The internet, cell phones, fax machines and pagers are a way of life in modern society. All these technologies rely on lasers and fiber optics. The principle behind a laser lies embedded in the heart of quantum mechanics. Einstein built on the theory of quantum mechanics to explain the photoelectric effect in 1905 and showed that electrons could absorb and emit the energy of photons. In 1917, he went on to discover that this emission could be “focused” so that it occurs at a single frequency. This is known as “stimulated emission”. Scientists applied this principle in the mid-1950s to stimulate emission of microwaves using a device called a maser. They then applied the same principle to visible light and used the term laser for this device. However, they could not produce a steady laser light, which was necessary for practical applications.

Research on semiconductors led to the development of semiconductor lasers. By the late 1960s, researchers had devised a method to operate lasers continuously at room temperatures using layers of semiconductors. Now they needed to find a method to transmit light across large distances (see Semiconductor Lasers). Although scientists knew that glass fibers could carry light over short distances, it was not a very efficient process. Theoretical work showing that light loss in glass fibers could be decreased dramatically spurred experimental efforts to produce such fibers. Researchers continued exploring techniques to decrease light loss in optical fibers.

It then became possible to take fiber-optic communication out of the laboratory and into everyday life. Meanwhile, scientists continued improving laser technology and by the late 1970s, commercial use of fiber-optic systems had begun (see Practical Systems Take Shape). As fiber optic cables began to be used world-wide, basic research continued to yield improvements in the systems. Yet more possibilities for improvement in high-speed data lines are available and looming on the horizon (see Basic Research Remains Vital).


THE INTERNET

In April 1995, a young Chinese chemistry student at Beijing University lay dying in a Beijing hospital. She was in a coma, and although her doctors had performed numerous tests, they could not discover what was killing her. In desperation, a student friend posted an SOS describing her symptoms to several medical bulletin boards and mailing lists on the Internet, the ever-growing international array of computer linkages through telephone lines. Around the world, doctors who regularly checked these electronic bulletin boards and lists responded immediately.In Washington, D.C., Dr. John Aldis, a physician with the U.S. Department of State, saw the message from China. He had recently served in Beijing; he knew the woman's doctors. Using the Internet, he forwarded the message to colleagues in America. Soon an international contingent of doctors joined the e-mail discussion.

A consensus emerged--the woman might have been poisoned with thallium, a metal resembling lead. A Beijing laboratory confirmed this diagnosis--the thallium concentration in her body was as much as 1,000 times normal. More e-mail communication ensued, as treatment was suggested and then adjusted. The woman slowly began to recover. Well over a year later, the international medical community was still keeping tabs on her condition through the electronic medium that saved her life.This story underscores society's increasing reliance on a system of global communication that can link you equally easily with someone in the next town or halfway around the world.

People in all walks of life use the telephone system every day to solve a problem or make a date or transfer money or hire an employee. They can do these things by making telephone calls from stationary telephones or from handheld mobile telephones, by sending faxes, or by using computers and dialing into the Internet.


USING VISIBLE LIGHT?

All forms of modern communication--radio and television signals, telephone conversation, computer data--rely on a carrier signal, a wavelike electromagnetic oscillation with a particular frequency. Electro-magnetic signals are described in terms of their wavelength (the distance between the peaks of two waves) or their frequency (expressed in hertz, the number of wave cycles per second); the shorter the wavelength, the higher the frequency. By modulating the carrier, we can encode the information to be transmitted; the higher the carrier frequency, the more information a signal can hold.

SEMICONDUCTOR LASERS

Transistors make use of the special properties of a class of materials known as semiconductors. Electric current is carried by moving electrons, and ordinary metals, such as copper, are good conductors of electricity because their electrons are not tightly bound to the nucleus of the atom and are freely attracted to a positive charge. Other substances, such as rubber, are insulators--poor conductors of electricity--because their electrons do not move freely.

Semiconductors, as their name implies, fall somewhere in between; they ordinarily behave more like insulators, but under some conditions they can be made to conduct electricity.Early work on semiconductors focused on silicon, but silicon itself cannot emit laser light. The invention of the transistor at Bell Laboratories in 1948 by William Schockley, Walter Brattain, and John Bardeen stimulated research on other semiconductors. It also provided the conceptual framework that would eventually lead to an understanding of light emission in semiconductors. In 1952, Heinrich Welker, at Siemens in Germany, described semiconductors from elements found in column III and V of the periodic table as potentially useful for electronic devices.

One of these, gallium arsenide, or GaAs, was to feature prominently in the search for an efficient communication laser. Necessary precursors to its full exploitation were basic studies of layer-by-layer growth of high-purity crystals, research into defects and dopants (impurities added to a pure substance to change its properties), and analysis of the effects of heat on the stability of compounds. With these advances, research groups at General Electric, IBM, and the Lincoln Laboratory at the Massachusetts Institute of Technology developed working GaAs lasers in 1962.