When to use fiber-optic cabling in your network installations

Just what is fiber-optic cabling? How does it compare to other cabling systems? What are some of its advantages and disadvantages? These are just a few of the questions that Dallas Releford answers today.

As opposed to most types of cable, fiber-optic cable (also known as optical fiber) uses light instead of electricity to transmit signals. Obviously, light is the fastest method of transmitting information, but fiber-optic cable has the additional advantage of not being subject to electrical interference. Thus, you can run it just about anywhere. Since light meets very little resistance, you can run fiber-optic cable over very long distances without having to boost or clean the signal. Some signals have been transmitted over 5,000 miles before they had to be processed. Imagine what that means for a normal network installation.

Fiber optics also involves speed. You can send signals at more than 10 GB per second. And even at that velocity, the signal is much cleaner than traditional electrical cabling. Comparing fiber-optic cabling to coaxial cabling is sort of like comparing digital information to analog information. (It really isn’t much of a comparison. Fiber optics is far more impressive.)

Still, when examining fiber optics, you must consider cost. Although you get a lot for your money, fiber-optic cabling is very expensive. Network Interface Cards (NICs) for fiber-optic cables can cost over $1,000 each. Right now, fiber-optic cable is used primarily for connecting network segments, making short runs, and connecting buildings and floors; it isn’t used for complete network wiring. As fiber optics becomes more popular, however, the price of fiber-optic cable (and related devices) should drop. Until then, you’ll want to compare different types of cables before you make any decisions.

Components of fiber-optic cable
The components of fiber-optic cable include the core, cladding, strength members, buffer, and jacket. Some types of cable also have a copper conductor that provides power to repeaters, concentrators, and other components.
  • ·        The core of the cable is made of one or more glass or plastic fibers, and it provides the pathway through which the transmitted light can flow. Plastic is more flexible than glass; consequently, plastic is cheaper and easier to manufacture, but it doesn’t work very well over long distances. The diameter of a core will measure from two to several hundred microns. A micron is about 1/25,000 of an inch. For networking considerations you should use core sizes of 60 to 100 microns. Most networking cables have two core fibers, which allow the cables to transmit in both directions at once.
  • ·        The core and cladding are manufactured as a single unit. The cladding is usually made from plastic, and it provides a refractive surface. Light that strikes this surface is reflected back into the core and continues its journey. The cladding has a lower refraction index, which means that it reflects light instead of absorbing light.
  • ·        The buffer consists of one or more layers of plastic. It surrounds the cladding and core. The buffer strengthens the cable and prevents damage to the core.
  • ·        The strength members are strands of very tough material, such as fiberglass, steel, or Kevlar. They provide extra strength for the cable.
  • ·        The jacket (which can be either plenum or nonplenum) is the outer covering or shield of the cable.

Fiber-optic cable comes in two forms: single-mode and multi-mode. Single-mode cable is so narrow that light can travel through it only in a single path. This type of cable is extremely expensive and very difficult to work with. Multi-mode cable has a wider core diameter, which gives light beams the freedom to travel several paths. Unfortunately, this multi-path configuration allows for the possibility of signal distortion at the receiving end.

Putting the components together
Fiber-optic cable must have a light source that generates a signal. Connectors, repeaters, couplers, and other components, which exist in most standard networking systems, serve to route, boost, and deliver the signal. First, you need something that will help you transmit light through the cable. This something is called a transmitter. Transmitters come in two varieties: LED (light emitting diode) and laser. The transmitter includes a light source and a driver, which modulates and uses an electrical signal to power the light source. Think of a fiber-optic cable as an unusually long laser that carries a light beam along a controlled path rather than emitting it through the air.

At some point, you’ll need to boost the signal that’s carried on the light beam. Use a repeater to boost the electrical signal that the light beam carries. Repeaters are composed of receivers and transmitters that are arranged in a specific series and separated by signal-cleaning components. Thus, repeaters pick up a signal, amplify that signal, and then transmit the signal down the cable.

Connectors allow you to put two fiber-optic cable segments together. These connectors are durable, inexpensive, and easy to use. You can use these devices to connect cables to other components (such as routers), too. If you need a more permanent connection, you might think about splicing your cables. A splice is a permanent connection between two segments of fiber-optical cable. This type of connection requires special equipment because the ends of both cables have to be cut and polished in such a way that they join perfectly.

On the other hand, if you need to split one signal into two or more signals, you’ll need to use a coupler. Couplers, which can be active or passive, are multipurpose devices that you can place anywhere in your cable system.

Finally, you need a receiver that will convert light signals back into electrical signals. Receivers possess photodetectors that convert light into electrical signals, amplifiers that boost signals, and output devices that transmit those signals.

The advantages of fiber optics
  • ·        There’s little interference from EMF devices, and fiber-optic cables don’t interfere with other devices.
  • ·        Fiber-optic cables are difficult to tap because they don’t emit signals that can be monitored. They are very secure.
  • ·        Fiber optics is faster than most other transmission mediums.
  • ·        The signal has a constrained loss rate, which means that very little of a signal is lost over rather long distances.
  • ·        Fiber-optic cables are safe to handle because high voltages aren’t involved.
  • ·        Fiber-optic cable is easier to install.

The disadvantages of fiber optics
  • ·        Fiber optics is expensive—though prices will fall as it becomes more popular.
  • ·        Components, such as NICs, are also expensive.
  • ·        Trained personnel should install fiber-optic cabling.
  • ·        Fiber-optic cables are somewhat susceptible to damage from the environment.
  • ·        Connectors tend to come loose after a period of time.
  • ·        Parts break more easily in fiber-optic cabling than in other cabling systems.

Dallas G. Releford has worked in the computer field as a programmer, an MIS manager, and a PC specialist. He has written a novel, which was published on the Internet and which led him to an interest in the electronic publishing field. He writes articles, electronic books, and just about anything else that involves the written word. To learn more about Dallas’ business, visit his Web site, which is called The Editor’s Eye .

The authors and editors have taken care in preparation of the content contained herein, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.