Knowledge of fiber optic splicingmethods is vital to any company or fiber optic technician involved in Telecommunications or LAN and networking projects.
Splicing is the practice of joining two fibers together without using fiber 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 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.
Many telecom and CATV companies invest in fusion splicing for their long haul singlemode networks, but will still use mechanical splicing for shorter, local cable runs. Since analog video signals require minimal reflection for optimal performance, fusion splicing is more suitable for this application. The LAN industry has the choice of either method, as signal loss and reflection are minor concerns for most LAN applications.
The basic fusion splicing apparatus consists of two fixtures on which the fibers are mounted and two electrodes. Figure 1 shows a basic fusion-splicing apparatus. An fiber 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 in commercial applications.
Figure 1- A basic fusion splicing apparatus
Fusion Splicing Method
As mentioned previously, fusion splicing is a junction of two or more optical fibers that have been permanently affixed by welding them together by an electronic arc.
Four basic steps to completing a proper fusion splice:
Step 1: Preparing the fiber – Remove the protective film, jackets, tubes, strength member, and so on. leaving only the bare fiber showing. The main concern here is cleanliness.
Step 2: Cleave the fiber – Using a good fiber cleaver here is essential to a successful fusion splice. The cleaved end must be mirror-smooth and perpendicular to the fiber axis to obtain a proper splice.
Note: The cleaver does not cut the fiber! It merely nicks the fiber and then pulls or flexes it to cause a clean break. The goal is to produce a cleaved end that is as perfectly perpendicular as possible. That is why a good cleaver for fusion splicing can often cost $1,000 to $3,000. These cleavers can consistently produce a cleave angle of 0.5 degree or less.
Step 3: Fuse the fiber – There are two steps within this step, alignment, and heating. Alignment can be manual or automatic depending on what equipment you have. The higher priced you use, the more accurate the alignment becomes. Once properly aligned fusion splicer unit and then use an electrical arc melting fiber, permanent welding the two fiber ends together.
Step 4: Protect the fiber – Protecting the fiber from bending and tensile forces will ensure the splice not break during normal handling. A typical fusion splicing have tensile strength between 0.5 and 0.5 pounds, and won’t break during normal processing, but it still needs to protect from excessive bending and drag force. Use heat shrinkable tube, silica gel, and/or mechanical crimping protector will remain joint protection from external elements and breakage.
In general, fusion splicing takes a longer time to complete than mechanical splicing. Also, yields are typically lower making the total time per successful splice much longer for fusion splicing. Both the yield and splice time are determined to a large degree by the expertise of the fusion splice operator. Fusion splice operators must be highly trained to consistently make low-loss reliable fusion splices. For these reasons the fusion splice is not recommended for use in Navy shipboard applications.