Just as a person who can read and write is said to be literate, a laser that can read and write can also be thought of as literate. Such a feat is possible because of the joining together of the laser and another modern supertool—the computer. Computers are able to process information thousands of times faster than human beings. For instance, hundreds of years ago when a scientist needed to solve a complicated math problem, he or she had to do all the adding and multiplying by hand. A single problem might take as long as three months to solve. Today's supercomputers can give the answer to the very same problem in only three seconds. What is more, computers allow all kinds of marketing and communications tasks—from supermarket scanning to office copying to sending documents and music files across the country—to be accomplished much quicker and easier than by traditional means.
Both scientists and consumers used to have one major problem with computers, however. To feed new information into the computer the operator had to type the words on a keyboard; and people can only type so fast. There was a similar problem at the other end of the computing process. In order for the information that came out of the computer to be readable, the computer itself had to use a keyboard. A computer can type much faster than a person, but the typing still took a considerable amount of time. So even though a computer could process information quickly, a lot of time was wasted during the input and output stages. The advent of laser scanning technology has greatly alleviated this problem; and the world is in the midst of a veritable revolution in laser-computer literacy that is changing the face of both businesses and homes.
A laser scanner is a sophisticated device; but its basic principle is fairly simple. On the input end, a tiny laser beam scans across a page of text, a bar code, a photograph, or another image to be scanned. As it moves, the beam reflects back into a sensor that records the alternating patterns of white and black or of various colors.
On the output end, when the computer has information ready to be printed out, the laser once more speeds up the process. The computer "orders" the laser beam to modulate its intensity, that is, to get brighter, then dimmer, then brighter, and so forth, as needed. The modulated beam is now scanned across a light-sensitive material, usually a TV screen or sheet of paper, as in the case of a laser printer. The beam literally "writes" the information on the material (and/or stores it in the computer's memory). A laser printer also prints out information gathered by a computer from online web pages.
This and similar laser-computer systems are used every day to make money transactions. For instance, almost everyone receives monthly bills (for electricity, gas, and credit cards) that have been printed with a laser, and the vast majority of payroll checks are printed the same way. Such laser printers also supply people with news and information. All major and even most small local newspapers now use lasers to make printing plates. The laser beam etches the information on the light-sensitive plate in roughly the same way it writes on a screen or on paper.
Laser scanning technology has helped make many traditional jobs easier and less boring. An excellent example is the kind seen in supermarkets. These devices, first seen in a few stores in the 1970s and now virtually universal in American supermarkets, read the bar code (Universal Product Code, or UPC) that appears on all food packages in the United States. The Supermarket Institute in Washington, D.C., introduced the bar code in 1973. With the scanner and bar code, the checkout clerk no longer needs to press cash register buttons for every item. This not only makes the clerk's job easier but also reduces the chance for errors. A beam of light is much less likely to make a mistake than a person who is distracted, nervous, or just plain tired. In addition, the customer gets through the line and out of the store more quickly than before.
Another advantage of the bar code system is that it helps the supermarket with inventory. For instance, suppose there are one hundred boxes of corn flakes on the shelves when the store opens. Each time one of these boxes is sold, the computer records it. At the end of the day, the store manager checks the records, and if the computer indicates that eighty-seven boxes of flakes sold that day, the manager knows the supply is low and reorders immediately. This obviously saves a great deal of time in walking up and down store aisles and counting cans and boxes.
A supermarket bar code laser works in the following manner: A twelve-ounce box of Kellogg's Corn Flakes carries a bar code whose stripes stand for the numbers 381100. When the box is pulled across the scanner the laser beam reads these stripes and relays the message to the computer memory bank. The computer knows (because it has been programmed to know) that these particular stripes stand for product number 381100. The computer also knows that product 381100 is Kellogg's Corn Flakes, twelve-ounce size. (Smaller or larger boxes of the same product have similar but unique bar codes.) After identifying the product the computer looks up the price, which has also been programmed in. Next, the name of the product and the price appear on the monitor above the cash register. The total elapsed time from scanning to readout on the screen is a mere fraction of a second. When all the customer's products have been scanned, the machine adds up all the prices and the total for the transaction appears on the screen.
