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.
Fusion Splicing Apparatus
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 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 usednichrome 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 Processing
The fiber optic fusion splicing process is basically the same for all automatic splicing machines.The process of fusion splicing normally 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.
Characteristics of Place of the Splicing Process:
Splicing activity must be done in a very clean place to prevent dust or any contamination that affects the splicing process. The temperature of the place which the splicing process can take place may vary from 15º C to 28º C.
Hint: Although the fusion splicing machine can work at temperature between -10ºC and +5ºC and the closure can be installed at temperature between -1ºC and +45ºC, we still need to ensure that the splicing technician work in the optimum conditions to give the maximum efficiency.
Four Basic Steps to Complete a Proper Fusion Splicing
Step 1. Preparing the Fibers
1. Strip jacket and remove an adequate amount of jacket, usually 2-3 m, for splicing and dressing the buffer tubes and fibers in the splice closure. Leave the proper amount of strength members to attach the cable to the closure. Refer to the splice closure directions for lengths needed. Clean all water-blocking materials using appropriate cleaners.
2. Remove buffer tubes exposing fibers for splicing. Generally, splice closures will require ~1 m buffer tubes inside the closure to and ~ 1 m fiber inside the splice tray. Clean all water-blocking materials.
3. Each fiber must be cleaned thoroughly before stripping for splicing.
4. When ready to splice a fiber, strip off the buffer coating(s) to expose the proper length of bare fiber.
5. Clean the fiber with appropriate wipes.
6. Cleave the fiber with an appropriate fiber cleaver.
7. Place the fiber into the fusion splicing machine and clamp it in place.
Step 2. Running the splicer program
1. Choose the proper program for the fiber being spliced.
2. The splicer will show the fibers being spliced on the video screen.
3. Fiber ends will be inspected for proper cleaves and bad ones like the one on the right above will be rejected.
4. Automated Splicing
5. Fibers will be moved into position.
6. Prefuse cycle will remove any dirt on the fiber ends and preheat the fibers for splicing.
7. The fibers will be aligned using core alignment method for that splicer.
8. The fibers will be fused by an automatic arc cycle that heats them in an electric arc and feeds the fibers together at a controlled rate.
9. When fusion is completed, the splicing machine will inspect the splice and estimate the optical loss of the splice. It will tell the operator if a splice needs to be remade.
10. The operator will remove the fibers from the guides and attach a permanent splice protector by heat-shrinking or clamping clam shell protectors.
Step 3. Evaluating Splices
Good Splices: Visually inspect splice after the program has run, using both X and Y views. Some flaws that do not affect optical transmission are acceptable, as shown. Some fibers (e.g. fluorine-doped or titanium coated) may cause white or black lines in splice region that are not faults.
Bad Splices: Some flaws are unacceptable and require starting the splicing process over. Some, like black spots or lines, can be improved by repeating the ARC step, but never more than twice. For large core offsets, bubbles or bulging splices, always redo.
Step 4. Protecting the fiber
Protecting the fiber from bending and tensile forces will ensure the splice not break during normal handling. A typical fusion splicing has tensile strength between 0.5 and 0.5 pounds, and won't break during normal processing. But it still needs to be protected 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.