When electrical contractors first decide to get into the fiber optic local area network (LAN) installation business, they have a plethora of factors to consider before ever making a single connection. Each choice about which connector to use, and its corresponding method of installation, will be critical to overall success. The first step in the selection process is to evaluate the various types of connectors available. In addition, the requisite tools for connecting fiber vary widely from method to method. Comprehending connector technologies and installation approaches begins with the basics.
There are three main types of fiber optic connectors commonly used: straight tip (ST), subscriber connector (SC), and small form factor (SFF). The ST is identified by its bayonet housing, which may be constructed of metal, ceramic, or plastic. The SC is identified by its square-shaped cross section, which is constructed of plastic. The latest development in fiber optic connectors is the small form factor. These connectors are similar in size and shape to traditional telephone line connectors-the ones that clip into the wall jack-and are as small as a modular eight-pin connector used on Category 5 copper cable.
The difference between ST and SC connectors and the SFFs, as Leviton Manufacturing Co., Marketing Assistant Anne Lanute explained, is that STs and SCs use an alignment sleeve for a typical male/female connection, while the SFFs need a plug and receptacle.
From a cost perspective, STs cost less than SCs and SCs cost less than SFFs. In addition, SCs and STs take about 5 minutes to terminate, including cable preparation and set up.
SFF connectors are manufactured in five different varieties, including the Optijack, the MT-RJ, the VF-45, the LC, and the SC-DC or SC-QC. However, each variety has a unique set of characteristics and particular application methods.
The Optijack from Panduit is the oldest SFF design, based on the traditional ST/SC 2.5mm ferrule. (A ferrule is defined as the alignment sleeve portion of a connector which protects and aligns the stripped fiber.) While the Optijack has a plug/jack configuration, a plug/plug adapter is also available. Active device mounts to develop transceivers and a plastic optical fiber version are under development. Common fiber optic tools are sufficient for termination, and it is designed to work with regular zipcord cable. It may be the simplest, most versatile design available, according to some experts.
Several manufacturers, including AMP Incorporated (a division of Tyco Electronics Corp.), The Siemon Company, and Corning Cable Systems (formerly Siecor), offer the MT-RJ-a molded-body, small duplex connector with two fibers spaced 750mm apart. It is designed for epoxy polish termination. Current designs have a prepolished fiber stub, known as "cleave and leave" technology. Polishing is tricky, especially between the molded ends on the male half. This is done before the connector is assembled. For all prepolished connectors, the use of inexpensive cleavers increases the probability of errors in field terminations, especially since two perfect cleaves (one per connector) are needed. AMP's MT-RJ is a field-installable, SFF, prepolished fiber stub connector.
Herb Congdon, market manager for fiber systems at AMP, discussed the company's MT-RJ, which went on the market in 1998. One MT-RJ costs less than two SCs, and the need for only one connector instead of two is based on the type of ferrule the connector has. The MT-RJ accommodates two fibers, while the SC duplex, also with two fibers, requires two SC connectors.
Congdon estimates training to take about five minutes, particularly because no special tools are required. AMP's MT-RJ has simple tooling. It has a throwaway actuator tool that looks like a miniature putter. "We call it a mouse putter," Congdon said.
Both MT-RJ and VF-45 connectors require very specialized termination processes. For example, the VF-45 requires polishing, while the MT-RJ does not. However, the loss may be higher with the MT-RJ. The maximum allowable loss is 0.75 dB.
The 3M Company's VF-45 connector, in the company's Volition line, incorporates "V-groove" splice technology, which effectively replaces a ferrule. It still requires polishing of the bare fiber. The VF-45 is comprised of a jack-and-plug design. Field termination will expand from jacks to patch cords. Based on part costs and ease of termination, this could be the least expensive SFF design. A single-mode Volition product is also available. It costs a quarter of what it costs to use two ST or SC connectors, and possibly half the cost of using other connectors, according to the manufacturer. (3M also licenses Baycom, Uconn Technology, and Infineon to manufacture the VF-45 under their respective names.)
The LC connector, manufactured by both Lucent Technologies and The Siemon Company, has a ceramic ferrule and plastic shell. It resembles the SC at half the size. According to Jim Hayes, president of Fotec, Inc., it may have the best performance and uses standard termination procedures. It uses a special half-size cable but is compatible with 3mm jackets and 900 micron buffered fiber.
