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. Copper cable (UTP) performance continues to be surprising. Although for most of us fiber to the desktop is not yet a practical reality, fiber-optic cable is touted as the ultimate answer to all our voice, video, and data transmission needs and continues to make inroads in the LAN market. Some distinct advantages of fiber-optic cable include:

● Transmission distances can be much greater than with copper cable.

● Potential 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,” or tap a fiber cable.

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 and slightly cheaper than 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 1.4) 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.

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 Factor about 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, i.e., they don’t have light passing through them. Telecommunications companies often lease out these extra strands to other companies.