Supermarket laser scanners most often use a heliumneon gas laser that emits a red beam. Very dependable, it is also one of the least expensive types of laser. This is important because supermarket chains buy hundreds, sometimes even thousands, of the devices and could not afford the more expensive versions. The beam is powerful enough to read the bar codes but not so bright that it will hurt someone's eyes if he or she accidentally looks at it.
Bar codes, which are also used on magazines, books, greeting cards, and most other consumer goods, are not the only things laser beams can read. Facsimile, or fax, machines use laser beams to read documents, which are then transmitted from one office or home to another. These locations can be thousands of miles apart, their only requirement being that each end have a fax machine.
Many fax machines employ a helium-neon laser not unlike the type used in supermarkets. The laser beam in the first office scans the page that will be sent (called the original document). The images contained in the reflected beam are converted into electrical energy and transmitted by wires or antennas to the machine in the second office. There the energy is reconverted into light images, and a laser burns these images onto a light-sensitive metal drum. Finally, the drum transfers the information onto paper, and the process is complete. The whole procedure takes only about two minutes or less, a fraction of the time taken by old-fashioned hand delivery.
Laser printers, which are in practically every office as well as in the majority of private homes, operate similarly to laser fax machines. The printers also use laser beams to burn images into light-sensitive materials. Such printers have revolutionized the printing and copying market in the past three decades because they produce many copies quickly; make unusually clear, clean copies; and allow a wide range of printing jobs to be performed in a office or home, including making flyers, wedding announcements, reports, and even entire books, as well as printing computerized addresses on envelopes.
One quality of laser light that makes it ideal for these and other kinds of information-exchange and communication is that it can carry a great deal of information. The amount of information light can carry depends on its frequency. Imagine going to the beach two days in a row. On the first day the ocean waves are long and lazy, their crests averaging about fifty feet apart. On the second day the situation is much different, with waves that are now much shorter and more energetic, their crests only about five feet apart. Obviously there are more waves (ten times more to be exact) breaking per minute on the second day than on the first. Because the waves on day two are more frequent, they are said to have a higher frequency.
Waves of the different types of radiation (radio, microwaves, or light, for example) behave somewhat like the ocean waves. The lower frequency radiation waves are long and lazy. The higher frequency waves are short and energetic. The important point here for communications is that the higher the frequency, the more information can be carried. Consider that the telephone transmits the human voice at a frequency of about three thousand waves, or cycles, per second. That sounds like a large number of waves until it is compared to a television signal. Television transmits at a frequency of about 108 million cycles per second. Obviously a lot more information can be carried by a television signal than by a telephone signal. In fact, that is why the telephone can only transmit a voice, whereas television can broadcast both voice and picture.
But even the frequency of television signals is small compared to beams of light. Visible light frequencies range between 400 trillion and 800 trillion cycles per second. That means that light has the capacity to carry more than a million times as much information as television. In communications, the amount of information exchanged is the most important factor. It is no wonder then that the laser, which uses light to transmit information, has been so revolutionary.
Such laser-based communications work in two basic ways. One way involves transmission directly through
Electromagnetic waves occur in a variety of frequencies, or waves (cycles), per second. The more waves per second, the higher the frequency, and the more information the waves can carry. The frequency of TV signals, for example, is 108 million cycles per second. Visible light has about 10 million times that many. Ultraviolet light, detectable by X-ray cameras, has a frequency ten times higher than visible light.
the atmosphere (or through space). The same principle that allowed the direct transmission of a laser beam to a mirror on the moon could be used to communicate with astronauts on a moon base, for example. In this case the beam would carry stores of information and would not bounce back to Earth. A receiver in the base would pick up the beam and a computer would decode it.
The same procedure is already in common use in many earthbound cities. Several businesses have set up systems to flash laser beams from building to building. Some park services also use the system to communicate with rangers stationed at bases on remote mountains, where installing telephone lines could be too expensive. The ranger has a radio, of course; but if a large amount of information must be sent, the laser is a better choice. A fellow ranger at the main headquarters sends a communications beam to a receiver at the mountain base. A small computer in the base decodes the beam.
Unfortunately, light does not travel well through the atmosphere. The individual molecules of air tend to absorb some of the photons as they travel along, so the farther the light goes the dimmer it gets. As a result, scientists have learned to bypass the atmosphere by sending laser light through enclosed cables, the basis of the science of fiber optics.
