Hello? New York-to-London: conversations on pulses of light

A glass hair 3,500 miles long? According to British researchers, that may one of the strongest connections between Britain and the United States in the next decades.

Telephone London from New York at the end of the century, and your voice may not be transmitted by electric current.

Instead -- depending on which circuits are free -- it could be turned into pulses of light, beamed down a cable containing an optical fiber, and be picked up at this end by a gallium-indium-arsenide "eye."

It is all part of a bid by British Telecom (the born-again public corporation renamed in recent weeks by splitting apart the Post Office's mail and telephone services) to retain a market it pioneered in 1850: undersea communication cables.

Since every communication between Britain and the rest of the world involves a sea crossing, engineers at the British Telecom Research Laboratories at this converted World War I airfield near Ipswich know they have a captive audience. For although 60 percent of Britain's intercontinental traffic is now on satellite, the cablemen think they can offer lower-cost fiber-optics transmission -- especially for such things as television signals and international computer links.

Since 1956, when the world's first transatlantic telephone cable carried 36 calls at a time, advances into silicon-chip technology have boosted that number to about 2,000 per circuit.

Part of the secret involves what engineers affectionately call "tasi" -- time-assignment speech interpolation -- which allows the system to transmit chunks of one person's information during the pauses in someone else's conversation.

Fiber optics, however, shifts the ground rules. It abandons the older "analogue" systems, where a flow of electric current matched the rises and falls of sound in the telephone mouthpiece. Instead, it uses a "digital" system, in which the signal is translated into thousands of simple yes-or-no questions each second.

Each of these answers is a "bit." It takes about 64,000 of them each second to reproduce a telephone call faithfully. Fiber optics technology points to systems that will carry 280 million bits per second -- double the present wire cable capacity.

One particular advantage to fiber optics is the comparatively low transmission loss. The present cables use "repeaters" or amplifiers spaced like beads at eight kilometer intervals across the ocean floor. Optical fiber systems need repeaters only every 30 to 50 kilometers.

The repeaters themselves are marvels of engineering, built to last unattended for 25 years under 7,500 meters of inhospitable sea water.

And the cost? Nowadays, cable telephone calls cost only 5 percent of what they cost in 1956. In the future, says one of the company's optical fiber engineers, the cost "will drop like a brick."

"It's effectively coming down exponentially," he adds.

Meanwhile, however, the brick certainly hasn't dropped: the users of Britain's 27 million telephones -- the third largest system in the world, soon to be transformed by the introduction of the all-electronic "system" -- face a 22 percent increase in charges in November.

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