Fusion splicing: Tools and techniques
Fusion splicers are being used in increasing numbers of applications, indoors and out.
Fusion splicers are being used in increasing numbers of applications, indoors and out.
The fusion splicer is a long-used tool in outside plant (OSP) fiber-optic installation, and in recent years has been more commonly used in indoor environments as well. In addition to being used on pigtails, fusion splicers are now commonly used to join optical fibers to splice-on connectors (SOCs).
Jim Hayes, president of The Fiber Optic Association, observed, “Our experience recently, including teaching a couple of courses, is fusion splicing is getting more economical and easier, and the SOCs are super. You can get a fusion splicer for practically the same price as a top-end prepolished/splice-connector kit, and the connectors are much cheaper. The results of terminations with SOCs are much faster terminations, and much better ones too.”
Another fiber-optic expert, Eric R. Pearson of Pearson Technologies Inc., recently commented about the use of SOCs, including from a dollars-and-cents perspective. “While the price of splicers has dropped considerably in the past 10 years, for many installers, the price is significant,” he pointed out. “Is the use of a fusion splicer and SOCs the best choice [versus other termination methods including field-terminating fiber connectors by hand]?
The TIC of SOCs
“The answer is my favorite: It depends on the total installed cost [TIC],” Pearson continued. “To be a logical business decision, the TIC of using SOCs should be lower than the cost of alternative connector installation methods. If the TIC of the SOCs method is lower than that of alternative methods, the savings pay for the splicer.
“This analysis is more complicated than it may appear, as it requires several steps. The first step is consideration of connector cost, process yield, labor cost, and labor utilization. Labor utilization is the ratio of the time spent in the activity of connector installation to the total time required for the connector installation. If the rate of installation by any method is 15 per man-hour, but the time spent in travel to site, setup and cleanup consumes 25 percent of total time, the actual rate per man-hour is 15x0.75, or 11.25 per man-hour.
“The second step in the decision to use SOCs is the determination of the number of connectors that the installer needs to recover the cost of the splicer. If that number is very high—20,000 connectors—and the installer expects to install 2,000 connectors per year, SOCs may not be the best choice.
“The third step in the decision is determination of how many fusion splicers will the installer need. A single installer requires a splicer. If the completion time for jobs is short, multiple splicers may be required. In such a situation, the total number of connectors that must be installed to recover the cost of multiple fusion splicers increases.
“At this time, there are splicer and SOC combinations that have TICs that are both higher and lower than alternative methods,” Pearson emphasized.
He also noted, “There are situations in which other factors predominate the decision to use SOCs,” and spelled out the following examples.
- The job is to replace connectors in an enclosure that does not have space for splice trays that must be used in pigtail splicing. SOCs are the best choice here.
- An activity requires connector replacement in an enclosure with hundreds of pigtailed connectors. Replacing the pigtails would require removing and replacing old with new. This may take more time than replacing connections with SOCs.
- The installation organization will perform midspan splicing, and therefore will have a splicer. Here, several activities justify purchasing a splicer capable of installing SOCs.
- Low link loss is essential for link operation, such as in data centers where links are established but are not necessarily permanent. Low loss provides maximum flexibility for future rearrangement of links without inducing excessive loss.
Pearson further emphasized that pigtail splicing can be an alternative to SOCs for initial fiber installations. He said cost per termination and yield often favor pigtail splicing over SOCs. “I like SOCs and recommend them to clients in certain situations,” he summed up. “But cost considerations do not always favor their choice.”
These two experts’ respective organizations, The Fiber Optic Association and Pearson Technologies, provide technical training and information about fusion splicing along with many other fiber-optic-related technologies and methods.
In “The FOA Reference Guide to Fiber Optics,” the association explains, “Singlemode fiber requires different connectors and polishing techniques [than multimode] that are best done in a factory environment. Consequently, most singlemode fiber is field-terminated by splicing on a factory-terminated pigtail or using prepolished/splice connectors.
“Prepolished/splice and splice-on connectors eliminate the need for field adhesives and polishing by terminating connectors to a stub fiber in a factory and attaching it to the fiber with a mechanical splice or a fusion splice. Terminating the fiber becomes a splicing process instead of a complicated polishing process. The terminating process involves cleaving the fiber and attaching the connector with a built-in mechanical splice or using a fusion splicing machine.
“Splicing is more common in OSP applications than premises cabling,” the FOA Reference Guide states. “Splicing is needed if the cable runs are too long for one straight pull, or you need to mix a number of different types of cables—like bringing a 48-fiber cable in and splicing it to six, 8-fiber cables. And of course, we often use splices for OSP restoration, after the number-one problem of OSP cables, a dig-up and cut of a buried cable.
“Fusion splices are made by ‘welding’ the two fibers together, usually by an electric arc,” the guide continues. “To be safe, you should not do that in an enclosed space like a manhole or an explosive atmosphere, and the equipment is too bulky for most aerial applications, so fusion splicing is usually done above ground in a truck or trailer for the purpose. Today’s singlemode fusion splicers are automated and you have a hard time making a bad splice, as long as you clean the fiber properly. Fusion splices are so good today that splice points may not be detectable in OTDR [optical time-domain reflectometer] traces. Some splicing machines can do one fiber at a time, but mass fusion splicers can do all 12 fibers in a ribbon at once.”
