Fusion-splicing technology sparks automatic operation at low cost
Fusion splicers come with a variety of features at equally varying costs. Choosing the right one depends on your application
dean cline, marty anderson
siecor Corp.
Fusion splicing has become the method of choice for permanently joining singlemode optical fibers. As fusion-splicing machines have developed, the splicing task has progressed from one of inconsistency to one that consistently yields low losses. Moreover, fusion-splicing machines are continually being improved to achieve easier and more cost-effective fiber coupling.
What is the status of fusion-splicing technology? To answer this question, we`ll address today`s fusion splicers, including features and price. We`ll discuss who uses fusion splicers, as well as applications and product requirements. In addition, we`ll consider how future applications and network designs will lead to new requirements for fusion splicers in the next decade.
Current fusion machines feature one-button, automatic splicing. For example, automatic-operating splicing machines position the fibers; check for cleave quality, dirt, or debris, and offset alignment; and then fuse the fibers, without interruption. Most automatic-operating machines can even estimate the splice loss.
All of these operational steps can be observed on a liquid crystal display screen, which is mounted on the splicing machine, within a 45-second cycle. The newer microsplicers are typically no bigger than a shoe box and weigh just a few pounds.
The task of automatically aligning the cores of two fibers is not simple, because a singlemode fiber core is typically 9 microns in diameter--or about 1/2500th of an inch. High-precision splicing machines provide alignment of the cores by analyzing a light signal injected into the fibers by the splicer or by performing a detailed image analysis to locate the cores. Micropositioners then move the fibers until the coupled light signals or images are optimally aligned.
Two methods of core alignment--local injection and detection, and profile alignment--dominate the fusion-splicer marketplace. In addition to these core alignment methods, cladding alignment of the fiber via fixed V-grooves or video imaging has also become popular as fiber geometry has improved to allow the fiber cores to be consistently located at the center of the cladding.
The splice-loss estimation feature is a common attribute of present fusion-splicing machines and has evolved to become one of the top features that customers request. It provides the technician with immediate feedback regarding the optical loss induced by the splice point. This loss measurement is particularly important when the technician does not have access to test equipment at the time the splice is completed. As with splice-loss performance, accuracy of splice-loss estimation is dependent on the capabilities of the fusion-splicing machine.
Some high-end fusion-splicing machines can take a power-through measurement before and after the splice is made to calculate the optical loss. Although not a replacement for a bidirectional optical time-domain reflectometer (otdr) or for insertion-loss testing, this method is sufficient to estimate splice loss. Low-end fusion splicers typically measure the alignment of the cladding of the two fibers being spliced before and after the splice to determine the estimated loss value.
Price range
The prices of fusion splicers can vary, depending on their features. A manual, fixed V-groove machine sells for about $8000, while a fully automatic splicer can cost $25,000. Specialized splicers can approach $50,000.
Fusion splicers priced from $8000 to $25,000 offer a mix of automatic-operating features and straightforward alignment methods. In order for technicians to determine the proper fusion splicer, they must clearly define the primary applications for which the machine will be used. They must also determine the splice-loss requirement for the application as well as the requirement for splice-loss estimation accuracy (see table). For technicians planning to use the fusion splicer in work environments where otdr testing is not available, the accuracy of the splice-loss estimator becomes critical.
Without exception, the price of the fusion splicer directly correlates to the quality of the splice loss and the accuracy of the splice-loss estimator. Currently, the accepted splice loss depends on the application.
The use of fiber-optic ribbon cables has increased, which prompts the need for so-called ribbon- or mass-fusion splicers. Ribbon fusion lets technicians apply single-fiber splicing skills and increase productivity. The newer fusion machines provide technicians with the capability to splice individual fibers and ribbon fiber counts from 2 to 12. High-fiber-count cables can also be "ribbonized" and spliced with available mass-fusion splicing machines with good results. The trends expected for ribbon fusion splicers in the next few years include increased miniaturization and portability (see photo).
