Optical fibers are made from either glass or plastic. Most are roughly the diameter of a human hair, and they may be many miles long. Light is transmitted along the center of the fiber from one end to the other, and a signal may be imposed. Fiber optic systems are superior to metallic conductors in many applications. Their greatest advantage is bandwidth. Because of the wavelength of light, it is possible to transmit a signal that contains considerably more information than is possible with a metallic conductor — even a coaxial conductor. Other advantages include: • Electrical Isolation — Fiber optics do not need a grounding connection. Both the transmitter and the receiver are isolated from each other and are therefore free of ground loop problems. Also, there is no danger of sparks or electrical shock. • Freedom from EMI — Fiber optics are immune to electromagnetic interference (EMI), and they emit no radiation themselves to cause other interference. • Low Power Loss — This permits longer cable runs and fewer repeater amplifiers. • Lighter and Smaller — Fiber weighs less and needs less space than metallic conductors with equivalent signal-carrying capacity. Copper wire is about 13 times heavier. Fiber also is easier to install and requires less duct space.