Fiber: Truth or Fiction?
Fiber-optic cabling has become big business. In recent years, fiber's advantages over copper Cat-X and coaxial wiring have become clearer to a larger number of AV systems integrators. Still, misconceptions persist and it can be hard for integrators, installers, and end users to separate hype from reality. We gave it a shot.
Moreover, fiber isn't the Mercedes-Benz of structured wiring any more. Fiber-optic cabling costs have come down significantly in recent years, an effect that's been enhanced by the rise in copper prices in the surging commodities markets. Fiber today costs around 25 cents or less per meter, virtually on-par with copper–22 cents per meter at press time.
Finally, there are other, sometimes less apparent, benefits of fiber. Fire code regulations often require the use of plenum-rated cable in certain AV installations, which can add as much as a 100-percent premium over the cost of standard coax and Cat-5 cables. On the other hand, plenum-rated fiber cabling carries only a 10-percent premium (often less) over standard PVC cable. Sure, copper may still cost less than fiber linearly, but when measured by capacity, fiber comes out on top.
So why doesn't everyone run fiber? Sure, it's not always the right solution for the job, although that hurdle is becoming lower and lower. The fact is, misconceptions about fiber cabling still exist among systems integrators. And sometimes, those who are educating the industry are at odds with each other. Hey, in some ways we're all still learning here. So PRO AV called around to assess the truthfulness of what integrators keep hearing in the market. Truth or fiction:
"Fiber requires special skills to work with and troubleshoot"
The transition from copper to fiber is in some ways a fairly small jump as they're both cables that channel a signal. But in other ways, the differences are significant–coax and Cat-5/6 channel electricity, while fiber channels light.
"Fiber is cut-and-dried; it either works or it doesn't. It's much less ambiguous than copper from a troubleshooting point of view," says Derek Miranda, director of marketing for manufacturer Communications Specialties Inc. (CSI). Basically, anything that lets light seep out of the cable can diminish the power level of the signal, which is measured in decibels (dB). An optical power meter, which measures the strength of the signal, can help troubleshoot most fiber installations. Since fiber's distance capabilities are rated in kilometers (fiber specifications in general tend to be expressed in metric rather than the imperial values used for copper and Cat-5/6, another common source of confusion), the much shorter runs typical for most AV applications mean that signal strength is rarely a problem.
Another concept unique to fiber is the loss budget, which determines the distance a wire run can go before it requires a boost from an optical distribution amplifier. Loss budgets in the 20-percent to 30-percent range are not unusual. (Download a Pro AV Cheat Sheet on measuring loss here .)
What copper wiring requires that fiber does not are equalization and de-skewing, in order to correct the synchronization of signals arriving at a destination, such as a video display. "There are no de-skewing [devices] or equalizer trimmers the way you find on copper products," Miranda explains. "Fiber products are plug-and-play. There's no configuration to be done."
"Fiber cabling is difficult to connect and terminate"
Many people have reservations about "connectorizing" fiber-optic cable based on problems they have heard concerning the "grinding and polishing" of glass. The reality is that this now takes less than a minute and is done within a simple tool. Once one is completely familiar with the process (which takes 30 minutes to an hour to learn), the longest time interval involved in the finishing process is waiting for epoxy to cure. "It is at least as easy to do as terminating a BNC on coax, and some of those who have done it will say it is even easier," Miranda says.
Several connector manufacturers offer "quick-crimp" optical connectors that are installed with various mechanical clamp arrangements and hot-melt or instant-bond adhesives. Some of these connectors, such as the Corning Unicam Connector System, even come with a pre-polished length of optical fiber in the tip, thereby eliminating the finishing step altogether. The main difference between connector systems is in the mechanical way that the connectors mate to each other. (Download a PRO AV Cheat Sheet on terminating fiber here .)
"Fiber can be dangerous to work with"
Because the only signal in the fiber cable is light, there is no possibility of a spark from a broken fiber, eliminating the risk of fire and electrical shock hazards for integrators and end users. However, looking directly into the business end of an illuminated fiber cable can cause permanent damage to the rod and cone photo receptors in the eye's retina, warns Chris Mitchell, general manager of TexelSPL, the structured cabling business division of integrator AVI-SPL.
Furthermore, Mitchell adds, users need to remember that communications fiber is made of Acrylite-coated glass. When it's broken in the process of terminating or cleaving, microscopic glass shards can result that need to be handled with care. "If you use compressed air to clean an area that has these shards, you run the risk of them getting into your eye, something that could require surgery to fix," Mitchell says, referring to a personal experience that happened to him 25 years ago, when fiber was still a fairly exotic cable.
"Multimode is the same as single-mode fiber, but with more capacity"
Intuitively it seems correct, but it isn't. Multimode actually has less capacity than single-mode fiber. Single-mode fiber is a single strand of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission, which typically propagates at 1310 or 1550 nanometers (nm). It carries higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width.
Multimode fiber also uses a single strand of glass fiber, but it has a different composition that scatters light into multiple modes (i.e., beams of light). This limits multimode fiber's bandwidth and distance. Jim Jachetta, senior vice president at MultiDyne Video & Fiber Systems, suggests the following analogy: "Multimode is like firing a shotgun down a conduit–you get a lot of pellets into it, but they tend to bounce off the walls so they don't go very far and aren't completely accurate. Single-mode fiber is like firing a rifle down the conduit–it's just a single bullet but it will go straighter, faster, and farther than the pellets."
Single-mode fiber offers a higher transmission rate and up to 50 times more distance than multimode. Multimode fiber can provide high bandwidth at high speeds (up to 4Gbps) but only over short distances. And in cable runs greater than 1,500 feet, multiple modes (beams) of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission.
But even this distinction can be somewhat blurry, giving rise to yet another misconception about fiber, namely that multimode fiber is for multiple signals and single-mode fiber is for a single signal.
Both multimode and single-mode fiber can transport multiple signals if they are time-division multiplexed together into one wavelength. In addition, multiple wavelengths can be optically multiplexed onto one fiber using wave-division multiplexing (WDM) and coarse wave-division multiplexing (CWDM). This WDM technique is used in telecom and IT applications for single-mode fiber but has been uncommon in the AV space until now. Jachetta says up to 18 wavelength channels on single-mode and multimode fiber is becoming more common in pro AV applications.
"The latest advancements in wave-division multiplexing now offer CWDM solutions over multimode fiber," he says. "We have completed several projects using CWDM technology over multimode fiber."