In lightwave communications systems, information is carried as pulses of light instead of electrical pulses. A light source, usually a laser, launches pulses of light down a hair-thin glass fiber, turning on and off to represent the ones and zeroes of digitized information. As they travel through the fiber, the light pulses broaden and lose their shape and need to be regenerated or amplified every forty miles or so. In an optically amplified system, the signals get a boost as they pass through spliced-in segments of fiber containing erbium. The optical amplifiers are pumped by semiconductor lasers that energize the signals as they pass through the fiber.
Optical amplifiers can handle various bit rates and modulation formats.
Unlike electronic repeaters, which have to be replaced if the bit rate or modulation is changed, optical amplifiers can handle varying system configurations. The world's first transoceanic lightwave system, TAT-8, went into service in 1988 and has a capacity of 40,000 simultaneous telephone calls. TAT-9, to be deployed in 1991, will handle 80,000 simultaneous calls. All rights reserved.