Smaller splicers needed
As fiber-optic cables are pushed deeper into the network, small-count splice points are projected to become the norm. Therefore, smaller splicers will be needed to allow quick setup and completion of the splice point. Furthermore, the punchdown blocks or Scotch locks used in traditional copper systems for rework or crossconnects will be replaced with fusion splices in future optical networks.
The requirement for low optical loss is not expected to be necessary in fiber-in-the-loop applications due to short span lengths. Whether the network provider concentrates on telecommunications, cable-TV, or competitive access services, residential area requirements should not need the use of high-end core aligning machines.
Aerial splicing, which is gaining popularity as fiber-optic cables move deeper into the residential network, is driven mainly by the need to remove excess fiber caused by slack loops. These loops have traditionally been used to lower fiber closures to a repair truck or van. However, these aerial splice points create a new set of splicing requirements. For example, the fusion splicer must be small and rugged enough to be used by technicians working outside "in the bucket" of a large truck crane, which doesn`t provide the same space as the splice-van setup for using cleavers and other accessories.
Thus, the technician must deal with cramped spaces and endure the weather, but still accomplish good splice results. Some aerial splices require a taut sheath splice, in which fewer than 20 inches of fiber are specified to minimize any extra use of fiber for accessibility. With a constraint of just 20 inches of slack, the fusion splicer must perform effectively the first time in a difficult environment.
Preterminated cable assemblies--consisting of a feeder cable and multiple drop cables--are manufactured in a shop environment using a no-slack closure that contains the fusion splice. As electronics manufacturers increase the production of amplifiers, couplers, and sensors, splicing fibers to active devices and splicing different fiber types will become common. These applications indicate that future fusion splicers will be smaller, but will accommodate various fiber types as networks employ multiple vendors and fiber grades.
Design trends
As their splicing needs increase, users are expected to demand less expensive fusion-splicing machines. However, machine manufacturers are not expected to incorporate high-end features, such as a precision, core aligning unit, into low-cost splicers. They have sacrificed some performance capabilities, as demonstrated by the V-groove alignment feature on inexpensive machines.
Fortunately, fiber geometry continues to improve. Consequently, the performance of a fixed V-groove machine will be appropriate for most future applications. In fact, the marketplace has accepted both single- and mass-fusion splicing machines that incorporate fixed V-groove alignment.
Newer machines are expected to evolve along the lines of PCs; that is, the structural appearance and performance of fusion-splicing machines, including software, display, and ergonomics, will be sleeker and more appealing. Software features will also include diagnostics checks to verify the unit is operating correctly in its mechanical, electronics, arc generating, and imaging systems.
Fusion splicing has been performed in the field since 1978. Many skills established then are still important today. The difference in the fusion splicers of the 1990s, however, is that the choices in products are numerous and sometimes confusing. Machine buyers must pay close attention to the level of performance required. Is a 0.20-dB splice good enough, or does it have to be 0.05 dB every time? Can the splice-loss estimator be a go/no-go gauge or one that provides results similar to those of an otdr? By specifying the necessary machine requirements, the most cost-effective and efficient fusion-splice machine can be chosen.
As we approach the year 2000, fusion splicers will offer some significant advantages over the machines of today. Tomorrow`s applications may require a smaller machine or one that prepares fibers and splices without human intervention. u
Dean Cline is product line manager and Marty Anderson is product specialist, both at Siecor Corp., Hickory, NC.
Major Subsections of a Modern Fusion Splicer and Their Function
Control panel and display--The control panel is a keyboard with universal symbols that lets the user select the appropriate splicing program, modify splicing parameters, and initiate splicing processes. The liquid crystal display provides the operator with an interface with the splicer to select and change programs, as well as view the fibers during the splice.
Workstation--Some manufacturers provide the convenience of a fusion-splicer integrated workstation that provides the user with a work space to accommodate the cleaver, splice- protection device, and universal tray holder, as well as offer storage for the built-in rechargeable battery, associated power cords, and the tool pouch.