The Siecor/IBM SC-DC or SC-QC comes in a "cleave and leave" version, but the initial design requires installers to terminate either two or four fibers on both ends at once.
Many SFF connectors can be polished and terminated two at a time, delivering an advantage-according to some experts-over ST and SC connectors. "Duplex connectors allow sending and receiving within the same connector," said 3M's Volition Product Manager Dan Silver. "There's one plug, one socket with two fibers inside."
VF-45 and other small form factors take about two minutes to terminate. The plug is field terminable; the socket is not. With the MT-RJ, the socket end is already terminated.
AMP's Congdon said that connections using MT-RJ technology require simple procedures. Some of his general guidelines for MT-RJ termination include the following:
- Keep the dust cap on.
- Maintain a clean environment, free of dust, or with minimal dust and dirt.
- When you strip the fiber, remove coating particles from the glass.
- Get a good cleave on the fiber. He recommends a beaver-tail cleaver that you can score and snap. "Use a proper cleaver; don't do a smash-and-go cleave."
- Prepolish the fiber first. If it is already prepolished, mate it to the fiber stub.
Tools and packaged systems approaches
Technician labor can cost a third of the total fiber optic LAN installation, experts say. Therefore, the selection of the system used on job sites is critical to bottom-line profits. Connectors are not simply offered as stand-alone items that are installed the same way in all applications. Instead, each connector type and each of the various manufacturers require different ways of connecting fiber.
Experts cannot pick the "best" way to terminate fiber because each situation is different. Each method may be different, but that doesn't make one method better than another one.
Because SFFs vary so widely, connectors and tools are designed to work best together. In fact, many tool kits are sold with connectors in a packaged approach. Manufacturers such as Hilti, Inc., Greenlee Textron, Klein Tools, Inc., and others, manufacture these prebundled kits. Greenlee's is currently introducing a new line of voice/data/video (VDV) tools, which improves upon current offerings. One of those current offerings is a line of KWIK CYCLE Crimping Tools, which are recommended for use with the entire KWIK CYCLE Crimping System.
With Leviton's Threadlock SC Fiber Optic Connector and Tightening Tool, only a basic tool kit is needed. Composed of diamond, tungsten, or sapphire, the tool is used for field termination of single-mode and multimode fiber optic cable. Effective use requires only the purchase of polishing film and alcohol wipes. Reportedly, termination takes two minutes.
Most SC epoxy-gluing or crimping mistakes are permanent, rendering the connector useless. "Ten to 25 percent of the time there are mistakes," said Leviton's Director of Sales and Marketing Michael Carter. Why? He said it is because operators' respective skill levels vary widely. Leviton's connector, however, gives technicians a second chance, because it is reusable, and therefore, more forgiving. "You simply re-prepare the cable," he added. "Multimode can be redone up to 25 times; single-mode up to 10 times."
AMP's Versacleave hand-held cleaver, which involves a short learning curve, is used for mechanical splices with SC or ST connectors.
AMP's Lightcrimp Plus Connectors are used for fiber-to-the-desk applications and can be installed in less than a minute, the company contends. The connectors use a splice-and-crimp technology, which requires limited training, fewer tools, and no consumables. Fibers are secured without the conventional epoxies, ovens, or ultraviolet curing. They also offer the Light Crimp, which is a quick-cure, adhesive style with no epoxy polish.
The Siemon Company's Lightspeed fiber adhesive is meant to save time and improve upon anaerobic terminations by eliminating termination steps and optimizing cure characteristics. The adhesive features a colored tint so technicians can see how much of it to use during insertion into the connector. The Siemon Company's Multimode ST and SC Duplex Connectors are simply designed with exacting tolerances, which enable easy termination and precise alignment for both multimode (50 micron and 62.5 micron) and single-mode fiber.
The company's automated Fiber Polisher is battery-operated and performs a high-quality, consistent polish on two multimode connectors in just 15 seconds, according to the company. The Siemon Fiber Termination Kit contains all the tools and consumables needed to terminate 200 multimode connectors.
Thomas & Betts' Aster Impact Termination System involves a cleaving/termination tool. It is used to impact the stainless steel around the ferrule. It is meant for T&B's line of ST and SC connectors. This automated, handheld device, according to the company, eliminates guesswork. This line of mechanical connectors, ferrules, and other fiber optic accessories eliminates epoxy and hand cleaving. It also allows installers to secure the fiber quickly at both ends of the terminated device. It is meant to allow more than 3,000 cleaves at an angle of 3 degrees or less. The T&B tool package includes a bench-mounting clamp and protective case.
