City of Light: The Story of Fiber Optics

4 CITY OF LIGHT
reach across the world. International dialing is easy. My fingers have memorized
the codes for the London office. I start with 011, the code for international
direct calling. Then comes 44, the country code for the United Kingdom,
and 207, the city code for central London. Those eight digits route the
call to the right region; four digits—a ‘‘1’’ and the area code—suffice for calls
in North America. Then I push seven more buttons and after a breath or two
a phone rings on an editor’s desk.
You cannot mistake a telephone voice for a live one; the telephone is not
a high-fidelity instrument. Some distort voices much more than others. With
a little practice, you can recognize speaker phones, cellular phones, or $9.95
discount-store specials. Yet without the effects of the telephone itself, it is hard
to tell a call from London from one from down the block. I can recognize the
editors’ voices; they can tell when sinus trouble clogs my nose, or laryngitis
roughens my throat. The telephone lines are as transparent as they sound.
A few miles from my home, my telephone calls shift from copper wires to
glass optical fibers.
The part of the telephone network we see is electrical. A microphone converts
the vibrations of air molecules shaken by my voice into electronic signals.
The phone sends the electronic signals through copper wires in my
house, which connect to wires that run to a telephone pole across the street.
From there, more wires carry the signals down the pole and through underground
ducts to a building a few miles away, where electronics convert them
to digital code—a string of ones and zeroes. The circuits decode the numbers
I dialed, figure out the call’s destination, switch the signals to a cable headed
in that direction, and shuffle the bits of my voice together with the digitized
signals from other phone calls being sent along the same digital highway on
their routes to their separate destinations.
The electronic bit stream switches off and on a tiny semiconductor laser
no larger than a grain of salt, turning my voice into pulses of invisible infrared
light. A hair-thin optical fiber collects the millions of pulses a second that
carry my words—and other voices and facsimile messages and computer
data—and sends them on their way south to New Jersey, where domestic
phone lines connect to fiber-optic cables that cross the Atlantic. At the international
switching center, other circuits amplify and reroute the bits of my
voice along with thousands of other digitized conversations. Then they travel
thousands of miles through optical fibers protected from the abyssal depths
by the layers of white plastic and metal shielding that make up a 0.827-inch
(21-millimeter) submarine cable. On the other side of the Atlantic, a British
international switching center reroutes them to other fibers that carry them
to London. In the British capital, more fiber-optic cables carry the light pulses
through a maze of underground ducts to the building that houses New Scientist.
An electronic receiver in a box somewhere in the building turns the
light pulses back into electrical signals that go through wires to the phones
on the editors’ desks.
We don’t see the optical fibers in the telephone system, any more than we
see the electronic chips that control a videotape recorder. If we were to see