Fiber optics upgrade is a national priority

Fiber-optics cables increasingly are becoming a part of the infrastructure landscape. While not nearly as pervasive as good old-fashioned copper phone wire, fiber optics is making inroads. Local telephone and cable television companies are installing hundreds of miles of the cables, and even mundane things like changeable traffic advisory signs are using fiber optics to create the messages.

The larger metropolitan areas in the country have access to fiber-optics networks, as do a significant percentage of the smaller metro areas. But beyond perhaps the top 250 cities, it is hit-and-miss. Even those communities that do have fiber-optics networks might find that the networks (often installed by telephone companies) are not configured for their needs.

Estimates of the total number of fiber kilometers in place in North America run to 16 million by 2001, up from 7.4 million in 1995. With this kind of growth, access should become increasingly easy.

Cities and counties may find many practical applications for fiber optics. For example, the technology may be used to accommodate local and wide area networks, to control and monitor arterial level traffic management systems, to connect schools and libraries for information-resource sharing, or as a method of extending an in-house telephone system to remote facilities.

Officials contemplating building or leasing a fiber-optics network need to familiarize themselves with the technology. Fiber optics consist of extremely thin and finely manufactured strands of glass, each about the thickness of a human hair. The glass is treated with certain materials so that it transmits light efficiently.

Optical fibers are used to transmit information and data in the form of pulses of light, typically at frequencies above the range of human vision, at very high speeds and over long distances. The fibers come in two basic types: multimode and singlemode. In multimode fiber, the light may follow many paths, or modes, down the fiber; in singlemode, the light follows one path.

A multimode fiber can transmit a limited amount of information over a limited distance before it needs an amplifier. This “bandwidth-distance limitation” means that the farther a multimode fiber goes, the less information it can transmit.

In general, multimode fiber is best suited for short-haul applications such as the internal wiring in a building for a local area network or a short connection between a video camera and a monitor. At best, multimode fiber is not run more than six miles with data volumes of more than 100 megabits per second.

Singlemode fiber, by contrast, generally is used for long-haul, high-data volume communication. A typical singlemode fiber link will extend up to 60 miles and can be used to handle data rates up to 20 billion bits per second. Singlemode often is used in applications such as long distance telephone lines or to transmit video signals for the cable television industry.

For many people, the choice between singlemode and multimode fiber comes down to the equipment and splicing costs. In addition to having the greatest capacity, singlemode fiber actually is cheaper to make than multimode. Ultimately, however, singlemode can be more expensive because it costs more to splice and because the equipment used to transmit on singlemode uses lasers instead of less costly light-emitting diodes (LEDs), which are used with multimode fiber.

In addition to being less expensive than lasers, LEDs are safer. Lasers used in singlemode fibers generally are not dangerous, but 10 percent have sufficient frequency and power to damage human eyesight.

Interference, long the bane of copper wires, is not a factor with fiber optics. Transmitting data by light rather than electricity virtually frees the lines from the interference caused by lightning or electrical discharges. Digital signals also improve the system’s ability to filter out noise.

Such immunity to electrical interference means that optical fiber cables could share the same space and conduit as power circuits. In fact, some power transmission lines also bundle optical fibers with the electrical cable. Fiber-optic cable also is free of sources of electrical discharge, meaning it can be installed in hazardous locations or run through gas and oil pipelines.

Fiber optics offers a number of other advantages as a means of transmitting information. The cables generally are very small, ranging from less than a quarter-inch in diameter for a two-fiber cable up to about three-quarters of an inch for a 216-fiber cable. The cables are tough and lightweight, and they can be pulled much greater distances than copper, resulting in reduced splicing costs.

In terms of its applicability, when combined with modern electronics, fiber has the capacity to act as a universal communication medium. Power transmission is about the only use for which fiber is not suited.

Conventional copper wiring requires three different kinds of cable, connectors and transmission equipment to route telephone, closed-circuit television and data from one place to another. A fiber-optics system, by contrast, can transmit all three over the same fibers simultaneously.

City and county officials considering using fiber optics must determine the technology’s availability in their area. They must then decide whether it would be more beneficial to build a network or lease existing infrastructure. That decision ultimately comes down to economics and need.

Municipal officials need to answer several questions before pursuing a single course of action: What are the community’s/government’s communication needs now, and what are they likely to be in five years? How much money is available in capital and recurring funds for construction and maintenance? How much will it cost to lease a system or a portion of one rather than to build one?

Once a local government determines its needs, officials can engage residents in a discussion of the possible costs and benefits of fiber-optics access. Telephone and communication service providers, as well as the local cable television company, all ought to participate in the discourse.

– Hunter Fulgham, manager of telecommunication systems, HNTB Corp., Bellevue, Wash.