Cleaver--The cleaver typically mounts directly on the fusion-splicer workstation and provides the critical, flat endfaces that allow high-quality splices.
Power control system--Modern fusion splicers offer the flexibility of workstation operation, as well as "stand-alone" operation accomplished with a rechargeable battery attached to the base of the fusion splicer.
Splice protection--Fusion splicers are typically equipped with a splice-protection device. The most popular method in the United States is heat-shrink sleeves, followed by mechanical protection devices and room-temperature vulcanization silicone sealant. Heat-shrink sleeves and mechanical protectors require an additional installation tool that mounts to the splicer or integrated workstation.
Electrodes--A high voltage applied across these nail-like metal conductors creates an electrical arc between the electrodes` sharp tips. The heat generated by this arc is high enough to melt the glass fibers for fusion. Like a spark plug, the electrodes should be cleaned to maintain a proper fusion arc.
V-grooves--The V-grooves are precise channels etched or milled into a hard material. These grooves serve as a trough to hold and align one fiber edge with the other.
Local injection and detection (lid) transmitter/receiver--Units equipped with an lid core-alignment capability will have a system that launches light directly into the core of the fiber before the splice point and detects that light signal just after the splice point. By monitoring the detected light level and moving the fibers up and down, forward, backward, and toward each other, the splicer is able to move the fibers until the detected level is maximized and, therefore, the cores are optimally aligned.
How do I actually make a fusion splice?
Fusion splicing consists of four basic steps, regardless of the sophistication of the machine being used: prepare the fiber; cleave the fiber; fuse the fiber; and protect the fiber.
Preparing the fiber is accomplished by stripping away all the protective coatings, jackets, and tubes until left only with the bare glass. The procedure is the same for mechanical and fusion splicing. The main concern is cleanliness because a clean fiber is essential for the cleaving step.
Cleaving the fiber properly is the key to successful splicing. It is virtually impossible to make a good fusion splice with a poor cleave. The idea is to have a mirror-smooth, perpendicular cut. A common misconception is that the fiber cleaver actually cuts the fiber in half. Actually, the process is the same as cutting a window pane to size, only on a much finer scale; the cleaver first nicks the fiber, and then pulls or flexes it to cause a clean break.
Fusing comes next and consists of aligning and heating. This is true for any fusion splicer, although there are many different methods for the fusion process. The goal is to match up the fiber ends perfectly so that light from one fiber will transmit directly into the other without losing power. Once the ends are aligned, it is time to fuse (or burn) them together. This is accomplished by generating a high-voltage electric arc that melts the tips of the fibers, which are then pushed together. A good splice is created by the interaction of three factors: fusion time (how long the fibers are heated), fusion current (how hot the arc is), and fiber feed (how much the fibers are pushed together).
Protecting the finished splice is the final step. A fusion splice typically has a tensile strength of 0.5 to 1.5 lbs. A good splice will not break during normal handling. For long-term protection, there are a number of splice protection methods. The most common are heat shrinks, mechanical protectors, and self-hardening silica gel.
What should you look for when selecting a fusion splicer?
The fusion splicer should be portable and contained within an integrated workstation.
It should be suitable for splicing telecommunications-grade optical fibers.
The unit should enable cost-effective splicing in the field.
The fusion splicer should be capable of operation under various environmental conditions (e.g., temperature, humidity, altitude) for all types of optical-cable deployments.
It should be user-friendly, and operation should require minimal training.
Automatic splicing programs should be available (if required) to remove operator and environmental dependence from the splicing process.
The controls of the fusion splicer should be designed ergonomically.
Communication with the fusion splicer should be conducted through a keyboard with universal symbols, and the dialogue with the splicer should be displayed on the monitor in the user-selected language.
Other specifications depend on the requirements of the customer`s applications.