Tuesday, October 20, 2009

What would life be like without lasers? Part B - Lasers and Fiber Optics in High-Speed Internet & Smart Phones

The Internet, fax machines, smart phones, and other mobile devices are a way of life in modern society. All these technologies rely on lasers and fiber optics.

The properties of laser beams that allow them to be excellent carriers of high-data-rate signals (like high-speed Internet) are: 1) they are extremely high-frequency (0.3 GHz) carriers; and, 2) they have the coherence properties of radio or microwave radiation. These properties allow laser beams to carry many concurrent high-frequency signals.

Laser beams travel through the air in straight lines except when they are bent by lenses or prisms or reflected by mirrors. Optical fibers permit the transmission, or “piping,” of laser beams in flexible cables that can be wrapped around corners or laid on the ocean floor. An optical fiber is a fine glass or plastic strand that carries light internally along its length. Fiber-optic cables, which consist of bundles of optical fibers, are used to transmit laser beams in high-data-rate (high-bandwidth) optical communication. Optical fibers prevent the laser signals from being blocked or scattered by clouds or other particles in the atmosphere or by electromagnetic interference. This means that laser beams can travel over long distances without significant distortion or attenuation.

Fiber-optic cables can support Internet systems with up to 3 trillion bits per second at transfer rates as high as 111 gigabits per second (Gb/s), although 10 or 40 Gb/s is typical. The fibers used in long-distance telecommunication applications are always glass because glass causes only minimal attenuation. Both multi-mode and single-mode fibers are used, with multi-mode fiber used mostly for short distances (up to 600 yards) and single-mode fiber used for longer distances.

The process of communicating using fiber optics involves five basic steps: Creating the optical signal by modulating the laser output beam, relaying the modulated laser signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting the signal into an electrical signal.

Optical fibers are widely used to transmit telephone signals, Internet communication, and cable television signals. Due to much lower attenuation and interference, optical fiber has significant advantages over electrical transmission in long-distance and high-demand applications. Because of these advantages, optical fibers have largely replaced copper wire in core communication networks in the developed world. For example, many landline cell tower connections are made over optical fiber.

As one of the most talked about technological breakthroughs of the last few decades, laser/fiber-optic Internet carries a big name and responsibility in today’s world. Through the use of lasers and fiber optics, the computer and the Internet have evolved into realities that not too long ago were considered purely imaginary. Computers that used to take up entire rooms can now fit in a person’s back pocket. The Internet, which was created to help secure U.S. military networks, has now united the world with information.

With lasers and fiber optics, the frustrating days of slow Internet connections are forever in the past. Some people argue that wireless Internet is still faster than fiber-optic Internet, but that is not true. Laser/fiber-optic Internet is nearly a million times faster than wireless. A fiber-optic Internet cable can carry up to around three trillion bits per second. At that rate, the Library of Congress could be downloaded to your computer within a minute, compared to about eighty years for a dial-up connection (Fiberoptics VP).

The first transatlantic fiber-optic cable was installed in 1988, using glass fibers so transparent that repeaters (to regenerate and recondition the signal) were needed only about every 40 miles. In 1997, the Fiber Optics Link Around the World (FLAG) became the longest single-cable network in the world, providing infrastructure for the next-generation Internet. The 17,500-mile cable begins in England and runs through the Strait of Gibraltar to Palermo, Sicily, before crossing the Mediterranean to Egypt. It then goes to Dubai and UAR before crossing the Indian Ocean, Bay of Bengal, and Andaman Sea, through Thailand, and across the China Sea to Hong Kong and Japan (National Academy of Engineering).

Transistors get a lot of attention in the digital world, but the backstage heroes are lasers. Red lasers brought us compact discs and cheap long-distance communication. Blue lasers, which cram even more data into a small spot, became a hit around 1999 and have made possible Blu-ray DVDs (Elizabeth Corcoran, Forbes Magazine, June 08, 2009).

Gordon Snyder, Director of the NSF/ATE ICT Center, says, “The entire landline infrastructure is being replaced with fiber.” More valuable comments about this from Gordon can be found at the following blogspots:

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