"It removes the human element of cleaving because it's an 'autocleave,'" said Randy Cochran, Thomas & Betts' technical marketing manager. "You simply push the lever, then polish it. It takes 15 or 20 seconds (not including polishing). It doubles the electrical contractor's input per hour. It also has superior electronic probability. The dB loss is 0.176, when the industry standard is 0.5."
The Siemon Company's MT-RJ Termination kit employs proven no epoxy/no polish termination technology. A two-fiber MT-RJ connector can be terminated in less than two minutes, or less than one minute per fiber. This kit comes complete with all tools required to terminate MT-RJ connectors in a durable carrying case.
Ideal Industries, Inc., offers the MINILITE-STRIP, a fiber stripper that works like two tools in one. It is designed with two V-notch precision apertures and can remove the buffer and coating from 125-micron and 140-micron fiber. The tool's blade grind design makes optical cable preparation fast and easy, according to the manufacturer.
Selecting termination methods
Now that we have examined some market players and their various systems and products, the next question is: Which approach is best for each situation? How do I choose? Several other questions must first be answered. Start by determining the following:
- Level of reliability needed (according to the environment in which it is to be installed).
- Tools needed and their cost.
- Connectors' cost.
- Time and labor required to terminate a typical connector.
- Consumables needed: epoxy/adhesive, polishing film, cleaning materials (wipes/alcohol). How long they last, how much is needed, and how much the cost is to buy more.
To determine the cost-effectiveness of various methods of terminating fiber, multiply the technicians' hourly rate by the minutes the termination (or other procedure) takes, and then add the cost of consumables. You must factor in the yield. (e.g., if you have a yield of 90 percent, you will attempt 111 connectors to make 100 good ones.)
Fusion splicing is welding two fibers together, usually with an electrical arc. Active alignment minimizes splicing loss. Large contractors and telephone companies use this equipment for outside plant applications, which require much skill to use and substantial amounts of money to either buy or rent.
Mechanical splicing, conversely, relies on tight dimensional tolerances in the fibers to minimize loss. It uses an alignment fixture to mate the fibers and either a matching gel or epoxy to minimize back reflection. The fibers are pushed together with an index-matching gel or epoxy between them. Reflection occurs because the process isn't perfect. Some mechanical splices use bare fibers in an alignment bushing, while others closely resemble connector ferrules, minus all the mounting hardware. Mechanical splicing is used in premises cabling.
"Mechanical splicing is easier and more cost efficient," said 3M's Silver. "It can do just as good a job and has a proven track record. Designs have changed and improved with experience."
An example is 3M's Fibrlok Optical Splice, which is a universal splice used with either single-mode or multimode fiber. In incorporates V-groove technology, which replaces a ferrule configuration. It works best in the campus environment, where mechanical splicing is done. Splice preparation kits and assembly tools are recommended for this method.
"You need three points of connectivity to hold the alignment," Silver said. "The V-groove holds the tolerance for proper core-to-core alignment." The best fiber alignment allows the maximum amount of light to transmit from one core to another.
Polishing improves reliability
Polishing helps combat reflection problems that can cause unreliable network performance. A rough fiber end scatters light. Dirt can scatter and absorb light. Isopropyl alcohol is a good cleaning agent, provided it is lab grade, not rubbing alcohol. It is especially effective when applied with lint-free wipes. Covering the fibers and refraining from touching them helps, since oils from peoples' skin can attract dirt to fibers.
Panduit's Optijack is a field-installable, non-adhesive, prepolished SFF connector. Its system is two-part epoxy. Panduit also uses anaerobic adhesives and a prepolished splice termination.
Epoxy two-part standard oven cured offers the best quality of termination, because it offers low-loss, high reliability. Every factory termination is done with epoxy and an oven. A drawback is that you need to carry a curing oven with you to do this in the field.
The basic steps for using epoxy as a termination method follow:
- Mix the resin and hardener of the epoxy.
- Load the mixed epoxy into a syringe.
- Inject the epoxy in the back end of the connector ferrule.
- Insert the prepared cable into the connector, such that the bare fiber is inserted into the ferrule hole, until the cable sets inside the connector.
- Crimp. If the connector is being installed onto jacketed fiber, a crimping operation is required to retain the connector onto the cable strength members and jacket. This is usually accomplished using a crimp sleeve, and in order to retain the connector on both strands of the cable's strength members and jacket, two crimps are typically required.