A crude version of fiber optics appeared in 1934 when an inventor named Norman R. French patented an idea for a device called the "light pipe." French proposed taking a hollow pipe and lining it with a reflective material. If someone shined a light into the pipe, the rays might bounce off the inner surface and keep going through the tube.
French did not intend to send information with his device but rather to find a way to carry illumination from one room to another. But scientists in the 1960s believed that the light-pipe idea could be adapted to the field of laser communications. They quickly realized that the pipe they needed could not actually be hollow because then it would still contain air, and the air would absorb the light as it does in the atmosphere. Also, the signal would lose some of its power because small amounts would be absorbed by the lining itself. Another problem was that light travels in straight lines and the pipe would have to curve now and then to avoid obstacles (especially since it would be placed underground). They had to find a way to keep the curves from blocking the beam.
A major breakthrough came in 1966 when two British researchers, Charles Kao and George Hockham, suggested that thin glass fibers might be able to transmit light over short distances. Other scientists quickly picked up the idea, and in 1970 Robert Maurer of the Corning Glass Works in Corning, New York, constructed the first long-distance optical fiber. The science of fiber optics was born.
The fiber-optic system uses glass fibers only a fraction of an inch in diameter. The fibers, which make up the core, are stuffed inside a small cable that is lined with a material known as the cladding. This is an extremely reflective type of glass that makes most of the stray photons bounce back into the core. The cladding eliminates the problem of the beam not being able to move around curves; as long as the curves are not too sharp, the beam hits the cladding at an angle, then moves on. Such cables now regularly carry phone conversations, e-mail and the Internet, television signals, and other kinds of information. According to the National Academy of Engineers:
By the end of 1998, there were more than 215 million kilometers [133 million miles] of [laser] optical fiber installed for communications worldwide. The optical fibers transmit light pulses up to 13,000 miles, and are handling data rates that are doubling each year. Today, optical fibers are the best conduit for delivering an array of interactive services, using combinations of voice, data, and video. 3
Since a laser beam can carry high-quality television signals, most pay-television providers now install cable TV lines that use laser fiber optics. (An alternative is satellite dishes, which collect television signals bounced off of satellites.) In some towns and regions, companies are also connecting groups of homes and/or businesses to each other in small networks. Utilizing such a network, a person can broadcast a daily exercise class from his or her living room and ten, twenty, or more subscribers (those paying for the service) can tune in and participate within the comfort of their own homes or offices.
Optical fibers are thin strands of glass through which a laser beam can travel for several miles. Since a laser sends signals on light waves, a single optical fiber can carry as much information as hundreds of heavy copper wires, which carry electrical signals. When electrical signals travel through copper wires, they are quickly weakened. Devices called repeaters are needed about every mile to strengthen the electrical signal. In a fiber-optic system, laser amplifiers are needed only every six or seven miles to strengthen the light signal.
One of the advantages of laser fiber optics is that several fibers can be wrapped inside one cable. This means that each cable contains many laser beams, each carrying billions of bits of information. This makes the optical system clearly superior to earlier systems. For instance, the old-style telephone cable used wires to transmit conversations. Obviously, to carry many conversations there had to be many wires in a single cable, which made the cable quite thick, heavy, and difficult to install. Also, since the metal wires had to be packed so closely together the separate signals sometimes interfered with each other and produced electrical noise. By contrast, the optical telephone system uses a much thinner, lighter cable that is easier to install. Beams of light do not interfere with each other, so there is no noise in the system. A large conventional telephone cable could carry as many as a few thousand conversations at one time. By contrast, fiber-optic cables now exist that can carry millions of conversations at one time.
Some local areas of the United States, Japan, and a few other industrialized nations are presently experimenting with fiber-optic systems that connect individual homes to libraries and other storehouses of information. When a person asks a librarian to enter a book, magazine article, or even a movie into the library computer, the local cable carries the requested information to a monitor screen in the person's home. As demand increases, such systems will become more widespread and eventually as commonplace as the telephone.
The choice of the laser for these future communications systems is inevitable because laser light can carry vast amounts of information. It has been estimated that more than 100 million television channels might be transmitted using the frequencies in the spectrum of visible light. Even if only one-tenth of 1 percent of this total is ever used, that is still one hundred thousand channels. Only laser light will be able to carry that much information and thereby transform the way human beings communicate.