Fiber-Optic Cable

As late as 1993, it seemed that in order to move toward the future of desktop computing, businesses would have to install fiber-optic cabling directly to the desktop. It's surprising that copper cable (UTP) performance continues to be better than expected. 

Note

Fiber versus fibre: Are these the same? Yes, just as color (U.S. spelling) and colour (British spelling) are the same. Your U.S. English spell checker will probably question your use of fibre, however.

Although for most of us fiber to the desktop is not yet cost-effective for traditional LAN networks, fiber-optic cable is touted as the ultimate answer to all our voice, video, and data transmission needs since it has virtually unlimited bandwidth and continues to make inroads in the LAN market. Some distinct advantages of fiber-optic cable include:

• Transmission distances are much greater than with copper cable.
• Bandwidth is dramatically higher than with copper.
• Fiber optic is not susceptible to outside EMI or crosstalk interference, nor does it generate EMI or crosstalk.
• Fiber-optic cable is much more secure than copper cable because it is extremely difficult to monitor, "eavesdrop on," or tap a fiber cable.

Note

Fiber-optic cable can easily handle data at speeds above 10Gbps; in fact, it has been demonstrated to handle data rates exceeding 500Gbps!

Since the late 1980s, LAN solutions have used fiber-optic cable in some capacity. Recently, a number of ingenious solutions that allow voice, data, and video to use the same fiber-optic cable have emerged.

Fiber-optic cable uses a strand of glass or plastic to transmit data signals using light; the data is carried in light pulses. Unlike the transmission techniques used by its copper cousins, optical fibers are not electrical in nature.

Plastic-core cable is easier to install than traditional glass core, but plastic cannot carry data as far as glass. In addition, graded-index plastic optical fiber (POF) has yet to make a widespread appearance on the market, and the cost-to-bandwidth value proposition for POF is poor and may doom it to obscurity.

Light is transmitted through a fiber-optic cable by light-emitting diodes (LEDs) or lasers. With newer LAN equipment designed to operate over longer distances, such as with 1000Base-LX, lasers are commonly being used.

A fiber-optic cable (shown in Figure 1) consists of a jacket (sheath), protective material, and the optical-fiber portion of the cable. The optical fiber consists of a core (8.3, 50, or 62.5 microns in diameter, depending on the type) that is smaller than a human hair, which is surrounded by a cladding. The cladding (typically 125 micrometers in diameter) is surrounded by a coating, buffering material, and, finally, a jacket. The cladding provides a lower refractive index to cause reflection within the core so that light waves can be transmitted through the fiber.

 

Figure 1: A dual fiber-optic cable

Fiber-Optic Cabling Comes of Age Affordably

Fiber-optic cable used to be much harder to install than copper cable, requiring precise installation practices. However, in the past few years, the cost of an installed fiber-optic link (just the cable and connectors) has dropped and is now often the same as the cost of a UTP link. Better fiber-optic connectors and installation techniques have made fiber-optic systems easier to install. In fact, some installers who are experienced with both fiber-optic systems and copper systems will tell you that with the newest fiber-optic connectors and installation techniques, fiber-optic cable is easier to install than UTP.

The main hindrance to using fiber optics all the way to the desktop in lieu of UTP or ScTP is that the electronics (workstation network interface cards and hubs) are still significantly more expensive, and the total cost of a full to-the-desktop FO installation (Centralized Cabling, per ANSI/TIA-568-C) is estimated at 30 percent greater than UTP. However, the Fiber-to-the-Telecommunications-Enclosure topology can bring fiber closer to the desk, while still using UTP for the final connection, and actually lower the cost compared to traditional topologies

Two varieties of fiber-optic cable are commonly used in LANs and WANs today: single-mode and multimode. The mode can be thought of as bundles of light rays entering the fiber; these light rays enter at certain angles.

KEY TERM: dark fiber

No, dark fiber is not a special, new type of fiber cable. When telecommunications companies and private businesses run fiber-optic cable, they never run the exact number of strands of fiber they need. That would be foolish. Instead, they run two or three times the amount of fiber they require. The spare strands of fiber are often called dark fiber because they are not then in use—that is, they don't have light passing through them. Telecommunications companies often lease out these extra strands to other companies.