Later in the guide, the FOA describes some of the processes of using the splicing machine: “First, choose the proper program for the fiber types being spliced. The splicer will show the fibers being spliced on a video screen. Fiber ends will be inspected for proper cleaves, and bad ones will be rejected. That fiber must be cleaved again. The fibers will be moved into position, prefused to remove any dirt on the fiber ends and preheat the fiber for splicing. The fibers will be aligned using the core alignment method used on that splicer. Then 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. 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. The operator removes the fibers from the guides and attaches a permanent splice protector by heat-shrinking or clamping clamshell protectors.
“Ribbon cables are fusion-spliced one ribbon at a time, rather than one fiber at a time. Thus, each ribbon is stripped, cleaved and spliced as a unit. Special tools are needed to strip the fiber ribbon, usually heating it first, then cleave all fibers at once. Many tools place the ribbon in a carrier that supports and aligns it through stripping, cleaving and splicing. Consult both cable and splicer manufacturers to ensure you have the proper directions.”
Eric Pearson also educates on fusion splicing in his textbook “Professional Fiber Optic Installation—The Essentials for Success, Version 10,” which was published in 2017. He states, “the fusion splicer alignment is one of two types—passive alignment, or active alignment. The splicer provides passive alignment through the use of a precision ‘V’ groove. With such a groove, the splicer design operates with two implicit assumptions: 1) fiber diameters, and 2) core-cladding concentricity are precise enough to achieve low power loss. These assumptions are valid for both the fiber made in North America and for much, but not all, of the fiber made overseas.
“Active alignment enables the splice to have the lowest loss, in spite of conditions of imperfect fiber. In other words, active alignment compensates for differences in core diameters, MFDs [mode field diameters], cladding diameters, core offsets, non-circular claddings. The splicing machine provides active alignment with one of two mechanisms: profile alignment, or local injection and detection.”
After using either the profile alignment mechanism or the local injection and detection mechanism, the active alignment splicing machine “creates an RF electrical arc across the fibers,” Pearson explains. “The machine controls the arc current, arc time and overrun. These parameters determine the power loss and strength of the splice. As these parameters are different for different fibers, the installer must set them. This setting is by choosing the type of fiber from a menu; the menu defines these parameters. Current-generation splicing machines include automatic identification of the fiber type and selection of the splicing parameters.”
Advantages and disadvantages
He further says that fusion splicing has four primary advantages over mechanical splicing: 1) low power loss, 2) low to no reflectance, 3) high strength, and 4) low cost. Of the fourth, he details, “The only unique consumable required for fusion splice is the splice cover. Low cost per splice results from the low cost of the splice cover ($0.40 to $1.00).
Fusion splicing has four disadvantages, he notes: 1) high cost of the fusion splicer, 2) potential for disruption of the profile of a multimode fiber, 3) no splicing in a manhole environment [safety risk], 4) potential multimode disadvantage.
So cost is an advantage and a disadvantage. Pearson says, “At the time of this wring , fusion splicer cost ranges from $2,100 to $9,000, with many below $5,000. Ribbon splicers are approximately $19,000. The cost of used fusion splicers can be as low as $2,000. The more expensive the fusion splicer, the faster it operates. In addition, the ribbon fusion splicer has a cost higher than that of a single-fiber splicer. For a small number of splices, purchase of a fusion splicer may be cost-prohibitive.”
Pearson qualifies the potential disadvantages related to multimode, explaining it may affect OM1 or OM2 grade multimode at some distances when midspan splicing is done. “However, testing by fiber manufacturers indicates no significant bandwidth reduction on fusion-spliced, laser-optimized fibers,” he adds. “In addition, there have been no reports of bandwidth reduction due to fusion splicing of multimode fibers. Apparently, such disruption, if present, is insignificant.”
The Fiber Optic Association offers the CFOS/S—Certified Fiber Optic Specialist/Splicing—specialist certification. To be eligible, an individual must already have obtained the FOA’s Certified Fiber Optic Technician (CFOT) certification. The association characterizes the CFOS/S as “a specialist certification covering fiber-optic splicing procedures intended for technicians involved in the installation of OSP fiber networks.” The certification covers fusion and mechanical splicing.
The association explains, “FOA-approved training for CFOS/S certification meets the following requirements: classroom sessions in all types of splicing, including fusion and mechanical splicing; hands-on training in appropriate splicing types including placement of the splice into a splice tray and closure; interpretation of splice loss on OTDR traces; instructor verification of achievement of advanced skills in splicing; course includes approximately 50 percent lab time.”
The FOA also requires field experience. Specifically, a candidate must make a total of at least hundreds of splices, including placement of the splice into a splice tray and closure; experience with both fusion and mechanical splicing, which may include termination of cables using prepolished/spliced connectors; experience with OTDR splice-loss measurements, including bidirectional measurements. Additionally, a manufacturer’s training on splicing will be considered as partial experience to qualify for the certification.
While the fusion splicing of optical fibers is becoming more widespread and being employed in growing numbers of applications, it is not a job for a beginner. Sufficiently preparing fibers for splicing, and properly using the splicing machine are essential for successful results. Splicer manufacturers, educational associations and private training providers are available to impart the necessary skills and knowledge to industry professionals seeking expertise in this area.