- Install the connectorized cable into the curing holder. The curing holder protects the protruding fiber from the possible damage from handling during the next step.
- Cure the epoxy. Place the connectorized cable and curing holder into an oven. A curing oven resembles a hot plate with 12 to 20 holes in it, in which connector/curing holders fit.
- Cleave the protruding fiber. Use a pocket pen-style scriber as close to the ferrule tip as possible and remove this excess fiber with a straight non-twisting pull.
- Dispose of the fiber. Deposit it on a piece of tape (masking tape works), or into a container for that purpose. Otherwise, the cleaved fibers can get stuck on your finger, then get in your eyes. Also, wear safety glasses.
- Polish. This is critical to optical performance. If you don't achieve a smooth finish on the fiber, the light rays will have difficulty passing through the connector and into the one it will be mated to. The first polishing step is intended to remove the excess epoxy from the ferrule tip with a relatively coarse grit polishing film. Increasingly fine grit polishes are used for subsequent polishes.
- Clean the ferrule tip/fiber, using a lint-free wipe dipped in 99 percent reagent-grade alcohol.
- Inspect the work you've done so far.
- Test. Optical testing is the only way to ensure that the quality of your terminated connector is good enough to transmit VDV signals with minimal degradation. For multimode, all you really have to test is insertion loss (amount of light passing through the connection). However, for single-mode, you also need to check return loss (amount of light reflected as a result of your termination).
Another means of terminating fiber is the quick-cure adhesive/anaerobic solution. Anaerobic termination is simpler and quicker, and is performed at a lower temperature. AMP, Siecor (now Corning Cable Systems), Lucent, Molex Fiber Optics, Fotec, and Methode Fiber Optic manufacture these types of connectors.
3M's Hot Melt connector has a built-in glue. You heat it (to 400 degrees) and put the fiber in. It can't get too hot.
While some installers prefer adhesives in fiber optic terminations, others prefer non-adhesive alternatives. It may be a speed issue.
According to Jen Pasek, Panduit's division marketing product manager, a non-adhesive mechanical crimp takes 27 percent less time than the adhesive prepolished version. The latter is 57 percent faster to terminate than non-prepolished. All times do not include the biggest time eater-setting up for the termination-nor do they factor in yield.
Frank Dundek, Panduit's assistant chief engineer for fiber optics, said field termination is best accomplished "by keeping enough pressure on the fiber to ensure you go all the way into the core. You go against the fiber and pull it out. How well you cleave depends on your cleaver."
The connectors, tools, and techniques available to electrical contractors are aimed squarely at optimizing the overall performance of the fiber optic network. Research and development has given birth to improvements that have tremendously improved the speed with which fiber optic terminations can occur. That speed will be increasingly critical to electrical contractors carving a niche in the VDV market. But, regardless of the methods used to terminate fiber, loss cannot-at least for now-be eliminated.
"The loss may be too low to register on the test equipment, but it happens, even with a perfectly polished fiber," said AMP's Congdon. "There is always a gap…always a loss." He added that the closest you can get to achieving zero loss is a fusion splice.
In addition, according to 3M's Silver, to maximize the benefits of using connector/tool packages, contractors and technicians should:
- Use the items in the termination or splicing kit.
- Pay attention to manufacturers' instructions very carefully. When the directions say to do a certain number of laps with a certain type of film, follow them. These directions were developed through many tests.
- Avoid contamination. The oil from fingers or dirt effects the splice. Use a good grade of alcohol for cleaning the fibers.
- Don't take shortcuts.
Choosing the fiber optic termination method that works best for your crews and your budget can be one of the most strategic and far-reaching moves you make in the VDV market. Please carefully consider all the factors, examine the tools and techniques, and choose wisely. Then, keep up on the latest innovations in connectors and methods.
Mentioned in this feature
3M Telecom Systems Division
AMP Incorporated (a division of Tyco Electronics Corp.)
Corning Cable Systems (formerly Siecor)
Ideal Industries, Inc.
Klein Tools, Inc.
Leviton Manufacturing Co., Inc. Telcom Unit
Methode Fiber Optic
Molex Fiber Optics
The Siemon Company
Thomas & Betts Corp.
DOHERTY is senior editor, voice/data/video systems for Electrical Contractor magazine. She can be reached by telephone at (301) 657-3110 or via e-mail at email@example.com.