Boston — TEN years ago, the frontier in telecommunications was 23,000 miles out in space. Now the cutting edge is underground and underseas. Optical fibers, gossamer strands of ultrapure glass, carry messages by pulses of laser light. They have already made major inroads against one other common carrier: copper wire.
This is largely because glass wires carry vastly more telephone calls than copper cable, and are more efficient. Indeed, American Telephone & Telegraph alone expects to have installed some 100,000 miles of the wispy strands across the United States by year-end. Until recently, most of these glass cables were laid along heavily trafficked telephone corridors in urban areas.
Now, however, fiber optics will increasingly carry long-distance communications as well -- the domain of satellites.
Besides being able to carry more calls than conventional copper cable, glass wires are free of weather interference, echoes, and the noticeable time lag that affect satellite systems. (Pulses take half a second to travel the 46,000 miles to a satellite and back, so a half-second delay is endemic -- whether the call is overseas or not.)
Moreover, because the signals are sent by light wave, they are immune to tapping by electronic eavesdroppers. Glass wires are also capable of carrying voice, video, and data signals, which makes them good candidates for handling electronic information chores of all kinds.
To be sure, communications satellites are not obsolete, says George Petty, director of network planning for AT&T Communications, but he expects they will be forced into a narrower niche as fiber becomes ``the Interstate Highway System of telecommunications.''
Since the January 1984 breakup of AT&T, the telecommunications industry has become hotly competitive. To keep up, companies dealing in satellite telecommunication are adopting fiber. According to Brian Hughs, executive vice-president of Tel-Optik, optical fiber is so effective that ``some systems are reporting one error a month in transmission.''
Satellites still hold the edge when it comes to point-to-multipoint communication (such as video distribution) and in situations Mr. Hughs calls ``geographic absurdity: linking areas that would otherwise be unthinkable, such as in remote parts of Alaska.'' Fiber becomes too expensive under those conditions. But experience has proved that satellites cannot compete with fiber optics on densely used point-to-point connections.
AT&T is jointly engaged in a $335 million project that will link the United States to Europe through two pairs of cables. The 3,607 nautical miles of cable will start being laid in 1988. The transatlantic fiber, called TAT-8 (for Trans-Atlantic Telecommunications), should be in full use before July of that year. According to Rick Brayall of AT&T, TAT-8 will be able to transmit 37,800 phone conversations simultaneously.
When TAT-8 is completed, the 60-percent chunk of transatlantic telecommunications traffic satellites now enjoy should go down to about 10 percent, says technology writer Fred Guterl.
The most ambitious domestic fiber network is that being developed nationwide by US Telecom. It will eventually have 23,000 miles of fiber cable. ``We're installing about 30 miles of cable per day,'' says Terry Yake, the company's vice-president for engineering. He says US Telecom expects to have spent $4 billion by 1994 -- half of that over the next four years.
Mr. Yake says that ``transmission speeds are ever-increasing.'' AT&T's 417-bit single-mode transmission system will be improved to 1.7 gigabits by 1988. To translate: That means a pair of cables which now carries 6,000 simultaneous conversations will be able to transmit 24,000; a one-inch cable of 20 fibers will have a capacity for 450,000 simultaneous telephone calls. These improvements can be made by upgrading the lasers, the repeating stations, and the terminating devices without touching the glass already underground, Yake says. According to Anthony Rutkowski of the Federal Communications Commission, this will allow for upgrading the system ``as the state-of-the-art progresses and better devices become available.''