables. It generally reaches lower insertion loss and very high return loss, i.e., the highest quality optical connections.
• Mechanical splicing can be done with comparatively simple equipment (although precision splicers can also be expensive), but one requires some consumables for each splice. The optical connection is tentatively of lower quality, although that depends on the circumstances. Temporary connections can often be made.

Splicing can be performed with both single-mode fibers and multimode fibers, but is tentatively more difficult to obtain with perfect quality in the former case. Splicing is possible for glass fibers but (with adapted processes) also with plastic optical fibers. Special challenges arise for some specialty fibers, including photonic crystal fibers and fibers with non-common cladding diameters or shapes.

Fiber splices can be made only after removing any protective coatings from the fiber ends. Therefore, they are often mechanically more sensitive than the original fibers, and should be properly protected. For example, mechanical splices are often put into splice trays, which do not only protect them against direct touching, but also to some extent against pulling the incoming fibers.

The article on fiber joints gives more details on optical losses and reflections which can occur with splices.

More to Learn

Encyclopedia articles:

• fiber joints
• mechanical fiber splices
• fusion splicing of fibers